Spray Hot-impingement System Optimization for Premixed Diesel Homogeneous Charge Preparation 2008-01-0014
In this study, a spray hot-impingement system was set up to analyze the spray characteristics when spray impinged onto a flat hot surface by high-speed photography technology. The angle between spray axis and normal line of the flat surface could be changed, and the surface temperature could exceed 400°C. The influences of surface temperature and heating power on spray atomization were investigated too. At atmospheric pressure, when the wall temperature was 340∼380°C, the impinging diesel spray was well atomized. In this experiment, the wall heating power could be set at 1∼25 Wcm-2. When the heating power was about 1.6 Wcm-2, the impinging spray atomized well, and when it was about 10.1 Wcm-2 the spray atomized better though the heating power requirement should be high. The angle (α) between nozzle hole axis and wall normal line apparently affected wall jet velocity
Then a segment of steel tube was fixed between the intake manifold and cylinder head in a direct injection natural aspirated diesel engine. The tube wall could be heated to be over 400°C by the heater enwrapped outside. Diesel sprays would impinge onto the hot inner surface of the tube and atomize quickly when the tube wall temperature was high enough. Then the fuel-air mixture would be drawn into the cylinder in intake stroke, and HCCI combustion could be fulfilled. The tube, heater, and injector constituted a spray hot-impingement system used on engines. And a new method for diesel homogeneous charge preparation was realized.
Based on charge homogeneity and inducted fuel ratio, the nozzle hole number and were optimized through comparison of 5 nozzle cases for premixed diesel homogeneous charge preparation by spray hot-impingement at intake manifold. The charge homogeneity was estimated by engine NOX emission and exhaust opacity. When α=15°, the hole number increase would reduce the exhaust opacity, but could not effectively increase the inducted fuel ratio. But when α=45°, it would effectively increase the inducted fuel ratio, whereas could not reduce the exhaust opacity. And NOX emission would decrease when hole number increased. If α decreases, the inducted fuel ratio could be enhanced, but there was a best α for NOX and exhaust opacity. For the 5 nozzle cases, the nozzle with 6 holes and α=30° was the optimized case.