Three Dimensional Simulation Study On Performance Improvement Of Combustion System Of A China Ⅳ Diesel Engine

The China IV emission standards will be fully implemented in January 1, 2015, the China V emission standards are also expected to be implemented overall in 2018. So the technology research about the China V engine is imminent. In this paper, the combustion system of a commercial heavy-duty diesel is optimized to provide theoretical guidance for the upgrade to the China V diesel, and this diesel engine has met the China IV emission standards without the after-treatment.In this paper, the three-dimensional calculations, emissions CFD software AVL-FIRE is used for simulation research. On the baseline combustion chamber, the microscopic field about the gas flow, air-fuel mixing distribution and so on is analyzed. Results showed that NOx is mainly originated from squish region, soot comes from the piston bowl, and their generation are influenced by the fuel distribution in the squish area and piston bowl. To this, three kinds of combustion chamber structure optimization scheme is designed, expect the new combustion chamber can improve economy and emission. The re-entrant position of the new combustion chamber SF4 down lmm based on the original combustion chamber SF1, and the combustion chamber diameter and re-entrant diameter of SF5 and SF6 are widened by 2.5mm respectively based on SF1 and SF4. The comparative study shows that, The re-entrant position down will affect a larger extent in the distribution of fuel in the squish area and the piston bowl, thereby affecting the economy and emissions. The new combustion chamber SF4 re-entrant position down so that the fuel distribution is more appropriate, and maintain good vortex. Therefore it achieve the expected objectives of the combustion chamber design optimization, to improve the trade-off relationship between NOx and soot, and fuel consumption also improve 1-6g/kW-h than the original chamber SF1.A study is carried out to match the new combustion chamber and post injection strategy. Simulated by high-pressure injection and post injection strategy in 1660r/min,50% load conditions, the injection pressure up to 1600bar and 1800bar. And in 1990r/min,100% load conditions, the ultra high injection pressure and post injection strategy are studied, he injection pressure up to 2000bar and 2400bar. Research shows that, the post injection strategy is an effective strategy to reduce soot emissions leaving little change in NOx emissions and without sacrificing too much fuel consumption. The post injection strategy can effectively reduced soot emissions mainly benefit from the two times fuel injection, and the main fuel injection mass is reduced, leading to the main-flame soot is reduced nonlinear. And the post injection fuel combustion is unaffected by the the main-flame, does not generate or generate very little the post-flame soot. Increase injection pressure, the dwell between the main and post injection influence the law of soot emissions unchanged, which increases the dwell, the emission of soot is first decreased and then showed a rising trend, and the best dwell corresponding to the lowest soot emissions is 4°CA. The post fuel injection mass influence the law of soot emissions also unchanged, which increases the post fuel injection mass, the emission of soot is also first decreased and then showed a rising trend, but best post fuel injection mass is influenced by the engine operating conditions and injection pressure.After optimized combustion system, for 1660r/min,50% load, when injecton pressure is 1800bar, the dwell is 4° CA, and the post fuel injection mass is 20% of the total fuel mass, obtain the best emission under this condition. Which the soot emissions is approximately 0.0145 g/kW-h, NOx emissions is approximately 1.48 g/kW·h. For 1990r/min,100% load, when injecton pressure is 2400bar, the dwell is 4° CA, and the post fuel injection mass is 8% of the total fuel mass, obtain the best emission. Which the soot emissions is approximately 0.0188 g/kW·h, NOx emissions is approximately 2.6g/kW-h. Therefore, this diesel engine has the potential to meet the China V emissions.