Next generation of guiding questions for basic turbulent combustion research

A two-day workshop was held to identify and compile research questions and needs to advance basic turbulent combustion research towards capabilities that allow predictive simulations at the design level for practical devices. Recognizing the state-of-the-art simulation capabilities and inherent limitations with computational resources the focus is on Large Eddy Simulations as a pathway to this goal. This report documents not only scientific and technical questions related to shortcomings in our current understanding of turbulent combustion, but also addresses procedural challenges. Key bottlenecks and research needs are addressed and described but the report also emphasizes that the conduct of research has to adapt to the complex nature of turbulent combustion by fostering collaborations and long-term funding horizons.This material is based upon work supported by the National Science Foundation under Grant Number 1438956. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundationhttp://deepblue.lib.umich.edu/bitstream/2027.42/108583/1/Next gen combustion research-report-20140729.pdfDescription of Next gen combustion research-report-20140729.pdf : Workshop repor

Laser-Induced-Fluorescence Detection of Nitric Oxide in High-Pressure Flames with A-X(0, 2) Excitation

Laser-induced fluorescence techniques have been used successfully for quantitative two-dimensional measurements of nitric oxide. The commonly applied D–X(0, 1) or A–X(0, 0) schemes are restricted to atmospheric-pressure flames and engines driven with gaseous fuels because of strong attenuation of the exciting laser beam by combustion intermediates. The properties of a detection scheme for which excitation in the nitric oxide A–X(0, 2) band was used were investigated. We discuss the advantages of the A–X(0, 2) system (excited at 247.95 nm) based on measurements in laminar premixed methane/air flames at 1–40 bars.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86764/1/Sick41.pd

Laser Applications to Chemical and Environmental Analysis: Introduction to the Feature Issue

This issue of Applied Optics features 16 papers describing chemical and environmental measurements made possible by lasers. Many of these contributions were presented at the Optical Society of America Topical Meeting on Laser Applications to Chemical and Environmental Analysis, held in Orlando, Florida, 9–11 March 1998.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86759/1/Sick33.pd

Infrared Borescopic Evaluation of High-Energy and Long-Duration Ignition Systems for Lean/Dilute Combustion in Heavy-Duty Natural-Gas Engines

Natural gas (NG) is attractive for heavy-duty (HD) engines for reasons of cost stability, emissions, and fuel security. NG cannot be reliably compression-ignited, but conventional gasoline ignition systems are not optimized for NG and are challenged to ignite mixtures that are lean or diluted with exhaust-gas recirculation (EGR). NG ignition is particularly challenging in large-bore engines, where completing combustion in the available time is more difficult. Using two high-speed infrared (IR) cameras with borescopic access to one cylinder of an HD NG engine, the effect of ignition system on the early flame-kernel development and cycle-to-cycle variability (CCV) was investigated. Imaging in the IR yielded strong signals from water emission lines, which located the flame front and burned-gas regions and obviated image intensifiers. A 9.7-liter, six-cylinder engine was modified to enable exhaust-gas recirculation and to provide optical access. Three ignition technologies were studied: a conventional system delivering 65 mJ of energy to each spark, a high-energy conventional system delivering 140 mJ, and a Bosch Controlled Electronic Ignition (CEI) system. CEI uses electronics to extend the ignition event, yielding sparks up to 5 ms in duration with up to 300 mJ of energy. Air/fuel equivalence ratios, λ, as high as 1.6 (with minimum EGR) and EGR fractions as high as 23% (stoichiometric) were tested; ignition delay, engine-out emissions, fuel consumption and image-derived parameters were compared. In most lean or dilute cases, the 140-mJ system yielded the lowest CCV. The imagery provided information about the early stages of ignition and combustion, where pressure measurements are not reliable. Image-based metrics also revealed that early flame kernels located further from the head yielded better combustion, showing that borescopic IR imaging can provide guidance for future engine design.The information, data, or work presented herein was funded in part by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Number DE-EE0007307. We also thank Dr. Hao Chen and Angela Wu for their help with software and James Elkins for engine-head modifications.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143838/1/2018-01-1149.pd

Influence of Early and Late Fuel Injection on Air Flow Structure and Kinetic Energy in an Optical SIDI Engine

The turbulent in-cylinder air flow and the unsteady high-pressure fuel injection lead to a highly transient air fuel mixing process in spark-ignition direct-injection (SIDI) engines, which is the leading cause for combustion cycle-to-cycle variation (CCV) and requires further investigation. In this study, crank-angle resolution particle image velocimetry (PIV) was employed to simultaneously measure the air flow and fuel spray structure at 1300 rpm in an optically accessible single-cylinder SIDI engine. The measurement was conducted at the center tumble plane of the four-valve pent-roof engine, bisecting the spark plug and fuel injector. 84 consecutive cycles were recorded for three engine conditions, i.e. (1) none-fueled motored condition, (2) homogeneous-charge mode with start of injection (SOI) during intake (50 crank-angle degree (CAD) after top dead center exhaust, aTDCexh), and (3) stratified-charge mode with SOI during mid compression (270 aTDCexh). The air flow structure (quantified by the objective metric – relevance index) and kinetic energy were examined to study the effect of the fuel spray on the air flow. The air flow was nearly identical for three conditions before the fuel injection. During fuel injection, the entrainment of air into the spray was observed near the spray but the flow structure further away from the spray was not significantly affected for both homogeneous and stratified charge modes. Right after the fuel was atomized, the spray increased the kinetic energy of air flow by 48±25% and 45±40% (average ± standard variation, with CCV included in standard deviation) for spray at intake and compression stroke, respectively. Spray changed the flow structure and kinetic energy immediately after injection for both conditions. The changes caused by injection during intake did not affect the flow and CCV at spark timing. For injection during mid compression, both the flow-structure and kinetic-energy CCV were apparently affected at spark timing.This work is supported by the Engine Systems Division of the General Motors – University of Michigan Automotive Collaborative Research Laboratory.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142812/1/2018-01-0205.pd

