Analysis Of Combustion Process Of Marine Diesel Engine Based On Simplified Mechanism Of Heavy Oil

In general,heavy oil is used as fuel for low-speed marine diesel engines due to fuel economy,while the environmental pollution caused by heavy oil combustion has become the focus of attention all over the world.In this paper,3 kinds of substitutes were selected as heavy oil and a three-dimensional fluid model coupled with the simplified chemical mechanism of substitution components was created to analize combustion process on marine diesel engine.The research results have theoretical significance and engineering application value for perfecting the heavy oil combustion theory and exploring the clean and efficient combustion of heavy oil.The main research contents are as follows:1.The configuration of heavy oil substitutes is designed.According to the similar density or calorific value,toluene,n-heptane and propylene were selected as the model components of heavy oil substitute and mixing ratio is set to 4: 5: 1.2.A simplified mechanism model of chemical reaction kinetics of toluene,n-heptane and olefin was constructed.DRGEP method,reaction path analysis and sensitivity analysis were used to simplify the detailed mechanism of three components,and the simplified mechanism model of chemical reaction kinetics for three alternative components was obtained respectively.3.The rationality of heavy oil substitute components can be verified by comparing the simplified mechanism model with detailed mechanism of toluene,n-heptane and olefin in three ways: ignition delay period,laminar flame velocity and concentration of important components.By coupling the simplified mechanism of three components,a integral mechanism model consisting of 121 components and 700 reactions was formed for heavy oil substitute.4.The three-dimensional fluid model of marine diesel engine is established,and coupled with the simplified mechanism model of chemical reaction kinetics of heavy oil substitutes,the in-cylinder combustion calculation model of marine diesel engine is established.The validity of the model is verified by means of indicator diagram comparison.5.The factors effect on heavy oil combustion performance of marine diesel engine were invstigated.The inflence of injection timing on in-cylinder spray,oil-gas mixing and NOx formation were studied.Results show that when the injection timing increased in a certain range corresponding to a specific working condition,the temperature and pressure in combustion chamber rised while the NOx emission increased.