Quote:
Originally Posted by oil pan 4
Gasoline engines seem to respond well to anything that can help reduce isentropic throttling losses while at light load cruise. Things such as warm air intake, egr, using a smaller engine and running it harder, regearing the final drive for lower cruise RPMs and maybe some form of steam injection cut down on these losses.
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Steam injection might could work, given a large enough external heat source to make the large amounts of steam that would be necessary. There is the problem, though, of uneven steam mixing with the air. There is also the fact that steam would encounter cooler environments and immediately condense out. The sides of the intake manifold come to mind. As soon as this occurs, the water condensate would pool inside the intake manifold, and might could become a hydrolock concern at some point down the road.
For these reasons, I'd probably lean toward port water injection, along with leaning out the air/fuel mixture to around 17:1. The water injection by itself would, of course, lower peak cylinder pressure as it cooled off the combustion charge being compressed, and Carnot efficiency would go down as a result.
However, these two factors would be more than offset by the reduction in throttling and pumping losses that would result from leaning out the fuel/air mix. The engine would be able to safely run this lean due to said lowering of combustion chamber temperatures. Engine power output would obviously decrease, compared to a similar engine that was running at stoich. The driver would then have to open up the throttle to compensate, and it'd have the same effect as lowered gearing, EGR, or shifting to a smaller capacity engine.