| The process of optimization of the combustion system is discussed in this paper about the engine YC6L350-20.The engine was designed in FEV corporation in German. The engine is a heavy-duty diesel, whose parameters are as follows: 6 cylinders in line; 4 valves; diameter: 113mm; It can produce large power with small displacement and its peak power can amount to 350 horsepower. When it is equipped with the mechanical in-line fuel pump, the emission can reach EURO Ⅱ. Moreover ,it can reach EURO Ⅲwith the electronic single unit fuel pump. The results are the leaders in the domestic heavy-duty engines. The design and the development results have been realized in FEV. YC Company has been checking the development results since Sept.2003. The acceptance tests are mainly related to the structure, the performances and the emissions on five engines assembled in the output state. (The engine numbers are: L3000300027, L3000300028, L3000300029, L3000300030, L3000300031). The acceptance tests are made according to the test method of vehicle engine performances in GB/T18297-2001, the quality inspection test method of the vehicle engine in QC/T901-1998, the emission limits and test method in compressed ignition vehicle engine. The results indicate: (1) According to the gas passage data, the control of the gas passage retention should be improved further because of bad air intake swirl ratio and bad retention. (2) The performances of engine L3000300029 are low and not qualified for the demand of the design in many aspects. And there are also unsatisfying aspects in another 4 engines. (3) It is indicated that the fluctuation of the torque and the free acceleration smoke is large in between 900rpm and 1000rpm according to the experiment data of the pump retention and the common pump among different engines. The small torque at low speed may result in inability of start and acceleration and overload so that it must be improved further. (4) The emission level is high in the engines and 4 engines is unable to reach EURO Ⅱ. The combustion system should be redesigned so as to reach higher emission level. During the acceptance tests, there are a few deficiencies especially the small torque at low speed and low emission level. To improve the overall performances of the engine YC61113ZLQ, new design and new performance development are done in consideration of power performance, economic performance, reliability, emission, the entire vehicle performances tests, the optimization of the drive system. They include: the improvement of the cylinder head gas passage, the redesign of the gas passage parameters and the combustion structure, experiment data analysis, the redesign of the fuel supply system, the improvement of the intake and exhaust system, the matching of the engine and the entire vehicle. The engine full load performance is improved in the scope of low-medium speed based on the reaching EURO Ⅱ. It is also improved in reliability so as to improve the entire vehicle reliability dramatically and the process of the experiments is good for the understanding of the demand of the engine overall performances. This paper is mainly related the improvement of the diesel YC6113ZLQ based on the problems occurring in the acceptance tests. It can be included that: (1) Three measures are taken to improve the nose bridge zone of the intake valve: using copper barrel; using water passage; using stress slot. (2) In consideration of the performances at both hign and low speed, the cylinder head swirl ratio is reduced to 1.4±0.05 from 1.6±0.05. (3) The combustion chamber Ⅲis chosen. (4) After overall consideration of the performances, common plunge fuel pump is chosen. (5) According to the experiment data, the injector P7238 is better than P628 and it is important to enhance the injection pressure for optimization. (6) The turbocharger 597AG/H14YE2B is chosen.(7) The following measures are taken to improve the emission level: improving the places where the oil can enter into the fuel system; improving the piston rings; improving the valve stem and the oil seal. (8) After the adjustment, the performances are optimized and problems are solved occurring in the acceptance tests. (9) The main threat is from CA6DL, ISCe and ISLe. (10) After the analysis, it is showed that the intake and exhaust system is the most important to the overall vehicle utilization, fuel supply system is the second, and the cooling system is the third. (11) The parameters are quantitatively acquired through bench test. (12) The entire vehicle test and evaluation should be done to get the best power, economy, reliability, emission and durability. (13) The test data show that the common road conditions should be considered when the drive system matching is done. (14) This topic successfully finalizesthe design of YC6113ZLQ and is important to the market investment. The methods of optimization and the methods of analysis of the data are good for further design of the same series.
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