排气管热负荷结构影响因素分析

STUDY ON STRUCTURE INFLUENCE FACTOR OF DIESEL ENGINE EXHAUST MANIFOLD THERMAL LOAD

排气管是发动机主要受热部件,工作环境恶劣,过高的热负荷会导致排气管变形失效甚至出现开裂,影响发动机的正常工作及其可靠性和耐久性。针对某高压共轨柴油机排气歧管热负荷问题,建立了排气歧管不同结构的流固耦合模型,分别进行了温度场和热应力分析,计算分析了不同结构因素对排气管热负荷的影响。研究结果表明:随着排气歧管出口长度的增加,最高温度由805.2℃升至820.8℃;随着出口直径的增大,最高温度由805.2℃升至819.4℃;出口位置变为中间对称部位,最高温度由805.2℃降低至784.0℃;排气管出口位置、长度和直径等结构因素对排气管热负荷影响很大,出口直径、出口长度分别为21 mm、5 mm,出口位置非对称时,排气管最大热应力为326.21 MPa;出口直径、出口长度分别为19 mm、5 mm,出口位置非对称时,排气管热应力出现最小值为174.1 MPa。

Exhaust manifold is a main heated component of engine,which has poor working conditions. High levels of thermal load can lead to deformation even cracking,which affect its normal working and reliability and durability. Aiming at the high thermal load of a high pressure common rail diesel engine,different fluid-solid coupling models was built and the temperature distribution and thermal stress of the engine exhaust manifold was stimulated and the influence of different structural factors on the exhaust manifold thermal load was calculated and analyzed. Results show that： the maximum temperature of the exhaust manifold changed from 805. 2 ℃ to 820. 8 ℃ as the outlet length increased,the maximum temperature of the exhaust manifold changed from 805. 2 ℃ to 819. 4 ℃ as the outlet diameter increasing,and the maximum temperature of the exhaust manifold dropped to 784. 0 ℃ as the outlet transferred to the body symmetry position. Structure factors such as exhaust outlet position,outlet length and outlet diameter had a great influence on the exhaust manifold thermal load. The maximum thermal stress value was 326. 21 MPa of the case of 21 mm outlet length and 5 mm outlet diameter outlet with the non-symmetry outlet position; the minimum thermal stress value was 174. 1 MPa of the case of 19 mm outlet length and 5mm outlet diameter with the non-symmetry outlet position.