The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Alfred Leipertz - One of the best experts on this subject based on the ideXlab platform.
-
Improvement of planar Laser Diagnostics by the application of a beam homogenizer
Journal of Physics: Conference Series, 2007Co-Authors: Sebastian Pfadler, M. Löffler, Frank Beyrau, Alfred LeipertzAbstract:For planar Laser Diagnostics, a most uniform beam profile is highly desirable for two reasons: first, subsequent corrections for an inhomogeneous intensity distribution are time consuming and prevent on-line engineering assessment and second, temporal fluctuations cannot be corrected anyway. However, in general for combustion and flow Diagnostics pulsed Laser sources are used to achieve a high temporal resolution which typically possess a rather poor beam quality compared to continuously emitting Laser sources. And, pulse to pulse fluctuations of the beam profile directly increase the noise in single-shot measurements. In this contribution we show the application of a micro-lens array based beam homogenizer whereby an almost homogeneous illumination of the region of in interest is achieved. This enables the on-line evaluation of the measured data without subsequent corrections. Thus a general advance of Laser techniques towards engineering practice is achieved. Additionally, statistical fluctuations of the beam profile are strongly reduced by the homogenizer what directly improves the local standard deviation of the measurement. These benefits are demonstrated by means of planar Laser-induced fluorescence (LIF) experiments.
-
application of a beam homogenizer to planar Laser Diagnostics
Optics Express, 2006Co-Authors: Sebastian Pfadler, M. Löffler, Frank Beyrau, Alfred LeipertzAbstract:The first application of a microlens array beam homogenizer to planar Laser measurement techniques in combustion Diagnostics is demonstrated. The beam homogenizing properties of two microlens arrays in combination with a Fourier lens for widespread applications are presented. An uniform line profile with very little temporal fluctuations of the spatial intensity distribution was generated resulting in a significant reduction of measurement noise and enabling an easier and faster signal processing.
Benjamin Böhm - One of the best experts on this subject based on the ideXlab platform.
-
Quasi-4D Laser Diagnostics using an acousto-optic deflector scanning system
Applied Physics B, 2017Co-Authors: Tao Li, Jhon Pareja, Lukas G. Becker, Wolfgang Heddrich, Andreas Dreizler, Benjamin BöhmAbstract:In this paper, a novel scanning system for Laser Diagnostics was developed and characterized. The system is based on the acousto-optic deflection of a high-speed pulsed Laser. Results showed that quasi-volumetric Laser illumination with high precision and accuracy can be achieved with a simplified and flexible optical setup. The feasibility of the method for performing high-speed quasi-4D Laser Diagnostics was demonstrated by the tomographic visualization of a lifted turbulent jet flame using Mie-scattering and multi-plane particle image velocimetry measurements of a turbulent non-reactive mixing case. Three-dimensional flame and flow structures can be detected and tracked with this new scanning system.
-
advanced Laser Diagnostics for an improved understanding of premixed flame wall interactions
Proceedings of the Combustion Institute, 2015Co-Authors: A Dreizler, Benjamin BöhmAbstract:Abstract This review discusses the role of Laser Diagnostics in combustion science and technology. In its first part, it may guide understanding of advanced diagnostic methods, and is particularly helpful for non-specialized experimentalists. Various challenges for future developments and applications of optical combustion Diagnostics are highlighted. In the second part of this review, flame-wall interactions are selected for a more in-depth discussion. Flame-wall interactions are scientifically interesting and are of great importance to any enclosed practical combustion process. Following a description of current understanding, the focus is on using optical Diagnostics to probe thermal, fluidic, and chemical properties of head-on and sidewall quenching. The review ends with a discussion of issues and implications for future experimental research and specific diagnostic needs.
-
New Perspectives on Turbulent Combustion: Multi-Parameter High-Speed Planar Laser Diagnostics
Flow Turbulence and Combustion, 2011Co-Authors: Benjamin Böhm, Christof Heeger, Robert L. Gordon, Andreas DreizlerAbstract:Over the past three decades Laser combustion Diagnostics have guided an improved understanding of turbulent combustion processes. Until recently, this was based on statistically independent sampling using sampling rates much slower than typical integral time-scales of turbulent flames. Recent developments in Laser and camera technology enabled an increase in sampling rates by more than three orders of magnitudes. Using these new instruments for particle image velocimetry (PIV) and planar Laser-induced fluorescence (PLIF) at high sampling rates (high-speed Diagnostics) allowed the resolution of integral time-scales of turbulent flames. This statistically dependent sampling is increasingly used to temporally track transients in turbulent combustion, such as flame extinction, ignition, flashback and cycle-to-cycle variations in IC engines. The simultaneous application of flow and scalar field measurements makes insights into these transients possible that were not when using statistically independent sampling with low data acquisition rates. Conditioning on distinct flame features with high-speed Diagnostics enables the inclusion of time as an additional dimension. This paper reviews the emerging field of multi-parameter, high-speed, planar Laser Diagnostics in combustion applications. The benefit of high data acquisition rates in turbulent combustion applications is discussed in detail as well as requirements and constraints imposed by the time-scales of the investigated phenomenon are addressed. Recent developments in Laser and detector hardware are highlighted, as these are the limiting factors of the sampling rate. Finally, multi-parameter high-speed measurements in combustion are summarized, with a few examples discussed in more detail.
