Simulation Of Lean-burn CNG Engine Working Process For Meeting China Stage V Emission Regulations

As a kind of clean and alternative fuel, natural gas is widely concerned by many morepeople. And natural gas engines have been implied on transport vehicles for good fueleconomy performance and low emission characteristic, however, it requires to optimizevarious operation parameters of CNG engine to meet china stage V emission regulations. Inthis paper, a diesel engine has been modified into natural gas engine, and its dynamic,economic and emission performance are calculated by means of simulation, finally, theemission performance meet china stage V emission regulations.The main work as follow:(1) The working process model of diesel engine is built, after confirming the modelreliability, CNG engine model which modified by the diesel engine is built and it’scompression ratio, air fuel ratio and ignition advance angle are optimized, at last, get themost suitable compression ratio, air fuel ratio and ignition timing map.(2) Different valve overlaps are calculated, the results show that the NOx and HCemission can be reduced by using smaller valve overlap. And then the valve timing isoptimized by means of orthogonal test, through compromising the dynamic, economic andemission performance, the most suitable set of valve timing is selected.(3) Turbocharger match simulate on the CNG engine is carried out. The results showthat the compressor mass flow of primary turbocharger is larger to the CNG engine andmost operation points in external characteristics curve of the engine locate at low efficiencyarea. A new turbo charger is calculated, which make the highest power of CNG enginematch with the new turbocharger to increase of3.9%compared with primary turbocharger.Moreover, the dynamic performance of CNG engine nearly achieve at the level of originaldiesel engine.(4) The NOx, HC and CO emissions at different load which effected by EGR ratio areanalyzed. The ESC of CNG engine without EGR and with EGR has been ca lculated,comparing the two kinds of emission result, it shows that the emission of CNG engine withEGR can meet china stage V emission regulations，except for CH4emission. Using DOCafter treatment CH4emission can be reduced to meet with stage V regulation.(5) The three dimensional model of EGR system has been built and the transient condition is calculated, it shows that the EGR uniformity of intake manifold is27.4%,which is so poor for cylinder2have the lowest EGR ratio, and cylinder1follow it.For this reason, it proposes to shorten the plenum length and separate inlet of intakemanifold2and3,4and5. Make sure that all intake manifolds have the same inlet diameter.