Investigation of Port Fuel Injector Spray Mass Distribution by Laser Induced Fluorescence

Modern internal combustion engines have stringent requirements for performance and reduced toxic emissions. The fuel delivery system, and particularly the fuel injectors, have a vital role in reducing unburned hydrocarbons (HC) and carbon monoxide (CO) in exhaust emission. The main goal of this study is to map the spatial and temporal distribution of the spray from a low-pressure gasoline fuel injector. To attain this goal, three tasks were performed: (1) the experimental investigation of the spray oscillation as functions of operating pressure and injector timing, (2) the determination of the appropriate dye/fuel combinations for one particular experimental technique, and (3) the demonstration of the capabilities of a Computational Fluid Dynamics (CFD) code, Fluent, in the dispersed two-phase flow solutions. An experimental technique, planar laser induced fluorescence (PLIF), was employed to investigate the spatial and temporal distribution of the spray mass from a set of four-hole, split-stream port fuel injectors. The spatial and temporal spray evolution in a horizontal cross-section was imaged instantaneously via detection of fluorescence intensities. The lateral displacement of the spray mass is clearly displayed in time sequence via the PLIF images, and the spray instability is shown to be sensitively dependent upon small geometric differences along the internal flow paths. In the course of a study to develop a quantitative PLIF diagnostic for the mass distribution emanating from a liquid fuel injector, spectroscopic results were assembled for certain dye/fuel solutions. Experiments were performed with combinations of hydrocarbon solvents and organic dyes. Results are presented in the form of absorption and emission spectra, including extinction coefficients with error analysis, comparisons with data in the literature, and Stokes shift estimates. A Computational Fluid Dynamics (CFD) code, Fluent, was employed to demonstrate its capabilities in the solution of dispersed two-phase flows. The dispersed two-phase flow consists of discrete elements surrounded by a continuous phase. The continuous phase equations were solved in an Eulerian reference frame. The Lagrangian approach was used to track packets of discrete phase elements. Inputs of the numerical dispersed two-phase flow model were obtained from the conditions of the PLIF experiments. Two cases were solved with the same input and boundary conditions. In the first case the spray consists of droplets with 100 μm diameter. A linear droplet diameter distribution between 40 and 100 μm was specified in the second case. Results indicate the existence of a core region with higher velocity values for both cases. The core region appears at the spray center close to the injection tip. The increase in the spray temperature towards the outlet boundary is larger for the constant droplet diameter case than the linear droplet diameter distribution case. Negligible evaporation is observed in the solution domain for both cases