ethanol and high compression
Oct 10, 2007, 11:52 AM
#1
ethanol and high compression
Ethanol-based engines
Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors and airplanes. Ethanol (E100) consumption in an engine is approximately 34% higher than that of gasoline (the energy per volume unit is 34% lower)[15][16][17]. However, higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than would be obtained with the lower compression ratio.[18][19] In general, ethanol-only engines are tuned to give slightly better power and torque output to gasoline-powered engines. In flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For maximum use of ethanol's benefits, a much higher compression ratio should be used,[20] which would render that engine unsuitable for gasoline usage. When ethanol fuel availability allows high-compression ethanol-only vehicles to be practical, the fuel efficiency of such engines should be equal or greater than current gasoline engines. However, since the energy content (by volume) of ethanol fuel is less than gasoline, a larger volume of ethanol fuel would still be required to produce the same amount of energy.[21]
A 2004 MIT study,[22] and paper published by the Society of Automotive Engineers,[23] present the possibility of a definite advance over hybrid electric cars' cost-efficiency by using a high-output turbocharger in combination with continuous dual-fuel direct injection of pure alcohol and pure gasoline in any ratio up to 100% of either. Each fuel is stored separately, probably with a much smaller tank for alcohol, the peak cost-efficiency being calculated to occur at approximately 30% alcohol mix, at maximum engine power. The estimated cost advantage is calculated at 4.6:1 return on the cost of alcohol used, in gasoline costs saved, when the alcohol is used primarily as an octane modifier and is otherwise conserved. With the cost of new equipment factored in the data gives a 3:1 improvement in payback over hybrid, and 4:1 over turbo-diesel (comparing consumer investment yield only). In addition, the danger of water absorption into pre-mixed gasoline and supply issues of multiple mix ratios can be addressed by this system.
Ethanol's higher octane allows an increase of an engine's compression ratio for increased thermal efficiency according to the formula given at [24]. In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19.5 with fuels ranging from neat ethanol to E50. Thermal efficiency up to approximately that for a diesel was achieved.[25] This would result in the MPG of a dedicated ethanol vehicle to be about the same as one burning gasoline.
Engines using fuel with from 30% to 100% ethanol also need a cold-starting system. For E85 fuel at temperatures below 11 °C (52 °F) a cold-starting system is required for reliable starting and to meet EPA emissions standards.[26]
Ethanol is most commonly used to power automobiles, though it may be used to power other vehicles, such as farm tractors and airplanes. Ethanol (E100) consumption in an engine is approximately 34% higher than that of gasoline (the energy per volume unit is 34% lower)[15][16][17]. However, higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than would be obtained with the lower compression ratio.[18][19] In general, ethanol-only engines are tuned to give slightly better power and torque output to gasoline-powered engines. In flexible fuel vehicles, the lower compression ratio requires tunings that give the same output when using either gasoline or hydrated ethanol. For maximum use of ethanol's benefits, a much higher compression ratio should be used,[20] which would render that engine unsuitable for gasoline usage. When ethanol fuel availability allows high-compression ethanol-only vehicles to be practical, the fuel efficiency of such engines should be equal or greater than current gasoline engines. However, since the energy content (by volume) of ethanol fuel is less than gasoline, a larger volume of ethanol fuel would still be required to produce the same amount of energy.[21]
A 2004 MIT study,[22] and paper published by the Society of Automotive Engineers,[23] present the possibility of a definite advance over hybrid electric cars' cost-efficiency by using a high-output turbocharger in combination with continuous dual-fuel direct injection of pure alcohol and pure gasoline in any ratio up to 100% of either. Each fuel is stored separately, probably with a much smaller tank for alcohol, the peak cost-efficiency being calculated to occur at approximately 30% alcohol mix, at maximum engine power. The estimated cost advantage is calculated at 4.6:1 return on the cost of alcohol used, in gasoline costs saved, when the alcohol is used primarily as an octane modifier and is otherwise conserved. With the cost of new equipment factored in the data gives a 3:1 improvement in payback over hybrid, and 4:1 over turbo-diesel (comparing consumer investment yield only). In addition, the danger of water absorption into pre-mixed gasoline and supply issues of multiple mix ratios can be addressed by this system.
Ethanol's higher octane allows an increase of an engine's compression ratio for increased thermal efficiency according to the formula given at [24]. In one study, complex engine controls and increased exhaust gas recirculation allowed a compression ratio of 19.5 with fuels ranging from neat ethanol to E50. Thermal efficiency up to approximately that for a diesel was achieved.[25] This would result in the MPG of a dedicated ethanol vehicle to be about the same as one burning gasoline.
