船用柴油机多孔喷嘴的喷雾不一致性及其对发动机性能影响的分析

Analysis on Spray Plume Inconsistency for a Multi-Holes Nozzle and Its Influence on Performance of a Marine Diesel Engine

关键词:  船用柴油机  多孔喷嘴  喷雾  发动机性能  燃烧热负荷

Key words:  Marine diesel engine  Multi-holes nozzle  Spray  Engine performance  Combustion thermal performance

摘要:

由于柴油机多孔喷嘴加工偏差、针阀抬起过程产生的抖动以及喷嘴内部的空穴现象等原因，各孔燃油喷射存在不一致的情况。为了探究多孔喷嘴各孔燃油喷射差异对大缸径船用柴油机喷雾、燃烧及缸内热负荷的影响，以高压共轨船用柴油机为研究对象，通过定容弹喷雾试验研究了高压共轨喷油器多孔喷嘴各孔喷雾发展的不一致性，并基于喷雾试验结果，通过CFD仿真研究了各孔喷雾不一致性对柴油机燃烧、性能及缸内热状态的影响。结果表明，在针阀抬起过程中，各孔喷雾贯穿距存在明显差异，各孔喷雾贯穿距离散系数为3%~40%，且随着针阀抬起离散系数逐渐减小，在针阀完全抬起后，各孔喷雾贯穿距基本一致，各孔喷雾贯穿距离散系数在5%以下；各孔喷雾不一致会导致各雾束的早期燃烧存在明显差异，对缸压、油耗、放热率、缸内平均温度、NO_x和Soot排放影响很小；各孔喷雾不一致会加剧活塞、缸盖、缸套的局部热负荷，同时会导致高温燃气向缸套的总体散热量增加9.1%，而活塞、缸盖总散热量不变。

Abstract:

There usually exists inconsistency in the fuel injection among holes of a multi-hole diesel nozzle， which may be caused by mechanical machining deviations， jitters due to the lifting of the needle valve， and/or cavitation inside the nozzle holes. In order to examine the effects of the fuel injection variation among nozzle holes on the spray， combustion and thermal load of a large-bore marine diesel engine， experimental measurements on spray characteristics of a high-pressure common rail injector was carried out through a high-pressure and high-temperature constant volume bomb， and a numerical model for the diesel engine simulation was built by use of the measurement results. Then， the effect of the spray inconsistency on the combustion， performances and thermal state of the cylinder in the diesel engine was studied by the CFD simulation. The results of the spray measurements show that during the lifting of the needle valve， there is a significant difference in the spray penetration distance of each hole. The coefficient of variation （COV） in spray penetration distance of each hole is from 3% to 40%， and the COV gradually decreases to a stable value as the needle valve lifts to a certain degree. After the valve is fully raised， the spray penetration distance of each hole becomes basically the same， and the COV of the spray penetration distance among nozzle holes is less than 5%. It has been proved by the simulation results that the inconsistency in spray penetration distance among nozzle holes cause a significant difference in the early combustion of each spray plume， while has little effect on the cylinder pressure， the fuel consumption， the heat release rate， the average temperature in the cylinder， and the NO_x and soot emissions. The inconsistency in spray plumes raise the local heat load of the piston， cylinder head and cylinder liner， and cause increase of 9.1% in overall heat transfer of high-temperature gas to the cylinder liner， while the total heat transfer to the piston and the cylinder head is almost unchanged.