Research On Combustion And Emission Characteristics Of Hydrous Ethanol/hydrogen Combined Injection Engine

Ethanol,as one of the carbon-neutral fuels for spark ignition（SI）engine,has been widely used.Dehydration and purification of ethanol during production process will lead to high energy consumption.If hydrous ethanol can be directly applied to the engine,the cost of use will be greatly reduced.Due to the high latent heat of vaporization of ethanol and water,it is necessary to consider the performance of atomization,evaporation,ignition and combustion stability when hydrous ethanol is used in engine.As a zero-carbon fuel,hydrogen has excellent characteristics such as low ignition energy,fast flame propagation speed and wide combustion limit.The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance.This study explores the combustion and emission characteristics of hydrous ethanol engine with hydrogen addition in a combined injection engine test platform.The main conclusions of this study are as follows:（1）In order to explore the influence of water blending ratio on the combustion and emission of hydrous ethanol engine,the first part of the experiment is carried out.At the same time,the optimal control parameters of hydrous ethanol engine can be optimized,so as to further study the influence of hydrogen addition on the combustion and emission characteristics of hydrous ethanol engine.The hydrous ethanol is injected into the intake port,and the combustion and emission characteristics of the engine are tested.Five water blending ratios of the hydrous ethanol（0%,3%,6%,9%,12%）are set to analyze the engine performance when the intake port is injected with hydrous ethanol with different water blending ratios,so as to seek a better water blending ratio.The operating points are set as follows:the throttle opening is fixed at 12%and the speed is 1200 r/min,1500 r/min and 1800 r/min respectively;the speed is fixed at 1500r/min,and the throttle opening is 10%,12%and 14%respectively.The performance of the engine with different water blending ratio of hydrous ethanol injected into the intake port is analyzed at different speed and load.The experimental conclusions are as follows:1)In the scope of the study,the combustion performance of hydrous ethanol engine is decreased due to water addition.The ignition delay and rapid combustion period lengthen with the increase of water blending ratio.Increasing the water blending ratio will cause the indicated mean effective pressure（IMEP）to decrease.The emissions of carbon monoxide（CO）will first decrease and then increase with the increase of water blending ratio,and the lowest is at 9%water blending ratio.The emissions of nitrogen oxide（NO_x）will decrease with the increase of water blending ratio.Hydrocarbon（HC）emissions will continue to increase.2)With the increase of speed,the ignition delay and rapid combustion period are prolonged,the engine torque decreases,and the temperature and pressure in the cylinder decrease.NO_x and HC emissions decreased,while CO emissions increased.Increasing the speed can enhance the air flow in the cylinder,which can improve the combustion of the mixture in the cylinder.3)With the increase of throttle opening,the ignition delay and rapid combustion period are shortened,the peak pressure and peak temperature in the cylinder are increased,the heat release rate curve is more concentrated and the crank angle occupied by the combustion process is shortened.CO and HC emissions are reduced,NO_x emissions are increased.Increasing the load can improve the thermal atmosphere in the cylinder,so the negative impact of increasing the water blending ratio is reduced.When the water blending ratio increases to 9%,the emission performance is the best and the combustion performance does not deteriorate too much.When the water content increases to 12%,the combustion and emission performance decrease significantly.（2）Base on the above tests,in order to explore the effect of hydrogen blending on the combustion and emission characteristics of hydrous ethanol,the second part of the test is carried out.The engine speed is set at 1500 r/min and the throttle opening is set at 10%.Based on the 9%water blending ratio,five hydrogen mixing ratios（0%,5%,10%,15%,20%）,five excess air ratios（λ）（1,1.1,1.2,1.3,1.4）are set to explore the effect of hydrogen blending ratio on the combustion and emission characteristics of hydrous ethanol SI engine.On the basis of the above work,twoλ（1,1.3）and five direct injection times（75°,90°,105°,120°,135°CA BTDC）are set to explore the effects of different direct injection timing on the combustion and emission characteristics of the engine.The experimental conclusions are as follows:1)The ignition delay and the rapid combustion period shorten with the increase of hydrogen blending ratio,which significantly improves the combustion performance and the stability of the engine operation.After hydrogen addition,the degree of constant volume combustion increases,which greatly increases the maximum cylinder temperature,maximum cylinder pressure and IMEP.The NO_x emissions increases,and the CO and HC emissions decrease with the increase of hydrogen blending ratio.2)With the increase ofλ,the ignition delay and rapid combustion period are prolonged,the peak cylinder pressure,temperature and IMEP decrease,the coefficient of variation of IMEP(COV_IMEP)increases.Under lean-burn conditions,the combustion effect is improved more obviously by adding hydrogen.In terms of emissions,the NO_x and CO emissions decrease.But the HC emissions decrease first and then increase.（3）When λ=1,the direct injection time is 105°CA BTDC,which is the best direct injection time,and the combustion and HC emissions reach the best;Whenλ=1.3,delaying the direct injection time can reduce the duration of combustion heat release,but it will lead to excessive HC emissions.It is more appropriate to choose 75°CA BTDC as the direct injection time.Based on the analysis of combustion and emission,hydrogen direct injection in the cylinder can improve the combustion performance of hydrous ethanol SI engine and achieve stable combustion of hydrous ethanol under theoretical air-fuel ratio and lean-burn conditions.When the water content is 9%,it is more suitable for the proportion of hydrogen direct injection in the cylinder to be 15%.