Compression Ignition Engine Smoke Emissions at Reduced Ambient Pressures and Temperatures 2024-01-2380

Smoke emission from compression ignition (CI) engines is directly tied to fuel atomization, vaporization, mixing and combustion processes. Engine boundary conditions such as ambient pressures and temperatures, particularly at higher altitudes, have significant impacts on both available ignition energy and on the mixing-controlled combustion process. However, the effects of boundary conditions are difficult to explore without thorough pressure and temperature control of the engine intake air and exhaust gas at higher altitude conditions. The objective of this research is to investigate the relationship between engine smoke emission and engine power in a CI engine fueled with jet fuel at various ambient conditions including higher altitudes. A multi-cylinder compression-ignition engine was operated on a jet fuel at various ambient pressure and temperature conditions, as low as 60 kPa and -12°C, respectively. Single and multi-injection strategies were applied depending on engine power. Detailed analysis was made on in-cylinder pressure, heat release, and the ratio of premixed combustion to mixing-controlled combustion as indicated by the heat release rate. Smoke opacity and filtered smoke number (FSN) measurements were made using an AVL Opacimeter and an AVL Smoke Meter, respectively, at sea level conditions as well as at reduced ambient temperatures and pressures. Depending on the engine power, a shift between premixed and mixing-controlled combustion occurred which significantly impacted the engine-out smoke. Further, the smoke emission was dependent on the injection strategies. Smoke emissions for the jet-fueled engine were examined with respect to heat release behavior and equivalence ratio. The capabilities and challenges of measuring smoke at higher altitude conditions are discussed.