Cracked piston on high mileage stock bottom end
- Thread starter bison
- Start date
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+1 I would think you would need a garden hose with dual nozzles and high timing to preignite. As along as you have the correct NOZZLE(kit) and proper amount of alky for our application we should be fine. I know I'm not in Don's league... Just posting my thoughts.
+1 I would think you would need a garden hose with dual nozzles and high timing to preignite. As along as you have the correct NOZZLE(kit) and proper amount of alky for our application we should be fine. I know I'm not in Don's league... Just posting my thoughts.
The information that I've run across suggests that the problem is more related to applications where large amounts of alcohol is being used with gasoline. I get the impression that small amounts used as a simple knock suppressant in a typical street application is not the problem.
The trick is keeping the methanol below the autoignition temperature before the correct ignition point.
Some chemistry of methanol.
Temperatures over 149F assist the vaporization of methanol.
A nozzle that finely atomizes the methanol will assist vaporization.
Methanol fully dissociates at around 600F at 1 atm.
At higher atms dissociation is inhibited to a degree.
As methanol dissociates, it absorbs heat.
Much of the heat used to dissociate the fuel comes from adiabatic heating from the compression of the mixture in the cylinder. The amount of methanol that has not dissociated by the time for ignition, will dissociate during the combustion process. The amount that dissociates during combustion will absorb a portion of the combustion heat from dissociation.
The autoignition temperature of methanol is 725-878F.
So methanol will fully dissociate and be ready for ignition at 600F, and will autoignite at temps between 725-878F.
I would think you would want a portion of the methanol available for dissociation during the combustion process to do a good job of controlling combustion temps and hence detonation of the gasoline.
Actually, a garden hose of methanol would do a good job of killing cylinder, compression and combustion temps. As long as the dissociation of available methanol can keep temps below the autoignition point, you'd be OK.
Since you're mixing fuels and the primary fuel is gasoline, it's possible that not enough methanol is available to keep temps down. And with gasoline, if the temps are too low, power is going to suffer, which would tempt the tuner to lean the mixture out for more power. Leaner mixture equals more heat, which would demand more methanol. It becomes a vicious circle.
If Don's theories are correct then by adding a small percent of water to the injected methanol should pull even more heat out of the combustion chamber as it boils and prevent the methanol form pre igniting. Probably lose a little power though. One thing i know for sure is my charge air temp in the intake is low. It would have to gain approx. 650* at 1 atmosphere to pre-ignite. Its probably possible since the compression of the mixture and the actual compression ratio will increase the temp of the charge in the cylinder. The compression ratio is 9.3:1 and i had 26psi at a max of 72*F in the intake. Timing was 22-23* on the latest engine. I had no problem running that till i hit the injector cut off
. I m going to be throwing even more methanol at it soon enough so we will see. It should be interesting if i run it on 93 pump gas and run in TAI. I plan on using 30gph of nozzles and switching to a 3 bar MAP for the alky.
vacuum 6
I have chuckers
- Joined
- Jan 6, 2006
~At what HP/ET range does this happen?
This is a fine line for an engine that is being pushed to the limits where cylinder and combustion temps are concerned. Any methanol that dissociates during the combustion process will most likely quench some of the combustion process. That would most likely be noted as a power loss. If combustion temps are at the limit and all the available methanol has already dissociated during the compression process and none is available to help cool the combustion process, you could be in trouble.
Generally, when a racer feels a loss in power, what does he do? He takes steps to raise combustion temps. Lean the mixture or increase timing, right?
Racing with methanol is all about controlling cylinder and combustion temps. As power levels increase, all temperatures increase and more methanol must be used. A/F ratios will generally increase as power levels increase. Much of the extra methanol that is used at higher power levels is not even burned and is used for one thing only. To cool the temperatures down below the autoignition temp of the methanol so that controlled combustion can be maintained. The mixture strength is a fine line that every methanol racer knows very well. There may be more power available if it's leaned just a little more, but would it blow the engine?
A safe power mixture with methanol always involves a small loss in power.
A true methanol engine may be run so rich at some power levels, that much of the methanol will not even dissociate until it hits the exhaust system. Some of it may even still be in droplet form by the exhaust system. I would expect that if a gas/meth mix engine was run at such a rich mixture, the power level would drop way off.
In fact, this is how my nitrous/meth anti lag system works. The nitrous/meth combination is so cold, and quenches combustion temps so much, that a very noticeable drop in the nitrous system hp rating occurs. Only a small percentage of the nitrous hit actually burns in the cylinder. It still nets a small increase in power over not using the nitrous system, but, depending on the size of the nitrous hit, there is a 50 to 85% loss in the system rating in the cylinder. The nitrous and meth that makes it out of the cylinder finishes dissociating in the exhaust system, and because the exhaust temps are above the autoignition point, with a little help from a retarded spark timing, the mix ignites in the exhaust system. The sacrifice of having so much of the nitrous hit light off in the exhaust system and help quickly spool the turbo is the lower power level that is extracted and transferred directly to the piston in the cylinder.
