Why it's WATER injection
12-20-2006, 05:51 PM
#1
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Why it's WATER injection
What WATER (not alcohol) injection does
There are two reasons blower cars tend to detonate. One is high inlet air temps, the other is higher cylinder pressure (which in turn further heats the charge). There are a couple of ways to deal with this. One is higher octane fuel, which is not practical for day to day use given what is available at the pump. Another is making the AF ratio very rich, which is used by all blower tuners. The extra fuel acts to cool the intake charge. This costs power, but not to a great degree. Another way is to retard timing under boost. This is also used by nearly all tuners. Timing retard also costs hp and has somewhat limited effectiveness at preventing detonation. Lowering engine temp by better cooling helps, to a small degree. Lowering CR is quite effective. Based on both theory and practice, if you have the choice between lower CR and more boost, or a higher CR and less boost the former will unequivocally produce more hp. The explanation is somewhat long winded and I don't have time to go into it now. The only downside is decreased fuel efficiency under light load (where a street auto engine spends 95% of its' time).
Lowering intake air temps can markedly decrease detonation. This is done by the use of intercooling. The resistance to flow through the intercooler will decrease apparent blower efficiency and hence cost power, but this is more than compensated for by the denser intake charge (due to cooler IAT) and the ability to run more boost without detonation. As noted above, extra fuel also cools charge temperatures. Methanol is a fuel. It has a much higher heat of vaporization than gasoline. So, using methanol instead of gasoline as the "extra" fuel is more effective than using extra gasoline. Methanol also has an octane rating of ~99, so it will raise the octane of the charge in amount proportional to the quantity compared to gas. Just like mixing a little race fuel with the pump gas.
This brings us to water. Water has an even higher heat of vaporization than methanol. It is not a fuel and has no "octane" at all. It cools better than methanol due to the higher heat of vaporization. It also slows the combustion process after ignition, this dramatically reduces detonation and is primarily why the most effective injection fluid is at least 50% water. Why not all water? Well, that does work. So does straight methanol, but not as effectively. What practice has shown is that a 1:1-2:1 water:methanol mix works best. I don't know the theoretical explanation for this. I suspect it has to do with water displacing air. Of course, methanol does too but it allows less gas to be used which will partially compensate. Water increases the need for a strong spark because it is so effective at slowing combustion. That's one limiting factor in it's effectiveness and maybe why some people report better results with methanol. BTW, the combustion slowing effect will require some of timing we already took out to be added back in.
So, max hp for a given octane fuel is obtained by lower CR, higher boost, water/methanol injection, intercooling, careful tuning, and a strong spark.
Cliff's Notes: If I hear "alky injection" one more time I am going to scream. Call it WATER injection or go home.
Rich
There are two reasons blower cars tend to detonate. One is high inlet air temps, the other is higher cylinder pressure (which in turn further heats the charge). There are a couple of ways to deal with this. One is higher octane fuel, which is not practical for day to day use given what is available at the pump. Another is making the AF ratio very rich, which is used by all blower tuners. The extra fuel acts to cool the intake charge. This costs power, but not to a great degree. Another way is to retard timing under boost. This is also used by nearly all tuners. Timing retard also costs hp and has somewhat limited effectiveness at preventing detonation. Lowering engine temp by better cooling helps, to a small degree. Lowering CR is quite effective. Based on both theory and practice, if you have the choice between lower CR and more boost, or a higher CR and less boost the former will unequivocally produce more hp. The explanation is somewhat long winded and I don't have time to go into it now. The only downside is decreased fuel efficiency under light load (where a street auto engine spends 95% of its' time).
Lowering intake air temps can markedly decrease detonation. This is done by the use of intercooling. The resistance to flow through the intercooler will decrease apparent blower efficiency and hence cost power, but this is more than compensated for by the denser intake charge (due to cooler IAT) and the ability to run more boost without detonation. As noted above, extra fuel also cools charge temperatures. Methanol is a fuel. It has a much higher heat of vaporization than gasoline. So, using methanol instead of gasoline as the "extra" fuel is more effective than using extra gasoline. Methanol also has an octane rating of ~99, so it will raise the octane of the charge in amount proportional to the quantity compared to gas. Just like mixing a little race fuel with the pump gas.
This brings us to water. Water has an even higher heat of vaporization than methanol. It is not a fuel and has no "octane" at all. It cools better than methanol due to the higher heat of vaporization. It also slows the combustion process after ignition, this dramatically reduces detonation and is primarily why the most effective injection fluid is at least 50% water. Why not all water? Well, that does work. So does straight methanol, but not as effectively. What practice has shown is that a 1:1-2:1 water:methanol mix works best. I don't know the theoretical explanation for this. I suspect it has to do with water displacing air. Of course, methanol does too but it allows less gas to be used which will partially compensate. Water increases the need for a strong spark because it is so effective at slowing combustion. That's one limiting factor in it's effectiveness and maybe why some people report better results with methanol. BTW, the combustion slowing effect will require some of timing we already took out to be added back in.
So, max hp for a given octane fuel is obtained by lower CR, higher boost, water/methanol injection, intercooling, careful tuning, and a strong spark.
