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Discussion Starter #1
Seeing as we're stuck with some type of ICE why not offer some options.

I would suggest a small turbo Disel as the first option. And i would like to see the motor tuned to run at only one speed, it's max eff. point for generating electric power. Any excess should be dumped into the battery. You could really change the ICE MPG if you tune them for an exact power point!

Second would be small gas turbine, again tuned to single power point.
 

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The engine is in a way set to charge at a max efficiency point, or more precisely, a number of them. Originally it was designed to run constant RPM, but they thought people would find it disturbing when you slowed down and the engine was still revved up. They instead tuned it to run at an efficient point based on the power required for driving.

I would love to see some new engine options. A small 1.0-1.5L turbo would be great, or as you mentioned, a turbo diesel. I've thought about the turbine engine as well, but I'm not sure its the best option for a car based on the extreme heat output.
 

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Previous discussion about this point out that turbo's are not very beneficial for electric power generators. When was the last time you saw portable electric generator advertised as "turbo-charged"? :)
 

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Previous discussion about this point out that turbo's are not very beneficial for electric power generators. When was the last time you saw portable electric generator advertised as "turbo-charged"? :)
I'm not an engine expert, so maybe someone who is can correct me if I'm wrong...

But isn't the idea here that a turbo-charged engine can allow for improved fuel economy because it allows you to use a smaller displacement engine while maintaining the necessary maximum power output with the help of the turbo?

I.e., under normal, low-to-medium power conditions, the smaller engine would provide improved fuel economy. But under heavy power demand (climbing a mountain, for example), the turbo could kick in to provide the extra necessary horsepower. (?)

This is how I understood the Ford EcoBoost approach, at least.

Also, why would the original Volt concept have used a 1.0L 3-cyl turbocharged engine if it wasn't well-suited to an EREV?
 

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Discussion Starter #5 (Edited)
emartin00 "They instead tuned it to run at an efficient point based on the power required for driving.
"

I'm not sure that's the case actually, I happened to do this little trick on my Volt. The car was in park and in "Mountian Mode", so the ICE was active. then while at a standstill, and in Park position, i pressed the gas pedal, the engine actually did rev up! I was perplexed actually:confused: Maybe they were expecting me to do a Nuetural Drop start to beat a Prius off the starting line :p

Also, I've purchased large 200-400KW generators for backup power at my work, they do have turbo chargers on them (though not advertised, true) even one that runs on Natural Gas. Now that would be and EXCELLENT ICE option come to think of it:cool:
 

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emartin00 "They instead tuned it to run at an efficient point based on the power required for driving.
"

I'm not sure that's the case actually, I happened to do this little trick on my Volt. The car was in park and in "Mountian Mode", so the ICE was active. then while at a standstill, and in Park position, i pressed the gas pedal, the engine actually did rev up! I was perplexed actually:confused: Maybe they were expecting me to do a Nuetural Drop start to beat a Prius off the starting line :p

Also, I've purchased large 200-400KW generators for backup power at my work, they do have turbo chargers on them (though not advertised, true) even one that runs on Natural Gas. Now that would be and EXCELLENT ICE option come to think of it:cool:
The original post was right. GM allowed you to speed the engine for familiarity, and in case you needed to speed charging for some reason. The gas pedal only does that when sitting stopped (though accelerating hard causes the engine to run faster too.)

For the larger case, you're thinking about one efficiency like it's the only thing to worry about. Running at a single speed means either a.) being limited in speed for long distance to the average power output, or b.) having too much power for most cruising cases - meaning you have to store that power and cycle the engine periodically.

The thing is, you lose ~20% of the power in the process of storing it and recovering it from the battery. By contrast, the difference between the 1400 rpm or 2700 rpm WOT bsfc and the best it can manage (which is at 1700 rpm,) is somewhere around 5%. So tell me, which one makes more sense and gets more economy? GM chose wisely. (When the car is using less power than the 1400 rpm WOT power output, the car adopts a different strategy that does involve cycling the engine.)

