Spray Impingement and Combustion in a Model Opposed-Piston Compression Ignition Engine

Spray impingement and combustion in a model opposed-piston compression ignition engine was investigated experimentally and computationally. A recently proposed pressure-dependent droplet collision model was implemented in the KIVA-3V computer program for the Reynolds Average Navier–Stokes calculation, which was validated against the time-averaged experimental data for the cylinder pressure. Compared with the widely-used O’Rourke model, the present model produces physically appraised predictions by accounting for the propensity of droplet bouncing upon collision at high engine pressures—a physical phenomenon overlooked in the previous models. The results show that droplet collisions can be promoted either by the impingement of the sprays from the oppositely placed three-nozzle fuel injectors under the condition of low engine speed and high load, or by the interaction of the sprays from each fuel injector in the presence of in-cylinder swirling flow. Motivated by fully utilizing the space of the combustion chamber, a new spray layout possessing the S₂ symmetry was proposed and computationally investigated in the study. Compared with Hofbauer’s spray layout of the C₂ symmetry, the present layout tends to produce more distributed premixed fuel mass and hence results in a longer ignition delay time but a higher peak heat release rate.