Shock accelerated vortex ring

The interaction of a shock wave with a spherical density inhomogeneity leads to the development of a vortex ring through the impulsive deposition of baroclinic vorticity. The present fluid dynamics videos display this phenomenon and were experimentally investigated at the Wisconsin Shock Tube Laboratory's (WiSTL) 9.2 m, downward firing shock tube. The tube has a square internal cross-section (0.25 m x 0.25 m) with multiple fused silica windows for optical access. The spherical soap bubble is generated by means of a pneumatically retracted injector and released into free-fall 200 ms prior to initial shock acceleration. The downward moving, M = 2.07 shock wave impulsively accelerates the bubble and reflects off the tube end wall. The reflected shock wave re-accelerates the bubble (reshock), which has now developed into a vortex ring, depositing additional vorticity. In the absence of any flow disturbances, the flow behind the reflected shock wave is stationary. As a result, any observed motion of the vortex ring is due to circulation. The shocked vortex ring is imaged at 12,500 fps with planar Mie scattering.Comment: For Gallery of Fluid Motion 200

Gas phase thermometry of hot turbulent jets using laser induced phosphorescence

This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2013 OSAThe temperature distributions of heated turbulent jets of air were determined using two dimensional (planar) laser induced phosphorescence. The jets were heated to specific temperature increments, ranging from 300 – 850 K and several Reynolds numbers were investigated at each temperature. The spectral ratio technique was used in conjunction with thermographic phosphors BAM and YAG:Dy, individually. Single shot and time averaged results are presented as two dimensional stacked images of turbulent jets. YAG:Dy did not produce a high enough signal for single shot measurements. The results allowed for a direct comparison between BAM and YAG:Dy, revealing that BAM is more suitable for relatively lower temperature, fast and turbulent regimes and that YAG:Dy is more suited to relatively higher temperature, steady flow situations

DOE Project: Optimization of Advanced Diesel Engine Combustion Strategies "University Research in Advanced Combustion and Emissions Control" Office of FreedomCAR and Vehicle Technologies Program

The goal of the present technology development was to increase the efficiency of internal combustion engines while minimizing the energy penalty of meeting emissions regulations. This objective was achieved through experimentation and the development of advanced combustion regimes and emission control strategies, coupled with advanced petroleum and non-petroleum fuel formulations. To meet the goals of the project, it was necessary to improve the efficiency of expansion work extraction, and this required optimized combustion phasing and minimized in-cylinder heat transfer losses. To minimize fuel used for diesel particulate filter (DPF) regeneration, soot emissions were also minimized. Because of the complex nature of optimizing production engines for real-world variations in fuels, temperatures and pressures, the project applied high-fidelity computing and high-resolution engine experiments synergistically to create and apply advanced tools (i.e., fast, accurate predictive models) developed for low-emission, fuel-efficient engine designs. The companion experiments were conducted using representative single- and multi-cylinder automotive and truck diesel engines

Turbulent flame boundary and structure detection in an optical DISI engine using tracer-based two-line PLIF technique

This is the Accepted Manuscript version of the following article: M. A. Attar, H. Zhao, M. R. Herfatmanesh, and A. Cairns, “Turbulent flame boundary and structure detection in an optical DISI engine using tracer-based two-line PLIF technique”, Experimental Thermal and Fluid Science, Vol. 68: 545-558, November 2015. The final published version is available at: https://doi.org/10.1016/j.expthermflusci.2015.06.015 © 2015 Elsevier Inc. All rights reserved.Design and development of new combustion system for Spark Ignition Direct Injection (DISI) engines requires thorough understanding of the flame as it develops from electric discharge and propagates across the combustion chamber. The main purpose of this work was to develop an experimental setup capable of investigating premixed and partially-premixed turbulent flame boundary and structure inside combustion chamber of a DISI engine. For this purpose the tracer-based two-line Planar Laser Induced Fluorescence (PLIF) technique was set up. In order to have a thermometry technique independent of photophysical models of dopant tracer, a specially designed Constant Volume Chamber (CVC) was utilized for quasi in situ calibration measurements. The thermometry technique was evaluated by measurements of average in-cylinder charge temperature during compression stroke for both motoring and firing cycles and comparing the results with temperature values calculated from in-cylinder pressure data. The developed technique was successfully employed to detect flame boundary and structure during combustion process in the optical engine. The present study demonstrated that as the two-line PLIF thermal images are independent of species concentration and flame luminosity they can be utilized as accurate means for flame segmentation. The proposed technique has the potential to be utilized for study of turbulent flames in non-homogeneously mixed systems.Peer reviewedFinal Accepted Versio

The competing chemical and physical effects of transient fuel enrichment on heavy knock in an optical spark ignition engine

