Combustion at the focus: laser diagnostics and control

Fifty years after the foundation of the Combustion Institute and almost 150 years after Michael Faraday’s famous lectures on the combustion of a candle, combustion diagnostics have come a long way from visual inspection of a flame to detailed analysis of a combustion process with a multitude of sophisticated techniques, often using lasers. The extended knowledge on combustion phenomena gained by application of these diagnostic techniques, combined with equally advanced numerical simulation of the process, has been instrumental in designing modern combustion devices with efficient performance and reduced pollutant emission. Also, similar diagnostic techniques are now employed to develop sensors for process control in combustion. This article intends to give a perspective on the potential of combustion diagnostics by highlighting selected application examples and by guiding the reader to recent literature. In particular, techniques are emphasized, which permit measurement of important features of the chemical composition, sometimes in conjunction with flow field parameters. Although a complete image of present research and applications in combustion diagnostics and control is beyond the scope of this article, this overview may be a starting place where ideas may be found to solve specific combustion problems with the aid of diagnostics.     

The application of chemical reduction methods to a combustion system exhibiting complex dynamics

A number of chemical model reduction techniques have been developed over recent years with a growing range of applications in combustion. The following work demonstrates the application of such reduction techniques for a combustion system describing the oxidation of carbon monoxide + hydrogen in a continuously stirred tank reactor (CSTR) at very low pressure. The system exhibits complex dynamics including oscillatory glow, oscillatory ignition and mixed mode oscillations. It is demonstrated that a range of local reduction methods can be applied to such complex systems, as long as sufficient coverage of the accessed regions of phase space are included in the reduction analysis. The methods include sensitivity analysis, the quasi-steady state approximation (QSSA) and repro-modelling based on the concept of an intrinsic low dimensional manifold (ILDM). The system is qualitatively different from some previous applications of ILDM methods where trajectories tend towards a fixed equilibrium. The underlying dimension of the system is seen to vary throughout selected trajectories with rapid increases occurring over very short time-scales during oscillatory ignition. Nevertheless, a final reduced model of only four variables is developed using fitted orthonormal polynomials describing the system dynamics on a slow manifold. The application serves to demonstrate that the relationship between local reduced model error and global errors can be complex for systems exhibiting complex dynamics, with regions of seemingly small local mapping gradients requiring tighter error control in order to control global errors. This feature may be common in cases where nearby trajectories are seen to diverge within the slow manifold over time.     

Quantitative laser-induced fluorescence: Some recent developments in combustion diagnostics

This report summarizes several recent applications of quantitative laser-induced fluorescence techniques for the determination of species concentrations and temperature in combustion processes. Several lines of further development are discussed.     

Modelling compression ignition engines by incorporation of the flamelet generated manifolds combustion closure

Tabulated chemistry models allow to include detailed chemistry effects at low cost in numerical simulations of reactive flows. Characteristics of the reactive fluid flows are described by a reduced set of parameters that are representative of the flame structure at small scales so-called flamelets. For a specific turbulent combustion configuration, flamelet combustion closure, with proper formulation of the flame structure can be applied. In this study, flamelet generated manifolds (FGM) combustion closure with progress variable approach were incorporated with OpenFOAM® source code to model combustion within compression ignition engines. For IC engine applications, multi-dimensional flamelet look-up tables for counter flow diffusive flame configuration were generated. Source terms of non-premixed combustion configuration in flamelet domain were tabulated based on pressure, temperature of unburned mixture, mixture fraction, and progress variable. A new frozen flamelet method was introduced to link one dimensional reaction diffusion space to multi-dimensional Computational Fluid Dynamics (CFD) physical space to fulfill correct modelling of thermal state of the engine at expansion stroke when charge composition was changed after combustion and reaction rates were subsided. Predictability of the developed numerical framework were evaluated for Sandia Spray A (constant volume vessel), Spray B (light duty optical Diesel engine), and a heavy duty Diesel engine experiments under Reynolds averaged Navier Stokes turbulence formulation. Results showed that application of multi-dimensional FGM combustion closure can comprehensively predict key parameters such as: ignition delay, in-cylinder pressure, apparent heat release rate, flame lift-off , and flame structure in Diesel engines.     

