eek - guess I better check that out. Thanks
You're also right on the slightly rich "pedal to the metal" Supras spew some black smoke when you get on it. It's also safer for the engine to run a little rich WOT (cooler).

www.mkiv.com

My main points were that the humidity at higher temps will increase the altitude density due to the fact water vapor is less dense than air. Also, the humidity will displace O2 in the air decreasing the power an engine can produce. The motor will run as though the air is less dense than it is. A double whammy to performance. Pilots are very familiar with altitude density. The article was warning them about moisture which can have a significant affect on power. To a pilot, small amounts of losses in power can be significant. Did I say a 50% decrease in power? No, maybe about 5 to 10% for humidity. Possibly a combination of up to 20% loss in power. I did mention that an increase in humidity of 25% can equal a temperature gain of 10 degrees. That much is probably noticeable. It will get worse as the temp rises. If you want cases and actual numbers, I could provide them when I get home.

If I remember from many years ago. The partial pressure is the pressure the gas would exert if the component gas filled the same volume at the same temperature. The ratios of water vapor and air components will change the partial pressures. The mass of the component gas can be correlated to the partial pressure and volume. I'm on vacation in California so I'm going from memory. I'll check when I get home to make sure I didn't say anything wrong. I still don't understand the reasoning behind statement of partial pressures earlier. I am interested.

I know that in many cases the water vapor in air can be considered an ideal gas mixture with very little error. I beleive that when the temp is close to the dewpoint temp, the model becomes less accurate. I'll check that when home, it's been years. Yes, there is error when comparing an ideal model to real life. That is the way life is....

The stoichiometric analysis is a simplification for internal combustion and not 100% accurate. It is only an approximation. The are hundreds of reactions that go on in the combustion process. I have a friend that based his doctoral thesis in writing code that more accurately models combustion. He still admits he is not a whole lot closer to an exact solution. It did keep him busy for quite a while. He also flies model planes, well rounded. Life would be great if we could explain everything on simplified models.

The article about water injection was interesting. If you read closely it is talking about boost applications or predetonation. Most WWII engines were boosted. The gain in power comes from compressing the air such that there is more mass, both air and fuel, in the combustion chamber, not the water. The water allows the engine not to knock or have preignition and be able to operate with the high boost. The water vapor will still decrease the total power because it does displace fuel and air. Energy of the fuel will also go to heat the water vapor adding more loss in power. That is how it cools the charge and retards detonation. It will only improve power, efficiency, and performace on an engine that has problems with detonation and doesn't run well because of it. That is why my car doesn't have water injection and would perform worse with it. I am sure I am safe to say humidity has a negative overall affect on model airplane engines (as well as most IC engines).

Back to the Vacation.