| The lean burn gasoline technology can reduce the harmful emissions and improve fuel economy, which has been one of the trends for advanced internal combustion engine technology. However, under the lean burn condition, the conventional Three-way Catalyst's ability of reducing NOx emission was limited because of excess oxygen in the exhaust. Thus, to reduce the NOx emission became a challenging problem for lean burn engine.This paper retrofitted a conventional gasoline engine (CA3GA2) through adding variable intake system with Exhaust Gas Recirculation (EGR). By changing the throttle opening and fuel injection system, the retrofitted engine could operate with a limited air/fuel ration 22. Characteristic of Lean NOx Trap (LNT) technology was also investigated. After that, the NOx reduction efficiency was researched with coupled EGR and LNT.The experimental result showed that LNT could reduce NOx emission from lean burn gasoline engine effectively. Specifically, the NOx conversation efficiency of LNT could reach more than 85% under low and moderate load and the highest NOx conversation was as high as 94%. When the LNT operated at the desorption stage, the air/fuel mixture was rich and the fuel consumption was high. The load transition had an important effect on the adsorption ability of LNT. The NOx conversation dropped as the engine worked under high load condition. The duration ratio of rich-lean burn and the frequency of transition between rich-lean burn had a significant impact on NOx emission. When the ratio of lean and rich duration increased, the NOx conversation dropped. When the frequency of transition between rich and lean increased, the fuel economy was deteriorated and the NOx conversation efficiency increased.Coupled EGR and LNT could reduce NOx emission effectively. However, if EGR rate was too high, the NOx conversation of LNT decreased. Proper EGR rate and LNT could reduce the fuel consumption, but too high EGR rate will deteriorate fuel economy. |
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