The analysis of influence of fuel spray angle on NOx fraction in the exhaust gas from marine 4-stroke diesel engine

The manuscript presents the analysis of influence of fuel spray angle on NOx fraction in the exhaust gas emitted from marine 4-stroke diesel engine. Analysis is based on computational fluid dynamic (CFD) model designed because of the motion mesh of combustion chamber of the marine engine cylinder and air inlet and exhaust gas ducts. Presented model consists of models of fuel injection into combustion chamber, breaking-up and evaporation of the fuel, mixing with air and turbulent combustion with heat transfer to construction elements of the engine cylinder. Mentioned CFD model is validated according to boundary and initial conditions taken from direct measurements. The chosen research object is laboratory 4-stroke turbocharged Diesel engine with direct injection of the fuel and mechanically controlled of both cylinder valves and the injector. The conclusion from the analysis is that the increase of fuel spray angle causes the increase of maximum speed of kinetic phase of the combustion and the decrease of maximum speed of diffusion phase of the combustion. The effect of this is the increase of maximum combustion pressure and the decrease of maximum combustion temperature. The result of presented changes in combustion process is the increase of NOx fraction in the exhaust gas. It should be noted that extended increase of the fuel spray angle cause close-up the fuel spray to the cylinder heads wall and the decrease of NOx fraction in the exhaust gas.