-
PLANAR Laser Diagnostics AT HIGH REPETITION RATES: ACQUISITION AND ANALYSIS OF TRANSIENT COMBUSTION PROCESSES
Volume 3: Combustion Fuels and Emissions Parts A and B, 2008Co-Authors: Christof Heeger, Benjamin Böhm, Isaac Boxx, Wolfgang Meier, Samer F. Ahmed, Epaminondas Mastorakos, Andreas DreizlerAbstract:This contribution highlights recent advances in Laser Diagnostics at high repetition rates. Based on recent improvements in all-solid-state, diode-pumped Laser and CMOS camera technology, well known methods such as Mie scattering, particle image velocimetry and planar Laser-induced fluorescence are adapted and extended to high repetition rates in the kHz-regime and ap
Walter R Lempert - One of the best experts on this subject based on the ideXlab platform.
-
review of ultra high repetition rate Laser Diagnostics for fluid dynamic measurements
Measurement Science and Technology, 2013Co-Authors: Brian S Thurow, Naibo Jiang, Walter R LempertAbstract:Recent advances in ultra-high repetition rate (100?kHz and above) Laser Diagnostics for fluid dynamic measurements are reviewed. The development of the pulse burst Laser system, which enabled several of these advances, is described. The pulse burst Laser system produces high repetition rate output by slicing the output of a low power continuous wave Laser and passing the resulting burst of pulses through a series of pulsed Nd:YAG amplifiers. Several systems have been built with output approaching 1.0 J/pulse over bursts of up to 100 pulses generated at between 50 and 1000?kHz. Combined with the capabilities of several types of commercially available high-speed cameras, these systems have been used to make a wide variety of high repetition rate and 3D flow measurements. Several examples of various high repetition rate Laser Diagnostics are described, including flow visualization, filtered Rayleigh scattering, planar Doppler velocimetry, particle image velocimetry, planar Laser induced fluorescence, molecular tagging velocimetry and 3D flow visualization.
Sebastian Pfadler - One of the best experts on this subject based on the ideXlab platform.
-
Improvement of planar Laser Diagnostics by the application of a beam homogenizer
Journal of Physics: Conference Series, 2007Co-Authors: Sebastian Pfadler, M. Löffler, Frank Beyrau, Alfred LeipertzAbstract:For planar Laser Diagnostics, a most uniform beam profile is highly desirable for two reasons: first, subsequent corrections for an inhomogeneous intensity distribution are time consuming and prevent on-line engineering assessment and second, temporal fluctuations cannot be corrected anyway. However, in general for combustion and flow Diagnostics pulsed Laser sources are used to achieve a high temporal resolution which typically possess a rather poor beam quality compared to continuously emitting Laser sources. And, pulse to pulse fluctuations of the beam profile directly increase the noise in single-shot measurements. In this contribution we show the application of a micro-lens array based beam homogenizer whereby an almost homogeneous illumination of the region of in interest is achieved. This enables the on-line evaluation of the measured data without subsequent corrections. Thus a general advance of Laser techniques towards engineering practice is achieved. Additionally, statistical fluctuations of the beam profile are strongly reduced by the homogenizer what directly improves the local standard deviation of the measurement. These benefits are demonstrated by means of planar Laser-induced fluorescence (LIF) experiments.
-
application of a beam homogenizer to planar Laser Diagnostics
Optics Express, 2006Co-Authors: Sebastian Pfadler, M. Löffler, Frank Beyrau, Alfred LeipertzAbstract:The first application of a microlens array beam homogenizer to planar Laser measurement techniques in combustion Diagnostics is demonstrated. The beam homogenizing properties of two microlens arrays in combination with a Fourier lens for widespread applications are presented. An uniform line profile with very little temporal fluctuations of the spatial intensity distribution was generated resulting in a significant reduction of measurement noise and enabling an easier and faster signal processing.
N. Vogel - One of the best experts on this subject based on the ideXlab platform.
-
SUBNANOSECOND RESONANCE Laser Diagnostics OF THE DISCHARGE CATHODE SPOT REGION OF LOW-CURRENT VACUUM
2020Co-Authors: S. Popov, N. Vogel, B. JiittnerAbstract:In this paper, the supplying of neutral atoms of the cathode material into the discharge gap at lowcurrent microsecond vacuum arc with liquid Ga cathode was investigated employing the method of subnanosecond resonance Laser Diagnostics. It has been shown that vapours ejection has a essentially non-stationary character and it occurs both isotropically and in the form of contracted lowionized lasma jets with atomic concentration of more than 10 ’ cm ’.
-
Subnanosecond resonance Laser Diagnostics of the cathode spot region of low-current vacuum discharge
20th International Symposium on Discharges and Electrical Insulation in Vacuum, 2002Co-Authors: S. Popov, N. Vogel, B. JuttnerAbstract:In this paper, the supplying of neutral atoms of the cathode material into the discharge gap at low-current microsecond vacuum arc with liquid Ga cathode was investigated employing the method of subnanosecond resonance Laser Diagnostics. It has been shown that vapours ejection has an essentially nonstationary character and it occurs both isotropically and in the form of contracted low-ionized plasma jets with atomic concentration of more than 10/sup 17/ cm/sup -3/.
-
Measurement of cathode spot parameters with pulsed Laser Diagnostics
IEEE Transactions on Plasma Science, 1995Co-Authors: N. Vogel, J. Heinzinger, F. CichosAbstract:The cathode spot formation in air within the first 170 ns was investigated by Laser absorption photography and ps-pulse interferometry. The discharge was initiated between electrodes made from Ag or Pd with cathode-anode distance below 300 /spl mu/m, the arc duration was some milliseconds, and the arc current 5-10 A. Picosecond holographic interferometry and momentary absorption photography yielded spatial-temporal density distributions in the ignition phase of the cathode spot. An absolute electron density value on the order of 4/spl times/10/sup 26/ m/sup -3/ has been found. In contrast to vacuum, the cathode spot plasmas broaden little with increasing distance from the cathode, thus narrow plasma channels are observed in the vicinity of the cathode surface having diameters
