Experiment Of Reducing NOx Emission In Quasi-Homogenous Lean Burn S.I Engine By NOx Adsorber Catalysts

The lean burn technology was been paid widely attention, because of its great potentialto improve fuel consumption and exhaust emission. However, how to reduce NOx emission inlean burn condition has become a key problem which determines that whether the lean burntechnology can be applied in practice in internal combustion engine or not. Based on theformer works of our research group, the variable induction and twice injection [PatentNo.98107693.9] technologies have been used on Toyota 8A 16 valves EFI lean burn S.Iengine, and realized quasi-homogeneous lean burn combustion below air fuel ratio 24. Basedon the achievement of quasi-homogeneous lean burn combustion in S.I. engine, authordesigned a new lean burn catalyst system, which combines the traditional three-way catalyst(TWC) with adsorber reduction catalyst. And with this system, NOx emission has beenresearched in lean burn condition. The test results show that the technological program thatadsorber reduction catalyst was placed behind TWC could reduce NOx of lean burn enginegreatly. In order to stabilize the lean burn engine the torque output, an electronic control systemof lean burn engine was been developed by author. When the A/F of the lean burn enginechanges from the state of lean burn (A/F=21) to the state of less oxygen (A/F≤14.7), thesystem adjust throttle and ignition time automatically so as to obtain constant torque output.The constant torque output control technology when A/F is changed abruptly has beenrealized. After analyzing chemical reactions in lean and rich burn process in adsorber reductioncatalyst, the equations of a dynamic transport-reaction model, orthogonal collocation andtime-scale reduction were applied in this paper. The model of calculating the storage abilityand NOx emission of lean burn adsorber reduction catalyst was provided. The calculatedresults show that the model calculating and test results have better consistence, and the modelcan be used into controlling strategy of the lean burn adsorber reduction catalyst in the leanburn gasoline engine reality. The lean burn adsorber reduction catalyst is a high efficiency method of reducing NOxemission of lean burn engine, and the biggest NOx emission conversion rate reaches 97.3% inthe experiment condition, which is much more than SCR (Selective-Catalyst-Reduction) andEGR (Exhaust-Gas-Recirculation), and the deteriorated fuel consumption was less than 3%.Using this system, the lean burn engine exhaust emissions can reach ultra-lower emissionstandard (EU Ⅱ standard, but quite closing to the EU Ⅲ standard in someconditions).Effects of the speed and load of lean burn engine on exhaust emission and fuelconsumption relate to the lean burn and reduction time ratio and the absolute continuancetime.Air fuel ratio (A/F) has an important effect on NOx conversion rate of lean burn adsorberreduction catalyst. The less A/F is, the higher NOx conversion is. NOx emission islowered ,but the engine fuel consumption is deteriorated .when the A/F is become small, TheCO,HC exhaust emission increased, but still kept at lower emission level. The lean burn adsorber reduction catalyst is sensitive to the sulfur in the fuel. Reducingthe sulfur in the fuel is the essential measure to increasing NOx conversion rate in thecatalyst.