Johansen, L., Denbratt, I., and Hemdal, S., "Drive Cycle Particulate and Gaseous Emissions from a Parallel Hybrid Combustion Engine and Electric Powertrain," SAE Technical Paper 2015-24-2538, 2015, doi:10.4271/2015-24-2538.
The emissions from a parallel hybrid combustion engine and electric powertrain operated on a modified New European Drive Cycle (NEDC) was investigated in order to determine the relation between emissions and the road and engine load profile. The effect of simulated electric motor assistance during accelerations on emissions was investigated as a means to reduce particulate and gaseous emissions. The time resolved particulate number and size distribution was measured in addition to gaseous emissions. The combustion engine was a downsized, three cylinder spark ignited direct injection (SIDI) turbocharged engine fuelled with gasoline. Electric motor assistance during accelerations was simulated by reduction of the vehicle mass. This reduced engine load during accelerations. Fuel rich engine transients occurred during accelerations. NOx emissions were reduced with electric assistance due to a reduction in engine load. CO emissions were the result of air to fuel ratio transients and increased slightly with electric assist. HC emissions occurred during deceleration with downshifts. Particulate emissions were attributed to soot formation from fuel rich engine transients during accelerations and fuel rich engine operation at large load and both particulate number and mass emissions peaked during accelerations. Particulate number emissions increased with electric assistance. The reduction of in cylinder temperatures with electric assist due to reduction in engine load is hypothesized to have resulted in reduced in-cylinder soot oxidation and the observed increase in particulate number emissions with electric assist. Both with and without electric assist the particle size distributions were centered at 100 nm. Simulated electric motor assistance during load accelerations reduced fuel consumption as expected.