Effect of gas flow on combustion and exhaust emissions in a dual fuel natural gas engine

In recent years, natural gas is attracted attention as alternative fuel for oil. This study focused on the dual fuel combustion system as a method to use natural gas for cogeneration engine. The purpose is construction of high power, high efficiency and low emission cogeneration engine by using lean burn and supercharged system. One of important parameters that affects on combustion is gas flow in cylinder. In this study, shrouds that are equipped near the intake valves were used to change the gas flow in cylinder. Combustion process was also observed by visualization. The engine performance and exhaust characteristics were compared to investigate effects of gas flow, that is, swirl, tumble and normal. This test engine has a single cylinder with bore of 96mm and stroke of 108mm. The compression ratio is 16:1. The engine was operated at 1000 rpm. Compressed natural gas was induced from an intake port and diesel fuel was injected into the cylinder near the compression TDC. After the diesel fuel with natural gas and air mixture is auto-ignited, the premixed turbulent flame develops from some ignition parts. The main results are as follows: The combustion process, engine performance and exhaust emissions are different, when gas flows like swirl or tumble exist in cylinder. In the case of swirl flow, unburned hydrocarbons emissions increase and output performance and thermal efficiency decrease. In the case of tumble flow, the combustion duration is shortened. And in leaner condition, the thermal efficiency and output power increase and unburned hydrocarbons are slightly reduced.

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