二/四冲程可变柴油机燃烧室热负荷的改善

doi:10.13229/j.cnki.jdxbgxb20200857

摘要/Abstract

摘要：

采用计算流体动力学（CFD）方法对一台二/四冲程可变柴油机在二冲程工作模式下活塞烧蚀的现象进行了研究，分析发现气流运动导致混合气在活塞碗沿处发生燃烧，从而产生了局部高温和局部过高热负荷。设计了两种燃烧室结构形式，通过调整油-气-室的配合以改善燃烧状况，研究发现，增大燃烧室碗口直径可以减少向活塞碗沿上方扩散的混合气，增大混合气在燃烧室内部的扩散空间，从而避免了在活塞碗沿处产生过高热负荷；增大燃烧室凹坑直径则有助于在凹坑内产生涡流，促进混合气的形成，缩短燃烧持续期。模拟计算结果显示，相比于原机，在2800 r/min@46 kW工况下两种优化设计的燃烧室在活塞碗沿上的热负荷得到明显改善，功率分别提高了4.11%和1.96%。加工设计一方案并在相同工况下进行对比试验，结果表明，相对于原机，优化设计后的柴油机油耗降低了6.93%，排气温度降低了21.1 K，活塞表面状态良好，无烧蚀发生。

关键词: 动力机械工程, 二/四冲程可变柴油机, 热负荷, 燃烧室设计

Abstract:

The in-cylinder combustion process of a two/four-stroke switchable diesel engine at high load conditions under two-stroke working mode was analyzed based on the three-dimensional CFD simulation. It was found that the movement of airflow causes the mixture to burn at the edge of the piston bowl， resulting in local high temperature and local excessive thermal load. Two optimized designs of combustion chambers were obtained to adjust the match of oil and gas with chamber to improve combustion. It was found that increasing the diameter of combustion chamber expands the diffusion space of the mixture and reduces the mixture diffused above the piston bowl edge， which can avoid excessive thermal load at the piston bowl edge. Increasing the diameter of the piston pit helps produce the vortex in the pit to promote the mixture formation and shorten the combustion duration. The thermal loads of the piston bowl edge of these two designs are significantly improved， and the combustion durations of the chamber Ⅰ and chamber Ⅱ increase the power by 4.11% and 1.96% respectively. The comparison test of the original machine and chamber Ⅰ was carried out under the ablation condition of the original machine at 2800 r/min@46 kW. Compared with the original machine， the fuel consumption of the chamber Ⅰ is reduced by 6.93%， exhaust temperature is decreased by 21.1 K and the piston surface is smooth without any ablation.

Key words: power machinery and engineering, two/four-stroke switchable diesel engine, thermal load, combustion chamber design

中图分类号:

TK421.2

张岩,刘玮,张树勇,裴毅强,董蒙蒙,秦静. 二/四冲程可变柴油机燃烧室热负荷的改善[J]. 吉林大学学报(工学版), 2022, 52(3): 504-514.

Yan ZHANG,Wei LIU,Shu-yong ZHANG,Yi-qiang PEI,Meng-meng DONG,Jing QIN. Optimization on thermal load of combustion chamber on two/four⁃stroke switchable diesel engine[J]. Journal of Jilin University(Engineering and Technology Edition), 2022, 52(3): 504-514.

图/表 24

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参数	数值	参数	数值
缸径/mm	110	排气门定时/°CA	102/230
冲程/mm	110	喷油时刻/°CA	347
压缩比	13.3	喷油量/mg	83.3
进气门定时/°CA	135/270

参数	原机	设计一	设计二
燃烧室口径D_k/mm	72.0	76.8	81.2
燃烧室深度H/mm	14.3	13.3	12.5
凹坑直径d/mm	8.9	20.0	14.9
燃烧室宽度D_l/mm	75.0	77.2	83.0

参数	原机	设计一	设计二
单循环放热/J	3750.45	3683.35	3638.98
平均有效压力/MPa	1.45	1.51	1.48
燃烧持续期/°CA	51.40	44.70	46.80
有效功率/kW	48.47	50.47	49.43
燃烧室传热/J	203.94	171.18	182.24

参数	原机	设计一
燃油消耗量/（kg·h^-1）	14.04	13.13
进气温度/K	322.40	323.80
进气压力/kPa	273.00	278.10
进气流量/（kg·h^-1）	415.00	396.80
排气温度/K	688.50	667.40