Study On Heat Transfer Characteristics Of A Low-speed Two-stroke Dual Fuel Engine

Gas engine technologies are getting more and more attentions because of increasingly stringent emission regulations for marine engines,there are obvious advantages in controlling emissions for premixed lean combustion dual fuel marine engines with Otto cycles,but premixed gas is prone to earlier ignition phenomenon with the improvement of engine performance,and researches have confirmed that the auto-ignition of cylinder oil is one of the main reasons of this abnormal combustion.In addition,the heating effect of the high temperature surfaces of the combustion chamber on the pre-mixed gas increases the heat release of low-temperature chemical reactions and the accumulation of intermediate active products,which to some extent will promote the pre-mixed gas premature combustion.In this paper,the characteristics of surface temperature distribution in combustion chamber and its heat transfer influence on the pre-mixed natural gas,the process of pre-ignition induced by chain reaction were studied.This paper analysis the thermal load of combustion chamber key parts with the fluid-solid coupling method first,and then simulate the natural gas dual fuel engine's combustion process using the numerical simulation software Converge to couple simplified reaction mechanisms.The main work of the paper is divided into the following parts:(1)The cooling oil system of combination piston a low-speed two-stroke engine was introduced,and a 3D CFD software was used to simulate the multiphase flow oscillation heat transfer process of cooling gallery,the oscillating cooling mechanism of the piston was explained based on the reciprocating movement of the piston and the stretching and compression of the telescopic sleeve;(2)Finite element analysis of piston crown was established,and thermal boundary conditions of piston crown were determined.The thermal boundary of piston top surface and cooling gallery walls were mapped from three-dimension CFD calculation results of combustion process in cylinder and heat transfer process in cooling gallery.The APDL command is programmed and the thermal analysis of the piston crown of diesel engine and dual fuel engine is carried out respectively by using the finite element software ANSYS;(3)The exhaust valve was divided into seven areas based on different relative position,and then thermal boundary conditions were determined.The APDL command is programmed and the transient thermal analysis of the exhaust valve of diesel engine and dual fuel engine is carried out respectively by using the finite element software ANSYS;(4)By simplifying assumptions,the 0.1 mm thickness of deposites surface temperature were calculated by one dimensional flat heat conduction formula,and then use the Converge software coupling methane-n-heptane simplified mechanism to simulate compression and combustion process of dual-fuel engine under two surface temperatures,and explore the heat transfer influence on natural gas by high temperature surfaces.