Chassis Dynamometer and On-Road Evaluations of Emissions from a Diesel-Electric Hybrid Bus

Recently Hybrid Electric Buses (HEBs) have been widely used in China for energy saving and emission reduction. In order to study the real road emission performance of HEBs, the emission tests of an in-use diesel-electric hybrid bus (DHEB) are evaluated both on chassis dynamometer over China City Bus Cycles (CCBC) and on-road using Portable Emissions Measurement Systems (PEMS). The DHEB is powered by electric motor alone at speed of 0~20km/h. When the speed exceeds 20km/h, engine gets engaged rapidly and then works corporately with the electric motor to drive the bus. For chassis dynamometer test over CCBC, emissions of NOx, particulate number, particulate mass, and THC of the DHEB are 7.68g/km, 5.88E+11#/km, 0.412mg/km, and 0.062g/km, respectively. They have all decreased greatly compared to those of the diesel bus. But the CO emission which is 3.48g/km has increased significantly. Then the Real Driving Emissions (RDE) of the DHEB are compared with the dynamometer test results. Particulate and CO emissions have increased because of the higher vehicle speed and more radical acceleration and deceleration driving conditions in on-road test. But NOx emissions of RDE have decreased because of the fast light-off and higher catalytic temperature of Selective Catalytic Reduction system. In all, emissions of the DHEB have decreased significantly compared with traditional powered diesel bus. But CO emissions have increased owing to the control strategy of engine. When it comes to RDE, emissions of the DHEB are affected by the required driving power of the road conditions directly or indirectly.