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i don't think desiel ngine economy is helped by the constant pressure combusion, it would be better if it was at constant volume. Deisel engine consumption is hurt by not having a stoiciometric mixture, let me explian like this: the efficiency of an engine, all else being equal, is related to the ratio of the maximum temp to the minimum. The minimum depends greatly on the expansion ratio, and here the diesel does well, but the highest temperature at the top of the stroke is accieved with a chemically correct mixture, and also in the shortest time.
With a diesel with constant pressure the fuel is injected over a period of time, lowering temperatures and efrficiency over what it could be, and also the fuel that burns further down the power stroke is expanded with a lower ratio.
neverthe less, I have 3 Priuses, and have used these and also a deisel Pajero for my 4km trip to work in traffic, and the diesel actually is not much heavier than the hybrids like this, and it's also lighter than my Daihatsu charade petrol! My favorite engine is the Isuzu 2.5 non turbo direct injection deisel in a ute I had, it got 14km/L in all conditions. Deisel's gains in efficiency more than compensate for any higher losses.....
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