Three-Dimensional Design And Oil-Gas-Chamber Matching Optimization Of The Combustion Chambers Of A Diesel Engine In High Altitude Conditions

In order to restore the plateau performance of a certain type of diesel engine,this thesis is based on the three-dimensional numerical simulation method for four commonly used direct combustion chambers,including the Combustion Chamber with a Higher and a Lower Reentrant Swirl Chamber,the Double-layer Stratified Combustion Chamber,the Combustion Chamber with a Large Swirl Chamber and the Prototype ω Combustion Chamber to adjust the Combustion Chamber of the Direct Injection Diesel engine that adapted to the plateau structure.Optimize the "oil-air-chamber" matching with the goal of improving the air utilization rate in the cylinder in the plateau environment.Adjusting the structural parameters include: the diameter-to-depth ratio of the Combustion Chamber with a Higher and a Lower Reentrant Swirl Chamber,the radius ratio of the Upper and Lower Swirl Chambers,the diameter-to-depth ratio of the Double-layer Stratified Combustion Chamber,the height of the clearance volume,and the swirl chamber’s radius of Combustion Chamber with a Large Swirl Chamber,the necking rate and the diameter-to-depth ratio of the Prototype ω Combustion Chamber.Fuel injection parameters include: fuel injection angle(the included angle between two fuel lines in the same vertical plane),fuel injection advance angle,and fuel types.The calculation results under the current calculation conditions show that:1.The Combustion Chamber with a Higher and a Lower Reentrant Swirl Chamber can form long-lasting longitudinal tumble flow and horizontally rotating vortex in the upper swirl chamber,which is conducive to the formation of mixed gas and can oxidize SOOT in the after burning period.With the increase of the diameter-to-depth ratio D/H of the combustion chamber,the SOOT emissions first decrease and then rise,while the NOx emissions first rise and then decrease,the cylinder pressure peak point gradually decreases,and the diameter-to-depth ratio D/H chooses remain about 3.1 are appropriate.With the increase of the upper and lower swirl chamber’s radius ratio r/R,NOx emissions first increase and then decrease;SOOT emissions first increase,then decrease and then again increase;the peak point of cylinder pressure first increases and then decreases.It is appropriate to choose 0.8-1.1 for r/R.With the increase of the fuel injection angle,SOOT emissions first increase and then continue to decrease;NOx emissions are w-shaped,undergoing a process of decline,rise,decline,and then rise successively;the peak point of cylinder pressure first rises and then falls.It is advisable to choose 155°-160° for the injection angle.2.The Double-layer Layered Combustion Chamber can increase the average pressure in the cylinder and reduce NO emissions.With the increase of the diameter-to-depth ratio,the amount of NO gradually increases,and the amount of SOOT gradually decreases.The diameter-to-depth ratio should be 2.9-3.1.Properly increasing the height of the clearance volume can reduce the emissions of NO and SOOT,and it should be set from 2.05 mm to2.25 mm.As the fuel injection angle increases,NO emissions gradually increase;SOOT emissions gradually decrease;and the peak cylinder pressure rises.The angle of injection should be 155-160°.3.The radius of the swirl chamber of combustion chamber with a large swirl chamber should be 9.12 mm.As the fuel injection angle increases,the peak point of cylinder pressure in the Combustion Chamber with a Large Swirl Chamber increases,and SOOT emissions decrease.If NO emissions increase,155° is appropriate.4.The throat of the Prototype ω Combustion Chamber changed from necking to flaring,and the peak cylinder pressure increased slightly,the NO increased;and the SOOT decreased.As the diameter-to-depth ratio of the ω combustion chamber increases,the peak cylinder pressure decreases;the NO and SOOT emissions gradually increase.The diameter-to-depth ratio should be 2.2.As the fuel injection angle increases,the peak cylinder pressure gradually rises,the NO increases,and the SOOT decreases.The fuel injection angle in 155° can give consideration to both power and emissions.5.Proper injection of fuel in each combustion chamber in advance can significantly increase the average pressure in the cylinder and reduce the SOOT emissions.Among them,the Combustion Chamber with a Higher and a Lower Reentrant Swirl Chamber has the strongest optimization potential,and the Combustion Chamber with a Large Swirl Chamber has the lowest optimization potential.6.Using B10 with the same quality as pure diesel in plateau environment can increase the average pressure in the cylinder and reduce SOOT emissions at the same time.As the in-cylinder mass fraction of biodiesel increases to 20%,the average in-cylinder pressure,SOOT,and NO all decrease.Among them,the NO emissions reduction potential of the prototype ω combustor is the largest,which from 382.97 ppm at B10 to 249.60 ppm,but the CO increase’s amount is the largest,from 2.96% to 3.16%;the SOOT reduction potential of the Combustion Chamber with a Higher and a Lower Reentrant Swirl Chamber is the maximum,dropped from 23.69 ppm to 21.91 ppm.