Heat Transfer Study On The Pre-chamber Assembly Of A Marine Gas Engine

Compared with conventional power systems, marine gas engine has the apparent advantages of better fuel economy and lower harmful emissions. Therefore this kind of engine has attracted great attention from the ship building industry. For the purpose of realizing high efficiency lean combustion, marine gas engine needs a pre-chamber to ensure stable ignition, increase ignition energy and accelerate burning speeding. As one of the kernel components, pre-chamber assembly works in an extremely harsh working condition. Since the pre-chamber assembly has to endure intensive high frequency, high temperature thermal load and high frequency mechanical load, its reliability should be tested. In order to analyze the thermal load of the pre-chamber assembly, the fluid-solid coupling method was used to analyze the temperature field in the pre-chamber assembly.Firstly, the working process of a gas-fueled marine engine was simulated by using a3D CFD software. Through the numerical simulation, this thesis analyzed the temperature field in different time in the main chamber and pre-chamber, as well as the heat transfer coefficient and heat flow in the fluid-so lid surface of pre-chamber. The simulation provided the thermal boundary conditions for the transient temperature field analysis of the pre-chamber assembly.Then a three-dimensional finite element model of the pre-chamber assembly was established. Analysis of temperature field of steady-state and transient-state was done. Based on the steady-state temperature field, the transient temperature field of pre-chamber assembly was analyzed by the fluid-solid coupled analysis method. The CFD simulation provided the transient thermal boundary conditions of the main surface, and these thermal boundary conditions were mapped to the surface unit of the elements in the Finite Element Analysis (FEA) model of the assembly. The results show that the temperature fluctuations are different in different parts of the pre-chamber assembly, and the surface around the orifices had the largest temperature fluctuation. The analysis of starting-state indicates that the increasing trend of temperature of pre-chamber assembly follows the exponential rule. Severe temperature changes could increase the dynamic thermal fatigue stress.Finally, based on the transient temperature field of pre-chamber assembly, the simulation of thermal stress field was done. With the consideration of the gas explosion pressure, the coupling stress field was analyzed. Based on the simulation results, the safety factors of the key parts of pre-chamber assembly were checked. Through the above work, the state of pre-chamber assembly’s temperature field and stress filed was acquired; the potential causes of the possible failure of pre-chamber assembly were analyzed. The work provides database for the structure optimization of the pre-chamber assembly.