Originally Posted by SPL

Smilin' Jack — Those two numbers for epsilon were just two numbers that I came up with when seeing how well I could match the predictions of the Maple worksheet (from which I excerpted the formulas above) with some fuel-consumption data that I gathered with my TCH. My main purpose at the time was to see if I could explain the consistent difference in fuel consumption that I found when driving the 125-km route from Waterloo to Toronto, Ontario, versus what I found when driving the same route in the reverse direction. After allowing for the elevation change, I satisfied myself that the difference was roughly consistent with the effect of the prevailing moderate westerly winds that occur in this region. The higher value epsilon2=0.33 was what I had read somewhere (I forget offhand where) for the Atkinson-cycle ICE's thermodynamic efficiency — high by ICE standards. The lower value epsilon1=0.185 gave a better match with my measured fuel-consumption data taken at 100 km/h. One could probably interpolate for intermediate values of epsilon, but I don't really think that my values have any real solid validity to them. No, I've not seen any BSFC curves for the TCH's ICE.

I have thought of trying some further experiments to refine the epsilon values, but haven't done any yet. Low-speed measurements (where air resistance is negligible) could refine the R0 value. High-speed measurements could then be used to refine the value of epsilon (around that ICE operating point). I encourage you (and others) to do some careful experiments.

Stan