Maybe this is why there are some claims of more power with water vapor injection?
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effect of flame speed on co-02 mixture with water vapor
- Thread starter maxc
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140Airpower
Automotive
azmios, Concentrated H2O2 is very unstable and can decompose violently with little provocation. In chemistry we had demonstrations using 40% H2O2 where the stuff reacts spontaneously on contact with other substances. I have seen this. You can get a fire. For rockets and torpedoes they use up to 90% H2O2. Metals are good for setting it off. It's dangerous, needs special materials to contain it and will decompose gradually even when refrigerated, liberating oxygen and filling the surrounding spaces, like a refrigerator, with pure oxygen. It will eat ordinary refrigerators over time. This is fairly typical of "good" oxygen generating compounds. They are unstable. Some are nasty in other ways as well.
There are other oxygen rich compounds that require heating or catalysts to decompose. You can use a catalyst to set H2O2 off. You get a lot of heat and free oxygen. If anything that can burn is around, you get a very hot fire.
No compounds like these are good as oxidizers in the type of engine you are promoting because they cost money. Efficiency of operation in universal power plants is pursued for reasons of economy. To get a better burn by using an expensive oxidizer in place of a free oxidizer makes no sense whatsoever. It is only appropriate for special applications like anaerobic environments under water or at very high altitudes. For this second purpose, they investigated pure oxygen for aircraft engines. They found that pure oxygen is very bad for combustion due to causing detonation. A MUCH better alternative was Nitrous Oxide which is a low pressure containment liquid. Nitrous is used in cars for power. It is way NOT economical compared to air.
There are other oxygen rich compounds that require heating or catalysts to decompose. You can use a catalyst to set H2O2 off. You get a lot of heat and free oxygen. If anything that can burn is around, you get a very hot fire.
No compounds like these are good as oxidizers in the type of engine you are promoting because they cost money. Efficiency of operation in universal power plants is pursued for reasons of economy. To get a better burn by using an expensive oxidizer in place of a free oxidizer makes no sense whatsoever. It is only appropriate for special applications like anaerobic environments under water or at very high altitudes. For this second purpose, they investigated pure oxygen for aircraft engines. They found that pure oxygen is very bad for combustion due to causing detonation. A MUCH better alternative was Nitrous Oxide which is a low pressure containment liquid. Nitrous is used in cars for power. It is way NOT economical compared to air.
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patprimmer
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I have a real life.
I am about to end this charade.
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Pat
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I am about to end this charade.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
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patprimmer
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maxc I really can't remember. I wish I could as I really want to refresh yo memory.
I don't think azmios will be back to further disrupt this or any other thread.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
I don't think azmios will be back to further disrupt this or any other thread.
Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules
140Airpower
Automotive
maxc, Humidity does have an effect on flame speed, but the effect of atmospheric humidity should be tiny compared to water injection. The behavior you describe is hard to explain since it is not a simple effect.
Speculating, engines often operate at a point of marginal preignition or detonation. It may be completely unnoticed. An increase in humidity could reduce the tendency to detonate and the effect will be a slight increase in power. Other than this effect, humidity constitutes a substitution of water for air and a proportionate reduction of oxygen thus a reduction in power. The loss should be very small since 100% humidity at 100 degrees F is only around 1% of a substitution. Notice one thing, water as a gas, humidity, does not have a cooling effect due to evaporation.
Gasoline tends to break down under the heat of the pre-spark compression. Unstable molecular fragments form and they begin to react with the oxygen in the mixture, producing even more heat. These reactions are called "cold flame reactions". They increase the tendency to detonate and they represent a slight direct loss of power since they occur before the optimum ignition point. Humidity, water in the mix, slows cold flame reactions.
One last thing, fog is another matter altogether. It's not just 100% humidity. There are droplets of water in the air.
Speculating, engines often operate at a point of marginal preignition or detonation. It may be completely unnoticed. An increase in humidity could reduce the tendency to detonate and the effect will be a slight increase in power. Other than this effect, humidity constitutes a substitution of water for air and a proportionate reduction of oxygen thus a reduction in power. The loss should be very small since 100% humidity at 100 degrees F is only around 1% of a substitution. Notice one thing, water as a gas, humidity, does not have a cooling effect due to evaporation.
Gasoline tends to break down under the heat of the pre-spark compression. Unstable molecular fragments form and they begin to react with the oxygen in the mixture, producing even more heat. These reactions are called "cold flame reactions". They increase the tendency to detonate and they represent a slight direct loss of power since they occur before the optimum ignition point. Humidity, water in the mix, slows cold flame reactions.
One last thing, fog is another matter altogether. It's not just 100% humidity. There are droplets of water in the air.
Hi Azmios,
In your 15 October post you said "All the papers that I have, mentioned about the power increase but none made convincing scientific explanations on why the power increases even if the ignition timing, boost, energy content remain the same."
I am still interested in which paper claims "the power increases even if the ignition timing, boost, energy content remain the same."
Slim3's descriptions of his experiments don't really qualify. (Although a water/alcohol mix would seem to bring the alcohol's BTUs to the party.)
I offer the the 1943 NACA paper as an example of the typical testing I'm aware of. 4 stroke, spark ignition, gasoline fueled. Appearing pretty frequently are phrases like "permissible decrease in octane number" and "maximum permissible power." The ignition timing was held at 20 BTDC and the inlet temp was held at 250F. They just played with boost, throttle position, A/f ratio and amount of water injected. On page 60 it talks about power, indicated mean effective pressure, or inlet pressure (boost) all being knock limited during the test.
They were able to make 80 octane fuel perform as well as 100 octane fuel, and their dyno ran out of capacity because the engine was "permitted" to make so much power before they were able to investigate more extreme water/fuel ratios.
Figure 6 (mentioned on the other thread) was testing done with constant near atmospheric pressure. Small increased in IMEP resulted when water was injected, but the authors noted was the result of greater air mass inducted (as the result of charge cooling?).
regards,
Dan T
In your 15 October post you said "All the papers that I have, mentioned about the power increase but none made convincing scientific explanations on why the power increases even if the ignition timing, boost, energy content remain the same."
I am still interested in which paper claims "the power increases even if the ignition timing, boost, energy content remain the same."
Slim3's descriptions of his experiments don't really qualify. (Although a water/alcohol mix would seem to bring the alcohol's BTUs to the party.)
I offer the the 1943 NACA paper as an example of the typical testing I'm aware of. 4 stroke, spark ignition, gasoline fueled. Appearing pretty frequently are phrases like "permissible decrease in octane number" and "maximum permissible power." The ignition timing was held at 20 BTDC and the inlet temp was held at 250F. They just played with boost, throttle position, A/f ratio and amount of water injected. On page 60 it talks about power, indicated mean effective pressure, or inlet pressure (boost) all being knock limited during the test.
They were able to make 80 octane fuel perform as well as 100 octane fuel, and their dyno ran out of capacity because the engine was "permitted" to make so much power before they were able to investigate more extreme water/fuel ratios.
Figure 6 (mentioned on the other thread) was testing done with constant near atmospheric pressure. Small increased in IMEP resulted when water was injected, but the authors noted was the result of greater air mass inducted (as the result of charge cooling?).
regards,
Dan T
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