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Abstract:

In this study, the occurrence of auto-ignition centers in a two-stroke SI engine was investigated using planar laser-induced fluorescence (PLIF). An experimental SI engine equipped with glass windows to enable full optical access into the combustion chamber was operated under knocking conditions. The pulsed output of two XeCl excimer lasers was formed into planar light sheets (300 μm × 4 cm), which were spatially overlapped and directed into the combustion chamber of the operating engine. Unburned fuel components fluoresce strongly when illuminated with XeCl laser radiation; burned regions display no fluorescence. Self-ignited regions therefore show up as dark sites in the fluorescence images, indicating local consumption of the fuel. The resulting PLIF images were recorded using fast-gated ICCD cameras. By delaying the second laser pulse a specific time (100 ns-600 μs), image pairs were acquired which allowed the temporal development and mutual influence of hot-spots to be studied. The short laser pulse duration (20 ns), the two-dimensional nature of the imaged region and the strong signals obtained from our detection scheme yield very detailed information of the self-ignited regions. Approximately 20 000 image pairs were recorded. As important quantities, spatial distribution and expansion velocities were extracted from the PLIF images and investigated statistically. Copyright © 2001 Society of Automotive Engineers, Inc.

Abstract:

A coherence mechanism that protects cavity QED dark states from motional entanglement was identified. It was shown that in the case of near coaxial standing waves, and in the Lamb-Dicke limit ηL,C2 ≪ 1, the decoherence rate is much smaller than an estimate based on the size of the laser or cavity field Lamb-Dicke parameters would suggest.

Abstract:

This paper has two parts. The first compares the measured burned gas temperature using Coherent Anti-Stokes Raman Scattering (CARS) with the predictions of a multiple zone computer simulation of combustion. The second part describes a system that is capable of determining the heat flux into the combustion chamber by means of measuring the chamber surface temperature. It is shown that the multi-zone computer simulation can accurately predict the burned gas temperature once the fuel burn rate has been analyzed and the model tuned correctly. The effect of different fuels (methane and iso-octane) on the burned gas temperature is reported. A high burn rate or more advanced ignition timing gave a lower burned gas temperature towards the end of the engine cycle. The surface heat flux was deduced from measurements of the surface temperature by using a finite difference method. From the experimental results, it was found that there are significant cycle-by-cycle variations in the surface heat flux in both the magnitude and phasing. Therefore, a cycle averaged heat flux has significantly different characteristics from a single cycle. These cycle-by-cycle variations in the heat flux were associated with corresponding variations of the propagation of the flame through the combustion chamber. This in turn is due to the variations in combustion. The effects of ignition timing and air-fuel mixture on the surface heat flux are reported. Comparisons between experimental surface heat flux measurements and established heat transfer models show large discrepancies. Copyright © 2000 Society of Automotive Engineers, Inc.