The combustion chamber consists of the main combustion chamber on the top of the piston, the auxiliary combustion chamber in the cylinder head and the passage between the main and auxiliary Chambers.

The high speed photography was applied to visualize the fuel spray and ignition process in main and prechamber in a swirl type diesel engine at cold starting condition.

The effect of the natural gas supply method, passage diameter and heated temperature of intake air on the ignition, combustion and emission are studied.