Characteristics of Transient NOx Emissions of HEV under Real Road Driving

To meet the request of China National 6b emission regulations which will be officially implemented in China, firstly including the RDE emission test limits, the transient emissions on real road condition are paid more attention. A non-plug-in hybrid light-duty gasoline vehicles (HEV) sold in the Chinese market was selected to study real road emissions employed fast response NO_x analyzer from Cambustion Ltd. with a sampling frequency of 100Hz, which can measure the missing NO peaks by standard RDE gas analyzer now. Emissions from PEMS were also recorded and compared with the results from fast response NO_x analyzer. The concentration of NO_x emissions before and after the Three Way Catalyst (TWC) of the hybrid vehicle were also sampled and analyzed, and the working efficiency of the TWC in real road driving process was investigated. It is found that when the engine is at high-speed and heavy-load conditions, especially when fuel is injected after fuel cut, instantaneous spikes in tailpipe NO emissions could be observed, which means that traffic positions such as crosswalks, speed bumps, expressway entrances, traffic lights, would lead to higher NO_x emissions, because the instantaneous fuel cut-off occurs during the acceleration shifting process, the TWC is in an oxygen-rich state. Obvious transient effects were revealed and the results could be used for further reducing NO_x emissions from automotive RDE and engine calibration of RDE.