Natural Flame Luminosity and Emission Spectra of Diesel Spray Flame under Oxygen-Enriched Condition in an Optical Constant Volume Vessel 2018-01-1781

The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity. It is found that with the rising of oxygen level, the period from the start of injection to the end of combustion shortened, the luminosity intensity in the flame core increased and the shape of the spray flame was shortened and narrowed. Meanwhile, an obviously blue region appeared at the tip of flame when the oxygen level was up to 60% or higher. To study the interesting blue region, the one-dimensionally resolved diesel spray flame emission spectra were investigated along the vertical axis of the spray. Results show that the transition point of the flame configuration was around 70 mm from the nozzle tip. Soot radiation dominated the flame natural luminosity in the range of 0-70 mm from the nozzle, while the chemiluminescence of carbon monoxide oxidation dominated in the range of 70-100 mm. For further consideration, in high oxygen level, the soot existing region is shortened and CO as well as UHC is oxidized more completely. Meantime, there is no NOx emission from the fuel combustion in nitrogen-free environment. Therefore, oxygen-enriched combustion will help to achieve the improvement of high efficiency and low emissions in internal combustion engines.