Study On Combined Diesel/Ethanol Fuel Combustion And Pollutant Formation

Oil is non-renewable energy, and ethanol is a kind of renewable energy.Ethanol has been used as blended fuel on the combustion of diesel engine, butthe application is not as common as on the gasoline engine. The reason is thatonce the mixing time of ethanol and diesel is long, they are easily layered. Sothe mixture of ethanol and diesel is not suitable for long-term storage.Chromatographic analysis shows that after absorbing heat, ethanol couldproduce mixture of many kinds of gases. In this paper, the following system istransformed. Ethanol is put through the small efficient heat exchanger which isinstalled in the diesel exhaust pipe. Ethanol absorbs exhaust heat, and ethanol ispartially decomposed. Then the gas mixture is put into the combustion chamberfor improving combustion. It provides a new way for the mixing combustion ofdiesel/ethanol.The research of different speed-constant power and rated speed-differentpower in diesel engine is done. The result is that the diesel engine system has agood fuel efficiency and energy efficiency whether the power is high or low.When the speed of the diesel engine is low speed-1500r/min, the best fuelefficiency is13.5%. When the speed is rated speed-2000r/min, the best fuelefficiency is5.7%which is similar to the effect of current ethanol diesel. Thefurther study of soot and NOx emissions is done, and the result is that the dieselengine system has little good efficiency of soot reduction in the condition of lowpower-low speed, and good efficiency of the other conditions. The bestefficiency is33.3%. The system has good efficiency of NOx reduction in allconditions. The best efficiency is64.7%. The system can effectively avoid thequestion of the storage of mixture of ethanol and diesel. And the gas mixturefrom ethanol absorbing heat can improve combustion better.Because the time scale of the combustion of diesel engine is very small and thereactions are very intense, it is impossible to grasp all the details and characteristics onexperimental methods. Simulation method becomes another important method forresearch. This paper presents construction of a three-fuel mechanism which is about the mixing combustion of alternative fuel of diesel (n-heptane and toluene) and ethanol.The mechanism is verified in kinds of different models. After analysis, the mechanism(Mix3) including106species and510reactions is constructed. The mechanism couldaccurately simulate the combustion of pure n-heptane and mixed fuel ofn-heptane/ethanol.A reduced gas dynamics mechanism (R-Mix3) is got on the combustion model ofdiesel engine using sensitivity analysis and reaction flow analysis to Mix3mechanism.The reduced mechanism includes47species and114reactions. Using A3as nucleation,a new fine carbon black model is constructed on the basis of R-Mix3mechanism. Themodel could accurately simulate the combustion of diesel engine and soot emissioncharacteristics in three-dimensional calculation.For the typical operating conditions of combustion of ethanol blended onthe transformed diesel engine system, zero-dimensional simulation used Mix3isdone. Important reactions for ignition delay and reaction paths of polycyclicaromatic hydrocarbons/NOx before and after ethanol or mixture of ethanol andhydrogen blended are got. Three-dimensional simulation used the fine carbonblack model coupling flow is done in the CFD software. Spatial distribution andprocess changes of temperature, pressure and main pollutions (polycyclicaromatic hydrocarbons and soot) of the combustion are got. It is effectivecomplement to the experiment.