Efficiency of Gas Engines

This is probably the most relevant forum for this topic since most automobiles are powered by gas engines. The main message I want to emphasize in this post is that the efficiency of a gas engine varies dramatically over its power range. Understanding what leads to this variation can help to devise systems that use gas engines more efficiently. I will recount relevant examples to bring the message home.

Consider a controlled test of one of Wayne Keith's pickup trucks performed at Auburn University. The test entailed running his truck at 55 mph on level ground. In one test the engine was fueled by gasoline. In another test the engine was fueled by wood gas generated from one of Mr. Keith's wood gasifiers. In the final analysis it was shown that the truck required 37% more energy when fueled by gasoline as compared to when fueled by wood. But wait, it gets much more interesting. Even a good gasifier sees thermal losses on the order of 30%. So, when these losses are negated, then it's clear that the engine was actually generating twice the work when fueled by wood gas as compared to gasoline! (that is, when one considers the energy actually delivered to the engine in the form of wood gas compared to the energy delivered in the form of gasoline). In other words, the thermal efficiency of the engine was twice as high on wood gas as compared to gasoline. The reason these results were seen is because the efficiency of a gas engine when fueled by gasoline is very low when it's operated at part load and at low speeds. During this test while fueled by gasoline, the engine was probably operating under 2500 rpm and with the throttle mostly closed. The engine in that truck is capable of achieving 25% thermal efficiency on gasoline, but was probably seeing only about half this efficiency under the test conditions. BTW, this dynamic is the main reason that hybrid cars see higher fuel economy. Gas engines operate most efficiently when the throttle is wide open as this increases the average engine pressure leading to the engine having to overcome proportionally less friction. Also, gas engines operate more efficiently at higher engine speeds which also leads to higher average engine pressure because there is less time during the power stroke for heat to be lost to the coolant (keeping the gas hotter will increase pressure all else equal). The reason the truck fared so much better on wood gas is mainly because wood gas burns so much slower than gasoline vapors. Also, the simpler fuel gases in wood gas are more easily fully combusted. So, the wood gas was slowly combusted during the power stroke to release its heat gradually. This led to lower peak gas temperatures with the result that heat was transferred to the coolant at a much lower rate (as compared to the much faster burning gasoline vapors). Now, if the engine speed were doubled and the throttle wide open, then the thermal efficiency of the engine would easily double when fueled by gasoline. However, this would equate to about 100 hp. How often do you need to deliver 100 hp to the wheels? Answer: only during rapid acceleration and when climbing steep hills at speed. The hybrid car takes a much smaller engine, then provides an electric drive motor to boost the hp during those rare occasions when the additional power is actually necessary. Now consider another example:

Mother Earth News describes a compact car (an Opel) that was converted to a series hybrid configuration during 1979. The car was driven entirely by an electric drive motor powered by four automotive batteries wired in series for 48 volts dc. A 5 hp lawnmower engine was used to drive a small generator that charged the battery system. The result was a vehicle that was more or less limited to city driving, but saw "up to 75 mpg" on gasoline. In short, this configuration was able to approximately double the fuel economy of the vehicle at low speeds normally seen during city driving. This is particularly interesting since the generator is only about 75% efficient, and the drive motor is not much better at perhaps 80%. So, even neglecting battery losses, only about 60% of the shaft energy provided by the gas engine in this case is actually transferred to the transmission. If we consider a generous estimate of 25% efficiency for the gas engine, then the overall efficiency is only 15% in this case. Now, the "up to 75 mpg" is likely an embellishment, but I have no doubt that the fuel economy is much higher than the stock counterpart. Also, this configuration does provide regenerative braking which can increase fuel economy. Bottom line is that the efficiency of the typical automotive gas engine is very low during city driving.

The purpose of this discussion is to bring home the fact that the efficiency of gas engines vary dramatically over their power range. A typical passenger car fueled by gasoline is operating at roughly 10-12% thermal efficiency while at 40 mph on level ground. This is shameful when one considers that these engines have the ability to deliver nearly 30%.

I wanted to add an interesting fact about the test performed with Mr. Keith's wood gas truck. The truck used for that test saw a fuel economy of 20 mpg on gasoline during the test. The equivalent fuel economy on wood is 37% higher at 27.4 "mpg". However, if we consider the thermal losses from the gasifier, then the equivalent fuel economy would be "mpg" in the high 30's. In other words, a gas engine is capable of delivering this fuel economy in this setting (i.e. full size truck at 55 mph).

I consider this interesting as we generally consider 20 mpg to be impressive efficiency for a full size truck. However, look at how much room there is for improvement! Unfortunately, it's damn hard to get around this with the efficiency of gas engines so variable. I had proposed in another thread a configuration where a vehicle is "dual-fueled" with a small wood gasifier. Since an automobile requires only a small percentage of its rated power most of the time, then the idea here is that a wood gasifier can provide the bulk of the fuel gases when the vehicle is undergoing slow acceleration and when maintaining constant speeds. Gasoline is delivered via the injectors at all times, but providing only what is normally provided during idle or even less. When power is desired above what the wood gasifier can provide, then the injectors can provide this additional fuel. Wood gas doesn't do well at higher engine speeds due to its slow burning characteristics, but adding a lot of gasoline in the mix will likely change things and allow for good efficiency at high engine speeds. The efficiency should also be high at low engine speeds since primarily wood gas would be used here. Most important, since a vehicle normally requires only a small percentage of the engine rated power the vast majority of the time, then most of the fuel consumed can be wood. I believe this kind of configuration can reduce gasoline consumption on the order of 80% (that is, only 20% of the gasoline otherwise consumed could be used for the same travel).

Marcos, you know where they are using this technology? -- North Korea



Since they have no oil resources but lots of tree covered hillsides, they have quite a few vehicles (trucks mostly) running on wood gas.

this is a very interesting discussion, Marcos, thanks for bringing it up.

We use a small toyota pickup for local driving, but we live in a mountainous area, so we do actually need the power of the engine at some times. But, a lot of the time, the engine is effectively "idling" because we're going downhill. To take the kids to school, it's about 7 miles round trip. 1/3 of that trip is uphill, 1/3 is downhill, and 1/3 is level ground (in the village).

I have been planning to convert this truck to wood gas to basically rid ourselves of the gasoline cost. I think it would be a great candidate, because for the majority fo the trip, we just need to keep the engine running, it's not really providing much power to the wheels.

This truck is a 1983 model, so it has a carburetor. I am wondering if it would be difficult to convert this truck into a gasoline/wood gas hybrid like you talk about. If the wood gas can power the vehicle for the 2/3 of the trip that we don't need power and then a bit of gasoline is used for that 1/3 that is uphill, we could see significant fuel savings.

Oh course, it might be simple to just convert to a wood gas system.

Abe Connally wrote:This truck is a 1983 model, so it has a carburetor. I am wondering if it would be difficult to convert this truck into a gasoline/wood gas hybrid like you talk about. If the wood gas can power the vehicle for the 2/3 of the trip that we don't need power and then a bit of gasoline is used for that 1/3 that is uphill, we could see significant fuel savings.

Oh course, it might be simple to just convert to a wood gas system.

Hi Abe. I see no reason why you couldn't admit a stoichiometric wood gas/air mixture to the engine intake manifold in parallel with the stoichiometric gasoline/air mixture provided by the stock carburetor. However, I do believe superior results will be seen with a modern fuel injected gas engine for two reasons: (1) the intake manifold on the modern truck has less resistance to air flow (carbureted engines purposefully add turbulence for mixing), and (2) the spark timing adjusts automatically on many modern engines, and wood gas does best with the spark advanced. That said, if you were to convert your truck to a gasoline/wood gas hybrid with a small wood gasifier, then the truck would be fueled with primarily wood gas only at low engine speeds that might not require much advance (due to the lower speeds). There would always be a small amount of gasoline in the mix, and there would be a higher proportion of gasoline at high engine speeds which should be fine with the stock timing. Finally, the gasoline added to the mix will make up for the power loss. I don't know how much you rely on this vehicle, but an older truck like this seems a good test bed. Personally, I consider the ability to use a much smaller gasifier/cooling/filtration system as a big plus.

