Impact of intake temperature on diesel engine combustion and emissions: a comprehensive analysis of spray impingement and adhered film effects on soot and NOx formation

Due to the critical challenges of heavy-duty diesel engines in cold-start performance and emission control under variable intake temperatures, especially in extremely low-temperature environments, a thorough understanding is necessitated. This study systematically investigates the effects of intake temperature from −10 °C to 20 °C on fuel-air mixing, combustion characteristics, power output, soot and NOx emissions through three-dimensional CFD simulation. The results demonstrate that as intake temperature decreases from 20 °C to −10 °C, IMEP increases from 8.62 bar to 8.85 bar due to enhanced premixed combustion and shortened main combustion period. NOx emissions rise nonlinearly from 1380 ppm to 1645 ppm driven by prolonged ignition delay and expanded high temperature zones. Soot emissions exhibit a non-monotonic trend with a minimum at 0 °C, resulting from two distinct formation pathways. At 10 °C and 20 °C, soot formation is dominated by thermal cracking of atomized fuel and rapid film evaporation, with limited OH oxidation leading to high soot residue. Conversely, at −10 °C, slow evaporation of fuel films during expansion generates secondary soot precursors such as A4 and C 2 H 2 , causing an emission rebound. The 0 °C condition achieves an optimal balance between soot formation and oxidation. Sensitivity analysis confirms that soot emissions exhibit the highest temperature sensitivity with an index greater than 1.6 under both low- and high-temperature conditions, whereas IMEP remains relatively stable. The research reveals the nonlinear influence of intake temperature on the cold-start combustion and emissions, providing theoretical and engineering guidance for optimizing cold-start strategies and emission control of heavy-duty diesel engines operating in extreme cold climates.