Insights into the Combustion and Emission Characteristics of the Diesel Engine in the Cold Start Stage

With the widespread adoption of diesel engine technology, the problem of pollutant emissions has become increasingly prominent. Especially in the cold start stage of the diesel engine, the instantaneous pollutant emissions may be several times or even tens of times that of stable operation, which adds to deterioration of the environment. Therefore, the combustion characteristics and emissions of a two-cylinder diesel engine at high altitudes and low temperatures were explored and analyzed in this research. By adjusting the injection timing and compression ratio (CR) experimentally, the optimal combination of parameters to simulate the emission at high-altitude and low-temperature conditions was determined. The results show that advancing the injection timing can improve the combustion efficiency, but higher CR and injection timing significantly influence the hydrocarbon (HC)/nitrogen oxide (NO X ) trade-off. While delaying the injection timing can reduce NO X emissions, it can increase HC emissions. Increasing CR from 18.5 to 20.5 raised peak instantaneous NO X emissions by approximately 27.7% but contributed to a reduction in HC emissions. In the cold start stage, HC concentration peaked sharply and gradually stabilized, while NO X concentration rose rapidly with more fluctuations. Under high altitude conditions, HC emission normally rises with altitude. When reaching 4000 m, the HC emissions increased by 27.9% compared with 0 m but the concentration decreased at 5000 m, the NO X emission decreased with elevation, and ambient temperature had little effect.