Hitherto, for example, in vessels such as tankers and shipping vessels, and in land power generating facilities, diesel engines have been used as their driving sources. However, exhaust gas of a diesel engine contains a lot of nitrogen oxide, sulfur oxide, and particulate material, etc, which serve as toxic substances that hinder environment preservation. Accordingly, in recent years, as an engine as an alternative for the diesel engine, a gas engine that can reduce a generation amount of toxic substance, etc., have come into widespread use.
Further, as an engine that is a combination of diesel engine features and gas engine features, there has been provided (see patent document 1 and patent document 2) a dual fuel engine that use a premixing combustion method in which gas fuel (fuel gas), such as natural gas, is mixed with air, and is supplied and burnt in a combustion chamber, and a diffusion combustion method in which liquid fuel, such as heavy oil, is jetted and burnt in a combustion chamber.