Cliff's Notes: If I hear "alky injection" one more time I am going to scream. Call it WATER injection or go home.
Rich
12-20-2006, 10:23 PM
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I get people all the time telling me that I can't drive my car in the rain.......when I say I have been through many downpours with it and it runs just fine (technically better) in the rain they act like I am full of crap 
12-20-2006, 10:26 PM
#8
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Although, the word usage has never really bothered me.. even though i run a 90% water mixture in my car, i still end up calling it meth injection in casual conversation alot.
12-20-2006, 10:38 PM
#9
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I disagree on the importance of water,
Methanol has a lower heat of vaporization, and it has a lower thermal conductivity constant (usually denoted k) but there is more going on than just that.
Methanol has a kick *** flame travel speed especially in a rich environment. The flame travel speeds even at stoich are better than gasoline by far which is nice because you do more positive work when more of your mixture burns at TDC. On top of that it is making use of space by adding heat while still offering a better cooling effect than gasoline. Anyway I'm rambling.
Water
Advantages
Methanol
Advantages
Disadvantages
I think pure methanol is much better than a mixture of water and methanol. I think this is also the common idea with the Buick guys who depend on alcohol injection. I think most injection manufacturers tell people to use a mix just so the fluid isn't so hard on the parts and pump.
I from personal experience have not had any issue at all seeing a gain with methanol injection. I have NEVER seen a gain with pure water injection. I've seen very mixed results with mixes of water and methanol. Usually after adding lots of timing we usually get back to where we started with most mixes. The extra timing is coming from the slower flame travel speeds!
My idea for an ideal kit is to use as much methanol as possible without damaging parts. Then, replace gasoline with as much methanol as possible.. So that means pull back on your fuel and add an appropriate amount of methanol.
Remember that methanol’s lower heating value is a good bit less than gasoline but the catch is you burn much more of it per lb of air so its total heat addition is actually higher than gasoline.
Also remeber that the higher heat of vaporization of water might sound attractive to pull heat out of the intake, but seeing how the water passes thru the combustion unchanged and it has a high specific heat it also carries ALOT of heat out of the combustion process. Heat that could otherwize be doing expansion work!!!
not to mention that again, its dead space.
Methanol has a lower heat of vaporization, and it has a lower thermal conductivity constant (usually denoted k) but there is more going on than just that.
Methanol has a kick *** flame travel speed especially in a rich environment. The flame travel speeds even at stoich are better than gasoline by far which is nice because you do more positive work when more of your mixture burns at TDC. On top of that it is making use of space by adding heat while still offering a better cooling effect than gasoline. Anyway I'm rambling.
Water
Advantages
- Higher heat of vaporization (pulls more heat out of intake)
- Higher specific heat. As water passes thru the combustion process it carries heat with it. That is heat that could be doing work.
- Makes for dead space in combustion
- Slows flame travel speed. More ignition advance is needed for both flame propagation AND flame degree. More of the mixture is started BTDC in order to balance as much mixture burning right ATDC so your doing more negative work. On top of that mixture is not burned as close to TDC where change in volume is happening fast relative to crank angle.
Methanol
Advantages
- Carries a good heating value
- Superior flame travel speed. Even better than gasoline
- 3 or 4 times higher heat of vaporization rate
- Adds to total heat addition to the process, instead of taking from it
- Its heat of formation of the products is less than that of what pure excess water's specific heat
Disadvantages
- Hard on parts?
I think pure methanol is much better than a mixture of water and methanol. I think this is also the common idea with the Buick guys who depend on alcohol injection. I think most injection manufacturers tell people to use a mix just so the fluid isn't so hard on the parts and pump.
I from personal experience have not had any issue at all seeing a gain with methanol injection. I have NEVER seen a gain with pure water injection. I've seen very mixed results with mixes of water and methanol. Usually after adding lots of timing we usually get back to where we started with most mixes. The extra timing is coming from the slower flame travel speeds!
My idea for an ideal kit is to use as much methanol as possible without damaging parts. Then, replace gasoline with as much methanol as possible.. So that means pull back on your fuel and add an appropriate amount of methanol.
Remember that methanol’s lower heating value is a good bit less than gasoline but the catch is you burn much more of it per lb of air so its total heat addition is actually higher than gasoline.
Also remeber that the higher heat of vaporization of water might sound attractive to pull heat out of the intake, but seeing how the water passes thru the combustion unchanged and it has a high specific heat it also carries ALOT of heat out of the combustion process. Heat that could otherwize be doing expansion work!!!
not to mention that again, its dead space.
12-20-2006, 10:51 PM
#10
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Also.. the increase from power can only come from a car thats running really rich, since water displaces fuel leaning out the mixture. But the amount of alcohol, and its relation to fuel used.. play a major role in creating power with straight alcohol.
Straight (alcohol)methanol will always yield more power. As a matter of fact, you'll make power without changes injecting methanol, unlike water that requires something else to change for power to occur. This statement is a proven.
Straight (alcohol)methanol will always yield more power. As a matter of fact, you'll make power without changes injecting methanol, unlike water that requires something else to change for power to occur. This statement is a proven.
