Study On Combustion Process Of Diesel Engine For Vehicle During Start Operating Condition

The tendency of automotive power is more and more moving towards to thediesel engine in these years. Currently, in the United States, Europe and Japans, therate of diesel engine using on heavy-duty vehicle and commercial vehicle is almostnear 100%.The development of Diesel Cars is also in a extraordinary speed. InChina, with the laggard diesel engine technology, the percent of diesel vehicles,especially diesel cars are very little in the market. In our country, the diesel enginetechnology is laggard behind the technology in foreign countries, and manytechnologies now widely used in foreign countries are during research or evenblank in our country. Speeding up the research on the technology of diesel engine ismore urgent.With the incremental retention of diesel vehicle in these years, the serious airpollution caused by diesel vehicle must be regarded. With more and more stringentemission regulation the lower exhaustion become to the target for diesel vehiclemanufacturer pursuing. Otherwise, diesel engine cold start combustion instabilitymust be improved as a serious problem that all diesel vehicle manufactures arefacing.The dependability and emission character of diesel engine cold start has beensearched after by examination in this paper. The emphases of this research isdeveloping a new diesel engine cold start strategy and make suggestions to reduceor eliminate combustion instability and reduce the emission during cold startprocess by analyzing the factors which affect combustion process during start.The completed works and the conclusions which was elicited by examinationswill be introduced as follow:1. For different aims of the examinations, two platforms were established forthe examinations of cold start. The researching objects of the two platforms isdifferent, one is a 4 cylinder diesel engine the other is a single cylinder dieselengine. The research of whole combustion process and combustion state innumbered cycles of start was carry out in the two different platforms respectively.2. Design and establish a platform of diesel electronic controlled fuel injectionsystem which take the electronic control distribution pump—VP37 as the primarycomponent for the single cylinder diesel engine. Base on the hardware designed byauthor, the electronic controlled fuel injection system was calibrated and the fueldelivery MAP was protracted.3.The process from starting to idling has been studied on a 4 cylinder dieselengine with the type is YC4112ZLQ. During the examination , based on transientspeed and pressure in cylinder the analysis was processed. According to thedifferent state of combustion and the characteristic of indicator chart, four typicalindicator chart was defined, include: child-mother peak , twin peak ,child-pregnancy peak and singleton peak .With the time of four kinds of typicalindicator char appeared ,compartmentalize the starting process to four phase,include: cranking phase, preliminary phase, transitional phase and steady phase.Contrast the indicator chars of two different state of start—cold start and warmstart, and the factors which caused the difference of two different state of start areanalyzed in this paper. Combined the analysis of the combustion during two stateof start the exhaust emission was contrasted. Concerned the conclusion that theexhaust emission during cold start is worse than warm start, the main reason whichcaused this result is regard as the conditioning temperatures is low and thelubricating system works on a execrable condition. Otherwise, the transient speedof the cold start is lower than the warm start, under the control of speed governor,the quantity of diesel fuel oil supply is risen , which is also one of the reasons thatcaused the exhaust emission more higher.4. The first firing cycle and the combustion characteristic of the numberedcycles also the exhaust emission during cold start has been studied on a singlecylinder diesel engine— ZS1100. With the electronic controlled fuel injectionsystem and the exhaust emission collecting system are taken as the maincontrollability condition, the cycle number of starting inject and the injection timeswere controlled during starting the engine. By changing the boundarycondition ,the analysis was carried out to make clear the infection which thecombustion state in forepart of numbered cycles during cold start bring to exhaustemission during start. The choice of boundary condition include the quantity ofdiesel fuel oil for each cycle, environment temperature, cooling water temperature,intake air temperature and so on. Base on a series of examinations, there are someconclusions has been made up: In the condition of low speed during the cold startin normal temperature, the combustion is instable at the beginning of cold start.The badness of heat atmosphere is the main reason which cause the diversity ofdifferent starts. At the beginning of start, the reliability and exhaust emission willbe affect by the quantity of diesel fuel oil injecting in each cycle. For enhance thereliability of start, the quantity of diesel fuel oil injecting in first few cycles shouldbe increased, but consider the exhaust emission, it must be treat in the other wayround or the emission will be manifold. Enhancing of the cooling watertemperature and intake air temperature will be propitious to reduce the number ofthe misfires cycles, shorten the retardation of firing, it also can enhance thereliability of each cycles during beginning of start, the HC emission could bereduced at the same time. Contrast the effects to improve the combustion state byenhancing intake air temperature and cooling water temperature heightened,theeffect of anterior one is more remarkable. During the beginning of start, the mostremarkable effect for HC emission is whether the misfire cycles appeared, oncethere is a misfire cycle the HC emission will increase rapidly. According to this ,toreduce the HC emission and stabilify the combustion, the misfire cycles must beeliminated or at least reduced. The retardation of firing will be shorten ,with puttingoff the cycle number of first firing , at the same time it will improve the exteriorcondition, reduce the numeral of misfire, increase the probability of firing in firstsprayed cycle. According to the examination and analysis, the start of diesel engineis regarded as an unstable instantaneous process, during the whole start processeach parameter may affect the combustion state more or less at the beginning ofstart.All these physical and chemical parameter during start may accelerate, restrictor transform each other. When made aimed at developing a new diesel engine coldstart strategy, all the boundary conditions both the parameters and the affectionthey effect to each other should be considered to optimize the start processremarkably.