I'd love to see the gas turbine, but you have to trade the benefits (reduced pollution, multifuel nature, simpler operation, possibly cheaper if built en mass) against the drawbacks (lower efficiency, especially since it'd be pure series at all time, greater development efforts, public image of danger, noise levels [which might be solvable if it runs at a single RPM - it's amazing what tuned echo chambers can do.]) On the whole, I doubt I'll be seeing the gas turbine soon, as much fun as it'd be.

Diesel offers little benefit and several drawbacks (I had a TDI for 8 years and enjoyed it, but it isn't the right choice in the EREV paradigm, I think.) First, the engines are ~30% heavier for similar dispalcements and power levels (and require turbocharging.) Second, meeting US emissions with diesels is *hard* (US emissions are designed for gasoline cars - my Jetta actually had to be dirtier [generate CO, which diesel don't natively] to meet the NOx emissions target.) As a result, the emissions controls are expensive, and the cars are sensitive to fuel quality (current generation TDIs eat their high pressure fuel pumps and spit metal shards throughout the fuel system if there's a little water in the diesel - TDIclub is full of stories.) A DI Atkinson or HCCI engine can get similar economy without the cost or emissions issues. About the only benefits to diesel in this application are the long term stability of the fuel and for the eco crowd the burgeoning availability of bio-diesel.

Natural Gas is hard to store in adequate quantities, and not readily available everywhere - the exact opposite of what you want for an EREV engine.
 

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Discussion Starter #8
Now we're talking! That Capstone seems interesting. I think you would have to go with the 65KW unit 65Kw/746w = 87 Hp which is close to the ICE they are using, but weights in at what 300Lbs, I forget the ICE weight, still at least an possible option. Thanks John for the info :)
 

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I'd like to see more use of rotary engines. My other car is a Mazda RX8, which has a "tiny" 1.3 liter engine with 232hp. Rotaries are very compact, very light, mechanically simple, and so smooth that you'd barely notice it running. Plus, Mazda has them running on hydrogen.
 

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Now we're talking! That Capstone seems interesting. I think you would have to go with the 65KW unit 65Kw/746w = 87 Hp which is close to the ICE they are using, but weights in at what 300Lbs, I forget the ICE weight, still at least an possible option. Thanks John for the info :)
Yup. So the turbine with its controller weigh 50% more, occupies four times the space (won't fit under the hood,) is sold for around $30k, and will reduce your fuel economy by 15-20% compared to the existing car (based on their 26-29% efficiency on the specsheet, assuming you figure out how to covert its 600V DC to the car's 360V without losing any of it or adding any weight.)
Sounds like exactly what we need...

Again, it's a cool idea, but the technology isn't quite there yet. I'll be interested to see if anything comes of Bladon's axial micro jet program.
 

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I'd like to see more use of rotary engines. My other car is a Mazda RX8, which has a "tiny" 1.3 liter engine with 232hp. Rotaries are very compact, very light, mechanically simple, and so smooth that you'd barely notice it running. Plus, Mazda has them running on hydrogen.
Keep your eyes on Audi. They proposed an electric car with a series range extender made from a .5 or .8 liter one rotor rotary. You lose some thermal efficiency from the lower geometric ratio (or from the awkwardly shaped combustion chamber if you crank it up,) but you gain size and weight benefits as well as better NVH and simpler engines. The traditional challenges with combustion gas blowby at idle won't be a factor in a EREV.
 

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Discussion Starter #12
Walter,
First i like the color of Our White Diamonds, my wife stuck to her guns on the paint, i just wanted the technology. She was right :)

What are your thoughts on a 2-stroke option? Could be a weight savings i'm guessing and tuned pipes could keep the noise down.

I think the rotary is an excellent option too. Esp. if you can get it to run on other fuel feeds.

I want to express that I fully respect the work they did do on producing this car in the first place! It is an engineering piece of artwork. But engine options just seem to me like the next logical step. Even just smaller or Large ICE opions would be a step.

Gotta go do an EV coffe run!

