Experimental Study On Lean Burn And Emission Characteristics Of A N-butanol/Gasoline Engine With Hydrogen Addition

This thesis is based on the analysis of the physicochemical properties of n-butanol and hydrogen,the injection mode of n-butanol/gasoline mixed fuel in the intake port and hydrogen direct injection in the cylinder as auxiliary fuel was proposed.The ignition engine is reformed to have a complete fuel supply system,which can meet the experimental requirements to realize the combined injection of n-butanol/gasoline mixed fuel and hydrogen.The engine control model is built with the help of dSPACE,and the relevant test equipment is connected and installed to realize the collection of combustion and emission data.Taking the ratio of n-Butanol and hydrogen as the core variable and the coefficient of excess air as the secondary variable,the selected operating points are mainly concentrated on the lean combustion condition with excess air coefficient greater than 1.The effects of the synergistic effect of n-butanol and hydrogen on lean combustion and emission of ignition engine are studied,and the experimental results are explained.The main conclusions are as follows.The analysis of lean combustion characteristics can be summarized as the following three aspects:?1?Analyzing the lean-burn characteristics of n-butanol/gasoline blends separately,the theoretical heat release of the blends decreases with the increase of alcohol ratio.Under lean combustion conditions,when the n-butanol ratio increases from 0%to 25%,n-butanol blending can promote combustion,and the combustion becomes worse as the n-butanol ratio increases to more than 50%.?2?Analyzing the effect of hydrogen addition separately.It is found that with the increase of hydrogen addition ratio,the lean-burn characteristics of n-butanol/gasoline blends are improved obviously.The cylinder pressure and temperature increase with the increase of hydrogen addition ratio,the flame development period and rapid combustion period shorten,the cyclic variation decreases,and the power performance improves to a certain extent.?3?Analyzing the synergistic effect of n-butanol and hydrogen on lean combustion characteristics.It is found that,although hydrogen has obvious effect on mixed fuel engine,the hydrogen addition ratio is insensitive to the relevant combustion characteristics of lower n-butanol ratio?0%²5%?and lower excess air coefficient?lambda=1.1?,but sensitive to the larger n-butanol ratio?50%¹00%?,and the improvement of large excess air coefficient?lambda=1.3?is very obvious.For the analysis of emission characteristics,the following conclusions can be drawn:?1?Under lean burning condition,the main influencing factor of NOx emission from n-butanol/Gasoline blends is excess air coefficient,which decreases obviously when excess air coefficient increases.With the increase of n-butanol ratio,the emission of NOx decreases as a whole;with the increase of hydrogen ratio,the emission of NOx of n-butanol/gasoline blends generally increases,but the increase of NOx is smaller under the conditions of larger excess air coefficient and smaller alcohol ratio?0%²5%?.?2?There are two main factors affecting HC emission from n-butanol/gasoline blends:n-butanol ratio and excess air coefficient.With the increase of n-butanol ratio,the main trend of HC emission decreases firstly and then increases,generally the minimum value appears at25%n-butanol ratio;the increase of excess air coefficient promotes the increase of HC emission,and the maximum HC emission is at lambda=1.3 in this paper;under the synergistic effect of n-butanol and hydrogen addition,hydrogen can promote the reduction of overall HC emission,but with the increase of ratio,it is smaller.The medium n-butanol ratio?0%⁵0%?has no obvious effect on the reduction,but it has obvious effect on the larger n-butanol ratio?50%¹00%?.?3?The main influencing factor of CO emission from n-butanol/gasoline blends is excess air coefficient,and the CO value is at a very low level under lean combustion.With the increase of n-butanol ratio,CO emission decreases overall,but increases slightly after hydrogen doping,and does not change significantly with the increase of hydrogen ratio.Comprehensive analysis shows that under lean-burn conditions,25%n-butanol ratio and?H₂=5%have a great improvement on the overall combustion characteristics.Cylinder pressure,in-cylinder temperature,dynamic performance index have been improved,cyclic variation has been reduced,combustion duration has been shortened;HC emissions have also been reduced under this condition,but NOx emissions have increased significantly.Combining with the favorable factors,this fuel ratio is the best parameter for lean burn and emission characteristics.For n-butanol/gasoline blends with high n-butanol ratio?50%¹00%?and large excess air coefficient,high hydrogen ratio should be adopted to improve combustion performance and reduce HC emissions,and to use the effect of increasing n-butanol ratio or increasing excess air coefficient on NOx emission to neutralize the adverse effects of increasing hydrogen ratio on NOx emission.