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Ethanol Direct Injection as an Enabler for Aggressive Engine Downsizing

MIT scientists are exploring the use of ethanol direct injection (DI) to support the use of small, highly turbocharged engines with substantially increased efficiency as a downsizing strategy to reduce fuel consumption and emissions.

The researchers project that ethanol DI could result in a part-load efficiency increase of 30% relative to conventional port-fueled injection engines. The proposed direct injection approach could thus potentially provide a more cost-effective alternative to current generation gasoline-electric hybrids and turbodiesels.

The foundation of the approach is the enhanced knock suppression resulting from such a use of ethanol, which could allow for more than a factor of two increase in manifold pressure relative to conventional, while also supporting an increase in compression ratio.

Knock refers to the autoiginition of unburned gas in the cylinder. There are a number of factors that contribute to knock, but two of the main ones are cylinder pressure, temperature and fuel octane.

Turbocharged boosting of an engine can contribute to engine efficiency, and thereby support the use of a smaller engine. The application of turbocharging, however, is limited by the occurrence of knock under higher cylinder pressures.

The ethanol direct-injection concept uses the high octane rating of ethanol coupled with the evaporative cooling from direct injection to support the higher-pressure, more efficient engines. For example, a 3.0-liter engine could potentially be replaced by an engine of about half its size, resulting in a 30% increase in fuel efficiency over a typical driving cycle, according to the researchers.

The ethanol direct injection system is controlled separately form the gasoline injection system, and the ethanol is stored in a separate tank. The gasoline system can continue to use conventional port-injection.

The ethanol injection is carried out so as to maximize evaporative cooling which occurs when it is directly injected into the engine cylinders. The resulting reduction in temperature of the fuel/air charge from the ethanol evaporative cooling is the major factor in enhancing the fuel octane rating and suppressing knock.

The concept would operate the engine with a wide range of ethanol consumption from a minimum of less than 5% up to 100%, A knock sensor would determine when ethanol is needed to prevent knock. During the brief periods of high torque operation, the fractions of up to 100% ethanol could be used. For much of the drive cycle, vehicles are operated at low torque and there is no need for the use of ethanol.

Only a small amount of ethanol—less than one gallon of ethanol for every twenty gallons of gasoline—may be required to achieve the large increase in efficiency.



Mark A

Will this offset the lower energy density of ethanol compared to gasoline? My guess would be no.

Does anyone automaker currently offer direct injection, of gasoline, in any vehicle currently for sale?


This appears to be a theoretical study without any prototype being built as yet--at least that's what appears from skimming the paper. Looks like a creative and very practical approach to improving fuel economy significantly with off-the-shelf technology. I hope to see more about this.



I don't think the lower energy density of ethanol is such an issues with this idea, since the engine would run on gasoline most of the time, adding ethanol when needed as an octane booster and knock inhibitor during hard acceleration, etc. You get a smaller gasoline engine running efficiently under part-load conditions (most of the time) and a high-boost turbo under load. You do have to fill up with two separate fuels, however.

Mark A

Thanks, I stand corrected. I misunderstood into thinking the engine was to be run on ethanol only, and not as an additive.


If GM is serious, I mean SERIOUS about producing flex-fuel vehicles, this technology, or one similar to it would be an excelent way to minimize one of the most significant disadvantages of ethanol - the lower energy density relative to gasoline. GM should really start to dole out some research dollars into technologies like this. Toyota and Honda has to invest heavily in hybrid technology to make them work, I expect GM will need to do the same for flex fuel vehicles as well.


"Does anyone automaker currently offer direct injection, of gasoline, in any vehicle currently for sale?"
Yes there are few of them: GM,VW, Mercedes. As a matter of fact my '91 Cadillac Seville had direct injection (I know because I had to replace those injectors few times)

gerald earl

MIT is now looking into creating an alternative energy research lab.I would encourage GM to offer a close working and funding relationship.
If this tech were scaled up and tested successfully it would leapfrog the patent holder ahead of hevs.This is one reason automakers are timid of plowing money into new tech.
I have been reading MIT Technology Review for years.Many stories I read about in the nineties are entering the market now.I believe an alternative energy reveloution is taking off .now


GM is not using direct injection in any gasoline engines...yet. The Solstice GXP will be their first application this fall though. Audi/VW have done a great job with it in their 2.0 Turbo that is used in the A3, A4, Jetta, and Passat. Lexus uses it on 3 naturally aspirated engines so far - a 2.5 and a 3.5 in the IS and a 3.0 in the GS. Mercedes is also using it, and BMW will be in the fall as well.