Frank
 

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While I'll admit it is fun to talk about alternate engines, especially things like natural gas, deisel, or tubine engines. One thing that I'm sure of is that the engineers thought of all of this already. First and foremost, I'm quite certain that gasoline is the best fuel for the job. The reason is that the primary fuel source on this vehicle is electricity. The secondary fuel source should be the most widely available, which is gasoline. It sort of takes some of the appeal of the car away if you tell the customer that when they run out of electricity that they can switch to another fuel, but that fuel will be just as hard to find as electricity.

That being said, I'm sure the engineers had to consider many factors in finding an engine:
  • Size
  • Weight
  • Cost
  • Fuel Efficiency
  • History of reliability
  • Noise Level
  • Emissions
  • Time required to design and implement said engine.
That being said, I fully expect the next generation of the Volt to use a different ICE. The reason is that I suspect they will have had more time to explore other options and fully test those options in prototypes and in the lab. With the first generation Volt there were under a bit of time constraint. I believe the same is true for the batteries.

As for turbo-charged. I'm not a big fan. The Volt is already a complex vehicle. I really think adding extra complexity is a bad idea. I'm already scared as to what a major repair might cost when the vehicle is out of warranty. Add a turbo, no thanks.

If there is any bright side to that. I'm hoping the Volt will turn out a bit like the Prius. One of the more interesting things about a Prius is that the engine and its peripheral components seem more reliable in the long run than traditional gasoline cars. In fact, I have two friends who are Toyota mechanics and they say they've never seen a Prius leaking oil, no matter how many miles it has on it. The reason is most likely that the engine simply doesn't get hot enough for long enough to damage the seals. The Atkinson cycle probably produces less heat, combined with the fact that the engine doesn't run as often or work as hard as in a traditional ICE. So, with any luck the same will be true, if not more-so in the Volt. From what I've seen so far our Volt's ICE only runs about 5% of the time the car is being driven, so at 100,000 miles the engine should only have about 5,000 miles on it.
 

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Any idea what the net electrical efficiency of the current ICE/generator/inverter combo are?

I found some early threads that calculate 24kw is what is needed in CS mode to sustain 70mph on level roads and a combined 55kw for a mountain climb.
We're not 100% sure, but I think the consensus of the forum is that GM sized the 55/60kW engine output to sustain the 100 mph governed speed indefinitely. Hill/mountain climbing varies a lot - there are a number of steep grades out west that 55kW isn't enough to climb at the legal limit (or more, as most are wont to do.) That's why GM put in Mountain Mode - those extra 3.5 kW (thus, total around 4.5 kW from where the engine hold charge to where the battery stops providing power to protect itself,) mean it can put out the full 110 kW for (4.5 kWh/55kW from battery (other 55 from engine/MG A)) = .082 hours = 5 minutes.) There's no hill that needs the full power for that long, even at 70 mph (there are several hills you'll be climbing for more than five minutes - but you don't need 110 kW to pull a Volt up them at 70 mph.)

As for efficiency, there's a bit of apples and oranges here. The thermal efficiency of the Volt engine in its normal operating range is around 33% based on the bsfc from the ecomodder bsfc/bmep chart. If the car always ran in series, you'd have to add a ~90-95% generator efficiency to that to get a direct electrical efficiency comparison - in which case the capstone turbine is almost equal in efficiency.

(Thermal efficiency of an ICE is defined as the amount of mechanical power output at the driveshaft divided by the amount of chemical energy in the fuel to produce it. As such, it varies with engine RPM and throttle setting; the Volt is always at WOT, and the bsfc/TE I used here is typical of the 1400-2700 RPM range the engine mostly lives in at WOT. I believe the electrical efficiency capstone is quoting is the amount of electrical power provided by the generator divided by the chemical energy from the fuel.)

However, GM set up the series/parallel mode so that the Volt pushes most of the power mechanically at any speed above 35 mph except for hard acceleration (different amount at different speeds/accelerations, hard to quantify; maybe the best simple single answer is the 71/29% torque split at the planetary gear, but that can be very misleading in either direction sometimes for specific operating conditions. I think it'll be fairly accurate overall.)

