Study On Combusion And Emission Characteristics Of A Butanol Engine With Hydrogen Addition

In physical and chemical properties,n-butanol is similar to gasoline,and it has low cost in industrial manufacture.When n-butanol is applied to the traditional gasoline engine that does not need to be changed too much in structure,which is convenient to implement.As a substitute fuel for internal combustion engine,n-butanol is of great significance to realize energy saving and emission reduction,which can improve the energy diversity and alleviate the energy crisis of our country.Because of its high latent heat of vaporization and viscosity,low saturated steam,n-butanol is not easy to be fully mixed with the air in the cylinder,which causes the combustion insufficiency,especially in the case of lean-burn.Therefore,hydrogen is used as the auxiliary fuel for the n-butanol engine to optimize the combustion,emission and the engine cycle variation.Hydrogen with excellent physical and chemical properties is a clean auxiliary fuel.In this treatise,with the small consumption of the hydrogen and the kind of hydrogen injection,there is no need to change the traditional gasoline engine too much,which is easy to implement widely.In the experiment,the hydrogen direct inject into the cylinder which can effectively avoid the problem of the engine power decline caused by the reduction of the charge coefficient,and can also avoid the danger of engine backfire.In this thesis,hydrogen is used as the auxiliary fuel of n-butanol engine.When the engine is in the middle load with the speed of 1500 r/min,the hydrogen is direct injected into the cylinder at 60°CA BTDC.This method is expected to construct a stratified environment in which hydrogen is enriched around the spark plug and gradually thinned out.In the early stage of combustion,the spark plug ignites the nearby hydrogen quickly,which can form a stable flame core,and then ignites the surrounding n-butanol to promote the full mixing of the unburned n-butanol.Thus,the combustion and the emission of CO,HC can be optimized.In order to meet the requirements of the test,the compound injection platform of direct injection of hydrogen into engine cylinder and injection of n-butanol into the inlet has been builded.Moreover the electronic control system of the engine is developed on the platform of dSPACE/Simulink,which can achieve the real-time adjustment of the ignition time,the ratio of hydrogen-butanol,and the timing of injection.It is convenient to explore the effect of hydrogen on the combustion and emission in n-butanol engine.The main conclusions of this thesis are as follows:?1?With the 10°CA BTDC of spark advance angle(?_ig),the addition of hydrogen can dramatic enhance the speed of combustion,temperature of the cylinder,Pmax?peak value of cylinder pressure?and the dQmax?peak value of heat release rate?.Meanwhile the CA of Pmax and dQmax are closer to TDC.The temperature increment can effectively alleviate the problem of uneven mixing caused by the large latent heat of vaporization of n-butanol.Compared with pure n-butanol,mixing a small amount of hydrogen can optimize the performance of n-butanol engine.However with the increase about the ratio of hydrogen to n-butanol,the sensitivity of combustion to hydrogen decreases.?2?Because of the high combustion speed and low ignition energy to hydrogen,the CA of MBT is closer to TDC,with the increase of the ratio about hydrogen to n-butanol.At the MBT point the hydrogen can also improve the combustion performance and the engine thermal efficiency.?3?About the performance of emission,the emission of NO_X increased,due to the addition of hydrogen,at the working condition of fixed?ig.It is important that the hydrogen extends the lean combustion limit of the mixture,and when the excess air coefficient???is larger than 1.4,the emission of NO_X is at a low level.And also at the working condition of MBT,the emission of NOX can be controlled by lean combustion without sacrificing the emission of HC.The attributes of n-butanol lead to the insufficient about the mixing and combustion,which is the main reason to the high emission about HC.The stable core of the flame can be formed with the addition of hydrogen,which can ignite the n-butanol,perfect the mixing and combustion.Therefore,the addition of hydrogen can significantly reduce the emission of HC.The hydrogen can reduce the emission of CO.But it is mainly influenced by the excess air coefficient???.?4?The engine cycle variation is evaluated by the cyclic variation of the IMEP.The addition of hydrogen can decrease the distribution of the IMEP,and increase its mean value.Therefore,as the auxiliary fuel,hydrogen can effectively reduce the COV_IMEP,especially in the environment with the larger excess air coefficient???.Meanwhile,hydrogen can effectively extend the lean combustion limit of the mixture.