Comparing estimates of fuel economy improvement via fuel-cell powertrains.

Several studies, conducted from 1997 to 2001, have employed vehicle and powertrain simulation models to estimate fuel economy gains for a variety of fuel-cell powertrains. Many of those studies have attempted to control for the comparability of performance between conventional and fuel-cell vehicles (FCVs), but different sets of performance goals and simulation models have been used. This paper reviews the estimates of fuel economy gain (in mpg) vs. varying measures of performance change for a set of those studies. We examine some of the potential causes for the variability of these estimates — fuel used, powertrain hybridization, vehicle raw energy requirements (load), and variations in analysts’ assumptions/estimates — when substituting several types of fuel-cell powertrains. Our study includes development of a database and detailed examination of the relationships among powertrain and vehicle characteristics and fuel economy gain estimates for the selected studies. We developed simple equations by powertrain type to systematically examine the causes of variation in mpg gain among those conventional/FCV pairs controlled to have the same peak kW per kg of vehicle test weight (a surrogate for acceleration capability).