For specific advise on such a conversion, I recommend the driveonwood.com forums. However, I expect those active on that forum to recommend against any "dual-fuel" configuration.

thanks, Marcos. I've joined the forum, but my account hasn't been activated yet. I have read a lot over there, though, and I was looking at making a simple fire to power a small generator, just to get my feet wet.

I have a lot of tree trimmings, but I need to figure out how to get them chipped/chunked for wood gas. I have been a member of the Yahoo Wood Gas group for a long time, and my plan had always been to build a LaRosifier design with brake disks and other junk parts for this Toyota.

We use the truck on a daily basis, and even though it is old, the engine has about 150K miles on it, runs perfect, and is just about bullet proof. These little 22R engines can last forever, and I've known a lot to go beyond 500K miles. I would certainly like to avoid destroying the truck, but at the same time, I think this engine will convert well.

I had never considered a gasoline/wood gas mix, but that might be a great way to go eventually.

Abe Connally wrote:I had never considered a gasoline/wood gas mix, but that might be a great way to go eventually.

I've never seen it done quite like I'm suggesting, but seriously, there is no fundamental/inherent reason why it cannot be configured this way. What I am considering is a particularly small gasifier that would normally be used to power a 10-15 KW stationary generator - a 3-4" restriction is probably suitable (vs. the 6-7" often used for trucks). Your tree trimmings might be perfect for a smaller gasifier like this. There would have to be a provision made to prevent the larger engine from drawing on the gasifier too hard, and a means to isolate the gasifier is necessary should fuel run out while driving, but there are many ways to go about this. Again, one of the main benefits to this approach I see is the prospect of converting a small truck to wood gas with a much smaller gasifier/filtration/cooling system. I think it's possible to make a conversion such that one cannot easily tell by inspection that the truck is converted. For example, a small hearth might be recessed below the bed level and a hopper contained in a tool box frame, and filters/cooler might be under the truck and/or engine compartment. Also, a benefit of the smaller gasifier is that it can be used for emergency power generation.

Check out the YouTube channel Flash001USA. He has recently built and has been testing a small Imbert gasifier with good results. Most interesting is how he built it. He makes very good use of existing components. His gasifier is a bit small for this purpose, but his videos should give you good ideas.

Mike LaRosa had a 3-4" model on his Chevy S-10 conversion. He used an old water heater and a wheel rim for the hearth, I believe. These smaller trucks don't need the same size as some of Wayne's v-8 conversions. After all, they are 4 cyclinder, small engines.

Abe Connally wrote:Mike LaRosa had a 3-4" model on his Chevy S-10 conversion. He used an old water heater and a wheel rim for the hearth, I believe. These smaller trucks don't need the same size as some of Wayne's v-8 conversions. After all, they are 4 cyclinder, small engines.

Ok, with the smaller engine it seems you could make the conversion and retain the means to operate the two different throttles independently. I doubt the smaller engine would draw too hard, especially when the engine speed is purposefully limited and the stock throttle is always open at least a little. In other words, in this case it seems no special provision might be necessary to dual-fuel, just operate the stock throttle when extra power is desired. It does seem that the carburetor might need to be adjusted to reduce gasoline provided during idle and/or allow the idle speed to increase to allow enough air to be drawn through the gasifier during idle. Does this all seem reasonable?

I have a mechanical fuel pump right before the carb, and I had always planned to just put a switch there to cut off the fuel supply completely, but figuring out how to control the flow through the stock throttle is a better method. I guess it would just mean adding an additional linkage or pedal. I'll look into it. Thanks for the suggestions!

Another possible benefit of a "dual-fuel" configuration discussed here is the gasoline admitted might eliminate tar deposits that accumulate. Of course, it's best to have a gasifier system that will not introduce tars to the engine, but I doubt any system can eliminate this entirely... and tars tend to accumulate over time. I understand gasoline to be a good solvent for removing tar deposits. Note again that I am speculating on this effect, but it does seem reasonable.

You might be interested in reviewing the vehicles page at the BioEnergy Lists: Gasifiers & Gasification website.

Marcos Buenijo wrote:In other words, the thermal efficiency of the engine was twice as high on wood gas as compared to gasoline.

I hate to burst the bubble. But somebody is pulling somebody's leg here.

The cycle thermal efficiency in a cylinder of a reciprocating internal combustion engine is determined by compression ratio. And actually even the Brayton Cycle efficiency in gas turbines is determined by the pressure differential (bypass ratio) of the combustor to the low pressure side of the hot section. This is the equivalent of compression ratio in a recip. If you combine the principles of the Brayton Cycle with the Otto or Diesel Cycles you can improve thermal efficiency with turbo or supercharging. But you cannot change it with the fuel. Anybody that tries to tell you that you can has inhaled too much carbon monoxide from their wood gasifier so their brain is no longer functioning properly.

The only thing you can change with the fuel is the specific heat ratio of the combustible gas in the combustion chamber. The specific heat ratio of the gas is is the ratio of the heat capacity at constant pressure (Cp) to heat capacity at constant volume (Cv). Mechanical engineers refer to it as the isentropic expansion factor where C is the specific heat capacity of the gas per unit of mass.

The specific heat capacity of producer gas is very low compared to gasoline - 5.7 MJ/kg for producer wood gas versus 44.1 MJ/kg for gasoline.

There's a lot of misinformation out there but no need to propagate it just because someone thinks they have the "answer" to so-called "alternative fuels".
--
Chris

Marcos Buenijo wrote:Gas engines operate most efficiently when the throttle is wide open as this increases the average engine pressure leading to the engine having to overcome proportionally less friction. Also, gas engines operate more efficiently at higher engine speeds which also leads to higher average engine pressure because there is less time during the power stroke for heat to be lost to the coolant

This is another somewhat misleading statement that should be quantified. Throttle opening, mean piston speed and loading have nothing to do with cycle thermal efficiency. What you are referring to is called Brake Specific Fuel Consumption. Otto Cycle engines achieve lowest BSFC at wide open throttle and peak torque. This is the point where volumetric efficiency is highest due to lower pumping losses.

Diesels, being unthrottled, and with their inherently high compression ratios, achieve thermal efficiency and low BSFC numbers at all loading that no Otto Cycle engine can match. Spark ignition engines are really dinosaurs. The only reason they ever became dominant in the North American market is because of what the petroleum industry can refine at peak profit, and what the automotive industry can build and sell at peak profit. So the refineries in North America are primarily designed to refine gasoline. And US car makers have long targeted the price point buyer with cheaper-to-build gasoline engines. Go to Europe and it's a whole different story. Over 50% of their auto fleet is diesel - and corresponding more efficient that what we drive in North America.

Wood gas is all the "rage" the last few years to replace petroleum fuels. But it has been around, fueling piston engines, for over 100 years. So while it works, some of these claims about it being close to a "miracle fuel" are greatly exaggerated. If you want high efficiency switch to diesel power and forget the spark plugs.
--
Chris

Chris Olson wrote:The cycle thermal efficiency in a cylinder of a reciprocating internal combustion engine is determined by compression ratio. And actually even the Brayton Cycle efficiency in gas turbines is determined by the pressure differential (bypass ratio) of the combustor to the low pressure side of the hot section. This is the equivalent of compression ratio in a recip. If you combine the principles of the Brayton Cycle with the Otto or Diesel Cycles you can improve thermal efficiency with turbo or supercharging. But you cannot change it with the fuel. Anybody that tries to tell you that you can has inhaled too much carbon monoxide from their wood gasifier so their brain is no longer functioning properly.

