Study On Lean Combustion Of 465 Gasoline Engine And Its NOx Emission Catalytic Control

Saving energy resource and protecting environment are two critical issues to realize consecutive development of human society. Development of IC engines has to meet the demands of low fuel consumption and low emissions. Lean combustion techniques in gasoline engines can both reduce fuel consumption effectively so as to reduce the emission of greenhouse gas-CO2 and lower the emissions of HC and CO significantly. However, the problem of controlling NOx emissions at lean conditions is limiting the development of the lean combustion gasoline engines. Therefore, the further studies on lean combustion and NOx emission control technologies are very important.Experiments were conducted on a 465 gasoline engine. The flow characteristics of the inlet port in the cylinder head were tested on a steady flow test rig. Ricardo method is used to assess the air motion in cylinder. The experimental results show that a rather strong tumble motion exists in the 465 gasoline engine. Tumble motion, combining fuel injection strategy, can achieve lean combustion and extend lean combustion limit to 21-22, which is helpful to reduce NOx emissions. It can save fuel for 12 percent. In this paper the characteristics and formation mechanisms of the NOx emissions at lean conditions were analyzed. The methods to reduce the NOx emissions in the cylinder were examined, including increasing air-fuel ratio, retarding spark timing, and using exhaust gas recirculation (EGR) and so on.In this paper the mechanism storing oxygen in three-way catalyst was analyzed. Based on the characteristics of emissions in gasoline engines at lean conditions, combining leaner combustion and a three-way catalyst, a better control method was provided, which makes air-fuel ratio change periodically from rich to lean and simultaneously uses a three way catalyst. It can reduce the O2 concentration in the exhaust effectively and use the reductive gas such as carbon oxide in the rich period. So the NOx conversion efficiency is increased to 45% at higher air-fuel ratios. The NOx emissions are lower than the equivalent level of Europe â…¡ emission standard.In this paper zeolite selective reduction catalysts to control emissions in lean combustion gasoline engines were studied. The ion-exchanged zeolite cordierite monolith catalysts are made using in-situ synthesized. The conversion mechanism and characteristics were investigated at real exhaust conditions of the lean combustion gasoline engine. Breaking through the traditional limits of HC-SCR mechanism, it is based on the CO-SCR conversion mechanism that some zeolite selective catalysts such as Ir-ZSM5 and Cu-Pd-ZSM5 can use CO in lean exhaust to reduce NOx. As a result, the NOx conversion efficiency is improved significantly and can even reach over 80% at lean combustion conditions. The bimetal zeolite catalysts were also investigated. They can also improve conversion efficiency and extend the temperature window, etc. Experimental results further show that for some catalysts, HC can change into CO during the HC-SCR reaction.Based on the above study results, three combined control methods were provided. (1) Combustion modification in engine with lean combustion with high air-fuel ratio and retarded spark time, combined with the zeolite catalysts having a high NOx conversion efficiency, (2) Combination of the control methods using the zeolite catalysts with different catalyst mechanism (HC-SCR that can form CO and CO-SCR), and (3) Variation of air-fuel ratio from rich to lean with the zeolite catalyst control methods. Each of three control methods can achieve the level of emissions in lean combustion gasoline engines equivalent to Europe â…¢ standard and it can save fuel for 8 to 10 percent.