Simulation Study Of The Inlfuence Of Multi-injection On Diesel Performance And Emissions

Internal combustion engines have undergone continuous development and improvementover one hundred years, and have been applied to every corner of people’s life widely. It bringpeople great convenience, and also bring serious energy crisis and pollution problems at thesame time. In recent decades, emissions control has been one of the hotspots in the research ofinternal combustion engines. Because high-pressure common rail system controlledelectronically is capable to control fuel injection parameters independently and flexibly, dieselengines can work in one cycle with sectionalized, repeated injection——multiple injectionstrategies，which can improve the combustion process and raise the performance of the dieselengine, especially in emissions control. At present，the domestic research of multipleinjections has just begun, and focus on test research mainly. So, with the help of commercialsoftware, using the method of simulation analysis to study the multiple injection strategies isof great significance.In this paper, a diesel engine with high-pressure common rail fuel injection systemcontrolled electronically is taken as the research object. Multiple strategies includingpilot-main injection, main-post injection, and pilot-main-post injection are used.Computational fluid dynamics (CFD) software AVL FIRE is applied to calculate thesimulative combustion process. The calculation results are analyzed comparatively. The ruleson the performances and emissions effect of the diesel engine using various injectionstrategies are summarized, and then the curve on fuel injection rate is optimized. Thefollowing is main research contents and conclusions:1. The theories of CFD simulation calculation are analyzed, reasonable mathematicalmodels are made, and a theoretical basis for computing is provided. In this paper the mainmodels required to calculate in FIRE software include the basic governing equations of acombustion chamber flow field,k εtwo-equation turbulence model, and WAVE spraymodel and so on.2.3D drawing software Pro/E is applied to create the geometric model of combustionchamber in the diesel engine. Opens the model and mesh it in AVL FIRE software. Then onthe basis of experience and the actual experiments the parameters needed for calculating aboutthe initial and boundary conditions are set. All simulation calculations are under theconditions of the maximum torque speed2400r/min and full load. Firstly the condition withthe original single injection is calculated, and the accuracy of the model is verified. On the basis, using the multiple strategies including pilot-main injection, main-post injection, andpilot-main-post injection, conditions are calculated.3. Keeping the total oil quality of every single cycle fixed, the delay period of the maincombustion can be shorten because of the pilot fuel heat, the percentage of premixedcombustion is reduced, the temperature of the cylinder is elevated，releasing heat is inadvance and the curves move near TDC. The pilot injection can make NOxemission raisedand Soot emission reduced. But overall, the total emissions of diesel engine can be reduced byselecting reasonable parameters of the spray; Post injection can oxidize the generated Soot, atthe same time the larger quantity of post injection oil can be used to improve NOx, butchoosing the reasonable post injection timing is needed; The parameters of the pilot injectionand post injection in pilot-main-post injection strategy are independent.In subsequent studyabout multiple injection, pilot injection and post injection can be studied separately.