Using the gear split, 71% of the Volt's CS mode power doesn't go through the series losses (which are more like 80-90% efficiency, since the car has to turn the power back into mechanical motion to be useful.) So 29% (capstone electrical efficiency) * .92 (assumed motor efficiency - certainly one of several efficiencies the Volt motor can have depending on torque output and speed) = 26.8% overall fuel to wheels vs 33% (1.4L thermal efficiency) * .85 (full series loop) *.29 (percentage assumed series) [=8.13] + 33% * .71 (direct gear driven) [=23.4] = 31.5% fuel to wheels efficiency.

Using very rough numbers, the current engine only needs (26.8/31.5) = 85% of the chemical energy in fuel to move the car the same distance at the same speed. Of course, the 1.4L has a lot more parts to fail, and is far pickier about what kind of fuel it drinks (though the fuel it needs is one that's currently widely available in good quality.)

You'll also note that much of this advantage comes from the series-parallel setup - using the same assumptions if it was a pure series car, the Volt's engine has 30.4% electrical efficiency (and would lose the power at the motor the same way the capstone does) - a less than 5% benefit over the turbine. That's why alternative power sources that can't be mechanically coupled have to be a bunch more efficient before they can produce a matching overall package. Most likely it'll happen, eventually - unless batteries and charging options improve enough to render the EREV obsolete first (possible, but my guess is EREVs will go fuel cell before batteries come down that far - and fuel cells aren't practical now and won't be for several years for cost reasons.)

There are a bunch of factors I'm neglecting to keep this simple (yes, this is the simple version) - but I believe they are neglected fairly - as in, they apply equally to both cases. I'm also assuming that both versions of the car have the same power requirements (changing the package to fit something the size of the capstone would be detrimental, as would it's extra weight. OTOH, with no parallel connection, the generator structure can be moved anywhere in the car, potentially allowing more radical aerodynamics. That's why this is still an art form, people. Constructive synergy happens, when the engineer is clever enough to find it. :) )
 

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Walter,
First i like the color of Our White Diamonds, my wife stuck to her guns on the paint, i just wanted the technology. She was right :)

What are your thoughts on a 2-stroke option? Could be a weight savings i'm guessing and tuned pipes could keep the noise down.

I think the rotary is an excellent option too. Esp. if you can get it to run on other fuel feeds.

I want to express that I fully respect the work they did do on producing this car in the first place! It is an engineering piece of artwork. But engine options just seem to me like the next logical step. Even just smaller or Large ICE opions would be a step.

Gotta go do an EV coffe run!

Frank
The White Diamond is nice - it contrasts with all the black bits to make a yin-yang appearance (especially with the black seats with white inserts and white console,) that I think suites the car's dual personality under the hood.

Two strokes - in theory they're a great thing. In practice most of the common versions have problems with emissions, throttling, and reliability. The ones you see in small applications, like lawn mowers or boats, or mostly "crankcase pumped" - that is, they use the crankcase as a compression chamber to push the exhaust air out and new air into the cylinder when the piston is down. That means putting gas into the crankcase, where it washes the oil film off causing wear, and sucking oil mist into the combustion chamber and burning it. It also means a long, uneven air path from carburetor to chamber - very hard to control mixture - and an engine that doesn't respond well to abrupt throttle changes.

On the other hand, Detroit diesel has for 60 years or so had a very successful business building large (from pickup truck sized through locomotive sized) two stroke diesel engines - which rely on an external mechanical supercharger (or in some cases, a supercharger combined with a turbocharger) to scavenge the cylinders and have a conventional oiled crankcase. So it's certainly possible to build two stroke engines that don't have the above problems...

With the technologies available right now, if you're going to depart from traditional piston ICEs, I think the most likely choice for an EREV is a compact rotary, like the one Audi was experimenting with. There's no reason such a motor couldn't be mechanically tied to the wheels like the current engine (though it'd prefer to have 2-3x the gearing/operating RPM - could put a fixed planetary stage into the engine housing along with the epicyclic gears you have to have anyway and thus be able to drop it directly into the existing packaging.)