The only thing you can change with the fuel is the specific heat ratio of the combustible gas in the combustion chamber. The specific heat ratio of the gas is is the ratio of the heat capacity at constant pressure (Cp) to heat capacity at constant volume (Cv). Mechanical engineers refer to it as the isentropic expansion factor where C is the specific heat capacity of the gas per unit of mass.

The specific heat capacity of producer gas is very low compared to gasoline - 5.7 MJ/kg for producer wood gas versus 44.1 MJ/kg for gasoline.

There's a lot of misinformation out there but no need to propagate it just because someone thinks they have the "answer" to so-called "alternative fuels".
--
Chris

(Note that I had been using the term "thermal efficiency" as synonymous with the term "Brake Specific Fuel Consumption" that you offered in another post. I believe this has led to some misunderstanding.)

Chris, the thermal efficiency (read: BSFC) of a gas engine varies a great deal over its power range. Since the compression ratio is constant over this range, then it must be that the thermal efficiency (read: BSFC) is determined by factors other than compression ratio. I agree that the peak thermal efficiency of an engine can be described as a function of compression ratio. However, I'm not considering peak thermal efficiency here.

We observe the dramatic variation in the thermal efficiency (read: BSFC) of a gas engine during its operation. So, what is the cause? I'll try to clarify my position here... I have proposed that a primary cause is the rate at which the fuel is combusted in the cylinder relative to engine speed. I suggest that the combustion rate of a gas/air mixture in the cylinder varies over a range that is more limited as compared to engine speed. Therefore, as engine speed decreases, the combustion rate of the gasoline cannot decrease by the same proportion (despite ignition timing adjustments). This leads to higher peak combustion temperatures at lower engine speeds, and this in turn leads to a higher heat transfer rates to the coolant. All else equal, this will decrease average cylinder pressure during the power strokes and engine thermal efficiency (read: BSFC) will suffer. Note that the effects of throttling are also important as this more directly affects the average cylinder pressure. However, I wished to emphasize the former dynamic as an explanation for the higher thermal efficiency (read: BSFC) demonstrated by a wood gas fueled truck as compared to gasoline. Please explain how this line of reasoning is flatly incorrect. If so, then I genuinely wish to be corrected.

Note that wood gas is NOT a practical alternative for transport fuels except perhaps for a very small subset of the population who desire to generate their own fuel. It is no "answer" to so-called "alternative fuels", and I never made such a claim nor have my statements implied this conclusion.

Chris Olson wrote:This is another somewhat misleading statement that should be quantified. Throttle opening, mean piston speed and loading have nothing to do with cycle thermal efficiency. What you are referring to is called Brake Specific Fuel Consumption. Otto Cycle engines achieve lowest BSFC at wide open throttle and peak torque. This is the point where volumetric efficiency is highest due to lower pumping losses.

Diesels, being unthrottled, and with their inherently high compression ratios, achieve thermal efficiency and low BSFC numbers at all loading that no Otto Cycle engine can match. Spark ignition engines are really dinosaurs. The only reason they ever became dominant in the North American market is because of what the petroleum industry can refine at peak profit, and what the automotive industry can build and sell at peak profit. So the refineries in North America are primarily designed to refine gasoline. And US car makers have long targeted the price point buyer with cheaper-to-build gasoline engines. Go to Europe and it's a whole different story. Over 50% of their auto fleet is diesel - and corresponding more efficient that what we drive in North America.

Wood gas is all the "rage" the last few years to replace petroleum fuels. But it has been around, fueling piston engines, for over 100 years. So while it works, some of these claims about it being close to a "miracle fuel" are greatly exaggerated. If you want high efficiency switch to diesel power and forget the spark plugs.
--
Chris

Chris, I'm going to address your comments in reverse order. Wood gas is no viable substitute for petroleum fuels except for a handful who desire to produce their own fuel, and who happen to be an a favorable position to take advantage of wood. Considering wood gas as a "miracle fuel" is laughable. The only person I know of in a position to use this technology in a practical and cost effective way is Wayne Keith who owns several large trucks with poor fuel economy on gasoline, and who happens to own a small lumber mill on his property. I completely agree that Diesel is the way to go for higher fuel economy, and I have taken this position for many years. It's a shame that there is not a wide selection of small Diesel powered vehicles in the U.S.

I suspect we are operating under different definitions. This often leads to misunderstandings. I had been using the term "thermal efficiency" to describe the proportion of chemical energy available in the fuel source that is converted to work at the engine shaft. It seems engineers generally reserve this term to describe the performance of an "ideal" engine cycle. I see how this can lead to confusion. Yes, the term "Brake Specific Fuel Consumption" you offer is the appropriate term.

A more thorough discussion of the controlled test performed on one of Wayne Keith's pickup trucks is briefly described at the link here: http://driveonwood.com/sites/default/files/pdf/Keith%20Final%20Report.pdf

I seems that I made an error during my original post in the thread. Based on the data provided at the link, it seems the thermal losses from the gasifier were considered during this test. Therefore, the efficiency of the engine was not nearly twice as high on wood gas as compared to gasoline, but 37% higher as reported by the study. I apologize for the error.

Marcos Buenijo wrote:
We observe the dramatic variation in the thermal efficiency (read: BSFC) of a gas engine during its operation. So, what is the cause? I'll try to clarify my position here... I have proposed that a primary cause is the rate at which the fuel is combusted in the cylinder relative to engine speed. I suggest that the combustion rate of a gas/air mixture in the cylinder varies over a range that is more limited as compared to engine speed. Therefore, as engine speed decreases, the combustion rate of the gasoline cannot decrease by the same proportion (despite ignition timing adjustments). This leads to higher peak combustion temperatures at lower engine speeds, and this in turn leads to a higher heat transfer rates to the coolant.

This is incorrect. Only a very, very small portion of the heat of combustion is transferred to the cooling medium. The great majority is lost out the exhaust port. It sometimes pays to look at the extreme when proving or disproving a theory. The extreme to consider is the Wärtsilä-Sulzer RTA96-C. It is the most thermally efficient piston engine on earth. This engine operates at 102 rpm, has 14 cylinders, and develops 108,920 Brake Horsepower. It uses a two-stroke Diesel Cycle. It has a bore size of 960mm, stroke of 2.50 meters, piston speed of only 8.5 m/s, and operates at a thermal efficiency >50% at full power, and very close to 70% at partial power.

If your theory was correct, the Sulzer, with its low speed and very low piston speed, should be one of the most inefficient engines ever devised. Except it is the exact opposite.

Cycle thermal efficiency, specific heat ratio, volumetric efficiency and combustion efficiency are all aspects that determine BSFC.

All else equal, this will decrease average cylinder pressure during the power strokes and engine thermal efficiency (read: BSFC) will suffer. Note that the effects of throttling are also important as this more directly affects the average cylinder pressure. However, I wished to emphasize the former dynamic as an explanation for the higher thermal efficiency (read: BSFC) demonstrated by a wood gas fueled truck as compared to gasoline. Please explain how this line of reasoning is flatly incorrect. If so, then I genuinely wish to be corrected.

The basic problem with your presentation is that the data in the "study" you point out is seriously flawed by somebody that is attempting to prove they have the "answer". They devised a comparison based on miles/MBTU without ever actually measuring the BTU output of the comparison fuels. Much the same way that Roy McAlister used lots of skewed data with his hydrogen presentations back in the day.

The undeniable facts for someone who has spent a good portion of their life designing engines is that the thermal efficiency on producer gas vs gasoline is going to be approximately the same in the same engine. The BSFC will be much higher with producer gas because it has lower specific heat. There is only one device ever invented to test this on - a dynamometer.

