Quote Originally Posted by Space Racer View Post
Let's say you are driving a hybrid car with RB whose battery is low, so it only uses the gas engine. The engine gets an average of 30 mpg when you are light on the gas pedal, and 20 mpg when you are heavy on it. The advantage of having a heavy foot is that there is a good amount of wasted energy, and some of it is used to recharge the battery. With a light foot, there is little wasted energy.

Would you drive with a heavy foot or a light one?
THe answer gets a little complicated. The reason accelerating fast consumes more energy is similar to who AC units and chillers are more efficient at part load. Under normal loads, IC engines in cars are most efficient at lowers RPM's and partial throttle positions. They burn the most lean and more improtantly, make full use of their compresssion ratio. Meaning that more energy goes into moving the piston and less into waste heat. At full throttle and high RPM, the mixture is more rich, and sice throttle positon is larger, more air is pushed into the piston, so pressures and heat increase and more energy is lost to waste heat.

However, on a electric motor and drive, the permenant magnet motors used make peka torque at 0 RPM and there's little change in efficinecy as RPM increases. However, the drive, is most efficient at full load. At part load it uses I beleive pulse width modulation and some waste heat is created switching on/off the circuits. So you want the electric motor at full load, but the IC engine at minimum RPM and throttle and more improtantly, if it's a automatic, it needs to have the torque converter locked up.


Oh... and jsut ot further comlicate matters, engine effciency and fuel economy are not nessesary the same thing. Efficiency would be fuel conmption rate per delivered HP. Fuel economy is fuel consumed per unit of distance traveled. Many engine reach peak efficiency I beileive right at the point where the torque curves begins to taper off.


OH and in reality, the instanataneous fuel consumption of a engine varies much more dramatically. Very lgiht throttle at low RPM's on a small 2.5L 4 cylinger for example is probably around 50mpg, but full throttle near redline is around 8-10mpg. AN IC engien at idle probably only makes about 5-10HP depending on throttle positon, AC and alternator loads. At a highway crusing speed of 65mph @ 2000RPM and part throttle, it's probably around 40HP and at a nice efficient 45mph, its' maybe just 20HP at 1500RPM.