| In recent year,dual-fuel low-speed marine engines employing natural gas with high calorific value and high hydrogen to carbon ratio as an alternative fuel have become a hot research area for ocean-going boats in order to battle climate change and minimize greenhouse gas emissions.Among them,the pre-combustion chamber type dual-fuel low-speed marine engine uses the premixed combustion concept and can meet the International Maritime Organization’s Tier III emission regulations without the use of after-treatment technology,which has attracted the interest of the marine industry.However,the pre-chamber type dual-fuel low-speed marine engine’s premixed combustion principle results in poor output power.As a result,performance improvement is required to boost output power,however there are few general phenomenological combustion models for pre-chamber type dual-fuel low-speed marine engines in performance optimization simulation.As a result,a full and universal phenomenological combustion model for pre-chamber type dual-fuel low-speed marine engines is created in this study.This paper develops a phenomenological combustion model based on the combustion process of a pre-chamber type dual-fuel low-speed marine engine,which includes a pilot fuel ignition sub-model,a pre-chamber combustion sub-model,a jet flame sub-model,a mainchamber turbulence sub-model,and a turbulent entrainment combustion sub-model.The existing mature models are used for the pilot fuel ignition submodel and the pre-combustion chamber combustion submodel,and the construction of the remaining three models is focused on.Firstly,the turbulence model of the main-chamber was constructed by referring to the mature turbulence model and considering the four factors of jet flame,piston compression,mixture combustion and gas sweeping process in the main-chamber;secondly,to simulate the jet flame participation in the combustion process of the main-chamber,the jet flame entrainment combustion sub-model was constructed based on the momentum and mass exchange between the jet flame and the mixture;then,based on the principle of turbulence coiling model,the turbulence entrainment combustion sub-model was constructed by considering the influence of laminar flame.Finally,a jet flame intensity model was constructed with reference to the mainchamber turbulence model,and coupling parameters were derived using jet flame intensity and turbulent kinetic energy,which were used to couple the jet flame entrainment combustion submodel and the turbulent entrainment combustion sub-model to simulate the combustion process in the main-chamber,and the NOx model and the intake and exhaust model are also bulit.A phenomenological combustion model of precombustion chamber dual fuel low speed Marine engine is developed.The calculation program was written by commercial mathematical programming software,and the model results were compared and verified by experimental data and CFD simulation data of different bore,different strokes,different number of pre-chambers and the same operating principle of the pre-chamber type dual fuel low-speed marine engine under different loads.The results show that the average relative error of cylinder pressure results in the combustion stage is less than 3.5%,the average relative error of CA10,CA50 and CA90 results is less than ±1°CA,the average relative error of burst pressure is less than 2%,the average relative error of indicated mean effective pressure is less than 6%.The model results are proved to be accurate and reliable,and can be used to study the combustion characteristics of precombustion chamber type dual-fuel low-speed marine engines with the same operating principle and similar structure.Finally,the effects of the pilot fuel injection timing,compression ratio,equivalent ratio and initial turbulence energy value on the combustion process and performance parameters were investigated by the validation model,and the sensitivity and applicability of the model to parameter variations were proved by theoretical analysis. |
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