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雷基林,王东方,邓晰文,辛千凡,文均.稳定和过渡工况下柴油机活塞顶面瞬态热负荷变化规律[J].农业工程学报,2018,34(21):65-73.DOI:10.11975/j.issn.1002-6819.2018.21.008
稳定和过渡工况下柴油机活塞顶面瞬态热负荷变化规律
投稿时间:2018-06-07  修订日期:2018-09-23
中文关键词:  柴油机  活塞  温度  过渡工况  稳定工况  热应力  热应变
基金项目:国家自然科学基金(51366006和51665021)资助
作者单位
雷基林 1. 昆明理工大学云南省内燃机重点实验室昆明 650500 
王东方 1. 昆明理工大学云南省内燃机重点实验室昆明 650500 
邓晰文 1. 昆明理工大学云南省内燃机重点实验室昆明 650500 
辛千凡 1. 昆明理工大学云南省内燃机重点实验室昆明 650500 
文均 1. 昆明理工大学云南省内燃机重点实验室昆明 6505002. 成都银河动力有限公司成都 610505 
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中文摘要:发动机活塞热疲劳失效主要有稳定工况下周期性热冲击导致的高周疲劳失效和在冷启动、急加速、急减速等过渡工况下热冲击引起的低周疲劳失效两种形式。为探究柴油机活塞在不同工况下活塞的热负荷变化情况,该文以一款非道路用高压共轨柴油机为研究对象,基于活塞顶面瞬态温度试验测试结果,采用热-机解耦方法建立了稳定工况及冷启动、急加速和急减速等过渡工况下的活塞热负荷有限元仿真计算模型,分析了发动机在稳定工况、冷启动、急加速和急减速过程中活塞的热负荷变化规律。研究结果表明:稳定工况下活塞的热负荷波动现象仅出现在活塞顶面、火力岸和第一环槽位置,且热负荷波动幅值随着距离活塞表面深度的增加而逐渐减小,温度波动深度范围为3 mm;活塞周期性瞬态热应力波动主要发生在活塞顶面,其他区域波动较小,热应力波动深度范围为5 mm,最大热应力波动幅值出现在燃烧室喉口区域,达到32.3MPa。过渡工况下活塞的热负荷变化较大,其中:冷启动过程中活塞的热应力出现跳跃性急剧升高,随后又快速降低的现象,活塞热负荷的变化幅度较大,温度、热应力和热应变分别达到200 ℃、42 MPa和0.3 mm;急加速过程中活塞温度场、热应力和热变形都急剧升高,虽然活塞的温度和热应变的变化量相对较小,为140 ℃和0.12 mm,但活塞燃烧室喉口热应力变化幅值达到93 MPa,易造成活塞热疲劳失效,从而对活塞可靠性和耐久性产生较大影响;急减速过程出现活塞各测点先短暂升高、后缓慢小幅度降低、并在200 s后趋于稳定的现象,急减速过程中活塞的温度、热应力和热应变的变化幅度均较小,最大变化量分别在30 ℃、10 MPa和0.02 mm以内。研究结果可为高强化柴油机铝合金活塞设计提供参考。
Lei Jilin,Wang Dongfang,Deng Xiwen,Xin Qianfan,Wen Jun.Transient heat load variation of piston top surface under steady and transition conditions[J].Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE),2018,34(21):65-73.DOI:10.11975/j.issn.1002-6819.2018.21.008
Transient heat load variation of piston top surface under steady and transition conditions
Author NameAffiliation
Lei Jilin 1. Yunnan Province Key Laboratory of Internal Combustion engines, Kunming University of Science and Technology, Kunming, China 650500
 
Wang Dongfang 1. Yunnan Province Key Laboratory of Internal Combustion engines, Kunming University of Science and Technology, Kunming, China 650500
 
Deng Xiwen 1. Yunnan Province Key Laboratory of Internal Combustion engines, Kunming University of Science and Technology, Kunming, China 650500
 
Xin Qianfan 1. Yunnan Province Key Laboratory of Internal Combustion engines, Kunming University of Science and Technology, Kunming, China 650500
 
Wen Jun 1. Yunnan Province Key Laboratory of Internal Combustion engines, Kunming University of Science and Technology, Kunming, China 650500
2. Chengdu Galaxy Power Co., Ltd., Chengdu 610505, China 
Key words:diesel engine  piston  temperature  transient condition  steady condition  thermal stress  thermal strain
Abstract: There are 2 kinds of thermal fatigue failure modes of engine pistons. One is the high-cycle-fatigue failure mode caused by cyclic thermal shock loading in steady-state conditions. The other is the low-cycle-fatigue failure mode caused by thermal shock loading under transition conditions such as cold start, rapid acceleration, and fast deceleration. Although piston thermal loading has been widely studied by previous domestic and foreign researchers, the work focused on the thermal loading of steady-state conditions and overlooked the impact of the drastic variations of piston transient thermal loading on piston reliability and useful life, and the research result cannot reflect true realistic variations of piston thermal loading, and cannot accurately predict and evaluate the thermal fatigue life of the piston. In order to study the thermal loads of diesel engine pistons in different operating conditions, a non-road high-pressure-common-rail diesel engine was analyzed by using the method of thermal-mechanical decoupling. The finite-element simulation model of piston thermal loading under the steady-state condition of rate power and the above-mentioned transient condition was established. The simulation model was developed based on the experimental results of transient temperature measurements of the piston top. The model was successfully used to reveal the variation trends of the transient thermal loads of the pistons under these conditions. The analysis results showed that the time-dependent or crank-angle-dependent fluctuation of the piston thermal load under the steady-state condition of rated power was only limited to the piston top, the firing deck, and the first ring groove. As the fluctuation penetration distance measured from the piston top increased, the fluctuation amplitude decreased. The maximum fluctuation penetration distance of temperature was 3 mm, and the maximum fluctuation penetration distance of thermal stress was 5 mm. Under the transient conditions, the fluctuation amplitudes of the thermal loads were greater than those under the steady-state conditions, with the fluctuation of the cold start process being the greatest. Specifically, the maximum fluctuation amplitudes of the temperature, thermal stress, and thermal strain of cold start process were 200 ℃, 40 MPa, and 0.3 mm, respectively. During the process of rapid acceleration, although the maximum fluctuation amplitudes of the piston temperature and thermal strain were smaller than those of the cold start process, being 120 ℃ and 0.12 mm, respectively, the maximum fluctuation amplitude of the piston thermal stress reached the greatest, being 50 MPa. Such a large variation of stress had a great impact on piston durability life. During the process of rapid deceleration, the maximum fluctuation amplitudes of the piston temperature, thermal stress, and thermal strain were the smallest among all operating process, being 20 ℃, 10 MPa, and 0.02 mm, respectively. During the rapid deceleration process, the measured metal temperatures of the piston in various locations all increased shortly, then gradually decreased by a small magnitude, and finally reached stable after 200 s. The maximum fluctuation amplitudes of the piston temperature, thermal stress, and thermal strain during fast deceleration conditions were the smallest among all operating conditions, being 30 ℃, 10 MPa, and 0.02 mm, respectively. The research of this study can provide good guidance for the design of highly intensified aluminum-alloy pistons of diesel engines.
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