To quantify how ambient temperature affects hybrid electric vehicle emissions, a diesel hybrid electric vehicle was tested under three different temperatures by a chassis dynamometer in this work. The results show that the total NOx emission factors follow the sequence of −10 °C > 25 °C > 40 °C and the particle number (PN) emission factors follow the sequence of 40 °C > 25 °C > −10 °C. Both NOx and PN instantaneous emission peaks corresponding to engine-starts can be found in each entire test cycle. The drastic temperature change of upstream SCR and DPF as a result of more frequent engine stop-and-goes may induce NOx and PN peaks. More attention should be paid to exhaust temperature management for hybrid electric vehicles to tackle this emission issue, especially for low-temperature condition.
Wang et al. (Sat,) studied this question.