Ammonia emissions from series and series-parallel plug-in hybrid electric vehicles under real driving condition

To better understand the impacts of energy mode (fuel- or electricity-priority), state-of-charge (SOC) of the battery (charge-sustaining or depleting), and power architectures, nine real driving emission (RDE) tests were performed on two series hybrid electric vehicles (SHEVs), and a series-parallel hybrid electric vehicle (PSHEV). The ammonia emissions from the three test vehicles were 2.7–6.3, 10.9–56.9, and 0.9–5.1 mg/km, respectively. Similar to conventional vehicles, ammonia emissions from plug-in hybrid vehicles (PHEVs) were observed after catalyst light-off with enriched mixtures. Frequent internal combustion engine (ICE) restarts, together with rapid increases in ICE load corresponding to harsh accelerations, underlined most of the ammonia peaks. In the tests, the fuel-priority mode and charge-sustaining state would remarkably increase ammonia emissions compared to the electricity-priority and charge-depleting state. Besides, a considerable amount of ammonia peaks was related to ICE starts at high driving speeds for all the test vehicles because high ICE loads mandated fuel enrichment and lit off the catalyst in a short while, creating a favorable condition for ammonia production.