The University of Wisconsin Engine Research Center (ERC) has continued development of it on-road demonstration vehicle for low temperature combustion (LTC) modes. The vehicle, a series hybrid architecture in a 2009 Saturn Vue vehicle chassis, was part of a previous collaborative project with the Hybrid Vehicle Team at the University of Wisconsin. The previous vehicle level testing identified improved systems-level and engine-specific improvements that offered vehicle performance improvements [1]. The current work implemented an improved electric drivetrain and additional instrumentation for engine calibration with the vehicle.
While concluding the previous vehicle testing, the traction motor drivetrain, a UQM Technologies PowerPhase Select 75 kW electric motor and inverter, suffered mechanical failure. Accordingly, to improve drivetrain performance, a Ballard Technologies Integrated Powertrain (IPT) was implemented with necessary chassis and suspension geometry modifications. Initial vehicle system modeling suggested an average 4.4 % fuel efficiency improvement over the previous Environmental Protection Agency (EPA) vehicle certification cycles, and it was of interest to perform vehicle test to confirm this prediction.
Following completion of the vehicle drivetrain improvements, engine performance improvements were implemented, including the installation of optimized pistons. While previous engine calibration with these pistons was performed on the stationary multi-cylinder engine in the laboratory at the ERC, dynamometer control capabilities prevented calibration at an increased engine load condition, which was of interest to assess the potential of the in-vehicle engine. Hight ethanol blend fuels were used to investigate increased load operation. RCCI engine operation with E85 at 8 bar BMEP was found to increase energy conversion by 15.6 % over diesel CDC operation while realizing a ten-fold reduction in engine-out NOx. However, thermal loads from the vehicle systems operating at the increased load prevented significant improvement in vehicle fuel efficiencies. Analysis shows that recovering the energy lost to the generator motor would yield RCCI vehicle fuel economy of 54.5 miles per gallon gasoline equivalent (mpgge) on the Highway Fuel Economy Test Cycle (HWFET). Analysis of further improvements in system efficiency, including and upgraded drivetrain and series-parallel engine operation, reveal pathways to 54.7 mppge fuel economy using an RCCI engine to directly provide vehicle tractive effort.