Effects of cabin heating and cooling on ammonia emissions from hybrid electric vehicles under extreme ambient temperatures.

Abstract

Ammonia (NH₃) is an unregulated by-product from NO_X reduction over three-way catalysts (TWCs), yet how hybrid vehicle NH₃ emissions respond to cabin thermal demand remains poorly defined. Four China VI gasoline hybrid passenger vehicles were tested on the Worldwide harmonized Light vehicles Test Cycle (WLTC) at -7, 23, and 40 °C. Heating, ventilation, and air conditioning (HVAC)-off tests were carried out at all temperatures, with heating-on and cooling-on tests conducted at -7 °C and 40 °C, respectively. Cycle-averaged NH₃, CO, and NO_X emission factors were analysed using second-by-second emissions, engine speed, lambda, coolant and catalyst temperatures, and battery state of charge (SOC). With HVAC off, all vehicles produced higher NH₃, CO, and NO_X at -7 °C than at 23 °C, while the 40 °C response was vehicle-specific. Heating at -7 °C increased NH₃ emissions for three vehicles and reduced emissions for one; cooling at 40 °C raised NH₃ of one vehicle approximately fivefold and cut that of another by nearly 50%. Transient results show high NH₃ coincides with intense, frequent reducing events under active catalyst conditions. HVAC modulates emissions via vehicle-specific energy management, engine engagement and engine-catalyst timing.