Personally, my guess is for the ELR and next generation Volt GM will take the smallest four from their next generation engine platform and provide it in a high compression ratio gasoline direct injected form - possibly dedicated Atkinson with a higher geometric CR (16:1?) possibly just with variable valve timing that mimics Atkinson when the loads are lower (which we're told the current 1.4L does.) (and thus a 12/13:1 CR.) If they're feeling really ambitious, and can sort the emissions challenges out (NOx...) it'll go into HCCI when the load conditions suit. Well established tech with production lines they can share cost on, and enough of a twist to add substantial economy.
 

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a 5 gallon exchange tank of Propane is pretty easy to find at Home Depot, Lowes, Costco, Walmart, etc ...
And how many people would be willing to drive across country in a Volt if they had to stop and look for a Wal Mart or some place to exchange a propane tank for? That was the whole point of the Volt is that you could drive across country if needed.

Don't get me wrong. I think it would be a very cool idea. It would appeal to me. But I just don't think it would appeal to the mainstream consumer.
 

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Discussion Starter #17
I agree that Propane isn't hard to come by at least in Oregon. Several local gas stations carry it. I have an RV so i know where they all are :) ( it has solar cells too). Nat Gas would be sweet if you could just hook it up to a home outlet. Oregon gas stations are a pain to use, part of the justification for Volt purchase cost here anyway. "Gas station anx" I LOVE IT :)

So there are some canidates for engine options and im pretty sure if there was a "relationship" deal in the works, the Capstone guys could do some R&D to reduce the weight and change the DC output and size to match the volts needs. But you are right, not in production. Diesel two stroke sounds TRICK! And does that come in BioDiesel compatable?

Of course we all want some kind of Nano-tech battery or such to POP-out of research and end our ICE but that's just not too likely. So i just want some kind of options.

Without trying to sound funny, what about using steam engine? They are often used to generate electicity and with todays computer power we could develop some awsome micro boiler that could prep itself for energy demands the engage when the time is right. and be flex fueled. Yep, still an R&D project at best :(

Back to the 2-stroke deisel!
 

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Rotary engines are terribly inefficient, at least in the way that Mazda has implemented them. Mazda's "1.3 L" rotary engine is very deceptive in that its realistic displacement is much higher (probably as much as twice, or a 2.6 L standard ICE equivalent). The horsepower output is adequate at 212 hp, but the torque is extremely low at 159 lb-ft. To make matters worse, the fuel economy is only 16 city/23 highway. And all of that from a "1.3 L." Maybe Audi can do it better?

I'm liking more and more the way that GM set up the series/parallel hybrid, but I'm still not sure that it was as good as it could have been. I know that some concessions needed to be made for the sake of cost and timely implementation, but I do see some ways that it could have been done better (at least in my opinion).

Staying on topic, purely in the realm of the engine, I think that a few changes could be made for the next iteration.

First, I would definitely like to see the switch to an aluminum block. Despite what the engineers have stated, a 30-40 lbs weight savings off of the engine alone would be significant.

Second, I think that the 1.4 L actually might be too much. I know that it is helping to lug around a 3,800 lb car, but given its 80 hp, I'm not sure that the displacement is justified. GM had a 1.0 L, three cylinder engine capable of outputting close to that much power 20 years ago. The smaller displacement certainly would also help with the size issues the GM engineers were concerned about by going with an aluminum block.

Third, I'd really like to see a switch in layout for the engine. I know that Americans have grown accustomed to front engine/front wheel drive, but I'd much rather see the layout switched to a rear engine/rear wheel drive (or possibly AWD). Moving the ICE and generator to the rear would reduce additional weight in the exhaust system, clean up the aerodynamics in the front and some of the underbelly (possibly a 0.02 improvement in Cd), and allow additional power to be regenerated from the rear wheels (unless someone can answer whether both the motor and the generator already are engaged through the front wheels while decelerating).

