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Originally Posted by BDC
On to alcohol.
Alcohol, on the other hand, is a fuel that burns and therefore lends itself more closely to the rules and practices of tuning. Depending upon which type of alcohol (ethyl vs. methyl), much more of it in volume is required compared to gasoline to create the same heat energy (Heating value in btu/lbs). For example, if running an all pump gasoline setup with even a 200cc/min replacement of gasoline with methyl alcohol, nearly 400cc/min of that alcohol would have to be used to produce the same heat energy and produce the same air/fuel ratio. Side note: This is also the reason, when fuel manufacturers swapped from MTBE (methyl tertiary butyl ether) as a fuel oxygenate over to ethanol up to 10% volumes, why some folks experienced suddenly running mild to moderately leaner air/fuel mixtures with nothing on the tune or hardware changed.
Other than consumption and alcohol's corrosivity (methyl alcohol in particular) which necessarily calls for strict hardware to be used in said injection system (teflon-cored, stainless steel braided lines w/ brass ends and not cheap nylon or rubber tubing for example), I think it carries multiple benefits over and above water:
-) Incredible charge coolant due to low flash temp; so much so that it's possible to run hot-air with big boost, therefore requiring less intake hardware and a shorter plumbing run
-) Even though only half as good as water, still a terrific chamber coolant
-) "Raises" the base fuel's chamber temperature tolerance due to it being a much more stable burning fuel over gasolines and having a higher "effective" octane rating
-) Much less change of knock due to high auto ignition temperature (almost 400*F above typical pump gasolines and about 200-300 over most leaded race gasolines)
-) Robust alcohol injection systems can inject massive amounts of alcohol, which enable the ability to run heavy ratios of gasoline to alcohol (80/20 and richer), therefore yielding the possibility of running a less hardware intensive fuel system (not needing to max out large injectors or run humongous fuel pumps)
One more advantage that alcohol has is this: it contains less carbon atoms than gasolines. Therefore, richer mixtures (in alcohol volume) can be run without flooding the motor and fouling out plugs. When one runs a gasoline to alcohol ratio like I've experimented with (70/30), where alcohol injection is at and over the 1500cc/min range, it's possible to run air/fuel mixtures in the 9's and experience none of the problems associated with that same mixture on an all gasoline setup. The benefit is this: the extra alcohol is used as a chamber coolant. We can throw even more cooling btu's in the mix while still producing power. It's no surprise folks like Howard Coleman run low 20lbs of boost with mixtures in the 10's:1 on gasoline/alcohol ratios around 80/20 to 75/25 and have zero knock. I've done the same thing at higher boost levels, without an intercooler, breaking all of the accepted "tuning rules", over and over and over again.
600cc/min of methyl alcohol injection is roughly equivalent to 300cc/min of water injection. It's got the cooling capacity of nearly 2000cc/min of gasoline. If you do the math, that's a lot of fuel injector.
Take a 680/1680 injector, large-shaft T4 turbo, street port setup. It can run about 25psi of boost on leaded race gasoline, aiming for a conservative 11.0:1 air/fuel mixture, at duty cycles around 90-95%. Total injector output is around 4200/4300cc/min. Removing one air/fuel mixture point (going from 11:1 to 12:1) would remove about 400cc/min of injection. Replace that 400cc/min with 800cc/min of alcohol to aim back to that 11:1 air/fuel mixture. Not only does that 9% replacement reduce the overall carbon being tossed into the motor (allowing it to realistically run a richer mixture without challenging the spark plugs), it's also increasing the cooling btu's of that 400cc/min (38lbs/hr at 5700btu's/hr) to 38500btu's/hr! That replacement of 400cc of gas with 800cc of methanol will cool 6.76 times better. It'll also make for a more stable fuel that burns colder as well as stretch out the maximum power output of the fuel system.
My experience over the last four years of messing with alcohol injection has shown me that alcohol is where its at. Again, I'm not trying to make another soon-to-be-closed thread that's devolved into Internet heroes fighting about "water vs. alcohol"; this is simply a subjective opinion based on observation. While I'm aware that there's a few folks that go for big boost with huge amounts of water injection (all of them pre-turbo, I think), I still like the idea of attacking the heat-related problems in this engine by pointing the guns at the base fuel and making that base fuel more stable and predictable (with alcohol) instead of trying to drown it in massive amounts of water. That's just me and so far that experience, plus the other beneficial effects of alcohol like being able to run a hot-air setup, have pointed me in that direction. Again, not trying to knock water; I like it for certain setups. I just see alcohol injection taking us further.
Those of us that've used alcohol extensively all conclude the same thing: The more alcohol, the better. The rotary loves it.
What's the overall goal here? We're cramming more and more air into the engine in an attempt to produce more power. What makes power? Density of charge. What comes with increase charge density via forced induction? Temperature. When pressure rises, temperature goes right along with it. We generate more pressure with our desire to run more boost and make more power. The high temperature is the negative byproduct of our efforts to run more boost. The rub is trying to keep this temperature within certain limits (depending primarily on the base fuel, spark plug temp heat range, and other hardware). I think the idea that some folks seems to draw glory from in running high boost on strictly pump gas is foolish as it reminds me of the idiot that stands at the end of the cliff, inching his tippy-toes ever closer to the edge, challenging himself on when he'll eventually fall off. This is where the magnificence of AI comes in and I think for the reliability factor on our engines we all ought to delve into it seriously; so seriously that we all consider it necessary in having a tuned street setup.
Barry? rx72c? Howard? Anybody else? Any thoughts?
B
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