Abstract
Keywords: CI engine, fuel injection, solution, indicator graph
Increasing restrictions concerning exhaust gases non-toxicity induce development of new methods that allow decreasing the emission of toxic components. The fuel injection and spraying process are one of the most significant factors affecting the combustion performance in diesel engines. To a large extend they determine the engine efficiency and the emission of toxic exhaust gas components. In modern engines the emission problem is effectively solved by means of an appropriate control of the course of injection (the injection performance) in accordance with engine operating conditions and fuel spraying improvement. The fuel spray improves owing to injection pressure increase to a value of 140 - 200 MPa. A combination of such high injection pressures, suitable injection control, and exhaust gas oxidation catalysts, allows reducing the emission of the toxic combustion products so that it meets relevant standard requirements. However, these high pressures cause problems at the stage of design, construction and exploitation of injection system [1, 2, 3]. Among others, the tightness, dimensional size and durability of the high-pressure elements in the injection system (delivery sections, injectors, etc.) are the basic problems. The spraying of fuel improved by injection pressure increase is a preferred tendency in modern injection system development in the compression ignition engines [4, 5].
In the injection systems currently used the dispersion of fuel stream into droplets is caused by one physical stimulus only. This is a velocity of fuel flow in the spray nozzle holes caused by the difference between pressures occurring in a nozzle and in a combustion chamber. The dispersion of the fuel stream initiated by this stimulus is amplified by a secondary factor, i.e. an inertial and discrete medium that the fuel is injected into. It is believed that due to a small compressibility of fuel the extension process does not play any significant role in the mechanism of spraying. Experience shows that the efficiency of the existing mechanism of spraying is limited. In order to obtain an environmentally satisfying spraying mechanism, it is necessary not only to use a very high pressure but also to control this pressure in accordance with the engine operating conditions. There are some physical implications which let one believe that the observed tendency in injection system development does not have to necessarily be the only possibility. The spraying mechanism can be improved owing to injection pressure increase or modification in the process of fuel stream dispersion.