Recent advances on amphiphilic polymer-based fluorescence spectroscopic techniques for sensing and imaging

Abstract

Amphiphilic polymers (APs) characterized with excellent water solubility, biodegradability, biocompatibility, and low toxicity have become popular materials for biological sensing and imaging in the recent years. Among the several sensing and imaging techniques, fluorescence-based methods show distinct advantages and present unique opportunities to address challenges afforded by other techniques. This review covers five different types of APs (amphiphilic-conjugated polymers, amphiphilic polysaccharides, amphiphilic molecularly imprinted polymers, amphiphilic block copolymers, and amphiphilic polymeric nanoparticles) and their application for fluorescence spectroscopic sensing and imaging, in particular how techniques have been progressed over recent years. Afterwards, the applications of APs in the diagnosis and treatment of diseases, water safety and environmental monitoring has been discussed.     

THz-Time Domain Spectroscopy system for applications to radical detection

In this paper, we present some preliminary results on a new terahertz-Time Domain Spectroscopy (THz-TDS) experiment. After a general introduction about the interest of the THz range, we particularly discuss some advantages of this technique for combustion applications and compare it with the classical linear and nonlinear optical techniques. The set-up developed in our laboratory is described and some results on NO displayed.     

预热温度影响甲烷高温空气燃烧特性的数值分析

为了深入认识近年发展起来的一种新型燃烧技术－高温空气燃烧的机理和超低氮氧化物排放特性,本文将扩散燃烧模型、热力ＮＯ生成模拟与完全湍流Ｎ－Ｓ方程相结合,数值研究了甲烷高温燃烧的火焰特性、空气预热温度对燃烧特性和ＮＯ排放浓度的影响规律。研究结果与实验数据符合良好,为在我国发展这项技术提供了依据。     

Recent advances in laser-based diagnostics for gaseous flows

Laser-based diagnostic techniques offer unique capabilities for experimentation on gaseous flows. In this paper, we overview recent progress of two concepts: spectrally resolved absorption and planar laser-induced fluorescence (PLIF) imaging. The absorption measurements utilize tunable diode lasers (TDLs) as light sources. Recent TDL applications include a wavelength-multiplexed system for rapid temperature sensing for use in combustion control, and absorption probes for time-resolved measurements of temperature, velocity and species concentrations in a hypersonic shock tunnel. Recent PLIF work includes applications to supersonic, exothermic flowfields relevant to ram accelerators, and development of a method for imaging temperature in air flows using acetone seeding.     

Application of X-ray fluorescence spectrometry in plant science: Solutions,threats, and opportunities

X-ray fluorescence (XRF) spectrometry is a nondestructive, rapid, simultaneous multi-elemental imaging methodology for plant materials. Its applications are broad and cover most of the elements with varying concentration below the parts per million (ppm). XRF is a well-established atomic spectrometric technique that is also being used as a field portable instrumentation. In recent decades, XRF has been considered a very versatile tool for plant nutrition diagnosis due to its fast and multi-elemental analytical imaging response directly from a solid sample. In this review, we have mainly focused on the recent developments and advancements in XRF spectrometry to analyze plant materials. We have also included the fundamental aspects and instrumentation for XRF spectrometry for its use in plants imaging. We have also covered the use of XRF for vegetal tissues and plant leaves. Mainly, we have briefly focused on some features of sampling procedures and calibration strategies regarding the use of XRF for plant tissues. Microchemical imaging applications by XRF, μ-XRF, μ-SRXRF, and TXRF have been covered for a wide variety of plant tissues such as leaves, roots, stems, and seeds.     

E. 高速全息摄影和激光干涉测量的进展

本文对高速全息摄影和激光干涉测量术的最新发展作了详细评述。