Search Results

An experimental setup using rapid compression machine to provide excellent optical access to visualize simulated high-speed small-bore direct injection diesel engine combustion processes is described. Typical combustion visualization results of diesel spray combustion under different EGR, swirl, and injection pressure and nozzle conditions are presented. Different swirl intensities are achieved using an air nozzle with variable orientations and a check valve to connect the compression chamber and the combustion chamber. Different EGR ratios are achieved by pre-injection of diesel fuel prior to the main observation sequence. Clear visualization of the high-pressure fuel injection, ignition, combustion and spray/wall/swirl interactions is obtained. The injection system is a high-pressure common-rail system with either a VCO or a mini-sac nozzle. High-speed movies up to 35,000 frame-per-second are taken using a framing drum camera to record the combustion events.

Results of Computational Fluid Dynamic (CFD) analyses of different diesel fuel injector nozzle configurations using a commercial CFD code are presented here. The emphasis of this study is on comparing cavitation models available in the commercial code with respect to their mathematical approach. One of the models is a simple single-phase model based on the Barotropic equation of state, while the other model is a two-phase model based on the bubble dynamic considerations. Results are compared for various 3-D diesel injector nozzles using the two cavitation-modeling approaches. Simulation results are observed to substantiate some of the experimentally established facts like; nozzle efficiency improvements by using techniques like rounded orifice inlets and conical orifices. Also, simulation results agree well with the experimental results. Spray characteristics are predicted based on a primary breakup model.

Precise control of fuel delivery and injection pressure is essential in modern DI diesel engines. Electronically controlled high-pressure injection systems provide features required by modern diesel engines such as precise injection quantity, flexible injection timing, flexible rate of injection with multiple injections and high injection pressures. A comprehensive experimental and numerical investigation has been performed to determine the influence of operating parameters and critical injector design parameters on the dynamic performance of advanced high-pressure electronically controlled diesel injection systems. The injection systems compared in this study are the High Pressure Common Rail (HPCR) and the Hydraulic Electronic Unit Injector (HEUI). Experiments are carried out using a Bosch type injection-rate meter. Needle lift, injection-rate/rate shape, and injection pressure are measured.