基于热机耦合的某型柴油机活塞应力及疲劳分析

Stress and Fatigue Analysis of Diesel Engine Piston Based onThermal-mechanical Coupling

柴油机活塞热负荷主要来源于缸内高温燃气的传热,某型船用柴油机排气背压由原型机2.5 kPa升高到10 kPa后,其涡轮膨胀比降低,从而导致压气机空气流量下降,进而影响到缸内燃烧状况及燃气温度,本文主要研究柴油机背压提高后,活塞在热负荷和机械负荷作用下应力场和疲劳分布,首先以试验结果校正仿真模型,在此基础上计算排气背压提高后活塞温度分布并得出其在热机耦合下活塞应力,最后进行活塞疲劳寿命分析,其安全系数满足要求,提高背压后柴油机通过一千多小时安全运行,满足实际使用要求。

The thermal load of the diesel engine piston mainly comes from the heat transfer of the high-temperature gas in the cylinder.After the exhaust back pressure of a certain type of marine diesel engine is increased from the 2.5 kPa to 10 kPa,its turbo expansion ratio decreases,which causes the compressor air flow to drop,which affects to the combustion status and gas temperature in the cylinder.This article mainly focuses on the distribution of stress field and fatigue of the piston under thermal load and mechanical load when the back pressure of the diesel engine changes,the simulation results and experimental results of piston temperature under exhaust back pressure are compared,the results of which are consistent.On this basis,the temperature distribution of the piston under exhaust back pressure is calculated,the stress distribution of the piston under thermal load and mechanical load is obtained.Finally the fatigue life of piston is analyzed.After increasing the back pressure,the diesel engine runs safely after more than 1000 hours and the piston meets actual requirements.