Quote:
Originally Posted by Old Mechanic
One thing that is fairly constant at RPMs and loads that are in the best BSFC range is mixture ratio. It does change when you go WOT, but in other areas of engine operation it is fairly consistent.
MAP or the reverse, vacuum is a good indication of the amount of air, relative to atmospheric pressure that actually enters the combustion chamber. I like to call this effective compression, because it can be calculated by knowing atmospheric pressure and intake manifold vacuum readings (or MAP).
This volume of air can be fairly accurately measured, and with that quantity know, the corresponding volume of fuel can also be calculated.
Best BFSC will be found at lowest manifold vacuum (highest MAP) that the fuel injection system will allow, without enrichment as you approach WOT.
The only other factor is RPM, and if you know the range where BSFC is highest you can stay in the range of RPM and load to minimise consumption per unit of power.
regards
Mech
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And that is exactly what I was referring to when I said that load % coupled with a good BSFC map (or graph, if you will) will give you a better idea of the mpg than the pulse width or duty cycle of the injector.
Does the difference in pressure from the fuel side to the air side of the injector, if maintained with the same differential, maintain the same flow for the same duty cycle?
Does a duty cycle of 30% for 1500 rpm and 3000 rpm consist of the same amount of fuel flow?