Abstract: The starting performance of diesel engine is one of the main performance indexes. The altitude environment has an important influence on the starting process of diesel engine. A diesel engine with 12 cylinders was test to research the influence of altitude environment on diesel engine starting process in altitude environment and plain environment, and the cylinder pressure, top dead center, and instantaneous rotational speed were measured. The experimental results indicate that the starting time is longer, the fluctuation of rotational speed is greater, and the proportion of bimodal combustion is larger during starting in altitude environment. The combustion analysis of starting process indicates that the starting process in altitude environment has a longer combustion delay period calculated with crank degree, and the combustion in cylinder in altitude environment appears more delay than that in plain environment. The starting process in altitude environment has a longer combustion delay period calculated with time than that in plain environment at the same rotational speed. Key

Key words: ordnancescienceandtechnology, dieselengine, startingprocess, altitudeenvironment, combustiondelayperiod