Optimization Of Combustion Chamber Structure Coupling With Intake Humidification And Combustion Research Of Marine Diesel Engine

Increasingly serious environmental problems had been paid attentions,the IMO took actions to issued stringent regulations to control NOx emissions of marine diesel engines,which is determined by the internal combustion process.How to enhance combustion efficiency,decrease NOx emissions and not to enhance soot emissions are of great importance.This paper uses simulation method to analyze the interactional effects of combustion chamber structures and intake air humidification on combustion and emission process.Moreover,different swirl ratios are used to study to improve the air and fuel mixing property,EGR is used to control the pollutant emissions.This paper used a six-cylinder turbocharged marine diesel engine.The study researched the combined effects of engine structure and air humidification on marine diesel engines.Besides,advantages and disadvantages were studied comparing EGR with intake air humidification,swirl ratio was investigated based on optimum scheme at last.Results showed that the chamber diameter and bowl depth have a great influence on combustion and emissions.Higher swirl numbers and uniformity index indicate stronger air motions and more sufficient air and fuel mixture property.Viewed from engine power and emissions,the re-entrant chambers with bowl lip structure can produce stronger swirl and combustion temperature with more sufficient combustion and higher in-cylinder peak mean pressure at a little price of more NOx emissions;the straight chamber has lower emissions at the same power level compared with the prototype.The open chamber is found to have a less sufficient combustion process.Air humidification can decrease the peak in-cylinder pressure as well as temperature,the ignition delay and combustion duration are longer,the CA50 is put off,finally the NOx emissions decrease greatly.Under the humidity ratio of 100%,NOx emissions of G0,G2 and G6 decrease by 59.1%,57.8%and 61.5%respectively compared with dry intake air,but area of higher equivalence ratio increases with decreasing oxidizing capacity and more soot emissions.So reasonable humidity ratio is required.The impacts of EGR have resemblance with air humidification.However,the decrease of combustion efficiency and enhancement of soot emissions are more distinct.All in all,air humidification has more potential in balancing the relationship of NOx and soot emissions as well as engine power compared with EGR.Enhancing the swirl ratio suitably can improve the air and fuel mixing property and decrease the area of thick fuel.Excessive high swirl ratio may cause interference of sprays and more soot emissions.Different engine structures with increasing swirl ratio have different NO_x emission trend,with growing swirl ratios,the NO_x emissions of G2 with re-entrant chamber firstly decrease and then increase,the soot emissions are less than that of G0 as a whole,which indicates a more sufficient combustion process.In conclusion,G2 with humidity ratio of 80%and swirl ratio of 0.85 can decrease NO_x emissions by 52%with in-cylinder peak mean pressure slightly increasing.