Now - can you run an Otto Cycle engine on producer wood gas? Absolutely. But the brake specific power output of the engine will be much lower than on gasoline. There are some arguments that can be supported on the basis that wood is a carbon neutral fuel and gasoline is not. However, this is not even really correct. Gasoline and diesel fuel are about as renewable as it gets. We live on a planet with a closed carbon cycle. If a carbon based fuel is burned, it release gasses like CO2 into the air. These gasses are eventually absorbed by plants. The plants die, become covered by mudslides (or whatever) and in a few million years the cycle is repeated. The problem the human race has is gross overpopulation of the planet, and burning these "fossil" fuels at a faster rate than mother nature can recycle the byproducts of combustion back into crude oil and natural gas.

In the end the Otto Cycle engine remains one of the most inefficient devices ever invented by man. And nothing you do to it or fuel it with is going to make a significant difference. It is a bad design from the word "go". When working with a bad design you need to start with a fresh sheet of paper and devise a new design - more on that below.

Note that wood gas is NOT a practical alternative for transport fuels except perhaps for a very small subset of the population who desire to generate their own fuel. It is no "answer" to so-called "alternative fuels", and I never made such a claim nor have my statements implied this conclusion.

There are going to be groups or individuals that "push" these so-called alternative fuels. And you have to be very careful when looking at the data because of the inherent design deficiencies of the Otto Cycle engine I noted above. When looking at new designs, there is only one energy source known to man that can be produced using zero resources from this planet - that energy source is electricity. It can be produced by flowing water, wind and sunlight - all of which do not consume any of the planet's resources. Admittedly, we do have to use some of the planet's resources to build the machinery or devices used to harvest these totally free "fuel sources" to generate electricity. But this impact is very, very minor compared to burning carbon-based fuels to provide motive power.

The true "answer" in the end is electric transportation with the electricity for it generated by the above mentioned sources. Many people consider this impossible, but they are wrong. If all the human race's resource that have been put into drilling, extracting, refining and transporting carbon fuels over the years had been put into electricity production from solar instead - every house and building would today be covered with solar cells and cars might even sport them on their roof. If you consider the total rooftop area of buildings in North America and consider that if every one of them was covered with rooftop solar, things would be a lot different today. We power our own home here - totally off-grid - with solar panels that cover only 15% of our home's roof area. My wife and I have electric appliances, electric scooters that we ride and recharge off our system, we even have electric lawnmowers to mow our lawn. We are waiting for electric cars to become more affordable - and when they do we will buy more solar panels to power an electric car too.

We still burn some carbon fuels here - but our carbon "footprint" is less than 10% of the average North American family for our home heating, power, and our personal transportation. Mine and my wife's goal is to become totally petroleum free in our lifestyle by 2018 - and yet not give up anything that other people have.

So my message to people messing with biofuels, "alternative" fuels, etc. and burning them in combustion engines is - you're playing with a dinosaur. It is horribly inefficient no matter what you do. The basic design of the engine you are using is bad from the word "go". There is a better way. The problem with using electricity for everything is in storing it. But I think a company in Pittsburg has come up with a way that makes it economical and feasible for the long term - the sodium-ion battery - it uses common materials for construction and salt water for the electrolyte:
www.aquionenergy.com

I have contacted this company about getting one of their AE12 Battery Modules for our system here. They will have their dealer network in place in Q1 2014 and then we can get one. These batteries are much lower energy density than lead-acid so they are larger and heavier. But they have 10x the cycle life of lead-acid at about the same price/kWh of storage.

This is the technology that will change how the human race lives and survives - not burning "alternative" carbon fuels.
--
Chris

Chris Olson wrote:This is incorrect. Only a very, very small portion of the heat of combustion is transferred to the cooling medium. The great majority is lost out the exhaust port. It sometimes pays to look at the extreme when proving or disproving a theory. The extreme to consider is the Wärtsilä-Sulzer RTA96-C. It is the most thermally efficient piston engine on earth. This engine operates at 102 rpm, has 14 cylinders, and develops 108,920 Brake Horsepower. It uses a two-stroke Diesel Cycle. It has a bore size of 960mm, stroke of 2.50 meters, piston speed of only 8.5 m/s, and operates at a thermal efficiency >50% at full power, and very close to 70% at partial power.

If your theory was correct, the Sulzer, with its low speed and very low piston speed, should be one of the most inefficient engines ever devised. Except it is the exact opposite.

Cycle thermal efficiency, specific heat ratio, volumetric efficiency and combustion efficiency are all aspects that determine BSFC.

I certainly don't mind being wrong. In fact, I consider it favorable as a learning opportunity. However, in this case I am not yet persuaded. First, I disagree that a "very small portion" of the heat of combustion is transferred to the cooling medium (in conventional gas engines such as automotive). Of course, what is meant by "very small"? I suppose we'll have to research this to find some measured rates.

I am aware of the Diesel engine you described. I was aware of 50%+ net thermal efficiency, but 70% amazes me. I'll check it out. One point I wish to emphasize here is that we're talking about a Diesel engine and NOT an Otto cycle. Rudolph Diesel conceived of the design while considering ways to approach isothermal expansion in a heat engine for optimal efficiency. While he was not able to achieve it, the Diesel was the practical compromise. The combustion event in a Diesel engine is better controlled as compared to the Otto cycle. Fuel oil is injected at a controlled rate during the power stroke to optimize the combustion event and to approach isothermal expansion. Some of this controlled combustion is achieved without precise control of injection timing simply because the fuel takes time to vaporize, and this delays combustion during the power stroke. However, I understand that modern Diesel engines also control carefully the timing of the fuel injection event. The ideal condition is to achieve the highest practical mean effective cylinder pressure with the least mass of fuel, and this requires that the amount of heat transferred to the coolant (or other heat sink) is minimized. The higher combustion temperatures will lead to this undesirable condition. Of course, incomplete expansion will also reduce efficiency... so timing is critical (not too little, too early, too much, too late, but just right). In other words, the effect I describe does not apply to Diesel engines... and this is a major reason why the efficiency of Diesel engines vary far less over their power range as compared to gas engines (NOT the only reason).

Chris Olson wrote:The basic problem with your presentation is that the data in the "study" you point out is seriously flawed by somebody that is attempting to prove they have the "answer". They devised a comparison based on miles/MBTU without ever actually measuring the BTU output of the comparison fuels. Much the same way that Roy McAlister used lots of skewed data with his hydrogen presentations back in the day.

The undeniable facts for someone who has spent a good portion of their life designing engines is that the thermal efficiency on producer gas vs gasoline is going to be approximately the same in the same engine. The BSFC will be much higher with producer gas because it has lower specific heat. There is only one device ever invented to test this on - a dynamometer.

Now - can you run an Otto Cycle engine on producer wood gas? Absolutely. But the brake specific power output of the engine will be much lower than on gasoline. There are some arguments that can be supported on the basis that wood is a carbon neutral fuel and gasoline is not. However, this is not even really correct. Gasoline and diesel fuel are about as renewable as it gets. We live on a planet with a closed carbon cycle. If a carbon based fuel is burned, it release gasses like CO2 into the air. These gasses are eventually absorbed by plants. The plants die, become covered by mudslides (or whatever) and in a few million years the cycle is repeated. The problem the human race has is gross overpopulation of the planet, and burning these "fossil" fuels at a faster rate than mother nature can recycle the byproducts of combustion back into crude oil and natural gas.

In the end the Otto Cycle engine remains one of the most inefficient devices ever invented by man. And nothing you do to it or fuel it with is going to make a significant difference. It is a bad design from the word "go". When working with a bad design you need to start with a fresh sheet of paper and devise a new design - more on that below.

How do you know the study is flawed?

I agree that the thermal efficiency of a gas engine on producer gas can be the same as when fueled by gasoline. However, not necessarily so at all conditions. For example, if a gas engine achieves 25% thermal efficiency on gasoline, then I believe it can see the same efficiency on producer gas. However, will this be seen at the same engine speed and power? If not, then why not?

