WAI commentary

[California98Civic]

Had breakfast with an older gent who specializes in the science and technology of combustion and currently builds alternative fuel power plants in places like China, the US, and Canada. I asked him about the WAI and whether he thought it would work, and if so how. He says that the heat-expanded air would cause, in effect a richer mixture, though no extra fuel unless the rate of inject were separately adjusted. The WAI certainly does not produce a leaner burn (many of you probably already know that). Any FE gains he thought would have to be produced by heat energy recovery in the hot air being re-introduced to the engine from the manifold. He thought the gains would be minimal (which is true, by my test anyway). But adjusting the flow of fuel would create further gains. Has anyone done that in addition to the WAI itself?

[Daox]

The fuel ratio is kept at stoichiometric by the O2 sensor. It can't run richer without the O2 sensor seeing this and correcting for it.

[California98Civic]

Originally Posted by Daox

The fuel ratio is kept at stoichiometric by the O2 sensor. It can't run richer without the O2 sensor seeing this and correcting for it.

Great informative response. Thanks. Question that reveals how newbie I am to the mechanics of all this (something I bet I reveal frequently): this stiochiometric repositioning by the O2 sensor would be true even in a slightly older car, like my 1998 Civic, correct?

[Daox]

Yeah, I think pretty much anything since the late 80s / early 90s has an O2 sensor.

[California98Civic]

So this means then that the WAI does in fact create a leaner burn by manipulating the way the O2 sensor balances the fuel/air mixture... perhaps heat recapture is relevant, but the mixture would be more relevant, it seems to me.

[Daox]

Nope, it keeps the ratio at stoichiometric. The result is lower power output for a given throttle opening. To maintain speed, you must therefore open the throttle further. This decreases pumping losses which increases efficiency. Also the warmer air promotes a faster burn I believe, which leads to higher peak cylinder pressure and additional torque.

[Joenavy85]

Originally Posted by Daox

The fuel ratio is kept at stoichiometric by the O2 sensor. It can't run richer without the O2 sensor seeing this and correcting for it.

which is why changeing Fuel Injector size does nothing for FE, new injectors might help (due to being clean) though.

[California98Civic]

Originally Posted by Daox

Nope, it keeps the ratio at stoichiometric. The result is lower power output for a given throttle opening. To maintain speed, you must therefore open the throttle further. This decreases pumping losses which increases efficiency. Also the warmer air promotes a faster burn I believe, which leads to higher peak cylinder pressure and additional torque.

If it does produce higher peak cylinder pressure, wouldn't that also accomplish one of the goals of advancing the timing a couple degrees?

[Daox]

I'm not sure how it would. If anything, running too hot will cause preignition and pinging and the knock sensor will see that and retard timing.

[cfg83]

California98Civic -

I tried to find a really good definition, but this is the best I could find :

Understanding air density and its effects

If the air is in a balloon, heating it will expand the balloon, cooling it will cause the balloon to shrink as the molecules slow down. If the heated air is surrounded by nothing but air, it will push the surrounding air aside. As a result, the amount of air in a particular "box" decreases when the air is heated if the air is free to escape from the box. In the free atmosphere, the air's density decreases as the air is heated.
...
Pilots use charts or calculators to find out how temperature and air pressure at a particular time and place will affect the air's density and therefore aircraft performance. In general, these calculations don't take humidity into account since its affects are so much less than the others. When the air's density is low, airplanes need longer runways to take off and land and they don't climb as quickly as when the air's density is high.

Air density also affects the performance of automobiles, with lower density decreasing performance in the same way it decreases the performance of aircraft engines.

I went here to find air density as a function of temperature :

Air - Temperature, Pressure and Density

And came up with this :



When I say pseudo-AFR I think I am being misleading. Maybe a better way of saying it is that you are reducing the *displacement* of the engine by the percentage in the 4th column. The AFR stays the same from the 02 sensor POV. It's just that less oxygen and therefore less fuel is being burned per volume of air.

If what I am saying is correct, then this would give you an idea of the possible "change" in engine displacement at different intake temperatures :



BTW - I am not a car-guy either, so my statements are subject to correction by others.

CarloSW2