Study On Lean Mixture Combustion And NO_x Emissions Reduction In A Four-Valves Gasoline Engine

Reduction of the fuel consumption, the carbon dioxide emission and the exhaust gas emissions is one of the major challenges that engineers and scientists in the automotive industry are currently facing. Lean burn concepts such as the homogenous A/F mixture gasoline lean burn engine or the direct injected gasoline engine may point the way of future automobile developments. A new point of view that the mixture preparation processes can been controlled by controlling fuel injection in multi-port fuel injection engine, in contrast to the traditionally point of view that the mixture formation is only controlled by induction flow. The technology of twice electronic fuel injection in premixed lean burn gasoline engine can realize the new controlling fuel injection concept. Through adjusting the controlling fuel injection--regulations of the two injection timings and proportions, an adequate air and fuel charge stratification was produced-we call it quasi-homogenous mixture and the lean burn was successfully realized in a product 4-valve S.I. engine whose structures aren't changed at all. Investigations show that twice electronic fuel injection can make the lean limit(A/F) increase by 1.5-2 units; the fuel consumption and exhaust emissions are improved remarkably, in partial load, compared with the product 4-valve S.I. engine , the fuel consumption decreases by about 19.1%. On the other hand, the fuel consumption of quasi-homogenous mixture lean combustion decreases by about 6.5% compared with homogenous lean mixture combustion.Three-ways catalyst (TWC)+ optimizing AFR technology is used to remove NOx emissions in oxygen containing exhaust gas. Lean-burn engine is operated at air-fuel(A/F) ratios of 21:1 and above, in addition, ignition is delayed, as a result of these technique, the NOx emissions are very low. Then TWC reduces NOx at a certain extent and almost all HC and CO. On the other hand, a new catalyst for selective reduction of NOx is also investigated in this thesis. Zeolites are in-situ synthesized on the surface of honeycomb-shaped cordierite under hydrothermal conditions. Investigations on a lean burn engine show that NOx can be removed by using HC and CO in the exhaust gas as reducing agents. When the catalyst is used , the rate of NOx conversion can reach a maximum of 74.4% at 400℃. Investigations also show that the catalyst shows good heat resistance in the presence of water and demonstrates high capability for mitigating SOx poisoning. In the end, a novel way controlling combustion is employed in a 1.342L S.I.engine, in which lean-burn, fast burn (tumble) and delay ignition make the engine provide much cleaner exhaust gas than that of a conventional premixed S.I. engine. Moreover, the de-NOx catalyst is mounted on the exhaust pipe. All these methods make it possible for emissions of lean-burn engines to completely meet the strict NOx regulations such as Euro Ⅱ, even Euro Ⅲ, at the same time, the fuel consumption decreases by 14.8%.