Experimental Study On Diesel Spray And Mixing Uniformity Characteristics

Diesel spray evaporation and the mixture of oil and gas are important boundary conditions of diesel engine combustion. Therefore, it is crucial for organizing combustion, improving engine performance and emission to research the influence factors and change rule of spray characteristic and reasonably evaluate the mixing uniformity of spray and gas.In this paper, firstly, based on a constant volume combustion device with high temperature and pressure and high-pressure common rail fuel injection system with highspeed cameras and schlieren system set up a platform of diesel spray characteristic test. Through the platform capture diesel free jet spray images under different background gases parameters and ejection parameters. In addition, under the injector installing combustion chamber module, capture diesel spray images in different fuel injection angle.Then,using MATLAB image processing module for free jet and impinging jet put forward new methods to process the spray images and work out tip penetration, spray angle, projected area, and spray injection volume for the gas phase and liquid phase.By calculating spray macroscopic characteristic, sum up the influence rules of background gas parameters and injection parameters. In terms of background gas parameters, with the background temperature rising, evaporation of diesel and the distribution of the fuel spray in the space improve; with the background density rising, spray volume decreases, the distribution of fuel spray in the space has not been improved but unit volume contains more background gas and fuel-gas mixing effect gets better. As for injection parameters, with the increase of injection pressure, evaporation of diesel improves, gas phase spray develops faster and further and liquid phase spray tip penetration basically remains constant. Injector with smaller aperture and more holes increases the total fuel evaporation capacity and improves the distribution of fuel spray in the space.Research on impinging jet spray finds that fuel injection angle has important influence on spray characteristics. Modify combustion chamber shape and select suitable fuel injection angle, total spray area and gaseous phase area increase, liquid phase spray area decreases, evaporation of diesel improves.For the actual engine, after fuel injected in cylinder, the formation of mixture directly influence the quality of ignition and combustion. So, new evaluation parameters are proposed in this paper. Summarize the rules of evaluation parameters changing with the temperature and density of the background gas, the pressure of fuel injection and the diameter of nozzle hole. Through the analysis of these rules, verify the rationality of the evaluation parameters.