I like your considering petroleum fuels as "renewable". You are absolutely correct: it IS a closed carbon cycle. Unfortunately, I think this would be considered as a strawman argument by the eco-nazis. After all, a closed cycle is not necessarily "sustainable". BTW, I don't buy into the "climate change"/"global warming" rubbish. I'm all for clean combustion and clean environmental conditions in general, but CO2 should not be considered as a pollutant to be scrubbed. It's plant food.

Chris Olson wrote:There are going to be groups or individuals that "push" these so-called alternative fuels. And you have to be very careful when looking at the data because of the inherent design deficiencies of the Otto Cycle engine I noted above. When looking at new designs, there is only one energy source known to man that can be produced using zero resources from this planet - that energy source is electricity. It can be produced by flowing water, wind and sunlight - all of which do not consume any of the planet's resources. Admittedly, we do have to use some of the planet's resources to build the machinery or devices used to harvest these totally free "fuel sources" to generate electricity. But this impact is very, very minor compared to burning carbon-based fuels to provide motive power.

The true "answer" in the end is electric transportation with the electricity for it generated by the above mentioned sources. Many people consider this impossible, but they are wrong. If all the human race's resource that have been put into drilling, extracting, refining and transporting carbon fuels over the years had been put into electricity production from solar instead - every house and building would today be covered with solar cells and cars might even sport them on their roof. If you consider the total rooftop area of buildings in North America and consider that if every one of them was covered with rooftop solar, things would be a lot different today.

I agree.

... well, actually, I am partial to a subcompact and highly aerodynamic car powered by a small Diesel engine. I also think there is potential in modern piston steam engines, but that's a stretch. The problem with EV's is not only the limited range of the batteries, but also their high weight and bulk.

Marcos Buenijo wrote:
How do you know the study is flawed?

19 years experience working for Cummins as a ME, designing and testing engines on dynamometers. When somebody comes along and claims increased thermal efficiency, lower BSFC, or increased brake efficiency from a lower specific heat fuel there has been either a deliberate manipulation of data, or an unintentional flawed conclusion made. In this case the data is seriously flawed because there has been a claim made of increased power output (more miles) from less energy input - this is thermal efficiency. This is right up there with the "run your car on water" hydrogen scams.

Again, can you run a spark ignition engine on producer gas or hydrogen? Absolutely. And producer wood gas has been used successfully for over 100 years in piston engines. But you'd better be careful with your claims on efficiency because I can spot a bogus claim from halfway across the planet. Now if you want to do a cost analysis per mile with producer gas vs petroleum fuels, THEN we might have some valid points. Because I believe the average homebuilder can probably produce energy from producer gas cheaper per BTU than you can buy petroleum fuels.

I agree that the thermal efficiency of a gas engine on producer gas can be the same as when fueled by gasoline. However, not necessarily so at all conditions. For example, if a gas engine achieves 25% thermal efficiency on gasoline, then I believe it can see the same efficiency on producer gas. However, will this be seen at the same engine speed and power? If not, then why not?

Producer gas is much lower heat content than petroleum gasoline. It's the same difference as comparing ethanol to gasoline in the same engine - on ethanol the engine will get poorer fuel mileage because the ethanol does not contain the heat energy that a gallon of gasoline contains. Producer gas contains less heat energy yet per unit of mass. People that start making claims of getting more from less are claiming violation of some of the most basic laws of conservation of energy in thermodynamics and mechanical engineering. It is no different than Roy McAlister's "Hydrogen Economy" that eventually put him in the poor house back in the day. He firmly believed in it - BUT - even though hydrogen might be the most abundant element in the universe, because of its association with other elements (namely oxygen) here on earth there has never been a way to separate it that provides increased energy efficiency over petroleum fuels.

Stars can use hydrogen to produce energy thru nuclear fusion. But we can't create the temperatures and pressures needed for that process in any man made device that is practical. So, use your brain - the stars (our sun) is converting hydrogen mass to energy by fusing it and forming heavier elements. The hard work is already done by the star - all you have to do is capture that energy that the star puts out and put it to use. It shines on us every single day. There's your "hydrogen economy". People many times fail to see the forest for the trees. Engineers get tunnel vision in that you have to burn something carbon based to make energy for motive or stationary power. You don't. There's another source that's way better - look up in the sky - it is the most advanced and efficient source of energy in the universe. The energy from it powers EVERYTHING on this planet. It can power your car too - you just have to figure out how to do it. And believe or not - the technology exists today TO do it - and on a practical large scale too.

The base problem is not the technology. It is money. The entire industrialized world runs on petroleum fuels and the money that governments and people that control it get from it. The industrialized world as we know it was invented and built by a man named John Davidson Rockefeller and Standard Oil. He invented the markets for kerosene and gasoline, and adjusted for inflation, became the richest man in the history of humanity.

In 1911, the Supreme Court of the United States found Standard Oil Company in violation of the Sherman Antitrust Act. The court ruled that the trust originated in illegal monopoly practices and ordered it to be broken up into 34 new companies. These included, among many others, Continental Oil, which became Conoco, now part of ConocoPhillips. Standard of Indiana, which became Amoco, now part of BP. Standard of California, which became Chevron. Standard of New Jersey, which became Esso (and later, Exxon), now part of ExxonMobil. Standard of New York, which became Mobil, now part of ExxonMobil And Standard of Ohio, which became Sohio, now part of BP.

This empire remains today as the controlling force in the industrialized world. NOTHING is going to change it, regardless of whether or not the technology exists TO change it, because it involves billions and billions of dollars that all comes out of the pockets of the consumer that flow to the people who run this system. The whole system has been designed so you the consumer have an insatiable demand for petroleum. The one and only thing that will collapse this world empire is if you the consumer stop buying their products.

So this is where wood gas is practical IMHO. It works. It's been done for over 100 years. If you can do it - go for it and do it. But don't try to prove that it's more thermally efficient, etc. Instead go about ways of proving that is practical as a replacement for petroleum. Like you said, Marcos, this whole Global Warming thing is a scam - another money making scheme by the powers that want to control things on earth that the powers who already control it have. There have been many periods in the earth's history, long before humanity appeared on the planet, when atmospheric CO2 was many times higher than it is today. Humans haven't been here long enough to know what the heck is going on.

But for permaculturists who are interested in sustainability, which will eventually determine how long the human race lasts on this planet, I urge that you look to that nuclear fireball in the sky for your energy needs. The technology exists today to use it to power virtually everything in your life that you find convenient and/or necessary. Some of that technology is not cheap - especially when it comes to converting it to electricity. But it can be used to heat your home, heat your water, cook your food, and even grow your food in the winter (with a greenhouse). And most of this can be done with some basic skills and lumberyard materials. But that nuclear fireball can also be used to power your home and power your car if you want to spend the money on doing it. And considering a new car costs upwards of $30,000 these days and all you do all the time you own is stick money in it to make it operate, the technology to power a car on solar is becoming economically feasible pretty fast.
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Chris

Marcos Buenijo wrote:The problem with EV's is not only the limited range of the batteries, but also their high weight and bulk.

Marcos, Elon Musk has proven with Tesla Motors that range and awesome performance that only a few production cars on earth can match is not a problem for electric cars. The problem is affordability for the average consumer. My wife and I are strongly looking at a Nissan Leaf and the necessary solar power to charge it. We've already done it with our little scooters that we put ~1,500 miles per year on, each, running errands.

My wife really wants a red one
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Chris

I had written a missive in response to the broader off-topic discussion, but it would not have been constructive so I deleted it.

Abe, if you have a bulletproof engine, I wouldn't play with it. If you want to experiment with wood gas, use an old beater engine you can afford to lose.

