Quote:
Originally Posted by cujet
Hydrogen is king with the best energy density
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Until you add in the weight of the tank required to store it and that the engine it is being burned in will have to be larger and heavier for a given power output. It does burn clean though.
I should think any fuel burned in a CI engine will be dirtier than that in a SI engine. They are always going to be run lean (= high NOx) and mixing the fuel and air is going to be more difficult (= high HC).
When considering a fuel, the energy released at a stoichiometric mixture, the moles of combustion products per mole of air and fuel mixture inducted (which with a given volumetric efficiency will affect the power output), the proportion of H2O and CO2 produced (and their specific heats at combustion temperatures) and octane or cetane rating are all going to effect the efficiency and, indirectly at least, the emissions per unit of useful work done.
In general, I suspect that the greater the proportion of H in the HC the better so yes, ignoring any knock on effect on vehicle weight, H2 will be the best. CH4 will look pretty good also.