Evaluating the Performance of a Conventional and Hybrid Bus operating on Diesel and B20 Fuel for Emissions and Fuel Economy 2020-01-1351
With ongoing concerns about the elevated levels of ambient air pollution in urban areas and the contribution from heavy-duty diesel vehicles, hybrid electric buses are considered as a potential solution as they are perceived to be less polluting and more fuel-efficient than their conventional engine counterparts. However, recent studies have shown that real-world emissions may be substantially higher than those measured in the laboratory, mainly due to operating conditions that are not fully accounted for in dynamometer test cycles. At the U.S. EPA National Fuel and Vehicle Emissions Laboratory (NVFEL), the in-use criteria emissions and energy efficiency of heavy-duty class 8 vehicles (up to 80,000 lbs) may be evaluated under controlled conditions in the heavy-duty chassis dynamometer test. The present study evaluated the performance of a conventional bus and hybrid bus for emissions and fuel economy under representative test cycles (including cold start and hot start conditions) with Diesel (#2) and Biodiesel (B20) fuel. The conventional bus was equipped with a Cummins ISL 8.3L engine and a Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC) after-treatment, while the hybrid bus had a Cummins ISB 6.7L engine with a Selective Catalytic Reduction (SCR), DPF and DOC after-treatment. Generally, the hybrid bus showed higher fuel economy (lower CO2 emissions) as compared to the conventional bus for both cold start and hot start test cycles. However, NOx emissions were observed to be somewhat higher for the hybrid bus over the cold start test cycle. In addition, the fuel efficiency and emissions for both bus configurations when operating on diesel fuel compared very closely to that with B20.
Rinav Pillai, Matthew Brusstar, Andre Boehman, Scott Ludlam
University of Michigan, US Environmental Protection Agency