Engines using fuel with from 30% to 100% ethanol also need a cold-starting system. For E85 fuel at temperatures below 11 °C (52 °F) a cold-starting system is required for reliable starting and to meet EPA emissions standards.[26]
so i want to start a discussion about some sort of vague topics.
firstly is there any benefit to increasing compression on a turbo charged motor while running e100?
now i ask this question with the following in mind:
we are already advancing timing when we tune for e100.
low compression in gasoline turbo charged engines have usually resulted in higher peak cylinder pressure which results in the most power for the octane given...??? so what i'm saying is that the lower compression gives more power because you can cram more air.
further questions... is it a noncomparable difference between e100 and gasline that makes it so you can get 19:1 compression on an e100 motor and nothing even close to that on a gasline motor (or is this wiki citation a race car?)?
so can we run something like 10.5:1 compression, boost 21psi, and still make tons of horsepower? i doooo feel like i'm missing a part of the picture here, because technically we should be semi optimised by advancing timing and cramming more boost.
i guess my real question is bottom line: does alcohol allow for inherently higher compression while still maintaining the same boost level. what if we boosted 26psi or whatever the e100 norm is, upped the compression, would we pull some timing and make MORE power?
Oct 10, 2007, 12:51 PM
#3
increased compression doesn't actually increase spool up. it increases the naturally aspirated ability of the motor running at a high efficiency, this makes the MOTOR move faster, but spool up would be the same if not delayed becuase you're not moving as much AIR (but you are moving what air you are moving more efficiently). moral of that story is that low torque would imporve due to improved n/a characteristics. this concept was divulged in a recent scc.
they only "like" it because lower compression gets you higher cylinder peak pressure because you were able to cram more air in.
what i'm trying to say is that with the limitations of gasoline (octane) you see lower compression turbo charged motors bringing in more power (than higher compression engines that are turbocharged) because you can move more air with lower compression (before you hit knock threshold).
can you move more air with HIGHER compression pistons and alcohol... and to what level can you do that? or is lower ALWAYS better even in the case of alkie?
they only "like" it because lower compression gets you higher cylinder peak pressure because you were able to cram more air in.
what i'm trying to say is that with the limitations of gasoline (octane) you see lower compression turbo charged motors bringing in more power (than higher compression engines that are turbocharged) because you can move more air with lower compression (before you hit knock threshold).
can you move more air with HIGHER compression pistons and alcohol... and to what level can you do that? or is lower ALWAYS better even in the case of alkie?
Last edited by trinydex; Oct 10, 2007 at 12:54 PM.
Oct 10, 2007, 01:14 PM
#4
I don't really understand what OP is trying to say. There's also "Alternative Fuel" section on this forum. But i'll try to answer anyway:
Article talks about NA engines where in order to use ethanol's higher resistance to detonation, compression ratio needs to be increased, therefore producing more power from increased cylinder pressure.
On a turbo motor, you would just crank up the boost.
Article talks about NA engines where in order to use ethanol's higher resistance to detonation, compression ratio needs to be increased, therefore producing more power from increased cylinder pressure.
On a turbo motor, you would just crank up the boost.
Oct 10, 2007, 01:40 PM
#6
so can we run something like 10.5:1 compression, boost 21psi, and still make tons of horsepower? i doooo feel like i'm missing a part of the picture here, because technically we should be semi optimised by advancing timing and cramming more boost.
i guess my real question is bottom line: does alcohol allow for inherently higher compression while still maintaining the same boost level. what if we boosted 26psi or whatever the e100 norm is, upped the compression, would we pull some timing and make MORE power?
i guess my real question is bottom line: does alcohol allow for inherently higher compression while still maintaining the same boost level. what if we boosted 26psi or whatever the e100 norm is, upped the compression, would we pull some timing and make MORE power?
So long as we have more than sufficient octane to support MBT ignition settings at the optimum point in crank rotation (e.g. 12-15 deg ATDC), we have room to increase cylinder pressure two ways - (1) increase SCR, (2) increase manifold pressure.
Obviously, a normally aspirated engine is limited to option (1). With a turbo engine, so long as we have enough reserve turbo efficiency, option (2) creates far more power potential than option (1).
WRC cars use a different strategy. They are turbo restricted, so they actually use 10:1 SCR and 40 psi of manifold pressure with pump fuel. They can get away with this primarily because the relatively low engine speeds and aggressive cam profiles reduce effective cylinder pressure to within acceptable octane limitations. So in this case, a relatively high SCR is favorable.
In consideration of these things, it would appear as though an engine with small turbo and relatively low rpm operation would benefit more from increases in SCR than would an all-out high rpm engine, all else (including fuel octane) being equal.
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Oct 11, 2007, 11:25 PM
#15
...Or 13.5:1 and 50psi in some apps. In the TA world 11.5:1 or so and a 100% OD 14-71 are the norm. Then there are the high helix superchargers that move even more air. It gets better yet, because some of them have problems holding enough heat at the line to keep them warmed up and make power during a pass. The compression helps some with that but of course its a bunch of compromises.
I know Lucas English is building some 10:1 motors for E98 but I havent heard what they dyno'd (if they have yet) at.
I know Lucas English is building some 10:1 motors for E98 but I havent heard what they dyno'd (if they have yet) at.