12-20-2006, 11:25 PM
#11
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I should use quotes, but I'm lazy tonite and mean no disrespect.
The heat carried out of the exhaust by the water is the heat we removed from the intake charge, this is the whole point afterall and why water is an excellent choice.
Methanol can actually induce detonation when used in this application in mixtures over 50%.
Injecting water is not going to displace fuel and lean the mixture. The fueling strategy knows nothing about the water injection and the same volume of fuel will be injected at the port. Water does not participate in the combustion process, but it does massively expand when turned to steam which contributes to in-cylinder pressure.
Hit the head of a piston at TDC with a hammer (in your imagination) and tell us what happens. The crank isn't going to rotate, the rod is inline with the crank throw. TDC is not where you want max pressure to occur.
There are numerous studies on water/anti-detonate fluid injection done with aircraft engines. Much of the serious work was carried out for the presecessor of NASA which places the info in the public domain and available. If water injection is effective for 1000+ hp force inducted aircraft it will be effective in our engines as well.
Effect of engine-operating variables and internal coolants on spark-advance requirements of a liquid-cooled cylinder
http://hdl.handle.net/2060/19930093147
above is a link to the pdf. This is not going to be for everybody, but if you're willing to study it there will be information that applies to us.
http://ntrs.nasa.gov/search.jsp?No=0...20matchall&N=0
edit: added a search link on DETONATION for the NASA / NACA archives.
The heat carried out of the exhaust by the water is the heat we removed from the intake charge, this is the whole point afterall and why water is an excellent choice.
Methanol can actually induce detonation when used in this application in mixtures over 50%.
Injecting water is not going to displace fuel and lean the mixture. The fueling strategy knows nothing about the water injection and the same volume of fuel will be injected at the port. Water does not participate in the combustion process, but it does massively expand when turned to steam which contributes to in-cylinder pressure.
Hit the head of a piston at TDC with a hammer (in your imagination) and tell us what happens. The crank isn't going to rotate, the rod is inline with the crank throw. TDC is not where you want max pressure to occur.
There are numerous studies on water/anti-detonate fluid injection done with aircraft engines. Much of the serious work was carried out for the presecessor of NASA which places the info in the public domain and available. If water injection is effective for 1000+ hp force inducted aircraft it will be effective in our engines as well.
Effect of engine-operating variables and internal coolants on spark-advance requirements of a liquid-cooled cylinder
http://hdl.handle.net/2060/19930093147
above is a link to the pdf. This is not going to be for everybody, but if you're willing to study it there will be information that applies to us.
http://ntrs.nasa.gov/search.jsp?No=0...20matchall&N=0
edit: added a search link on DETONATION for the NASA / NACA archives.
Last edited by markinkc69z; 12-21-2006 at 12:24 AM.
12-21-2006, 12:03 AM
#12
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Methanol can actually induce detonation when used in this application in mixtures over 50%.
Injecting water is not going to displace fuel and lean the mixture. The fueling strategy knows nothing about the water injection and the same volume of fuel will be injected at the port. Water does not participate in the combustion process, but it does massively expand when turned to steam which contributes to in-cylinder pressure.
I don't know why I quoted razor on that. I'm guessing he ment to say that they (tuned) leaned out the mixture on the spray.. who knows.
Hit the head of a piston at TDC with a hammer (in your imagination) and tell us what happens. The crank isn't going to rotate, the rod is inline with the crank throw. TDC is not where you want max pressure to occur.
There are numerous studies on water/anti-detonate fluid injection done with aircraft engines. Much of the serious work was carried out for the presecessor of NASA which places the info in the public domain and available. If water injection is effective for 1000+ hp force inducted aircraft it will be effective in our engines as well.
Last edited by Alvin@pcmforless.com; 12-21-2006 at 12:43 AM.
12-21-2006, 12:46 AM
#13
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Actually if you read the entire text there is power to be gained by increasing the charge density with water injection assuming the injection point is not right at the port, regardless of knock limitations.
For a given volume of water/coolant injection there is a finite amount of heat/energy that it will absorb and remove from the cylinder.
I am looking for print studies on methanol induced detonation as it pertains to our use. I will post the link(s) when I have it for your consideration.
For a given volume of water/coolant injection there is a finite amount of heat/energy that it will absorb and remove from the cylinder.
I am looking for print studies on methanol induced detonation as it pertains to our use. I will post the link(s) when I have it for your consideration.
12-21-2006, 08:29 AM
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Location: St.Petersburg,Fl,USA
Posts: 65
Water displaces fuel. Easy.
Methanol is a fuel.. of very high octane.
Which can make more power.. easy.. which one burns.
Thousands of dyno pulls... tell the story.
Whether someone chooses to believe.. thats a whole other story. Without data.. real world.. its all smoke and mirrors.
Methanol is a fuel.. of very high octane.
Which can make more power.. easy.. which one burns.
Thousands of dyno pulls... tell the story.
Whether someone chooses to believe.. thats a whole other story. Without data.. real world.. its all smoke and mirrors.
