In-cylinder soot imaging and emissions of stratified combustion in a spark-ignited spray-guided direct-injection gasoline engine
- 16 September 2011
- journal article
- Published by SAGE Publications in International Journal of Engine Research
- Vol. 12 (6), 549-563
- https://doi.org/10.1177/1468087411418167
Abstract
The combustion in a spark-ignited spray-guided gasoline direct-injection engine operating in a stratified mode has been studied by in-cylinder imaging of the fuel, OH*, and soot distributions. Information on the fuel distribution was obtained by laser-induced fluorescence imaging of the aromatic molecules in the gasoline. The OH* and soot distributions were simultaneously visualized by detection of the natural emissions at 306 nm (OH*) and around 530 nm (soot) using two intensified charge-coupled device cameras. In addition to the in-cylinder observations, engine-out soot emissions, NOx, and HC were measured. The engine was operated at a speed of 2000 r/min and an indicated mean effective pressure of 2.5 bar, with a fully open throttle, resulting in a globally lean combustion with a fuel–air equivalence ratio of about 0.25. The gasoline was injected in single or double injections by an outward-opening piezo-actuated injector. The combustion was ignited efficiently at locally fuel-rich conditions. The soot formation and oxidation were investigated for the two injection strategies, each with three injection timings and two fixed ignition timings. The results showed that soot was efficiently formed and oxidized. From the in-cylinder measurements, it could be seen that the soot luminescence intensity quickly rose and then declined, while the combustion temperature was still increasing. Furthermore, the OH* intensity was still increasing as the soot luminescence was declining. The soot incandescence peak intensity occurred at a crank angle degree close to 50 per cent mass burned, and the OH* intensity peak arose later, shortly before the maximum soot temperature around top dead centre (TDC). When the injection timing was retarded, with constant ignition timing with respect to injection, it was found that the total soot luminosity increased. In addition, less OH* chemiluminescence was observed during the decrease of the soot incandescence, implying conditions less favourable for efficient soot oxidation in the later part of the combustion for retarded injections. This was confirmed by the engine-out soot emission measurements, which showed increased soot levels as the injection was retarded. It was also found that fuel impinged on the spark plug during the injections, resulting in a persistent jet flame close to the spark plug in the centre of the cylinder, which is believed to contribute to engine-out soot emissions.Keywords
This publication has 14 references indexed in Scilit:
- Fuel concentration measurement of premixed mixture using spark-induced breakdown spectroscopySpectrochimica Acta Part B: Atomic Spectroscopy, 2009
- Self-tuning gross heat release computation for internal combustion enginesControl Engineering Practice, 2009
- Full-bore crank-angle resolved imaging of combustion in a four-stroke gasoline direct injection engineProceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2007
- Stratification of fuel for better engine performanceFuel, 2006
- High-speed imaging of OH* and soot temperature and concentration in a stratified-charge direct-injection gasoline engineProceedings of the Combustion Institute, 2005
- Local fuel concentration, ignition and combustion in a stratified charge spark combustion in a stratified charge spark ignited direct injection engine: Spectroscopic, imaging and pressure-based measurementsInternational Journal of Engine Research, 2003
- Experimental and numerical analyses of the combustion process in a direct injection gasoline engineInternational Journal of Engine Research, 2000
- Laser Diagnostics for Temperature and Species in Unsteady CombustionPublished by Springer Science and Business Media LLC ,1996
- Fuel and soot oxidation in diesel-like conditionsSymposium (International) on Combustion, 1994
- Chemical aspects of soot particles oxidation in a laminar methane-air diffusion flameCombustion and Flame, 1990