Experimental Investigation On Combustion Characteristics And Emission Characteristics For A Diesel Engine Fueled With Diesel-Methanol Blend

Diesel engines have the advantages of high thermal efficiency,good reliability and strong applicability,but they also face the problem of increasingly depleted diesel and environmental pollution.The development of suitable alternative fuels is an important guarantee for the continued use of diesel engines as the main source of power for industry,agriculture and transportation.Among the many alternative fuels,methanol has become one of the most promising fuels due to its advantages of high latent heat of vaporization,abundant yield,economical efficiency and liquid state at room temperature and pressure.Since the high spontaneous combustion temperature and low hexadecane value of methanol make it difficult as a single fuel to directly compress it on a diesel engine,this paper studies the alternative possibility of blending methanol with diesel.To be more specific,methanol is injected into the intake manifold of diesel engine to mix with the fresh air,and diesel is injected into the cylinder to ignite the premixed mixture,so as to generate power at the shaft end of the engine through the coordinated combustion of methanol and diesel.Firstly,a heavy-duty diesel engine is reformed because of blending methanol.Then,the influence of diesel replacement rate(the ratio of mass flow rate saved by diesel oil to mass flow rate saved by pure diesel fuel combustion mode)on engine performance is studied.So the main factors restricting the improvement of diesel replacement rate can be refined,and the highest diesel replacement rate and the in-engine emission baseline are also determined.Finally,the effects of the combination of diesel oxidation catalyst(DOC),particulate oxidation catalyst(POC)and selective catalytic reduction(SCR)on reducing the emission of alcohol-fueled engine pollutants are studied,and a post-treatment scheme for the exhaust pollutants of alcohol-fueled engine are proposed.The main research contents and conclusions of this paper are as follows: The mixture of methanol with diesel engine can significantly reduce the fuel cost of the engine.The maximum explosion pressure and combustion noise in the cylinder are the main factors limiting the increase of diesel substitution rate.After mixing methanol into diesel engine,particle emissions are significantly reduced.Though the total NOx emissions are not significantly changed,the proportion of NO2 is remarkably increased,and high concentrations of CO,HC,formaldehyde and unburned methanol can be found in engine exhaust.The results of engine emission test show that the conventional and unconventional emissions of alcohol-fueled engine can be effectively controlled by using DOC+SCR+DOC technology,and the emission results can meet the emission limit requirements of the fifth stage in China.