Fourth, while I understand that the primary purpose of the ICE range extender is to provide power directly to the electric drive motor, it is still wasting a significant amount of energy in the form of thermal loss. I would love to see something implemented (possibly even a TEG unit) to recapture lost thermal energy and use it to recharge the battery. The amount of power regained wouldn't be enough to run the electric motor directly, but depending on the efficiency of the unit, it could produce several kWh over the course of a long trip.
 

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So there are some canidates for engine options and im pretty sure if there was a "relationship" deal in the works, the Capstone guys could do some R&D to reduce the weight and change the DC output and size to match the volts needs. But you are right, not in production. Diesel two stroke sounds TRICK! And does that come in BioDiesel compatable?
I hadn't intended to suggest that a two stroke diesel was GM's best option for the car. Certainly the existing Detroit engines are highly unsuited - the smallest AFAIK is the 3-53 - 159 cubic inches (something like 2.6 liters - similar to a 5.2 liter 4 stroke v6 in air flow/fuel flow per minute at a given RPM,) with around 120 hp at the ~2800 rpm high end and weighing around a thousand pounds.

The big advantage of a 2 stroke is you can have a little 3 cylinder that purrs as smoothly as a traditional inline 6 BMW.

The current detroit engines certainly handle Biodiesel fine - but they don't have the kind of high pressure injectors that manufacturers use to meet modern emissions (which need massively high rail pressures (35000 psi!) that are provided by close tolerance high pressure fuel pumps that are lubricated by the fuel and get mad if it isn't exactly what they thought it'd be (the current problem for a lot of diesels.)

I shouldn't encourage you, since I'm not at all sure the research makes any sense, especially for a car whose engine isn't even running most of the time. :)

Having said that, there are some interesting bits:

The only way you have a chance at making emissions with a two stroke diesel is by external scavenging. This would normally mean you'd need a supercharger blowing air through the engine.

There are a couple companies out there who have been toying with electric turbochargers (a normal turbocharger with an electric motor tied into the driveshaft somehow.) They're doing it mainly to eliminate turbo lag - the theory being it'll use the motor to push the compressor wheel until the exhaust gases catch up - but it has other uses... done properly, one of these could be your scavenging blower for a 2 stroke, while allowing you to extract additional electric power from the exhaust when the engine is running hard. It also would have the advantage of letting the ECM specify whatever boost pressure it wants for a given power condition, which might help in developing emissions.

If designed from the beginning for biodiesel or variable fuel quality, you could manage it easily enough - the main thing you'd need is an alternate way to pressurize the fuel rail that doesn't depend on the fuel's lubricative qualities or viscosity (possibly a HUEI injector like the 7.3 power stroke used as a way to charge the rail of modern piezo injectors for the cylinders?)

For a diesel, it all comes back to emissions. These days, you'd pretty much have to have a particulate filter, which also means having a plan for burning the filter clean periodically. Most recent cars have gone to urea injection for selective catalytic injection to meet the challenge of NOx requirements.

So my notional solution would be a ~.5.-.8 liter three cylinder two stroke diesel with electric turbocharger and HUEI charged rail. It's doable. It'd be lighter, smoother, and quieter (turbo eating the engine pulses) than the existing engine. It could possibly be done to meet emissions. I have serious doubts about it being worth the development money - would you pay $3-10k more for a car with this engine and (estimated - far too many assumptions involved to be confident) ~1 extra electric miles from reduced weight, 50-55 mpg on diesel or bio (which have ~10% more chemical energy per gallon, before the efficiency differences.)?

GM's betting you won't, in a car that uses it's engine ~20% of the time. So they went with simple, inexpensive, well understood and reliable, at least for the first generation.
 

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A purpose built E85 engine might actually be the best solution. In a parallel/series hybrid, the electrical system could be used to keep the fuel at the ideal temperature (even during winter, which offsets the need for E50-E70). Also, E85 is better suited for Atkinson-style engines and is better able to cope with lean-burn environments without spewing out massive amounts of NOx. Worst case scenario, throw in a bottle of 190 proof Everclear when you run out of fuel. The only problem is that the volumetric energy density is about 30% less than gasoline, so the mileage would suffer a bit.
 
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