However, to the best of my knowledge, none of them are using the most advanced super high pressure "micro piezo" versions yet (I believe Mercedes will in their upcoming BluTec Diesel). That is where the big gains in fuel efficiency will come from, because of the ability to run a very lean air-fuel mixture.


Since we're all giving advice to GM, I may as well join the party: GM, combine this technology with your inexpensive mild hybrid (BAS/Vue Greenline, etc) technology for a potentially much less costly solution compared to full hybrids that competes with them in both stop-and-go conditions and on the highway.

Sid Hoffman

Mazda is also using direct injection on their Mazdaspeed 3s, or whatever it's called. Honda uses direct injection on a version of the Stream minivan, although it has never been sold in the USA. DI is just about the last big thing for gasoline engines as far as increasing volumetric efficiency. After DI is commonplace, nearly all further gains will have to come from downsizing, forced induction, and hybridization.


Maybe a little more complicated than you were thinking, but GM is taking a similar approach through Saab:

30mpg on E100, on an AWD convertible (which is a good deal heavier than a sedan) with a 5-speed auto. A lighter FWD sedan with a CVT would add a few more MPG.


Direct injection has nothing to do with volumetric efficiency.

Volumetric efficiency is a measure of how much air your engine pumped relative to it's displacement.
Air is the limiting reagent in the chemical reaction, more air lets you use more fuel = more power.
A higher volumetric efficiency lets you get more work out of an engine with smaller displacement.

variable valve timing/lift etc is a big thing for engines as far as increasing volumetric efficiency.

There are many times where you want to operate at less than 100% power ... so you throttle the engine with the carb/ throttle body but this increases pumping losses.

The BMW valve-tronic adjusts valve timing and lift and eliminates the throttle plate.

Because most vehicles have a fixed number of discrete gear ratios the engine has to operate over a range of speeds.

This is bad for efficency, the intake / exhaust manifolds cam shaft(s) that work great at 6000 rpm suck at idle.

This is why you see variable length intake manifolds and variable valve timing systems to try make the engine run well over a wide rpm range.

GM uses an exhaust cam that can be advanced or retarded, honda uses 2 camshafts one for high rpm and one for low rpm operation.

Chrysler, GM, and others use cylinder deactivation to reduce fuel consumption under low load.

DI + variable valve timing does allow you to do some cool things like stratified charge combustion.
Reading on this subject is left as an exersize to the reader.



Your cogent comments on throttling, pumping losses, etc. are not contrary to the thrust of this development. As I read the paper, DI is only used for ethanol; gasoline would still be port injected. The efficiency benefit is gained by running a smaller engine at wider-open throttle most of the time (part load), closer to it's efficient operating range. When you need more power, you increase manifold pressure (turbo) and meter in the ethanol through DI to eliminate preignition. It looks like most of the efficiency would be gained by the part-load optimization, if I'm not mistaken, not by DI.


How sad that no one (in the USA) ever realizes that Mitsubishi was the first company to mass market a Gasoline Direct Injection powered vehicle. They had a 1.8L 4 cylinder GDI engine back in 97 being used in the Japan market Lancer. Now it is a 2.0L GDI and turbo 2.0L GDI engine in the Lancer. They use a 40:1 air fuel ratio thanks to GDI.

Many drag racers have used ethanol injection when they turbocharged naturally aspirated motors and did not want to put in lower compression pistons. Hyundai McIntyre in El Paso, TX (well it is owned by someone else now but back in the late 90s it was owned by McIntyre) used to spit out turbocharged vehicles with Ethanol injection to support the additional power. They would have 140hp 2.0L motors pushing 300hp with no intercooler on stock compression, stock internals (with a t3/4 hybrid garrett turbo) simply through the use of ethanol to cool the incoming air and provide fuel to support the extra power.


thanks to RI for sorting out a lot of terms people should just know if they talk about this subject.

i agree that stratified combustion is where some neat savings will be. i will be really startled if cam and valve tricks can go much further in helping mileage.

the old Otto cycle has given us a wonderful century of thrilling rides and, sometimes, fits when the mechanicals broke. the batteries and cell replacements are unlikely to be as much fun but alas, they are needed.

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