Characterisation of Powertrain Technology Benefits Using Normalized Engine and Vehicle Fuel Consumption Data 2018-01-0318
Vehicle certification data are used to study the effectiveness of the major powertrain technologies used by car manufacturers to reduce fuel consumption. Methods for differentiating vehicles effectively were developed by leveraging theoretical models of engine and vehicle fuel consumption. One approach normalizes by displacement per unit distance, which puts both fuel used and vehicle work in mean effective pressure units, and is useful when comparing engine technologies. The other normalizes by engine power, a customer-relevant output metric. The normalized work/power is proportional to weight/power, the most fundamental performance metric. Certification data for 2016 and 2017 US vehicles with different powertrain technologies are compared to baseline vehicles with PFI naturally aspirated engines and six speed automatics. The most efficient baseline vehicles are low-performance and achieve EPA efficiencies of 30% Highway, 20% City and 23% Combined cycles. The data show that efficiency drops linearly as the weight/power ratio decreases. The data shows turbocharging, cylinder deactivation, Atkinson cycle and eight speed transmissions providing larger benefits in higher performance vehicles, so that a common best efficiency of 24% EPA Combined is achieved across a wide range of vehicles sizes and performances. The improvements on intrinsically efficient low-performance vehicles are limited. Continuously variable transmissions are found to provide substantial benefits across the vehicle performance range, mainly on the EPA City cycle. The data also show that most technologies have distinct preferred ranges of application.