| The development of the automobile industry has been greatly affected by the more and more severe problems of energy source lacking and environment pollution. To develop the new and advanced gasoline engine products with high power, energy saving and ultra-low emissions has become the crucial task of nowadays internal combustion engine researchers. Because lean burn technology has great potential to reduce emissions and improve fuel economy, it has become one of the most important developing trends of automotive gasoline engine. The rich oxygen exhaust gas caused by lean burn makes the reduction of NOX emissions by the current three way catalytic converter to be impossible, and the special lean-NOX catalytic converter is still in its infant stage. Therefore, a newly-developed exhaust gas recirculation (EGR) system on automotive gasoline engine was developed in this thesis. It made recirculating exhaust gas moderate stratification with fresh mixture gas in the combustion chamber. It is unnecessary to change any structure of the engine, the total cost only slightly increases. When the EGR system, the swirl variable device, the electronic controlled port fuel injection system and the three way catalytic converter (TWC) are combined and adopted on a Xiali 2000 8A type 4-cylinder 16-valve automotive gasoline engine, an effective NOX purifying system was constituted. A series of performance and emission experiments has been done. The experimental results are shown as follows. The experiment of the air motion's impact on lean burn gasoline engine performance and emissions showed that compared with using tumble singly, moderate inclined swirl ratio can reduce NOX emission and HC emission and improve fuel economy more. NOX emission decreased 40.3%, fuel consumption decreased 7.23%. but inclined swirl has little effect on CO emission, especially in lean burn condition, the effect is very small. The experiment of the EGR's influence on lean burn gasoline engine performance and emissions showed that using moderate EGR ratio, NOX emission can be effectively reduced without suffering much fuel economy and power output and HC emission of the engine. With the increasing of EGR ratio, NOX emission decreased more than 90%, at the same time, HC emission and fuel consumption increased, but EGR has little impact on CO emission. Compared with using EGR and tumble technology singly, when EGR and inclined swirl are combined to work, NOX emission can be reduced more, the fuel economycan be improved some. So, to combine EGR with inclined swirl technology on lean burn gasoline engine is imperative. The experiment of TWC's converting efficiency to lean burn gasoline engine emissions showed that only in stoichmetric air fuel ratio, can the converting efficiency of NOX, HC, CO simultaneously reach their optimum value. When air fuel ratio is less than 14.7, the converting efficiency of HC emission and CO emission is very low. and when air fuel ratio is more than 14.7, the converting efficiency of NOX emission is rather low. Therefore, in the lean burn gasoline engine, if the NOX emission is asked to be reduced to very low value or even zero, it is necessary to develop advanced and favorable lean-NOX catalytic converter as soon as possible, besides optimizing engine structure, adopting swirl system and EGR system and so on. Now, EGR technology or even swirl and EGR combination technology can be said to be a very simple and quite effective NOX emission purifying technology, and the combination technology which combining swirl and EGR with three way catalytic converter can be used to efficiently purify NOX, HC, CO emissions simultaneously. The further analysis showed that EGR and tumble or inclined swirl are combined to work, the emissions of engine reached the EUâ…¡standard. When EGR and the three way catalytic converter are combined to work, the emissions of engine reached not only the EUâ…¡ standard, but also quite closing to the EUâ…¢ standard in some conditions.
|
PDF Full Text Request