Heat release rate markers for premixed combustion
TL;DR: In this paper, the validity of the commonly used flame marker for heat release rate (HRR) visualization, namely the rate of the reaction OH+CH 2 O⇔ HCO+H 2 O is re-examined.
About: This article is published in Combustion and Flame.The article was published on 2014-12-01 and is currently open access. It has received 75 citations till now. The article focuses on the topics: Combustion.
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TL;DR: In this paper, the effect of hydrogen addition on the combustion characteristics of natural gas was investigated with a ChemkinⅡ/premix code with the detailed chemical reaction mechanisms with the Soret effect taken into account in all the calculations.
Abstract: With the increasing use of natural gas, improving the thermal efficiency and reducing emissions has become the major goals in its combustion. The objective of the present work is to investigate the effect of hydrogen addition on the combustion characteristics of natural gas. A ChemkinⅡ/Premix Code with the detailed chemical reaction mechanisms was employed with the Soret effect taken into account in all the calculations. With the mole fraction of hydrogen in the fuel varied from 0 to 40% at different initial temperatures (298–500 K) and pressures (1–8 atm), the results showed that the laminar burning velocities (LBVs) and the adiabatic flame temperatures of the C1 C4 four alkanes increased with increasing hydrogen-doping ratio. The LBV and the adiabatic flame temperature of methane displayed the maximum increase with the hydrogen-doping ratio. Additionally, the generation of active radicals H, O, and OH during the combustion process was strongly correlated with the LBV. The sensitivity of the flame temperature in four alkane fuels present in the natural gas at the maximum temperature gradient was analyzed. At a constant hydrogen-doping ratio, the LBV and the adiabatic flame temperature increased significantly with the increasing initial temperature. With increasing the pressure, the LBV gradually decreased while the adiabatic flame temperature increased.
81 citations
01 Jan 2017
TL;DR: In this article, a 3D direct numerical simulation (DNS) of an experimental turbulent premixed jet flame at high Karlovitz number was studied, and the results were comparable with other values reported for various experimental flames.
Abstract: A three-dimensional (3D) direct numerical simulation (DNS) of an experimental turbulent premixed jet flame at high Karlovitz number was studied. The DNS resolution adequately resolves both the flame and turbulence structures. A reduced chemical mechanism for premixed CH4/air flames with NOx based on GRI-Mech3.0 was used, including 268 elementary reactions, and 28 transported species. Consistent post-processing methods were applied to both the DNS and experimental data to evaluate turbulent burning velocity-related statistics, namely the flame surface density (FSD), and the flame curvature. Good agreement was achieved for the 2D comparisons. The DNS data were further analysed and provide 3D statistics unattainable from the experiment. The ratio of the 3D and 2D flame surface densities was estimated. The results are comparable with other values reported for various experimental flames. The 3D and 2D flame curvatures were also compared and their distributions are shown to be quite different owing to the round on-average geometry. Instantaneous images of the heat release surrogate, [CH2O][OH], between the DNS and experiment agreed qualitatively. Various other experimentally obtainable surrogates for heat release rate including [CH2O][H], [CH2O][O], [HCO], and [CH] are also evaluated and compared using the DNS. The inner structure of the flame was compared between the DNS and experiment in terms of the joint PDFs of OH concentration and temperature. Generally good agreement was obtained; discrepancies may be due to the inconsistency of assumed equilibrium levels of OH concentration in the co-flow.
79 citations
TL;DR: In this article, a series of premixed turbulent methane/air jet flames in the thin reaction zone and distributed reaction zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements.
79 citations
TL;DR: It is suggested that HCO prompt dissociation should be included when simulating flames of hydrocarbons and oxygenated molecules and that prompt dissociations of other weakly bound radicals may also impact combustion simulations.
Abstract: Weakly bound free radicals have low-dissociation thresholds such that at high temperatures, time scales for dissociation and collisional relaxation become comparable, leading to significant dissociation during the vibrational–rotational relaxation process. Here we characterize this “prompt” dissociation of formyl (HCO), an important combustion radical, using direct dynamics calculations for OH + CH2O and H + CH2O (key HCO-forming reactions). For all other HCO-forming reactions, presumption of a thermal incipient HCO distribution was used to derive prompt dissociation fractions. Inclusion of these theoretically derived HCO prompt dissociation fractions into combustion kinetics models provides an additional source for H-atoms that feeds chain-branching reactions. Simulations using these updated combustion models are therefore shown to enhance flame propagation in 1,3,5-trioxane and acetylene. The present results suggest that HCO prompt dissociation should be included when simulating flames of hydrocarbons a...
