1,019 research outputs found
Visualization and imaging methods for flames in microgravity
The visualization and imaging of flames has long been acknowledged as the starting point for learning about and understanding combustion phenomena. It provides an essential overall picture of the time and length scales of processes and guides the application of other diagnostics. It is perhaps even more important in microgravity combustion studies, where it is often the only non-intrusive diagnostic measurement easily implemented. Imaging also aids in the interpretation of single-point measurements, such as temperature, provided by thermocouples, and velocity, by hot-wire anemometers. This paper outlines the efforts of the Microgravity Combustion Diagnostics staff at NASA Lewis Research Center in the area of visualization and imaging of flames, concentrating on methods applicable for reduced-gravity experimentation. Several techniques are under development: intensified array camera imaging, and two-dimensional temperature and species concentrations measurements. A brief summary of results in these areas is presented and future plans mentioned
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
Quantitative Assessment of Flame Stability Through Image Processing and Spectral Analysis
This paper experimentally investigates two generalized methods, i.e., a simple universal index and oscillation frequency, for the quantitative assessment of flame stability at fossil-fuel-fired furnaces. The index is proposed to assess the stability of flame in terms of its color, geometry, and luminance. It is designed by combining up to seven characteristic parameters extracted from flame images. The oscillation frequency is derived from the spectral analysis of flame radiation signals. The measurements involved in these two methods do not require prior knowledge about fuel property, burner type, and other operation conditions. They can therefore be easily applied to flame stability assessment without costly and complex adaption. Experiments were carried out on a 9-MW heavy-oil-fired combustion test rig over a wide range of combustion conditions including variations in swirl vane position of the tertiary air, swirl vane position of the secondary air, and the ratio of the primary air to the total air. The impact of these burner parameters on the stability of heavy oil flames is investigated by using the index and oscillation frequency proposed. The experimental results obtained demonstrate the effectiveness of the methods and the importance of maintaining a stable flame for reduced NOx emissions. It is envisaged that such methods can be easily transferred to existing flame closed-circuit television systems and flame failure detectors in power stations for flame stability monitoring
Measurements in a turbulent counterflow flame
Imperial Users onl
Microgravity combustion science: Progress, plans, and opportunities
An earlier overview is updated which introduced the promise of microgravity combustion research and provided a brief survey of results and then current research participants, the available set of reduced gravity facilities, and plans for experimental capabilities in the space station era. Since that time, several research studies have been completed in drop towers and aircraft, and the first space based combustion experiments since Skylab have been conducted on the Shuttle. The microgravity environment enables a new range of experiments to be performed since buoyancy induced flows are nearly eliminated, normally obscured forces and flows may be isolated, gravitational settling or sedimentation is nearly eliminated, and larger time or length scales in experiments are feasible. In addition to new examinations of classical problems, (e.g., droplet burning), current areas of interest include soot formation and weak turbulence, as influenced by gravity
Microgravity Combustion Diagnostics Workshop
Through the Microgravity Science and Applications Division (MSAD) of the Office of Space Science and Applications (OSSA) at NASA Headquarters, a program entitled, Advanced Technology Development (ATD) was promulgated with the objective of providing advanced technologies that will enable the development of future microgravity science and applications experimental flight hardware. Among the ATD projects one, Microgravity Combustion Diagnostics (MCD), has the objective of developing advanced diagnostic techniques and technologies to provide nonperturbing measurements of combustion characteristics and parameters that will enhance the scientific integrity and quality of microgravity combustion experiments. As part of the approach to this project, a workshop was held on July 28 and 29, 1987, at the NASA Lewis Research Center. A small group of laser combustion diagnosticians met with a group of microgravity combustion experimenters to discuss the science requirements, the state-of-the-art of laser diagnostic technology, and plan the direction for near-, intermediate-, and long-term programs. This publication describes the proceedings of that workshop
Simultaneous measurement of flame temperature and absorption coefficient through LMBC-NNLS and plenoptic imaging techniques
It is important to identify boundary constraints in the inverse algorithm for the reconstruction of flame temperature because a negative temperature can be reconstructed with improper boundary constraints. In this study, a hybrid algorithm, a combination of Levenberg-Marquardt with boundary constraint (LMBC) and non-negative least squares (NNLS), was proposed to reconstruct the flame temperature and absorption coefficient simultaneously by sampling the multi-wavelength flame radiation with a colored plenoptic camera. To validate the proposed algorithm, numerical simulations were carried out for both the symmetric and asymmetric distributions of the flame temperature and absorption coefficient. The plenoptic flame images were modeled to investigate the characteristics of flame radiation sampling. Different Gaussian noises were added into the radiation samplings to investigate the noise effects on the reconstruction accuracy. Simulation results showed that the relative errors of the reconstructed temperature and absorption coefficient are less than 10, indicating that accurate and reliable reconstruction can be obtained by the proposed algorithm. The algorithm was further verified by experimental studies, where the reconstructed results were compared with the thermocouple measurements. The simulation and experimental results demonstrated that the proposed algorithm is effective for the simultaneous reconstruction of the flame temperature and absorption coefficient
Flame front propagation velocity measurement and in-cylinder combustion reconstruction using POET
The objective of this thesis is to develop an intelligent diagnostic technique
POET (Passive Optical Emission Tomography) for the investigation of in cylinder
combustion chemiluminescence. As a non-intrusive optical system, the POET system
employs 40 fibre optic cables connected to 40 PMTs (Photo Multiplier Tube) to
monitor the combustion process and flame front propagation in a modified commercial
OHV (Over Head Valve) Pro 206 IC engine.
The POET approach overcomes several limitations of present combustion
research methods using a combination of fibre optic detection probes, photomultipliers
and a tomographic diagnostics. The fibre optic probes are placed on a specially
designed cylinder head gasket for non-invasively inserting cylinder. Each independent
probe can measure the turbulent chemiluminescence of combustion flame front at up to
20 kHz. The resultant intensities can then be gathered tomographically using MART
(Multiplicative Algebraic Reconstruction Technique) software to reconstruct an image
of the complete flame-front. The approach is essentially a lensless imaging technique,
which has the advantage of not requiring a specialized engine construction with
conventional viewing ports to visualize the combustion image. The fibre optic system,
through the use of 40, 2m long thermally isolated fibre optic cables can withstand
combustion temperatures and is immune from electronic noise, typically generated by
the spark plug.
The POET system uses a MART tomographic methodology to reconstruct the turbulent combustion process. The data collected has been reconstructed to produce a
temporal and spatial image of the combustion flame front. The variations of lame
turbulence are monitored by sequences of reconstructed images. Therefore, the POET
diagnostic technique reduces the complications of classic flame front propagation
measurement systems and successfully demonstrates the in-cylinder combustion
process.
In this thesis, a series of calibration exercises have been performed to ensure
that the photomultipliers of the POET system have sufficient temporal and spatial
resolution to quantitatively map the flow velocity turbulence and chemiluminescence
of the flame front. In the results, the flame has been analyzed using UV filters and blue
filters to monitor the modified natural gas fuel engine. The flame front propagation
speed has been evaluated and it is, on average, 12 m/s at 2280 rpm. Sequences of
images have been used to illustrate the combustion explosion process at different rpm
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