Simulation Research On Effect Of Hydrogen Blending On Starting And Idling Performance In Butanol Ignition Engine

As the properties of butanol are similar to gasoline,butanol has been widely studied as a kind of good alternative fuel for internal combustion engine.As butanol is a kind of oxygenated fuel,CO and HC emissions will be effectively reduced.However,when incomplete combustion of butanol occurs in cylinder,there will be acetaldehyde emissions in exhaust,which is harmful to human' health.Compared with gasoline,butanol is a kind of fuel with higher vaporization latent heat and pretty lower saturated vapor pressure.Therefore,when butanol is used as a kind of substitute fuel for engine,there will be a poor evaporation and atomization performance in cylinder,especially in starting condition,when the wall temperature of the engine is very low,leading to starting hard in butanol fueled engine.Aiming at solving a series of problems existing in the starting process of butanol ignition engine,the method of mixing hydrogen in cylinder is put forward.Because of the low ignition energy and high flame propagation speed of hydrogen,hydrogen is easily to be ignited in cylinder.After that a large amount of heat will be released,and the temperature of mixture in cylinder will improve in a short time.As a result,combustion performance will be improved and pollutant emissions will be reduced.In this thesis,the modeling of a complex injection engine has been built in a CFD software named CONVERGE,and the modeling has been verified correct by the result of bench test.Then effect of hydrogen blending on starting and idling performance has been studied by simulation.The First part is starting condition.In this thesis,initial conditions and boundary conditions are set up to simulate different ambient temperature.And in this part,combustion and emissions performance has been explored by changing ambient temperature and whether or not with 10% hydrogen blending.The second part is idle condition.The hydrogen blending fraction is varied from 0% to 15%,and then effect of hydrogen blending fraction and ignition timing on combustion and emissions has been studied,especially on the aldehyde emissions.Main conclusions of the paper are follows:1)For butanol fueled engine,ambient temperature has a significant effect on combustion and emission in starting conditions.When the ambient temperature rises from 10? to 25?,the evaporation and atomization performance of butanol is improved,and the amount of mixture in cylinder increases,the combustion speed of mixture is accelerated as well.As a result,the peak value of cylinder pressure and cylinder temperature is greatly improved.And the maximum appears earlier.Because the combustion conditions in cylinder are improved,CO and HC emissions reduce.For aldehydes emissions,the formation and oxidation of aldehydes depend on the temperature distribution in cylinder.When the temperature in cylinder increases,the formaldehyde and acetaldehyde emissions will effectively reduce.2)Compared with the pure butanol injection engine,the 10% hydrogen blending engine has a breakthrough improvement on the combustion performance and pollutant emission.When hydrogen is added,combustion rate of the mixture in cylinder is accelerated,and the cylinder pressure is raised rapidly as well as cylinder temperature after ignition.The maximum of cylinder pressure and cylinder temperature is greatly increased.And the peak value appears earlier.The molar concentration of CO and HC emissions are reduced to nearly half of that in pure butanol injection engine.Meanwhile,the emissions of formaldehyde and acetaldehyde are reduced by more than 60%.This conclusion is reasonable when the ambient temperature is 10? or 25?.3)As for hydrogen blending engine,the effect of ambient temperature on combustion and emissions is not so remarkable as pure butanol injection engine.4)Under idle condition,the influence on combustion and emissions of different hydrogen fraction has been studied.It has been found that with the increasing of hydrogen fraction,the cylinder pressure,heat release rate and the cylinder temperature were all increased,and the peak value appear earlier.When the hydrogen fraction is 5%,the enhancement of combustion performance is the most significant.However,with the continuing increasing of hydrogen blending fraction,the enhancement of combustion performance is not so remarkable.As for emissions,with the hydrogen fraction increases,HC and CO emissions are decreased,aldehyde emissions are also continuing decreased.In addition,it has been found that the effect of hydrogen blending on acetaldehyde emissions is more significant than that of formaldehyde.5)Under idle condition,the cylinder pressure,heat release rate and cylinder temperature all increase with the ignition timing being advanced in 5% hydrogen blending engine,and the peak value appears earlier.As for pollutant emissions,HC emissions are very sensitive to the change of ignition timing.In 5% hydrogen blending engine,the HC emissions are decreased gradually with the delay of ignition.However,when the ignition time is varied from 5°CA BTDC to 25°CA BTDC,the molar concentration of CO emissions is kept around 1.7%.Formaldehyde and acetaldehyde emissions are greatly affected by ignition timing,and the molar concentration of aldehyde emissions is decreased,with the ignition timing being put advanced.6)In the process of exploring the formation of aldehyde emissions,it is found that acetaldehyde emissions are higher than formaldehyde emissions in butanol fueled engine.Aldehyde emissions are affected by two factors,reaction time and cylinder temperature,and the latter plays a more important role.In the cylinder region where temperature is between 800 K and 900 K,there is a strong reaction of creating aldehyde.The formation temperature of acetaldehyde is slightly lower than that of formaldehyde,and with the continually increase of temperature in the cylinder,When the temperature is over 1200 K,the oxidation consumption of aldehydes is violent,and the concentration of aldehydes decrease rapidly.