Assessment of Changing Relationships between Vehicle Fuel Consumption and Acceleration Performance 2020-01-5067

In light-duty vehicles, there is a fundamental trade-off between fuel consumption and acceleration performance, if other vehicle attributes are held fixed. Earlier econometric studies have estimated the magnitude of this trade-off - the elasticity of fuel consumption with respect to performance - based on historical vehicle data. The majority of these studies assume, a priori, that elasticity is constant across the model year, vehicle power, and technology content. However, there is evidence that the content in the underlying powertrain technology packages is shifting in a way that reduces the value of the elasticity of fuel consumption with respect to performance, such that historical trends would not predict future behavior. This paper presents an alternative strategy for studying vehicle fuel consumption versus performance trade-off. The magnitude of this trade-off was determined by modeling a “fleet” of vehicles, each identical, save for engine power, and simulating fuel consumption and acceleration performance. The study was performed on five powertrains representing over 40 years of advancement in technology content, including a feasible future powertrain. The study found that the elasticity is variable and depends on baseline performance, powertrain technology content, and the fuel consumption cycle. Historically, these dependencies have nearly balanced so that the elasticity of fuel consumption with respect to acceleration times over the regulatory combined cycle has declined only gradually. However, with new advanced technology engines being produced, this gradual trend is unlikely to continue. Indeed, for more advanced powertrains driven on the more aggressive US06 cycle, the elasticity is essentially zero over a range of engines covering the lower half of the acceleration performance range of the current fleet. This indicates that, in some cases, there may be no fuel consumption disadvantage associated with improving vehicle acceleration performance through means such as increasing engine power.