Comparative study on low ambient temperature regulated/unregulated emissions characteristics of idling light-duty diesel vehicles at cold start and hot restart

Since it is common for vehicles with idle engines to be stored indoors during the winter season to remain warm, better constraints are needed for idling emissions at low ambient temperature. CH₄ (methane), C₂H₆ (ethane), C₂H₄ (ethylene), HNCO (isocyanic acid), N₂O (nitrous oxide), NH₃ (ammonia), C₃H₆ (propylene), and HCHO (formaldehyde) from many unregulated exhaust emissions were selected and measured by a Fourier Transform Infrared Spectroscopy (FTIR) analyzer in this study. This paper investigates the idling regulated and unregulated emissions of Euro 5/6 diesel vehicles at cold start and hot restart near 0 °C conditions. The impact of cold start and hot restart on NO_x idling emissions was lower than CO and HC idling emissions in diesel vehicles. With regard to unregulated emissions, high fuel–air equivalence ratios and longer ignition delay in the idle cold start condition may increase incomplete combustion and affect the thermal cranking processes, leading to the increase of CH₄, C₂H₄ and C₃H₆. Furthermore, as the formation of N₂O is considerably affected by the equivalence ratio and cylinder temperature, a high fuel-air equivalence ratio at low ambient temperature in the cold start condition resulted in the increase of N₂O emissions.