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BOOK DESCRIPTION
The book explains a complex, multifaceted subject from the perspective of a vehicle engineer.
Engine fuel efficiency is defined as the rate at which the engine consumes fuel to produce a certain torque output at the flywheel, at a given engine speed. It is measured with the engine installed in a brake dynamometer, where, for each of a series of engine speeds (say, 1,000, 2,000, 3000, 4000…etc. rpm), the load on the engine is increased in fixed increments (say, 25, 50, 75% and WOT throttle) and the torque output and fuel consumption are measured at each speed and load condition. These values are expressed in terms of pounds of fuel consumed per horsepower-hour, with these values referred to as the engine’s brake specific fuel consumption (BSFC).
BSFC values for gasoline engines can vary substantially throughout the range of engine speed and load conditions, roughly by a factor as high as 2.5:1. Although some engine designs have inherently higher fuel efficiency characteristics than others, all have similar speed/load distribution for BSFC characteristics.
Vehicle fuel efficiency is a different subject. If an engine with outstanding fuel efficiency characteristics is installed in a vehicle with high rolling and air resistances, poor mpg will still be likely. If a vehicle has low rolling and air resistance characteristics but is saddled with transmission and/or axle gear ratios that cause the engine to operate at engine speed/load points associated with poor BSFC, mpg will most probably be poor as well.
A discussion of vehicle fuel efficiency must therefore involve engine fuel efficiency but also factors such as the rolling, mechanical and aerodynamic resistances, driveline friction and parasitic loses, matching of overall gear reduction ratios (transmission and final drive) to engine characteristics, weight, tire pressure, wheel alignment, vehicle attitude, etc.
The book covers petroleum based and alcohol fuels, and gas-electric hybrid vehicle powertrains. Like it or not, the vehicle fuel efficiency subject will be with us, in spades, from now on. This book is intended to expand and elevate your level of understanding.
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