| As the crisis in energy grows and climate pollution mounts up， energyconservation and emission reductions are the two theme for internal combustionengine development. Due to the low fuel consumption and the low emission thetechnology of Lean burn becomes the major development direction. Because the AFRdeviates from the equivalence ratio, the efficiency of the TWC decreases, so that theNOx exceeds the Regulations limit and the researchers propose the LNT.Based on the experiment of decreasing the efficiency and the emission, focus thepresent work on the numerical simulation of indicated efficiency and the NOxemission.With the model of the engine are several factors researched: the adiabaticexponent, compression und expansion work, heat transfer and combustion efficiency.The result shows: In the low AFR region adiabatic exponent decreases with theincreasing of AFR and the combustion efficiency is the dominated factor; With theincreasing of AFR the influence of compression and expansion work is weakened. Inthe middle and high AFR region the adiabatic exponent and the heat transfer are themajor factors of increasing the indicated efficiency, which decreases in the high AFRregion due to the decreased combustion efficiency. When the AFR is higher, is thetrend of knocking higher in the condition of the same power output.In the foregoing experiment are the3schemes tested: TWC+LNT, LNT+TWCand LNT. Under the three schemes shows TWC+LNT the best effect. So is a model ofthe aftertreatment system builded, in order to analyze the influence of the forwardcoupling TWC on the LNT. The result shows that: The TWC promotes the NOxdesorption process in the LNT, at the beginning of rich phase TWC retards the NOxdesorption, but accelerates it from the aspect of the whole rich phase. At the samelean/rich time rate, TWC promotes the NOx reduction of LNT with longer absolutetime, therefore mitigate the influence of adsorption sites invalidation, which reversesin shorter absolute time. |
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