Regardless of the efficacy of Mauricio's dual-fuel idea, keeping the engine at peak efficiency is an important factor in conserving fuel. One of the techniques used by hypermilers is to pulse the engine (pulse and glide). The greatest savings are realized with hybrid engines because they turn the engine off when not accelerating. Check out this video that explains using pulse and glide in a Prius (I recommend you also review the ecomodder site for useful recommendations, and some not so useful, for improving the efficiency of your vehicles.)

I found the Mother Earth News article. I remember reading it back then. It was when Mother Earth News was worth reading.

The Scottish company, Artemis, has a prototype hydraulic series-hybrid that pulses the engine to charge the pressure tank. This doubles the city driving efficiency of their BMW 530i test vehicle. PSA-Peugeot-Citroen plans to manufacture their hydraulic hybrid "Air" car by 2016. They claim similar improvements in efficiency (35% improvement in mixed-driving). There are a few US companies working on hydraulic hybrids, a couple of the big manufacturers as well, but no one has announced a date yet.

Hydraulic hybrid can be used with electric as well. It can keep the size of the electric system down, lowering weight and cost, and give it far more efficient regenerative braking .

Chris Olson wrote:Marcos, Elon Musk has proven with Tesla Motors that range and awesome performance that only a few production cars on earth can match is not a problem for electric cars. The problem is affordability for the average consumer. My wife and I are strongly looking at a Nissan Leaf and the necessary solar power to charge it. We've already done it with our little scooters that we put ~1,500 miles per year on, each, running errands.

My wife really wants a red one
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Chris

I don't disagree. However, I consider that the weight and bulk of batteries (i.e. low energy density) contributes to the affordability problem. The added weight and bulk also works against efficiency. I believe a better prospect is to design very compact, lightweight, and highly aerodynamic automobiles with conventional internal combustion power plants. I believe it's within reason for such an automobile to approach 100 mpg highway, especially when a Diesel is used. With fuel economy that high, I doubt an EV of similar performance can be justified on purely economic grounds. The fuel savings of the EV would never add up.

I recently became aware of an automobile that may see market next year. It is a very compact design (two seater) that sees 84 MPG highway and 49 MPG city (gas engine). The retail price is projected at $6800. I am skeptical of some of the claims, but I believe there is a ready market for this new class of automobile. See www.eliomotors.com for a description. Personally, if such a vehicle could be reasonably safe and prove well built and reliable, then I would certainly make the purchase.

Chris, I am addressing some of your claims you made in your previous most lengthy post. First, let me note again that the advantage of fueling an automobile with wood is energy independence. I don't consider it to be a practical option in the vast majority of settings. It really is suitable only for the zealots. However, I do find the prospect appealing for personal reasons, and this explains my interest (call me a zealot). Now, that said, I am confident that you have made errors in your analysis. In the interest of clarity, I will explain my position. The efficiency of an engine is not necessarily a function of the specific heat of the fuel. What I believe you have done is conflate the concept of MPG or BSFC with thermal efficiency. BSFC or MPG is fine as a proxy for thermal efficiency, but only when the fuel source is a constant. For example, the lower specific heat of ethanol as compared to gasoline will lead to lower MPG on ethanol. However, again, this has nothing to do with efficiency. The engine may very well operate at the same thermal efficiency on ethanol as compared to gasoline, yet deliver lower MPG on ethanol simply due to the lower energy density of this fuel. During the test described the vehicle in question maintained the same conditions of speed and power when fueled by producer gas as when the engine was fueled by gasoline. Therefore, the average cylinder pressure must have been similar in both tests. I have no doubt that the total energy of a full charge of air/producer gas cannot approach that of gasoline. However, at the low engine speeds and power seen during the test the throttle was not nearly fully open when fueled by gasoline. So, to see the same cylinder pressure the throttle must have been open more when fueled by producer gas in order to compensate for the lower energy content of producer gas. If we assume the same efficiency on producer gas as compared to gasoline, then the total energy of the charge must have been the same in each test. Yet, according to the test the total energy of the producer gas charge was significantly less. The test entailed measuring the composition of the fuel gas. While I am not certain, I believe this analysis was used to estimate the energy content of the fuel gas. I do note that the energy content of the producer gas estimated during the test was similar to what is provided by other sources. Also note again that I made a silly error in my first post where I ASSumed that the thermal losses from the gasifier were not factored. I made this error based on secondary accounts of the test, and I realized my error only after I had access to the test description provided by the original author.

In summary, the specific heat of the fuel gas has no bearing on efficiency. It does affect the power of the engine. Yet, there is more than enough energy in producer gas to meet the power requirements seen during the test (mainly because the power required was low). I see no reason to reject the findings of the test. It seems clear to me that the engine was in fact operating on producer gas at an efficiency roughly 37% higher as compared to gasoline as indicated by the test results. Now, HOW this was possible is up for debate. The best explanation I've considered is the one I described previously. Namely, a combination of (1) the slower burning character of producer gas lowered peak combustion temperatures to lessen thermal losses to the coolant, and (2) there was more complete combustion of the simple fuel gases in producer gas as compared to gasoline (perhaps (2) is the more significant dynamic). I find it interesting that even with the thermal losses from a gasifier at roughly 30%, the increased thermal efficiency of the engine on producer gas compensates to make the net thermal efficiency on wood similar to gasoline. Also, the heat from the gasifier could be used to dry the wood fuel. (again, just an interesting observation - I make no implications about the viability of this technology - fueling a vehicle with wood will never and should never be a common practice).

Also note that there are other sources that describe increased thermal efficiency of engines when fueled by producer gas. If you reference the Handbook for Biomass Downdraft Gasifier Engine Systems, it is claimed that a Diesel engine dual-fueled with producer gas will see increased thermal efficiency (perhaps more complete combustion?). Also, the net electrical efficiency of the wood gas engine systems made by All Power Labs have been measured at 16% (percentage of total energy in the wood fuel converted to electricity). When one considers the thermal losses from the gasifier and conversion losses in the generator, then it's clear that the Kubota gas engine used during the test was operating near its highest thermal efficiency. In other words, the low specific heat of producer gas clearly did not adversely affect the thermal efficiency of the engine. It is well known that the efficiency of a gas engine varies dramatically over its power range. However, I see no reason to believe that this efficiency profile remains constant with all fuels. In fact, I would be shocked to see this remain constant. I have no trouble whatever accepting the test results that show signficantly higher thermal efficiency on producer gas as compared to gasoline, at least at the low engine speed and power seen during the test.

Marcos

I think you need to do some research on the leading woodgas engine manufacturers Jenbacher. If you look at there generator results you will see conversion rates of 36 percent using woodgas but then if you research how they achieve this you will find that they have to modify a standard natural gas engine to run on woodgas by increasing the compression ratio due to the lower energy content of the woodgas.

In respect of your petrol v woodgas results that to me is just a function of an inefficient carburettor unable to monitor fuel at low rpm. Ferguson tractors overcame the problem back in the 1950's by use of a vaporising carburettor which also allowed kerosene to be burnt directly in a petrol engine. Modern cars do not have this problem with fuel injection and the electronics to create a lean burn engine.

r john wrote:I think you need to do some research on the leading woodgas engine manufacturers Jenbacher. If you look at there generator results you will see conversion rates of 36 percent using woodgas but then if you research how they achieve this you will find that they have to modify a standard natural gas engine to run on woodgas by increasing the compression ratio due to the lower energy content of the woodgas.

Exactly. The same holds true with ethanol or methanol fuels. The compression ratio has to raised to > 11:1 to achieve any increase in thermal efficiency with a lower heat specific fuel. Attempts to compare an engine that is running overly rich on gasoline and dumping hydrocarbons out the tailpipe to running an ideal to lean mixture on producer gas is fundamentally flawed. You can get the same results by replacing the fuel system with a lean burn type on gasoline.

And this is my point - there is only one way to improve the thermal efficiency of the Otto Cycle - either turbo or supercharge it or raise the compression ratio. This has been a fundamental law of piston engine design for over 100 years.

