Numerical Simulation Of Combustion Process Of An Engine Powered By Mixing Fuel

Natural gas and hydrogen are clean fuels, natural gas is cheap and plenty of resource. The application of natural gas and hydrogen on marine engines is both benefical to solving the problem of energy shortage and lessening the pollution from emissions. In this paper, based on a diesel engine for marine purpose, a model of combustion chamber of the engine was developed, simulations were carried out by AVL FIRE software. Simulations were performed under the assumption of volumetric ratio between hydrogen and air about 80%, direct injection of the natural gas. Researches undertaken are as follows:(1) Develpoment of calculation grid of the engine combustion chamber. Natural gas was injected into the cylinder through 8 holes evenly distributed around the combustion chamber. The model for the combustion chamber was firstly developed by Pro/E software, and the grid meshing was then realized by work-flow manager in AVL FIRE software. The models involved in calculation were k-ε model, KHRT model, Multi-component evaporation model, O-Rourke model, Walljet1 model, modified Shell model, EBU vortex cloud model, extended Zeldovich model as well as kinetic model. Accuracies of above models were verified by experimental data.(2) Influnce of mixing ratio of the fuels on the engine combustion performance and emission. Simulation results show that the engine powered by diesel oil brings about the highest pressure and temperature of the gas in combustion chamber, but it will also result in the largest concentration of NO in the exhaust gas. However, the injection of natural gas and hydrogen will cut down the pressure and temperature in the combustion chamber and decrease the SOOT concentration in the exhaust gas as well.(3) The influence of natural gas adding ratio on engine performance and emissions. Diesel injection duration covers from 701.4CA to 710.2CA, injection angle is 160°, natural gas injection duration is from 710.2CA to 730.8CA and injection angle 45°. Results show, when the natural gas mixing quality varies from 70% to 90%, the highest temperature in cylinder changes from 2142 K to 2034 K and the highest pressure changes from 10.18 MPa to 9.98 MPa correspondingly. Results also reveal that the highest temperature and pressure in cylinder decreases in the increment of natural gas. The concentration of NO is reduced, but that of the SOOT is increased, the dynamic performance of the engine is deteriorated.(4) The influence of natural gas injection duration time on engine performance and emissions. The injection angle of diesel and natural gas is respectively 160°and 45°. It shows that, while the injection duration covers from 710.2CA to 720.2CA, the highest temperature and pressure in the cylinder will be changed from 2018 K to 1688 K and 10.6MPa to 9.8MPa, respectively. Results also show that the later the natural gas injection time, the lower the maximum temperature and pressure in cylinder, and it will bring about less NO but more SOOT.(5) The influence of natural gas injection angle on engine performance and emissions. Natural gas injection ratio and injection time is respectively set as 90% and 710.2CA. Simualtions shows that, while the natural gas injection angle varies from is 75°to 30°, the highest temperature and pressure will be changed from 2122 K to 1673 K and 10.6MPa to 9.9MPa. Results also reveal that the concentration of SOOT will be the maximum where the injection angle of natural gas is 30°, and the dynamic performance and emission of the engine is the best while the injection angle is 45°.