Visualization and understanding of combustion processes using spatially and temporally resolved laser diagnostic techniques

doi:10.1016/j.proci.2010.09.004

Proceedings of the Combustion Institute

Volume 33, Issue 1, 2011, Pages 69-97

https://doi.org/10.1016/j.proci.2010.09.004 Get rights and content

Abstract

Laser diagnostic techniques have for more than 30 years added very valuable input for a deepened understanding of combustion processes. The present paper will focus on techniques developed for visualization of important parameters with the ability to get detailed information in space and time. The paper is not meant to be a complete review of the entire research field but rather a survey with a majority of the contributions from the authors’ laboratory. After a short introduction and background, essentially three techniques will be highlighted. Planar Laser-Induced Fluorescence, PLIF, will be described in terms of further development directed towards the use of a high-power Alexandrite laser, in some cases yielding a substantially increased sensitivity as compared to the more conventional Nd:YAG and Excimer lasers. There will also be a description of possibilities for high-speed visualization, 3D imaging and the potential to visualize species requiring a two-photon excitation process. Regarding thermometry, the paper will describe and exemplify the use of Thermographic Phosphors, mainly for surface measurements but also in droplets and gas flows. The third area to be described is the use of Polarization Spectroscopy, PS, for spatially and temporally resolved measurements in the IR spectral region, e.g. CO₂ and H₂O, various hydrocarbons, HCl and HCN. The last chapter focuses on present challenges and future applications. A major challenge is diagnostics in environments with limited optical access. Two methods that are applicable under such conditions are discussed, namely endoscopic approaches and picosecond LIDAR. Another challenging area addressed is application of diagnostics in optically dense environments, e.g. sprays, where a new technique, Structured Laser Illumination Planar Imaging, SLIPI, has been developed for suppressing the influence of multiple scattering. Finally, approaches for measurements of “new” species, challenges associated with LIF quantification, as well as measurements in environments possessing strong background radiation are discussed.

Section snippets

Introduction and background

Despite its impressive age, combustion is still of crucial importance in many pivotal human activities, e.g. heating, transportation and waste handling, and it will remain so for years to come. The economies of many countries rely strongly on combustion for propulsion and power generation in industries producing cars, trucks and related products. Research, which will allow improvements in the efficiency and cleanliness of engines, gas turbines, furnaces, to optimize chemical processes, decrease

Further developments and applications of Planar Laser-Induced Fluorescence, PLIF

Laser-induced fluorescence, LIF, is a widely used optical measurement technique in combustion diagnostics with the strength of imaging capacity, high sensitivity, high spatial resolution, species specificity and applicability in harsh environments.

LIF is based on laser excitation of atoms or molecules from a lower energy state, most often the ground state, to a higher excited state. Upon relaxation back to the lower state the atom/molecule re-emits radiation. This radiation can be analyzed and

Thermographic phosphors

Temperature is one of the most frequently required parameters for measurements in a wide variety of combustion applications. Besides measurements of gas temperatures, there is also a high demand for accurate measurements of surface temperatures since this information may lead to extended and optimized material durability and understanding of heat transfer phenomena which are of crucial importance for various combustion apparatus, e.g. IC engines, gas turbines and furnaces.

Traditional techniques

Coherent techniques – Infrared Polarization Spectroscopy, IRPS

One of the first coherent nonlinear laser techniques to be used for combustion diagnostics was CARS, with applications in engines already in the late seventies [75]. Despite the attractive diagnostic feature of this technique, in that the signal is generated as a new laser beam, in contrast to the 4π sr. emission of LIF, this technique suffers from a relatively low sensitivity and experiments are mainly restricted to point measurements of major species. Thus, there has been a desire to combine

Challenges and future applications

As indicated above the development of laser techniques for combustion diagnostics has been of utmost importance for a deepened understanding of phenomena involved in combustion and thus for an optimum practical application. Still, there are several challenges where new ideas/approaches are needed. In this section some of these challenges and potential approaches to address them are outlined.

Concluding remarks

In terms of understanding combustion phenomena, it is clear that besides the introduction and use of fast computers for simulations, the application of various laser diagnostic techniques have been the most important development during the last few decades. The techniques and their application, divided here into three categories, are all very important. For example in order to use the techniques for a deepened understanding of IC engine combustion, it is of crucial importance that proper

Acknowledgments

The authors acknowledge all persons participating to the work presented. Especially the present and past members of the Division of Combustion Physics. Also the very fruitful and close collaboration with the members of the Depts of Energy Sciences and Fire and Safety Engineering within Lund University are greatly acknowledged. This work has also massively benefited from a close collaboration with various international groups, e.g. from Univ. Duisburg, Univ. of Darmstadt, Univ. of Erlangen,

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Laser diagnostics in combustion and beyond dedicated to Prof. Marcus Aldén on his 70<sup>th</sup> birthday
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Laser diagnostics has been one of the most powerful tools in advancing state-of-the-art combustion research over the last five decades. Prof. Marcus Aldén, one of the most well-known pioneers in this field, has contributed many influential original publications over more than 40 years of his research career. In this paper, we will review some selected contributions, with emphasis on optical techniques developed and applied by Marcus and the group in Lund under his leadership, which are expected to play important roles in facing the challenge of the transition to a carbon-neutral energy system.
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