UBC Theses and Dissertations
Developing pyrometric and chemiluminescence optical diagnostics for investigation of modern alternative CI engine combustion strategies Khosravi, Mahdiar
Its inherent economic and environmental advantages as a compression ignition (CI) engine fuel make natural gas (NG) an attractive alternative to diesel fuel. Limited optical studies of the NG combustion strategies have been reported in literature. The current work focused on developing optical characterization techniques to study in-cylinder processes in cleaner combustion strategies, such as those involving natural gas. An experimental facility supporting optical diagnostics via a Bowditch piston arrangement in a 2-litre, single-cylinder research engine was used in this study. In order to facilitate quantitative soot analysis for low soot combustion strategies, the performance of the pyrometric method was improved by nearly 40% increase in the resolved signal fraction through modifications in numerical algorithm, calibration and implementation of the method, and image processing. The enhanced pyrometry method was implemented simultaneously with high-speed OH* chemiluminescence imaging to pilot-ignited direct-injected natural gas (PIDING) combustion for the first time. The results revealed that a standard PIDING operation can be characterized by low-sooting non-premixed combustion of the NG along the jet axes and of a partially-premixed charge at the wall region, followed by onset of detectable soot at the points of NG jet impingement on the bowl wall. This results in formation of a soot cloud adjacent to the wall, which then grows towards the center with continued soot formation and reflected momentum of the NG jets impinging on the bowl wall. The relative timing between NG injection pulse and peak HRR, and the P_inj, showed strong influence in the rate and extent of soot formation and peak concentration levels. Rugged probe designs afford optical measurements from all-metal engines. Comparisons between 2D and probe based 0D pyrometry measurements were made under optical engine configuration, for the first time, to better characterize the 0D probe signal. The 2D and 0D results showed reasonable agreements, especially when field-of-view geometry differences were taken into account. 0D two-color pyrometry measurements in an all-metal engine led to similar conclusions on soot in-cylinder processes, albeit with signs of enhanced late-cycle soot oxidation, attributed to the conventional omega shaped piston bowl geometry.
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