Comparisons of the simulated emissions and fuel efficiencies of diesel and gasoline hybrid electric vehicles

This paper presents results from gasoline-and diesel-powered hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs) that account for the interaction of drive cycle transients and engine start-stop events with after-treatment devices and their associated fuel penalties. These simulations were conducted using the Powertrain Systems Analysis Toolkit software combined with after-treatment component models developed at Oak Ridge National Laboratory. The present authors employed a three-way catalyst model for gasoline emissions control and a lean nitrogen oxide (NO_x) trap model to simulate diesel exhaust NO_x reduction. A previously reported methodology based on experimentally calibrated corrections to steady state maps was used to simulate engine-out emissions and thermal variations. As expected, the simulations indicate a higher baseline fuel efficiency for diesel-powered hybrid vehicles, but this advantage is reduced by about a third for both HEVs and PHEVs when the fuel penalty for the lean NO_x trap is included. These preliminary studies demonstrate that existing engine and exhaust systems models can capture important features of the highly transient engine operation in hybrid vehicles and can provide useful comparisons between advanced hybrid vehicle engine options.