Research On Process Of Mixture Formation And Combustion For Engine With Hydrogen/Gasoline Combined Injection

The performance of the traditional gasoline engine can be improved by adding hydrogen by using its excellent physical and chemical characteristics.The hydrogen requirement is small by adding it into the gasoline engine and there is no need to provide relevant infrastructure on a large scale and change the engine largely.Hydrogen direct injection in cylinder,one of hydrogen adding methods,can make the process of hydrogen injection more precise and flexible and avoid reducing the charging efficiency and the power compared with hydrogen port injection.Meanwhile,hydrogen direct injection can avoid the backfire and preignition probably caused by hydrogen port injection.So it's a reasonable and efficient way to inject hydrogen in cylinder.Supported by the National Natural Science Foundation of China,this thesis aims to build a hydrogen/gasoline fuel combined injection mode by hydrogen direct injection on spark ignition engines in order to form lean combustion mode with partial hydrogen enrichment,whose effect on combustion and emissions can be studied afterwards.An experiment platform was established with engine including hydrogen direct injection and gasoline port injection.The external Exhaust Gas Recirculation?EGR?system was modified.And the engine measurement and control system was developed based on dSPACE rapid prototyping system,adjusting parameters including hydrogen injection strategy,fuel ratio,ignition timing,EGR rate and other parameters on line is realized..The mixture distribution pattern with partial hydrogen enrichment around spark plug was formed caused by hydrogen injection strategy and flow in the cylinder.The effects of different mixture distribution patterns on combustion with and without EGR were explored.The main research and conclusions are as follows:1.The simulation model of the combustion chamber was built.The effects of hydrogen direct injection on mixture distribution in cylinder were studied.The low ignition energy and fast flame propagation speed of hydrogen contributes to the stable ignition and concentrated combustion in traditional gasoline engines.The combination of flow field and hydrogen injection strategy can form ideal mixture stratification state with hydrogen partial enrichment around the spark plug.It's easiest to form stratified mixture contributing to combustion under 1200r/min by using hydrogen injection strategy and higher speed needs larger hydrogen injection pressure.2.The effects of hydrogen injection pressure and timing,ignition timing on the combustion of stratified mixture were studied.The effects of hydrogen injection pressure on combustion are larger than that of injection timing and the influence of hydrogen injection strategy becomes less with increasing speed.Ideal mixture distribution can greatly improve the combustion.The power and emissions can be improved obviously depending on reasonable hydrogen injection strategy under the same fuel ratios and heat input per cycle.3.The performance of the combustion and emission in the engine with combined injection were studied.The results show that adding a little hydrogen can improving the combustion greatly,reducing cyclical variation and the duration of flame development and rapid combustion,making the heat release more focused.And the oxidation of unburned HC and CO is accelerated.But the power of the engine increases modestly with increasing hydrogen ratio.The NO_x emissions always increase with the increase of hydrogen ratio.4.The stratified mixture with hydrogen partial enrichment caused by hydrogen direct injection,leads to stable ignition and then ignite the lean mixture in the cylinder,which can improve the lean burn stability and greatly expand the lean burn limit.The lean burn can be realized by increasing the throttle opening when using hydrogen/gasoline combined injection,reducing the throttle loss and increasing the thermal efficiency.Adding a little hydrogen can increase the lean burn limit of the gasoline and keep the combustion stable.A higher hydrogen ratio can make the lean burn limit to 2.65 excess air factor.Otherwise,the temperature under lean burn decreases,reducing the formation of the NO_x.5.The effects of hydrogen ratio,EGR ratio and other parameters on combustion and emissions were studied.The NO_x emissions are reduced while the power can be increased for the combined effects of hydrogen direct injection,lean burn and EGR.The effects of hydrogen ratio are larger than hydrogen injection strategy with EGR.Hydrogen direct injection improves the power and thermal efficiency and also increases the NO_x emissions largely.EGR can reduce the throttle loss and NO_x emissions while affecting the combustion stability.So the cooperative control of the hydrogen direct injection and EGR under lean burn can increase the power while reducing the NO_x greatly.