Publications

Abstract not provided.

Mixture formation in an optically accessible hydrogen-fueled engine was investigated using Planar Laser-Induced Fluorescence (PLIF) of acetone as a fuel tracer. The engine was motored and fueled by direct high-pressure injection. This paper presents the evolution of the spatial distribution of the ensemble-mean equivalence ratio for six different combinations of nozzle design and injector geometry, each for three different injection timings after intake-valve closure. Asymmetric single-hole and 5-hole nozzles as well as symmetric 6-hole and 13-hole nozzles were used. For early injection, the low in-cylinder pressure and density allow the jet to preserve its momentum long enough to undergo extensive jet-wall and (for multi-hole nozzles) jet-jet interaction, but the final mixture is fairly homogeneous. Intermediately timed injection yields inhomogeneous mixtures with surprisingly similar features observed for all multi-hole injectors. Fuel is concentrated near the cylinder wall, an unfavorable scenario were the engine to be fired. Results for late injection depend more on the particular injector configuration. The 13-hole injector shows complete merging of all jets, consistent with results in the literature. The influence of intake-induced bulk-gas tumble is minor for the current injector and combustion-chamber configurations.

In an optically accessible single-cylinder engine fueled with hydrogen, acetone planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) are used to evaluate in-cylinder mixture formation. The experiments include measurements for engine operation with hydrogen injection in-cylinder either prior to or after intake valve closure (IVC). Pre-IVC injection is used to produce a near-homogeneous mixture for PLIF calibration experiments and to establish a baseline comparison for post-IVC injection. Calibration experiments and a temperature correction allow conversion of the acetone fluorescence signal to equivalence ratio. For post-IVC injection with start of injection (SOI) coincident with IVC, PLIF results are similar to pre-IVC injection. With retard of SOI from IVC, mixture inhomogeneities increase monotonically, with high hydrogen concentration spatially located near the injector and within a smaller volume. For injection late in the cycle, the turbulent fuel-rich area is sharply delineated from the more quiescent fuel-lean region. The PIV vector plots suggest that the observed spatial distribution of hydrogen for SOI retarded from IVC is a consequence of the in-cylinder flow field generated by the injection event. Specifically, in the measured r-θ plane of the cylinder and in the field of view imaged, the vector plots show a large-scale mean flow towards the injector. It is conjectured that the observed flow field results from jet-wall interactions that redirect the leading edge of some of the fuel jets back towards the injector, creating a counter-flow with respect to the other fuel jets, which inhibits further jet penetration. The net result is a high hydrogen concentration near the injector. This scenario confirms that the injector tip geometry, injector location, and injection timing are critical parameters with respect to in-cylinder mixing in direct-injection hydrogenfuelled engine.

Abstract not provided.

Two-dimensional laser Rayleigh measurements of thermal gradient structures are performed in a turbulent non-premixed jet flame. The measurements focus on the near field (10 nozzle diameters downstream of the jet exit) where traditional scaling laws from the self-similar far field of non-reacting jets are not necessarily applicable. The optical performance of the high-resolution imaging system is characterized. The square of the temperature gradient field is analyzed by calculating the power spectral density (PSD) and by directly measuring the thicknesses of the layer-like structures. Fully resolved spectra extending over three orders of magnitude in PSD are obtained using a new noise cancellation technique. Some spatial filtering (smoothing) is necessary to reliably measure the layer-normal structure widths in the images. The probability density function (PDF) of the layer widths is found to be approximately log-normal. The PDFs of the 20-percent-full-width layer thicknesses have peak values at 216 and 368 μm for rid = 0 and r/d=1, respectively. The peak of the layer-thickness probability density function (PDF) occurs at a length scale where the PSD is at approximately 0.5 percent of its maximum in both the low-temperature centerline region and the region near the maximum mean temperature. © 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Abstract not provided.