Research On Realization Of GDI Engine Direct-start Process

With increasing of car ownership year by year, energy and environmental issueshave become more serious. All of cars in city roads have to be commanded by trafficlights. And engines of cars waiting for red light to pass tend to remain idle, whichundoubtedly give rise to wasting of fuel and increasing of emissions of pollutants.However, many people focus on the energy conservation and emission reduction.Therefore, stalling the engine could effectively reduce fuel consumption and pollutantemission during waiting for red light to pass. And frequently starting car not onlyreduces the service life of starter motor, but also affects driving comfort. Based onabove issues, direct-start methods of GDI engine have been raised. GDI engine is oneof the best supporters for direct-start for reason that it is able to be ignited and injectedfuel into cylinder directly. With this feature of GDI engine, this paper primarilystudies the realization of the reverse direct-start mode and forth direct-start mode.Reverse direct-start mode means that to inject a proper amount of fuel into cylinder incompression stroke (compression cylinder) firstly, then fuel will be ignited andcombustion energy will be released to make engine slightly reversed. Cylinder in theexpansion stroke (expansion cylinder) will be compressed during engine reversed,after injecting fuel into this cylinder and igniting mixture crankshaft will turn forward.Energy of igniting mixture in expansion cylinder should drive piston of expansioncylinder to transfer over360°CA. Forth direct-start mode refers to that injecting aproper amount of fuel into cylinder in expansion stroke (expansion cylinder) firstly,then fuel will be ignited and releasing combustion energy will make engine rotate.After engine rotating certain angles, fuel will be injected into cylinder in compressionstroke (compression cylinder), then to ignite mixture as piston of compressioncylinder reaching to top dead center. Energy should make crankshaft rotate180°CA.However, effects of different initial boundary conditions and control parameter forboth direct-start modes are obvious. This paper studies realization on effects ofdifferent initial boundary conditions and control parameter of two direct-start modes.Conclusions have been shown as follows:Reverse direct-start mode:Control parameters has a significant impact on reverse direct-start mode, withchange of initial boundary conditions, optimized control parameters matching withthem are changed. Initial position of compression cylinder piston is too small or too big which willnot have benefit for realization of reverse direct-start mode. Initial position of pistonbetween60-70°CA ATDC has benefit for realization of reverse direct-start mode andthe improvement of start responsiveness.Improving injection pressure with using optimized control parameters matchedhas benefit for realization of reverse direct-start mode and reducing energyconsumption of start. When cooling liquid temperature at70℃and80℃, engine canobtain better rotation properties.When cooling liquid temperature is80℃and injection pressure is more than0.5MPa, initial position of compression cylinder piston between-50--85°CA ATDCcan realize reverse direct-start mode; When injection pressure is0.8MPa, coolingliquid temperature changes between60-90℃and initial position of compressioncylinder piston between-50--85°CA ATDC, reverse direct-start model can be realizedsuccessfully. Reverse direct-start model can be realized at a wide range of initialboundary conditions and control parameters, and it has great application prospect.Forth direct-start mode:Control parameters of expansion cylinder influencing on engine speed is samewhen initial position of expansion cylinder piston is different, initial position ofexpansion cylinder piston has little impact on optimized control parameters. Forinfluence on control parameters of compression cylinder, conclusion is same.Changes of cooling liquid temperature cause corresponding changes ofoptimized control parameters. When cooling liquid temperature is low, optimizedexcess air coefficient showed a trend of decrease, and ignition timing in a larger rangeof temperature do not change too much, when temperature drops to50℃, optimizedignition timing need to retard to784ms. When cooling liquid temperature is at70℃and80℃, rotation properties of engine can be obtained.Initial position of expansion cylinder piston is too small or too big which will nothave benefit for realization of forth direct-start mode. When cooling liquidtemperature within scope of50-70℃, range of initial position of expansion cylinderpiston is at80-110°CA ATDC which can realize forth direct-start mode. As coolingliquid temperature rised, range become narrowed gradually. Forth direct-start modealso has great application prospect.