Higher Peak Heat Release Research Articles

Simulation analysis of the effects of methanol-polyoxymethylene dimethyl ethers blends on combustion and emissions of a PCCI engine

The effects of methanol/polyoxymethylene dimethyl ethers (PODE) mixture with different blending ratios on premixed charge compression ignition (PCCI) combustion and emission performance have been researched through the anlysis of CFD software CONVERGE. Premixed combustion is achieved by a single early injection of fuel into the cylinder. The results show that the combustion start point delays and the peak pressure decreases with the increase of methanol blend ratio. The effects of injection timing on the combustion and emission characteristics of PCCI were studied by using a mixture of the same proportion of methanol. The results show that the advance of injection time leads to more homogeneous mixture and higher peak heat release. But too early injection reduces the temperature in the cylinder and makes the combustion worse, resulting in the increase of HC, soot and CO emissions. NOx emissions decrease with the advance of the injection time.

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

ABSTRACTSpray 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.