Methanol engines will always run safer if there is a reserve of methanol available to quench combustion temps below detonation limits. The trade off is a small loss in power. If you can't deal with that, you have no business playing with methanol, or your wallet is thick enough to deal with the consequences.
The article statements were vague and didn't give any concrete numbers. I would imagine that the limit is going to be unique to every situation.
Even 100% methanol engines are very unique animals. One engine liking to run richer than another. The common factor between them all is the tuner trying to tune up to that fine line between having enough fuel to control temps or having the engine blow apart due to crossing the line and going into preignition. Temperature control is the secret.
The hard thing about methanol is, knock sensors are useless. If you get knock with a methanol engine, it's already too late. Time to pull the engine. At the very least you're going to have a bent pin. If you're running a gas/meth engine at the limits of the fuels, and you're using a knock sensor to tune it,...GOooOD LUCK!
I'm trying to find the best way to explain this so that others can understand. It's clear in my head, it's just a matter of putting it into words.
As safe power levels increase, safe cylinder and combustion temps rise. We'll ignore intake temps for now. The active word here is safe.
In a gasoline engine that temperature rise in relation to power increase can be plotted to provide a curve. The same can be done with a methanol fueled engine. The resulting curves are different. Gasoline engines will operate safely under high load at cylinder and combustion temps that are higher than a methanol fueled engine. That is very well evidenced by the different target exhaust temps between the two engines. As power levels increase, there's going to be a point where the temperature curve of the gasoline engine is going to cross the safe temperature curve of the methanol. Methanol engines operate at cooler temps than gasoline engines.
There will be a power level with a gasoline engine where cylinder and combustion temps are going to be too high for the methanol and it will preignite. Throwing more methanol at it to cool the engine down to temps that the methanol can survive in will just be lowering the temps below where the gasoline can still make appreciable power. The solution may appear to be to lean the a/f mixture to get combustion temps up, but now the power level has drawn a clear line in the sand where it comes to temperatures that the methanol can withstand without going into preignition, and that's where you get into trouble.
For a methanol racer, judging combustion temperature is his best tuning tool. If he knows where his combustion temps are, he's in real good shape. The best way to judge combustion temps is the spark plug.
EGT will give a good relation to combustion temps, but a methanol racer will rely on a spark plug reading sooner than an egt reading.
And what about egt readings? What's a good egt reading for a high horsepower turbocharged gasoline engine?
How does that compare to a safe egt reading for a methanol engine?
I'll tell you right now. They're a lot different.
As safe power levels increase, safe cylinder and combustion temps rise. We'll ignore intake temps for now. The active word here is safe.
In a gasoline engine that temperature rise in relation to power increase can be plotted to provide a curve. The same can be done with a methanol fueled engine. The resulting curves are different. Gasoline engines will operate safely under high load at cylinder and combustion temps that are higher than a methanol fueled engine. That is very well evidenced by the different target exhaust temps between the two engines. As power levels increase, there's going to be a point where the temperature curve of the gasoline engine is going to cross the safe temperature curve of the methanol. Methanol engines operate at cooler temps than gasoline engines.
There will be a power level with a gasoline engine where cylinder and combustion temps are going to be too high for the methanol and it will preignite. Throwing more methanol at it to cool the engine down to temps that the methanol can survive in will just be lowering the temps below where the gasoline can still make appreciable power. The solution may appear to be to lean the a/f mixture to get combustion temps up, but now the power level has drawn a clear line in the sand where it comes to temperatures that the methanol can withstand without going into preignition, and that's where you get into trouble.
For a methanol racer, judging combustion temperature is his best tuning tool. If he knows where his combustion temps are, he's in real good shape. The best way to judge combustion temps is the spark plug.
EGT will give a good relation to combustion temps, but a methanol racer will rely on a spark plug reading sooner than an egt reading.
And what about egt readings? What's a good egt reading for a high horsepower turbocharged gasoline engine?
How does that compare to a safe egt reading for a methanol engine?
I'll tell you right now. They're a lot different.
Another thing I've learned. And learned the hard way.
If you're running a tuneup that happens to be pushing the methanol to the temperature limit, the one thing that will always get you into trouble first is going to be a hot spark plug ground electrode. It will be enough to set the methanol off. Either run the methanol richer, which will undoubtably cause a small loss in power, or for goodness sake, install a spark plug with the shortest, shortest,... SHORTEST!!! ground electrode you can find.
If you're running a tuneup that happens to be pushing the methanol to the temperature limit, the one thing that will always get you into trouble first is going to be a hot spark plug ground electrode. It will be enough to set the methanol off. Either run the methanol richer, which will undoubtably cause a small loss in power, or for goodness sake, install a spark plug with the shortest, shortest,... SHORTEST!!! ground electrode you can find.
