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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.

Previous studies have indicated that longer torque increase time benefits the reduction of emissions during transient process for a diesel engine. However, quantitative conclusions on reduction of emissions and effects on fuel economy have not been made clear so far. The aim of this study was to evaluate the transient process of diesel engine under different torque increase time, and to find the quantitative statement between torque increase time, fuel economy and engine-out emissions. To do this, experiment was carried out on a 7L common rail diesel engine used for commercial vehicles. Three engine speeds (1100r·min−1, 1300r·min−1 and 1500r·min−1) were chosen to represent an engine working range. For each speed, the engine torque is increased within different time (0.5s, 1s, 2s and 5s). It was shown that, in the transient process mentioned above, engine torque increase time effects fuel economy, smoke opacity and CO emission.