Quote:
Originally Posted by jonr
A really light foot with slow acceleration hurts FE*. People would be better off with a BSFC readout during acceleration. Preferably one that would display negative numbers when you hit the brakes.
* you get good instant FE numbers, but it also takes longer to get up to speed. So it is misleading.
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I don't know about that. I don't have an engine map for my vehicle but I assume it looks generally like the ones I've seen. It's clear that ultra slow acceleration doesn't utilize the most efficient areas of the map, but there's another factor.
Looking at the vehicle as the system boundary and outside as the environment (that is, ignoring the rotating masses in the drivetrain, etc.), fuel is used to do two things: overcome resistance (rolling, aerodynamic drag) and to add kinetic energy during acceleration (assuming level ground). If I accelerate slowly, that portion of fuel that goes to add a given amount of kinetic energy is burned over a greater distance - the calculations are quite easy and I can show it if anybody wants. But if I accelerate at half the rate, I'll go twice as far to get up to any given speed and that portion of the chemical potential energy that is converted to added kinetic energy is used more efficiently in that sense.
Combining this with bsfc on the engine map turns out to be a fairly thorny mathematical problem, though I'm working on it using a "generically" shaped engine map with a few tweaks to accurately represent those few spots I know about on my vehicle. Maybe somebody here has modelled this? It's a problem in numerical integration.
Sorry to hijack the thread.