Analysis of NOx and NH3 emission characteristics from heavy-duty diesel vehicles under cold and hot start conditions in the summer

FENG Qian; SHEN Xiu-e; LU Yang; WANG Peng-rui; ZHOU Yan-qing; YANG Yan-yan

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China Environmental Science ›› 2026, Vol. 46 ›› Issue (1) : 91-100.

Analysis of NO_x and NH₃ emission characteristics from heavy-duty diesel vehicles under cold and hot start conditions in the summer

FENG Qian¹, SHEN Xiu-e¹, LU Yang¹, WANG Peng-rui¹, ZHOU Yan-qing¹, YANG Yan-yan^1,2

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Abstract

This study investigated cold and hot start processes of diesel vehicles under different load conditions in summer using a heavy-duty chassis dynamometer, with a focus on analyzing NO_x and NH₃ emission characteristics and influencing factors. The results showed that during cold starts, the exhaust gas temperature and coolant temperature rose slowly, and the NO_x sensor was delayed in activation, with over 82% of NO_x emissions occurring before the sensor became operational. During hot starts, the SCR system and sensor entered operation rapidly due to higher system temperatures, leading to significantly lower NO_x emissions. NH₃ emissions were significantly affected by the start condition and simulated load. In the initial phase of cold starts, the NH₃ emission factor was higher than average because of low SCR temperatures. During hot starts, rapid urea hydrolysis without sufficient reaction with NO_x resulted in increased NH₃ emissions. Micro-scale operational modal analysis revealed that the difference in NO_x emissions was mainly determined by engine and SCR temperatures, whereas the difference in NH₃ emissions was associated with SCR temperature and urea injection quantity. The study emphasizes the need to address pollutant emissions during summer cold-start processes and proposes synergistic optimization of temperature control and SCR urea injection strategies to reduce the environmental impact.

Key words

diesel vehicles / summer emissions / cold start and hot start / NO_x / NH₃

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FENG Qian, SHEN Xiu-e, LU Yang, WANG Peng-rui, ZHOU Yan-qing, YANG Yan-yan. Analysis of NO_x and NH₃ emission characteristics from heavy-duty diesel vehicles under cold and hot start conditions in the summer[J]. China Environmental Science. 2026, 46(1): 91-100

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