It is worth noting that the Diesel Cycle is inherently less thermally efficient than the Otto Cycle at the same compression ratio. Diesels achieve their considerably higher thermal efficiencies by using compression ratios that are well above what spark ignition engines can run at without causing detonation of the air/fuel charge.
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Chris

Chris

While working at Cummins have you been involved in coal/charcoal slurry injection. I know there was a Cummins engine in the US government trials.

Marcos Buenijo wrote:
I don't disagree. However, I consider that the weight and bulk of batteries (i.e. low energy density) contributes to the affordability problem. The added weight and bulk also works against efficiency.

Yes, the battery is the weak like in current electric vehicle design. And storing electricity is not easy. But I saw a fellow a few week ago that had an older Suzuki mini-SUV that he had put a big forklift traction motor in. He was running it with the rear seat and cargo area full of a bunch of used marine deep cycle batteries he had picked up there and there. While I was admiring his work he was telling me about it and claimed he gets 30 mile range out of it in city driving before it gets really "weak" and he drives it back and forth to work every day. Charges it at home with a regular battery charger.

I'm looking at this and thinking - heck, he achieved what GM achieved with the Volt at way less cost and probably higher reliability on electric power range.

We love our little electric scooters. But can't use them in the winter time. Our little electric scooters don't pull hardly any energy off our RE system to charge them and they have saved us better than a thousand gallons of gasoline or diesel fuel by using them to run errands into town in the non-winter months. They are three years old and just have little SLA 24V battery packs in them. We have two electric lawnmowers too and they also have little SLA 24V battery packs. We have been extremely happy with them - they perform every bit as good as a gas mower - without need for gasoline or changing oil and the other maintenance that goes with combustion engines. At three years the battery packs don't show any signs of getting "weak" yet.

So we are interested in electric cars. I believe one can replace 90% of our driving miles in the winter for running errands into town. And with a suitable slow charger that doesn't draw more than about 1 kW we should be able to recharge it off our RE system.
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Chris

r john wrote:Chris

While working at Cummins have you been involved in coal/charcoal slurry injection. I know there was a Cummins engine in the US government trials.

Yes, we designed and built the KT's for mining operations, running on coal slurry. With Tier IV, that is now more of a challenge but it is being worked on for the QSK-series high-speed engines.

http://cumminsengines.com/qsk78-mining#overview
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Chris

r john wrote:Marcos

I think you need to do some research on the leading woodgas engine manufacturers Jenbacher. If you look at there generator results you will see conversion rates of 36 percent using woodgas but then if you research how they achieve this you will find that they have to modify a standard natural gas engine to run on woodgas by increasing the compression ratio due to the lower energy content of the woodgas.

In respect of your petrol v woodgas results that to me is just a function of an inefficient carburettor unable to monitor fuel at low rpm. Ferguson tractors overcame the problem back in the 1950's by use of a vaporising carburettor which also allowed kerosene to be burnt directly in a petrol engine. Modern cars do not have this problem with fuel injection and the electronics to create a lean burn engine.

The Jenbacher specs are not relevant. Of course thermal efficiency goes up with increased compression ratio. This has no relation to the test that I referenced. That test shows that an unmodified engine can see significantly higher thermal efficiency on producer gas v gasoline under certain conditions (namely low engine power/speed). Also, not sure what you mean by "your petrol v woodgas results". It must be that you never referenced the study/test in question. The vehicle used during that test was fuel injected.

Chris Olson wrote:
We love our little electric scooters. But can't use them in the winter time. Our little electric scooters don't pull hardly any energy off our RE system to charge them and they have saved us better than a thousand gallons of gasoline or diesel fuel by using them to run errands into town in the non-winter months. They are three years old and just have little SLA 24V battery packs in them. We have two electric lawnmowers too and they also have little SLA 24V battery packs. We have been extremely happy with them - they perform every bit as good as a gas mower - without need for gasoline or changing oil and the other maintenance that goes with combustion engines. At three years the battery packs don't show any signs of getting "weak" yet.

So we are interested in electric cars. I believe one can replace 90% of our driving miles in the winter for running errands into town. And with a suitable slow charger that doesn't draw more than about 1 kW we should be able to recharge it off our RE system.
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Chris

Chris, just wanted to say that your discussions of your RE system here on permies has influenced me in a positive way. I had been showing increasing interest in photovoltaics over the last couple years largely due to the rapid decline in hardware costs. As far as I'm now concerned, any off grid (and even grid tie in some cases) RE system should be firmly rooted in PV. I even checked out electric lawn tools AND electric scooters for interest, and it's interesting to me that you have put these to use in your system. I even saw an electric skateboard in action recently - with impressive performance! I'm still skeptical on the value of an electric car mainly for the range restriction and battery weight/bulk/cost required to extend the range. Series hybrid maybe? I think the battery kills the EV, and it seems a mistake to try and design an EV to perform as a conventional automobile. The battery hobbles the project from the get go. That said, I will be moving to east Texas next year (barring unusual circumstances), and I will be selecting a modest home that has good prospects for supporting an off grid RE system. It's helpful for those who are considering this leap to actually see and learn about existing systems, so thank you for sharing.

This whole discussion is getting theoretical and hair-splitting, and starting to approach ludicrous speed (Spaceballs reference for those who didn't get it). The main observation that interests me is that the efficiency of a gas engine varies so dramatically over its power range. This quality has detrimental effects on the fuel economy of automobiles. Adding a small wood gasifier to dual-fuel a vehicle is not a practical solution despite being an interesting prospect for the zealot in me. A series hybrid would see higher fuel economy as conventional automobiles, but still see significant energy conversion losses. EV's have the battery problem. A modern piston steam engine can see high efficiency with peak efficiency at a low part load, but it doesn't exist. Diesel seems the best solution as its efficiency profile is much flatter than the gas engine, along with higher thermal efficiency to boot.

The last comment I'll post on the main contention at hand is that there is no reason to doubt the results of the test in question (rejecting the results off hand is not rational). It should seem clear that Mr. Keith's pickup truck operates a lot more efficiently on producer gas v gasoline while maintaining 55 mph on level ground. The physics behind this result is up for debate. Delayed combustion causing the cycle to more closely approach Carnot (i.e. isothermal expansion)? More complete combustion of the simpler fuel gases? Both? Who knows. I don't care anymore.

Marcos Buenijo wrote:
Chris, just wanted to say that your discussions of your RE system here on permies has influenced me in a positive way. I had been showing increasing interest in photovoltaics over the last couple years largely due to the rapid decline in hardware costs. As far as I'm now concerned, any off grid (and even grid tie in some cases) RE system should be firmly rooted in PV. I even checked out electric lawn tools AND electric scooters for interest, and it's interesting to me that you have put these to use in your system. I even saw an electric skateboard in action recently - with impressive performance!

We use PV, but we also use wind power, and gas and diesel generators to fill in what the PV and wind can't do on bad days. We are not minimalists and we burn the fuel in generators so we don't have to change our daily habits when the weather is bad. Over a year's time the PV is the great bulk of our energy production though. We have a Conext ComBox on our XW Power System that is now logging our data for us so we can make better informed decisions.

I believe in using these tools to analyze what you have to see if it is working properly, or how you can make it work better. By analyzing these power logs I am able to see that many days we don't use our full solar capacity as the loads do not use it up and the battery gets charged. So the system cuts the solar panels (and wind turbines) back and does not use them to their full potential. Adding a bit more capacity and then using it to charge an electric vehicle makes sense to me.

Yes, the cost will be higher for us doing this than it would be to just buy a regular car. But the cost is not an issue for us. It is the principle of the thing. Yes, EV's are extremely limited in their range and performance because of the battery. BUT - if the EV fits your daily driving range and habits, why not use it instead of just burning gas? The way I look at it is that many people can't use one. But many people can. If we can get one and power it from our system, once we own the equipment to harvest the energy and put it to use we drive on the only true source of totally "free" energy known. The cost involved is in acquiring the equipment to do it.

