| With the rapid development of industry,overexploitation of fossil fuels and environmental pollution have become worldwide problems.Many scholars turn to search for advanced combustion technologies and alternative fuels to meet these challenges.Among them,methanol and biodiesel have attracted widespread attention as renewable clean fuels.Combustion and emission characteristics of methanol-biodiesel engine were investigated by means of bench test and numerical simulation in this thesis.Experiment were carried out on a four-cylinder,direct-injection compression-ignition diesel engine fueled with methanol-biodiesel blends of 0,10%,15%and 20%mass fraction,which were recorded as BMO,BM10,BM15 and BM20 respectively.The combustion and emission of blends were investigated at different load,EGR rate and injection timing.In addition,the effects of multi-injection strategy on combustion and emission characteristics of diesel engine were studied by simulation software AVL-FIRE.The results showed that the addition of methanol increased in-cylinder pressure and heat release rate at high load and decreased in-cylinder pressure at low load.Due to the low cetane number of methanol,the addition of methanol prolonged the ignition delay and shorten the combustion duration,while higher latent heat of vaporization increased the brake specific fuel consumption and reduced the brake thermal efficiency.In addition,the addition of methanol increased NOx,HC and acetaldehyde emissions at medium and high loads,but 1,3-butadiene and benzene emissions and soot emissions decreased with the addition of methanol.In addition,the increasement of EGR reduced the in-cylinder pressure and heat release rate,BM15 and BM20 even misfired under large proportion of EGR.And with the increasement of EGR the ignition delay and combustion duration prolonged,the brake specific fuel consumption increased.NOx emissions decreased,HC and benzene emissions increased,while 1,3-butadiene,soot and acetaldehyde emissions decreased first and then increased.However,with the injection timing advanced the in-cylinder pressure and heat release rate increased,and the ignition timing advanced.And the ignition delay shorten first and then prolonged,while the brake thermal efficiency increased first and then decreased with the injection timing advanced.NOx emissions increased,1,3-butadiene and benzene emissions decreased,while HC and acetaldehyde emissions decreased first and then increased,and soot emission increased first and then decreased.Meanwhile,the simulation results showed that the in-cylinder pressure and heat release rate reduced with the pilot injection timing advanced,the average temperature and NO emission decreased first and then increased,and the soot emission first increased and then decreased.As the increasement of pilot inj ection ratio,in-cylinder pressure and soot emission increased,but the heat release rate,average temperature and NO emission decreased.The addition of post injection strategy had slight effect to heat release of main combustion stage,which could mainly reduce soot emissions and slightly reduce NO emissions.And multi-injection could reduce both NO and soot emissions.A comprehensive study of the combustion and emission characteristics of diesel engine fueled with methanol-biodiesel was conducted in this thesis by the combination of experimental and theoretical research method,which will provide a reference for the application of methanol-biodiesel in diesel engines. |
