Study of fuel spray characteristics using a high-pressure common rail diesel injection system by the method of Schlieren

Abstract

The supercritical atmosphere created by the increase in temperature and pressure in the diesel engine cylinder is the key factor that causes changes in the fuel atomization process. In this study, the differences in spray morphology of n-heptane under different ambient temperature and pressure conditions were investigated using a constant volume combustion bomb combined with the Schlieren method. Based on the Peng-Robinson equation of state (PR equation), several transport characteristics models are constructed to predict the transport characteristics of n-heptane under different operating conditions. During the experiment, the injection pressure and fuel temperature were kept constant (80 MPa, 300 K), the ambient pressure was varied from 2 to 5 MPa, and the fuel temperature was changed from 400 to 800 K, spanning from subcritical to supercritical state. Three different spray regions have been identified based on the fuel temperature and spray geometry: liquid phase region, gas-liquid interface mixing layer, gas phase region. The results show that in a subcritical environment (400 K, 2 MPa), the fuel injection and atomization process is dominated by evaporation. The degree of heat exchange between the fuel and the medium gas is very low, while a small amount of phase change occurs. When the fuel is in low (600 K, 3 MPa) and medium supercritical (600 K, 4 MPa) ambient atmosphere, turbulence becomes the dominant factor in the fuel atomization process. The mixing layer at the gas-liquid interface at the edge of the liquid jet increases significantly. When the fuel is in a high supercritical (700 K, 4 MPa; 800 K, 5 MPa) atmosphere, the jet takes on a shape similar to that of a gas jet, and the mixing layer at the gas-liquid interface becomes the main part of the spray projection area.

Study of the Optimization of Rail Pressure Characteristics in the High-Pressure Common Rail Injection System for Diesel Engines Based on the Response Surface Methodology

“…Based on the above research on the injection characteristics of L, D and R parameters, to optimize the fuel injection characteristics of the HPCRIS for diesel engines, the response surface methodology (RSM) will be used to optimize the common rail pipe pressure and the common rail pipe pressure fluctuation characteristics. Response surface methodology [17,[28][29][30][31] searches for the best combination of independent variables by analyzing the relationship between target variables and independent variables through optimization methods based on statistical principles, and is used to optimize complex functions with multiple independent variables. RSM also encompasses regression design, which further enhances its ability to analyze and model the relationship between variables.…”

“…Wang [17] studied the influence of the common rail pipe diameter, plunger diameter, high-pressure tubing length, and other geometric parameters on the fuel injection characteristics and the common rail pressure fluctuations in a certain type of electronically controlled, high-pressure, common rail fuel injection system for diesel engines and screened out several parameters with a greater influence on the system based on the experimental design and data-processing methods. He used a Pareto genetic optimization algorithm to improve the fuel injection pressure and reduce the rail pressure fluctuations as the objective function, optimized and analyzed the system, and finally obtained a new type of common rail pipe structure.…”