On the performance issue, our little electric scooters are WAY more "snappy" and powerful than a comparable 250cc gasoline scooter. And they will easily take most production automobiles off the line from the stoplight. They go about 60 mph and we can typically ride them 60 miles between recharge. The new ones now use Li-ion battery but ours are three years old and have SLA. They are Vectrix VX-1's - my wife has a red one and I have a black one:



http://www.vectrix.com/

They are very, very impressive and you have to ride one to believe it. You pull up to a stop sign and there is no energy being wasted by an idling engine. And they recharge the battery during braking and decel. You snap open the "throttle" and you'd better be hanging on because they will hit 60 mph from a dead stop in under 7 seconds. They cost us $11,000 apiece. It was our first experiment with an EV, and they have been very fun, zero maintenance, and turned out to be very practical. We run into town on errands all the time with them and rarely drive our car or trucks in the summer. We have a club here with 4 couples that have them. There are many days that we go out riding on them just because we can, just for fun. And they are an attention getter where ever we go on them. People look at them and can't believe it.

At present the Nissan Leaf is the only real affordable electric car that we have been looking at. Ford's electric is too expensive. There are many options in Sweden, where my wife comes from, but getting a Swedish electric into the US is quite expensive. We just wish there was more options for affordable electric cars in the US.
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Chris

While I don't wish to get into a new conversation about the efficencies of a standard gasoline engine, I did wish to point out that there are a class of gasoline & vapor fueled hybrids that are somewhat common among fleet vehicles. Trucks that can use either normal pump gasoline or liquid propane (called "autogas" in this context) are very common in South America, and somewhat common in the US. They are generally set up to idle on propane and accelerate on gasoline and/or favor one fuel over the other depending upon relative costs of the fuel. It's hard to say, with any certainty, if such engines can use propane more efficiently than gasoline, but it's no question that gasoline is better at accelleration. Straight 'autogas' vehicles are slow, and oftern are only found on off-road or construction vehicles. Construction, because it's cheaper and safer than gasoline, in the event that the construction vehicle turns over. (autogas tanks provide liquid to the propane 'carborator', and don't care which way is up, and can't spill) Off-road vehicles for similar reasons. It would be difficult, however, for a straight propane powered vehicle to accelerate to freeway speeds in a reasonable distance or time.

Creighton Samuiels wrote:It's hard to say, with any certainty, if such engines can use propane more efficiently than gasoline, but it's no question that gasoline is better at accelleration.

You can never get as much power from propane as you will get from gasoline. The limiting factor is how much energy you can stuff into the combustion chamber and provide enough oxygen to burn it. Propane is a less energy dense fuel, so it takes up more room in the combustion chamber, which means less room for the oxygen required to burn it. However, diesels can use LPG fairly effectively because most of them run about 50% on the lean side of stoich at full power. So there is an abundance of oxygen in the combustion chamber of a diesel to burn supplemental fuels like LPG.

LPG can, however, be utilized more efficiently than pump gasoline in a spark ignition engine if the compression ratio is raised to take advantage of the higher octane number.
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Chris

A couple interesting tidbits from the Wiki on wood gas and its use over the years:

Wood gas vehicles were used during World War II, as a consequence of the rationing of fossil fuels. In Germany alone, around 500,000 "producer gas" vehicles were in use at the end of the war. Trucks, buses, tractors, motorcycles, ships and trains were equipped with a wood gasification unit. In 1942 (when wood gas had not yet reached the height of its popularity), there were about 73,000 wood gas vehicles in Sweden, 65,000 in France, 10,000 in Denmark, and almost 8,000 in Switzerland. In 1944, Finland had 43,000 "woodmobiles", of which 30,000 were buses and trucks, 7,000 private vehicles, 4,000 tractors and 600 boats.

[.......]

Efficiency of the gasifier system is relatively high. The gasification stage converts about 75% of fuel energy content into a combustible gas that can be used as a fuel for internal combustion engines. Based on long-term practical experiments and over 100,000 km drive with a wood gas-powered car, the energy consumption has been 1.54 times higher compared to the energy demand of the same car on petrol (not including the energy needed to extract, transport and refine the oil from which petrol is derived, and not including the energy to harvest, process, and transport the wood to feed the gasifier).

http://en.wikipedia.org/wiki/Wood_gas

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Chris

Chris Olson wrote:

r john wrote:Chris

While working at Cummins have you been involved in coal/charcoal slurry injection. I know there was a Cummins engine in the US government trials.

Yes, we designed and built the KT's for mining operations, running on coal slurry. With Tier IV, that is now more of a challenge but it is being worked on for the QSK-series high-speed engines.

http://cumminsengines.com/qsk78-mining#overview
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Chris

Chris

Do you have any contacts for injectors/pumps as I am drawing a blank with Cummins UK when it comes to coal/charcoal slurry

r john wrote:
Do you have any contacts for injectors/pumps as I am drawing a blank with Cummins UK when it comes to coal/charcoal slurry

For what engine series? The Cummins 5.9 and 8.3, pre ISB/ISC, were the only ones that had injection pumps. Otherwise all Cummins engines have cam operated unit injectors. The older NT-series had the PT pump, which was used for years. But only the K-series, 2,000hp and above, was ever certified for coal slurry. And there are very strict guidelines on micron size of the coal particles for pumpability and injection reliability.
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Chris

Chris Olson wrote:

r john wrote:
Do you have any contacts for injectors/pumps as I am drawing a blank with Cummins UK when it comes to coal/charcoal slurry

For what engine series? The Cummins 5.9 and 8.3, pre ISB/ISC, were the only ones that had injection pumps. Otherwise all Cummins engines have cam operated unit injectors. The older NT-series had the PT pump, which was used for years. But only the K-series, 2,000hp and above, was ever certified for coal slurry. And there are very strict guidelines on micron size of the coal particles for pumpability and injection reliability.
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Chris

Chris

Looking for a new engine capable of driving a minimum 500kw generator. I appreciate the micron size but we have that covered as our charcoal slurry is technically an emulsion.

r john wrote:
Looking for a new engine capable of driving a minimum 500kw generator. I appreciate the micron size but we have that covered as our charcoal slurry is technically an emulsion.

Cummins has nothing that small, and nothing at present the meets Tier IV/EU Stage IIIB. In the KT's that we modified for mining use in the late 90's we used conical pattern injectors with 20 micron slurry. None of those engines are in service anymore. There were several problems. Standard injectors do not work at all because the coal particles are very abrasive to injector tips. There was also excessive wear to the liners, top piston ring and ring land due to abrasives in the fuel. I don't know how you managed to turn coal dust into a liquid to get an emulsion though. An emulsion would usually suggest two liquids. If it has solids in it, then there has to be a micron size for the solids, and when you have solids in the fuel you have filtration issues and abrasives that must be dealt with.

Frankly, the huge hurdle right now for all engine manufacturers is meeting US EPA and EU Stage emission specs. Here in the US the directive for 15 ppm sulfur fuel (ULSD) was necessary to be able to use DPF and NOx absorbers. This gets increasingly hard with coal dust. So most of the current push in research is in coal-to-liquid diesel fuel production where the sulfur can be removed in the gasification treatment when making diesel fuel with the Fischer-Tropsch process.

The Cummins QSK-series is presently available in dual fuel configuration for diesel fuel only or diesel/natural gas. And, according to my associates that work at Cummins, alternative fuel technology is constantly being worked on, including coal slurry. But there is nothing commercially available at present. And more than likely, when it does become available it will be for the QSK78 and QSK95 at power ratings of 3,500hp and up. The investment in engineering time to develop special fuel engines that meet EPA is not justified in sub-2,000 hp classes because it is not profitable.
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Chris