62 citations
TL;DR: In this article, a simplified prechamber/main-chamber system is investigated using direct numerical simulation (DNS) with detailed chemical kinetics, and the progress and topology of flame evolution, and mean burning velocity in the main chamber are analyzed in detail.
61 citations
References
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01 Sep 1989
3,517 citations
01 Jan 1998
TL;DR: In this paper, a Fortran computer program that computes species and temperature profiles in steady-state burner-stabilized and freely propagating laminar flames is described.
Abstract: This report documents a Fortran computer program that computes species and temperature profiles in steady-state burner-stabilized and freely propagating premixed laminar flames. The program accounts for finite rate chemical kinetics and multicomponent molecular transport. After stating the appropriate governing equations and boundary conditions, we discuss the finite difference discretization and the Newton method for solving the boundary value problem. Global convergence of this algorithm is aided by invoking time integration procedures when the Newton method has convergence difficulties. The program runs in conjunction with preprocessors for the chemical reaction mechanism and the transport properties. Transport property formulations include the option of using multicomponent or mixtureaveraged formulas for molecular diffusion. Discussion of two example problems illustrates many of the program's capabilities.
1,533 citations
TL;DR: In this article, the authors investigated low-frequency vortex-driven combustion instability in the case of a multiple inlet combustor with dump and showed that lowfrequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system.
Abstract: Combustion instability is investigated in the case of a multiple inlet combustor with dump. It is shown that low-frequency instabilities are acoustically coupled and occur at the eigenfrequencies of the system. Using spark-schlieren and a special phase-average imaging of the C 2 -radical emission, the fluid-mechanical processes involved in a vortex-driven mode of instability are investigated. The phase-average images provide maps of the local non-steady heat release. From the data collected on the combustor the processes of vortex shedding, growth, interactions and burning are described. The phases between the pressure, velocity and heat-release fluctuations are determined. The implications of the global Rayleigh criterion are verified and a mechanism for low-frequency vortex-driven instabilities is proposed.
562 citations
TL;DR: In this paper, the authors investigated the utility of several experimental observables as measurements of local burning and heat release rates for a premixed stoichiometric N2-diluted methane-air flame in two-dimensional unsteady vortical flow.
537 citations
01 Jan 1992
TL;DR: A review of combustion instabilities coupled by pressure waves and of the related pulse combustor and active control principles and applications can be found in this paper, where the basic mechanisms leading to combustion oscillations are first identified from experimental evidence gathered in recent years.
Abstract: This article contains a review of combustion instabilities coupled by pressure waves and of the related pulse combustor and active control principles and applications. The basic mechanisms leading to combustion oscillations are first identified from experimental evidence gathered in recent years. It is shown that in the presence of pressure waves, the flow features large scale motions which drive the instability. The dynamics of the flame is then dominated by processes of hydrodynamic instability, vortex roll-up, vortex interactions, front and reacting stream pulsations, periodic extinctions and reignitions, self acceleration. Knowledge accumulated on these various aspects has provided guidelines in combustor design. Progress accomplished in the special domain of pulse combustors is surveyed. These devices which operate under sustained pressure oscillations have been the subject of intensive research with as objective the understanding of the dynamics of the flow in various geometrical situations in order to improve the heat transfer efficiency and diminish the level of pollutant formation. While pulse combustors use pressure oscillations in normal operation, in most circumstances the presence of pressure waves causes problems of vibration, enhanced heat fluxes to the walls, cyclic fatigue, and in some cases important damage to the combustor. One generally wishes to eliminate or attenuate these waves. This is usually achieved by changes in the geometrical design and in the operation of the system. New possibilities based on active control have been investigated in recent years. The basic principles and the initial demonstrations of active instability control are first reviewed. It is then shown that such methods constitute a promising technology and that they are also a unique tool in the experimental investigation of combustion instability and pressure related phenomena.
295 citations