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An investigation of methane autoignition behaviour under diesel engine-relevant conditions Iaconis, Jean-Louis

Abstract

As an extension to recent experimental methane ignition delay time measurements conducted at diesel engine-relevant temperatures and pressures, further work has been conducted in an attempt to more closely converge shock tube results with actual engine operating environments. This was performed in three phases that involved reviewing previous homogeneous autoignition delay time data, characterizing a gaseous fuel injector for use in non-premixed ignition studies, and finally conducting non-premixed autoignition delay time measurements in a shock tube. First, in response to recent homogenous methane autoignition delay results that questioned the applicability of existing induction time correlations at low temperatures/high pressures, a series of homogeneous methane autoignition experiments were conducted to isolate whether pressure or temperature differences between recent results and existing correlations were responsible for observed discrepancies. Shock tube experiments were conducted at pressures between 2-4 bar and temperatures between 1100-2000 K, facilitating direct comparison with existing correlations over high temperatures and with recent results at lower, engine-relevant temperatures. These experiments indicated existing correlations could predict ignition delay times at low pressures, but differences in ignition detection methods caused noticeable scatter between correlations. Subsequently, the characteristics of a gaseous fuel injector were investigated to determine the influence of injection parameters on the injector's performance and on the jet produced. These experiments investigated the influence of injection duration and pressure on resultant jets, along with exploring the effects of pulsed injection, and the effects of various obstructions and of an enclosure on overall jet development. These experiments yielded correlations for predicting the injector's behaviour under all intended operating conditions. Finally, the coupling between chemical kinetics and fluid mechanics was explored in a series of non-premixed autoignition delay experiments. These shock tube experiments utilized a standard reflected shock technique, but with fuel injected into the shock-heated air after reflection of the incident shock wave. Chemical kinetic effects were explored by varying air temperatures and pressures, while the effects of fluid mechanic parameters were investigated by varying the fuel injection pressure and duration. These experiments suggested that high-pressure, partially premixed, pulsed direct injection could form an autoignition delay reduction strategy for diesel engines.

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