Quote:
Originally Posted by CNGBiFuel
I kinda grasp that CR is dependent on far more than fuel, combustion chamber shape and no least what the chamber can take with a full chrge of fuel and air. But it's been a long time since i read up on this stuff, I'm an electronics engineer, no motor tuner! I'm worried about hassling you but please a few more related Qs?
1) Am I correct is saying the reason LPG needs more advance than petrol, and CNG still more, is the slower flame-front.
2) Both are harder to ignite in the first anyway, correct?
3) But if this so, why am I told they run hotter, when I would expect cooler, or is it that once alight the flame is hotter?
4) In the ideal engine, one that only runs on one of the gases, removing any comprmises to run petrol, how would this 'ideal-engine' differ?
5) So a little bit of where I came in... no matter how much I thkweam and thweam, in three theoretical engines, Petrol; LPG; CNG, each optimised for its particular fuel, 'theoretically' we will never finish with the same power with the gas fuelled engines because no matter what else you do, the density of hte gases, means that per cycle the gas-engines will never able burn as much energy, simply because you've less room for the oxygen needed to burn it.
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1) yes
2) yes
3) knowing the answer to 1 and 2 is the expert in the pub wrong? Well mostly yes he is wrong. The burn is not as hot. The engine will not run any hotter or cooler as the running temprature is controlled by the cooling system. Is the pub expert right in any way? Yes a little as LPG does not have any cooling effect or lubrication it is harder on the valves.
4) the engine would not differ much, possibly a slightly higher CR and a ignition map optimised for the fuel
5) The energy for a given volume is the limiting factor with vapour dosing. Direct liquid injection could possibly give more power than petrol but that would take some working out