Volume-resolved gas velocity and spray measurements in engine applications

The ability to visualize in-cylinder phenomena in a three-dimensional (3D) manner is critical to further understand the complex physical and chemical processes within internal-combustion (IC) engines. Recently, plenoptic imaging techniques have been introduced to engine studies because they enable 3D measurements using a promising and simple single-camera setup. The fundamental concept is to record both the origin and direction of each light ray into a single light-field image by inserting a micro-lens array in front of the photosensor. Therefore, a single image contains enough information to reconstruct the 3D volume. In this study, we present the implementation of a plenoptic technique that allows 3D measurements of fuel-spray structure, as well as three-dimensional, three-component (3D3C) particle tracking velocimetry (PTV) of engine in-cylinder air flow. Flow-spray interactions and the impact on the 3D geometry of fuel sprays were investigated with single-shot plenoptic imaging. Volume-illuminated fuel sprays from a multi-hole injector were examined in an optically accessible four-valve gasoline direct-injection engine. The impact of air flows during the intake and compression strokes on the shape of the fuel plumes could readily be observed for individual sprays without averaging. The air flow was measured in a free jet flow and a steady-state engine flow bench employing a 3D3C PTV algorithm that analyzed volume-resolved images taken with a plenoptic camera. Silicone seed oil droplets were added to the air flows and were illuminated by the volume-expanded beam of a double-pulsed laser. Mie scattering from the droplets was recorded by the plenoptic camera, which was operated in double-frame mode. Results from the 3D3C PTV measurements were compared to two-dimensional (2D) planar particle-image velocimetry (PIV) and demonstrate the capability of the 3D velocimetry approach, presently delivering averaged flow fields.This material is based upon work supported by the National Science Foundation under Grant No. CBET 1402707.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139882/1/Chen_Sick_AVL2016.pd

Single-shot imaging of OH radicals and simultaneous OH radical/acetone imaging with a tunable Nd : YAG laser

Single shot imaging capability for OH radical distributions in various atmospheric pressure methane flames upon excitation with a tunable frequency-quadrupled Nd : YAG laser is demonstrated. The laser wavelength can be tuned with an intra-cavity etalon to produce laser-induced fluorescence (LIF) signals from OH via absorption in the OH A–X (2,0) P 1 (10) line. Simultaneous single-shot imaging of the burnt and unburnt zones in laminar nonpremixed, premixed and turbulent flames is presented. The unburnt areas are visualized with LIF of acetone that is seeded to the methane fuel. Acetone levels are set to match signal intensities to that of the OH signals to allow imaging on a single intensified CCD camera.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47048/1/340_2004_Article_1545.pd

Detection of Methyl Radicals in a Flat Flame by Degenerate Four-Wave Mixing

We report the spatially resolved detection of methyl radicals in a methane–air f lat flame, using degenerate four-wave mixing (DFWM). A frequency-tripled dye laser pumped with a frequency-doubled Nd:YAG laser was used to access the Herzberg b1 band of methyl near 216 nm. Using a nearly phase-conjugate geometry, we detected methyl with high spatial resolution [0.2 mm (0.3 mm) vertical (horizontal) and ,6 mm longitudinal] and with good signal-to-noise ratio in a rich sf _ 1.55d flame. Compared with laser absorption spectra, DFWM spectra were much less influenced by a broad featureless background. From the absorption data, we measured the peak methyl concentration to be 650 parts in 106, resulting in an estimated DFWM detection limit of 65 parts in 106.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86762/1/Sick48.pd

Fluorescence imaging for the anterior segment of the eye

Diagnostic technologies for the anterior segment of the eye, especially for hard-to-diagnose diseases such as microbial keratitis, are still lacking. Although in vivo confocal microscopy and optical coherence tomography are becoming more widely applicable to a variety of conditions, they are often prohibitively expensive, require specialized training and equipment, and are intrinsically insensitive to chemical changes. Here, ultraviolet-fluorescence imaging is proposed as a new technique to aid in investigation of the anterior segment. In this work, a novel two-color line-of-sight fluorescence imaging technique is described for imaging of the anterior segment. The technique is applied to seven ex vivo porcine eyes to illustrate the utility of the technique. The image data was used to estimate an effective fluorescence quantum yield of each eye at 370 nm. The eyes were then inoculated with bacteria to simulate microbial keratitis, a common sight-threatening infection, and the measurement was repeated. A simplified fluorescence-extinction model was developed to describe and analyze the relative intensities of the eye and biofilm fluorescence. Overall, the technique appears to have utility in clinical practice and with proper development may be suitable for detecting chemical changes in the eye, or the presence of foreign matter; however, further investigation is needed to develop the technique and analysis procedures into a quantitative diagnostic tool