Recovering lost heat energy in engine coolant...

[cRiPpLe_rOoStEr]

Originally Posted by t vago

From reading the multi-page thread about vapor carbs, I have hypothesized that the main benefit from the WAI is its ability to cause the gasoline to vaporize more readily. The gasoline vaporizes when its vapor pressure reaches that of the surrounding air, and the vapor pressure is of course dependent on the gasoline temperature. Now, when you spray a mist of gasoline into a mass of warm air, its temperature will quickly rise to that of the surrounding air, and as it does, the gasoline's vapor pressure will also rise to the point where it will vaporize. This raises the pressure of all of what's actually being sucked into each cylinder, causing the engine to work a bit less at drawing in the air/fuel mixture than it would otherwise.

Sure, but then there is always some point when adding heat to the intake stream would require a richer mixture in order to overcome the knocks. No wonder carburettor-fed aircraft and some earlier dedicated-ethanol trucks from my country have an adjustable air box in order to allow a more accurate temperature control.

[teoman]

This is an awesome idea.

It could be the missing component to enable lean burn.


Doesn anyone see any down sides to implementing it with LPG?

[teoman]

Originally Posted by t vago

Part Load Pumping Losses in an SI Engine

This website page gives a pretty concise explanation about pumping losses in a gasoline engine. Well worth a read.

Changes of Low Load Engine Parameters by Temperature of Mixture

This technical paper goes over the effects of installing a hot air intake onto a test engine driving a small load. For purposes of discussion here, I have considered only the testing temperature of 90 C (194 F). I have not considered the testing temperatures of 140 C (284 F) and 190 C (374 F) because they are a bit higher than is reasonable. I want to save fuel, not bake things.

For 90 C, the paper mentions that pressure inside the intake manifold rises by a small but measurable amount, which supports the pumping loss reduction idea.

However, the pressure rise (about 2%) is a bit less than the 7% reduction in BSFC seen in the paper. The paper further shows a negligible increase in throttle position. I have seen this effect as well on my ScanGauge - whether going up or down inclines, or even on straight and level roadways, the truck's manifold pressure and throttle position do not appear to have noticeably changed. I used to think that HAI gains were solely from lessening pumping losses. The smaller-than-expected pressure rise and the negligible throttle opening do not really support this idea.

The paper also shows warmer air leading to faster combustion rates, and the effect is certainly seen in the graphs at the end of the paper. Combustion peak pressure appears to move leftward from baseline, which is equivalent to advancing ignition timing by a few degress. This makes sense. In fact, the paper goes on to infer that faster combustion rates are the primary factor in HAI gains.

I think that this paper is showing that the resulting gain in fuel economy from installing a HAI is a combination of the two factors. In any case, the gains I've seen are real, and they merit further investigation.

Edit: Hey! That might could explain why MAF-based cars don't really see any sort of improvement using a HAI. Their engine computers might be overcompensating for higher intake temperatures.

The second link seems to be broken. Would you happen to have it?

Thanks.

[t vago]

Originally Posted by teoman

The second link seems to be broken. Would you happen to have it?

Thanks.

Yah. Once I get home tonight, I'll upload it to my website and provide a link here.

[t vago]

There ya go...

Changes of Low Load Engine Parameters by Temperature of Mixture