Numerical Simulation Study Of Combustion Process In A Diesel Engine Blended With Bio-diesel

Nowadays, the world is faced with the threat of oil depletion and environmental pollution, and the relevant scholars and experts are eager to find alternative energy to traditional fossil fuel. Bio-diesel is a kind of renewable energy, and it is drawing more and more people’s attention to the research of diesel engine combustion process blended with bio-diesel, which is of great theoretical significance and application prospects.The combustion characteristics and emission characteristics of 186FA diesel with different proportions of bio-diesel were analyzed through the combination of numerical simulation with experimental study. In this paper, indicator diagram, combustion noise and heat release regularity of B0, B20, B50, B100 fuel were studied through the bench test. Results show that, the peak of cylinder pressure increased and the corresponding crank angle got advanced as the bio-diesel blending ratio increased. At the same time, the peak heat release rate decreased, and the combustion starting point got earlier. The combustion efficiency and fuel economy were improved when the fuel was blended with bio-diesel. After the fuel was blended with bio-diesel, some certain parameters which affect combustion noise increased. At the same load, the smoke value of fuel decreased as the bio-diesel blending ratio increased, and the NOX emission of B100 fuel increased as the bio-diesel blending ratio increased.In this paper, the combustion characteristics and emission characteristics of 186FA diesel blended with bio-diesel were analyzed through the numerical simulation. Based on the 3D model of the combustion chamber established by using the software Pro-E, the mesh of the combustion chamber was made by using the software HyperMesh and AVL-FIRE, and the combustion process of three different fuel (B0, B50 and B100) was simulated by using the software AVL-FIRE. The precision of standard k-ε model, LES model and PANS model was analyzed by comparing the simulation indicator diagram and experiment indicator diagram. Simulation results show that the ignition timing and the in-cylinder pressure predicted by the PANS model were more accurate than that of the LES model, and the PANS model’s ability to capture the turbulent vortex group was better than that of the standard k-ε model. The simulation results show that after the fuel was blended with bio-diesel, the density and viscosity of fuel were larger, and the fuel spray distance of B50 and B100 fuel was longer than that of BO fuel, and more fuel was attached to the cylinder wall. The atomization, vaporization and mixture formation conditions of B50 and B100 fuel were not as good as BO fuel, because bio-diesel was oxygenated fuel, which increased the local air-fuel ratio, and the local combustion temperature and NOX emission of the B50 and B100 fuel were higher than that of BO fuel. The combustion process was promoted by the oxygen in bio-diesel, and the O2 mass fraction area of B50 and B100 fuel was larger than that of BO fuel. The two factors make more soot to oxide, as a result, soot emission of B100 and B50 fuel decreased. The generation of the pollutants can be controlled by changing the eddy current ratio and fuel injection advance angle.