Uticaj poremećaja u procesu ubrizgavanja goriva na radne procese u cilindrima dizel-motora

Abstract

Neujednačenost radnih procesa u cilindrima dizel-motora se može desiti iz više razloga. Dva najuticajnija faktora na ovu pojavu, a koji se odnose na poremećaje u procesu ubrizgavanja goriva, su: poremećaji u pogledu trenutnog položaja (ugla obrtanja) kolenastog vratila kada započinje ubrizgavanje goriva u nekom od cilindara, tzv. ugao predubrizgavanja, i poremećaji u količini goriva koja se isporučuje pojedinim cilindrima tokom jednog radnog ciklusa, tzv. ciklusna količina goriva. Navedeni poremećaji su daleko izraženiji kod klasičnih, mehaničkih sistema za ubrizgavanje goriva (pumpa visokog pritiska, pumpa-brizgač, itd.), i vrlo često se ne mogu preduprediti pri vanmotorskim ispitivanjima i podešavanjima sistema ubrizgavanja goriva. Simulacija opisanih poremaćaja u realnim uslovima rada dizel-motora, i proširivanje saznanja o njihovom pojedinačnom i zajedničkom uticaju na radne procese u cilindrima, nije nimalo jednostavna. Međutim, danas postoje komercijalni programi koji imaju ugrađene module zasnovane na proverenim jednačinama termodinamike, teorije sagorevanja i teorije strujanja, koje omogućavaju da se ova simulacija izvrši primenom računara. Jedan od takvih programa je program BOOST AVL. Rezultati simulacija dobijeni primenom ovog i sličnih programa mogu biti i pouzdaniji od simulacija u realnim uslovima rada motora, pošto je kod mehaničkih sistema ubrizgavanja goriva, vrlo teško kvantifikovati stepen poremećaja koji se želi simulirati. Dobijeni rezultati mogu biti iskorišćeni za razvijanje metoda identifikacije uticaja opisanih poremećaja na srednji indikatorski pritisak svakog cilindra, pa i celog motora, tačniju procenu mehaničkih gubitaka (stepena mehaničke korisnosti), itd.

Unevenness of working processes in diesel engine cylinders can happen for several reasons. The two most influential factors to this phenomenon, which are related to disturbances in the fuel injection process are: disturbances in terms of the current position (rotation angle) of the crankshaft when the fuel injection in one of the cylinders starts, so-called pre-injection angle, and disturbances in the quantity of fuel that is supplied to individual cylinders during one work cycle, the so-called cycle amounts of fuel. These disturbances are more prominent in classical, mechanical fuel injection systems (high-pressure pump, pump-injector, etc.), and very often can not be prevented during the out engine testing and the fuel injection system adjustments. The simulation of disturbances described under real operating conditions of diesel engines, and expanding the knowledge of their individual and joined impact on the working processes in cylinders, is not at all simple. However, today there are commercial software which have built-in modules based on the proven equations of thermodynamics, combustion theory and the theory of flow, which makes it possible to carry out these simulations by using a computer. One such software is AVL BOOST. The simulation results obtained using this and similar software can be more reliable than simulations in real conditions of the engine, because in the mechanical fuel injection system it is very difficult to quantify the degree of the disturbance which is to be simulated. The given results can be used to develop methods of identifying the impact of described disturbances on the mean indicated pressure of each cylinder, as well as the entire engine, a more accurate assessment of mechanical losses (degree of mechanical utility), etc.