Research On Fuel Injection Control Strategy Of TWC+NSR Coupling System Of Lean-Burn Gasoline Engine

With the increasingly strict emission regulations and fuel consumption regulations,the lean burn strategy has become a key research direction for vehicle companies.Lean-burn gasoline engines can greatly improve fuel conversion efficiency,thereby reducing fuel consumption.However,traditional TWC cannot effectively remove NO_X in exhaust gas under lean burn conditions,which has become a key factor restricting the development and application of lean burn gasoline engines.Therefore,the development of an efficient aftertreatment system suitable for lean-burn gasoline engines has become an urgent need of relevant manufacturers.The NSR catalyst can effectively remove the NO_X emitted by lean-burn gasoline engines,but it is necessary to control the gasoline engine to constantly switch between lean-burn and rich-burn.In addition,at high temperature and high space velocity,the NO_X removal efficiency of the NSR catalyst decreases significantly.However,if hydrocarbon fuel is injected at a certain frequency at the front end of the NSR catalyst,the reducing active intermediate species-CN and-NCO can be formed on the catalyst.During fuel injection,active species are continuously generated and consumed to reduce the NO_X adsorbed on the NSR catalyst,so that the NSR catalyst can be regenerated.Using this technology,the gasoline engine can always run in lean-burn conditions and avoid switching to rich-burn conditions.As a result,combining the characteristics of TWC and NSR,a technical route for aftertreatment suitable for lean-burn gasoline engines has been formulated.The lean-burn gasoline engine model was established by GT-POWER software to obtain simulated original row data.Then compared the simulated original row data with the experimental data in the literature.The error was within 10%,which was acceptable.Therefore,the simulation of lean-burn gasoline engine emissions can provide data support for the simulated exhaust gas in subsequent sample tests.A small sample test system was built to explore the performance of TWC catalyst and NSR catalyst at lean burn.The test results showed that under lean burn conditions,the TWC catalyst can efficiently remove HC_Sand CO,but cannot effectively remove NO_X,while the NSR catalyst had very low NO_X conversion efficiency when the exhaust gas temperature was greater than 350℃.When C₃H₆ was injected at the front end of the NSR catalyst at a low frequency,the NO_X removal efficiency was above 90%in the range of 350℃to 550℃,which greatly widened the temperature window of the NSR catalyst.In addition,it was determined that the best injection frequency of C₃H₆ at different temperatures was 0.25 Hz,and the amount of C₃H₆ required to be injected was the least at this frequency.A lean-burn gasoline engine aftertreatment system was built.The self-developed gasoline injection control system and Horiba gas analyzer were used to verify the feasibility of the post-processing technology,which was coupled with the TWC catalyst and the NSR catalyst,and injected gasoline at the front end of the NSR catalyst at low-frequency.Through the lean-burn gasoline engine aftertreatment system,the influence of gasoline injection frequency on NO_X removal efficiency was first explored,and the best gasoline injection frequency was determined to be 0.25 Hz.Next,the influence of air-fuel ratio,speed and load on NO_X removal efficiency were explored,and it was determined that the NO_X removal efficiency was more than 85%when the air-fuel ratio was 1.2～1.6,the speed was 1500～2500rpm,and the load was 16～64 bar.In addition,the optimal gasoline injection quantity required for each operating point in the steady state was determined,and the fuel loss was within 1%.Finally,the influence of gasoline injection pressure on NO_X removal efficiency was explored,and it was determined that the NO_X conversion rate can reach more than 90%when the pressure was 4 bar and 6 bar.However,when the pressure was 4 bar,the NO_X removal efficiency was more stable.