| Lean burn is one of the effective measures to improve the fuel economy of gasoline engines.However,under the condition of homogeneous and lean mixture,the gasoline engine with traditional ignition system is faced with such problems as large cycle fluctuation during combustion process.For this reason,this paper proposes the use of high-energy ignition and multi-pulse non-equilibrium plasma ignition technology to improve the combustion stability of lean-burn gasoline engines through multiple ignition coupling methods,and uses numerical simulation methods to study the effect of high-energy ignition and multi-pulse non-equilibrium plasma ignition strategies on the ignition and combustion process of homogeneous lean gasoline mixture at 1000 and2000 r/min and different circulating oil rates.The results show that:when the excess air coefficient（λ）is 1.8,compared with single ignition,there is the coupling effect between two adjacent ignitions under multiple ignition strategies.Changing the discharge time interval between two adjacent ignitions can change the coupling mode of the energy injected between the two adjacent ignitions,and they have different effects on the oxidation process of the fuel.Under the two-ignition strategies with one discharge of 200 m J,with the advance of the second ignition time,the coupling region of the energy injected by the two adjacent ignitions increases,and the coupling promoting effect of the two ignitions on the initial combustion heat release increases,which leads to the shorten of the ignition delay period and combustion duration,and the increase of IMEP and indicative thermal efficiency.Under the condition of single ignition energy of 50 m J,the optimized four-ignition strategies can obtain higher IMEP and indicated thermal efficiency than that of the two-ignition strategies of single ignition energy of 200 m J.Plasma ignition increases the concentration of H,O,OH and HO2 active radicals in the cylinder before ignition,and improve the development speed of flame kernel.As the ignition frequency increases from 20 k Hz to 60 k Hz,the generation rate of hydrogen and oxygen atoms increases during plasma discharge,and the low temperature oxidation process before ignition becomes more intense when the cyclic ignition energy and ignition times remain unchanged.Under the condition of homogeneous and lean gasoline mixture with excess air coefficient of 1.8,and at 1000 r/min and the cycle mass of fuel is 9 mg and at 2000 r/min and the cycle mass of fuel is 18 mg,the ignition delay period of plasma at 60 k Hz is shortened by 15°and 12.2°CA,and the indicative thermal efficiency is increased by 2.8%and 4.9%,respectively,compared with that at 20 k Hz.When the plasma ignition frequency is 50 and 60 k Hz,the ignition process atλ=2.0can be carried out quickly.However,whenλincreases from 1.8 to 2.0,the mass fraction of O and H free radicals produced by plasma collision decomposition decreases gradually.Whenλis unchanged,with the increase of plasma pulse number,the ignition energy and mass of O and H atomic increases in the process of ignition,which promoted the ignition and combustion process of lean burn gasoline mixture. |