The work was concerned with improving understanding of the chemical and physical trade-offs when employing transient over-fuelling to control auto-ignition in gasoline spark ignition engines under knock intensities not usually tolerated in optical engines. The single cylinder engine used included full bore overhead optical access capable of withstanding unusually high in-cylinder pressures. Heavy knock was deliberately induced by adopting inlet air heating and a primary reference fuel blend of reduced octane rating. High-speed chemiluminescence imaging and simultaneous in-cylinder pressure data measurement were used to evaluate the combustion events. Under normal operation the engine was operated under port fuel injection with a stoichiometric air-fuel mixture. Multiple centred auto-ignition events were regularly observed, with knock intensities of up to ~30bar. Additional excess fuel was then introduced directly into the end-gas in short transient bursts. As the mass of excess fuel was progressively increased a trade-off was apparent, with knock intensity first increasing by up to 65% before lower unburned gas temperatures suppressed knock under extremely rich conditions. This trade-off is not usually observed during conventional low intensity knock suppression via over-fuelling and has been associated with the competing effects of reducing auto-ignition delay time and charge cooling/ratio of specific heats. Overall, the results demonstrate the risks in employing excess fuel to suppress knock deep within a heavy knocking combustion regime (potentially including a Super-Knock regime)

Investigation of Flame-Front Equivalence Ratio during Stratified Engine Combustion

Stratified engine combustion was investigated using simultaneous imaging of the fuel distribution and flame front in an optically accessible direct-injection spark-ignition engine. Planar laser-induced fluorescence of 3-pentanone doped into iso-octane and the OH radicals naturally occurring in the combustion products were imaged with two intensified CCD cameras. The 3-pentanone images provide a quantitative measure of fuel concentration and the OH images allowed for the position of the flame front to be accurately determined. These results represent the first data taken during stratified combustion using a two-camera technique. Using the image data a novel method was developed to determine the flame-front equivalence ratio during stratified combustion. The results of the method provide insights into the stratified combustion process. Additionally, engine-out NOx and CO measurements are presented and an effort to determine a correlation between the flame-front equivalence ratio and measured emissions is made where the flame-front equivalence ratio is thought to be a major factor in pollutant emission formation during stratified combustion. The effects of engine speed, engine load, spark timing, and ignition timing were investigated. The data indicate that a wide range of equivalence ratios are present along the flame front. The limited field of view was found to significantly influence the data. The flame-front equivalence ratio data taken for conditions with varying injection and varying spark timing at equivalence ratios of ? = 0.32 and ? = 0.42 at 600 rpm showed little correlation with the measured emissions. However, the NOx data did clearly reflect the trends of peak pressure. The available field of view may have been one cause for the lack of correlation, but the pressure trends and emissions data also indicate that combustion phasing has a strong influence on NOx emissions with changes in spark timing of 10 crank angle degrees causing almost a factor of two change in measured engine-out NOx

Targeting Inflammatory T Helper Cells via Retinoic Acid-Related Orphan Receptor Gamma t Is Ineffective to Prevent Allo-Response-Driven Colitis

Intestinal graft-versus-host disease (GvHD) is a life-threatening, inflammatory donor T cell-mediated complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the light of the reported efficacy of interleukin-23 (IL-23)-blockade to mitigate syngeneic intestinal inflammation in inflammatory bowel disease patients, targeting IL-23 and thereby interleukin-17a (IL-17a) producing T helper (Th17) cells as the T cell subset assumed to be mostly regulated by IL-23, has emerged as a putatively general concept to harness immune-mediated mucosal inflammation irrespective of the underlying trigger. However, the role of Th17 cells during allo-response driven colitis remains ambiguous due to a series of studies with inconclusive results. Interestingly, we recently identified granulocyte-macrophage colony-stimulating factor (GM-CSF+) T cells to be promoted by interleukin-7 (IL-7) signaling and controlled by the activating protein-1 transcription factor family member basic leucine zipper transcription factor ATF-like (BATF) as critical mediators of intestinal GvHD in mice. Given the dual role of BATF, the contribution of IL-23-mediated signaling within donor T cells and bona fide Th17 cells remains to be delineated from the regulation of GM-CSF+ T cells in the absence of BATF. Here, we found in a complete MHC class I-mismatched model that genetic inactivation of the IL-23 receptor (IL-23R) or the transcription factor retinoic acid-related orphan receptor gamma t (RORγt) within donor T cells similarly ablated Th17 cell formation in vivo but preserved the T cells’ ability to induce intestinal GvHD in a compared to wild-type controls indistinguishable manner. Importantly, RORγt-independent manifestation of intestinal GvHD was completely dependent on BATF-regulated GM-CSF+ T cells as BATF/RORγt double-deficient T cells failed to induce colitis and the antibody-mediated blockage of IL-7/IL-7R interaction and GM-CSF significantly diminished signs of intestinal GvHD elicited by RORγt-deficient donor T cells. Finally, in analogy to our murine studies, colonic RORC expression levels inversely correlated with the presence of GvHD in allo-HSCT patients. Together, this study provides a crucial example of a BATF-dependent, however, IL-23R signaling- and RORγt-, i.e., Th17 fate-independent regulation of a colitogenic T cell population critically impacting the current understanding of intestinal GvHD