Analysis of Heat Release Rate in the Partially Premixed Flame Structures During Autoignition of Unstrained, Laminar Mixing Layers

2012 ◽  
Author(s):  
Inkant Awasthi ◽  
George Gogos
Keyword(s):  
Heat Release ◽  
Release Rate ◽  
Diffusion Flame ◽  
Mixing Layer ◽  
Premixed Flame ◽  
Release Rates ◽  
Laminar Mixing ◽  
Flame Structures ◽  
Partially Premixed Flame ◽  
Fuel Stream

Autoignition in an unstrained, laminar mixing layer of methanol/air is investigated using detailed reaction mechanism and full multicomponent mass diffusion formulation. The temperature of the fuel stream is varied from 400 K to 1200 K, whereas the oxidizer stream is held at a fixed temperature of 1200 K. The calculations are performed for pressure p = 1 bar. Transient evolution of the autoignition kernel from initial partially premixed flame structures to final diffusion flame is demonstrated. The flame structures have been analysed for individual heat release rates. For equal fuel and oxidizer stream temperatures (1200 K), heat release in extremely fuel rich locations (with mixture fraction values up to 0.8) is found. A transient triple flame structure (two deflagrations and, one diffusion flame) is shown to exist even in cases when the temperature difference between the two streams is large. The heat release rates in the deflagrations depend on the temperatures of the two streams. When compared with the surviving diffusion flame, the heat release rate in the short-lived deflagrations is one to two orders of magnitude higher. It is shown that increasing the fuel stream temperature also decrease the ignition delay time in the mixing layer.

scholarly journals Combustion Instability of Swirl Premixed Flame with Dielectric Barrier Discharge Plasma

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1405
Author(s):  
Kai Deng ◽  
Shenglang Zhao ◽  
Chenyang Xue ◽  
Jinlin Hu ◽  
Yi Zhong ◽  
...  
Keyword(s):  
Transfer Function ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Instability ◽  
Premixed Flame ◽  
Oh Radicals ◽  
Acoustic Frequency ◽  
Planar Laser ◽  
Barrier Discharge Plasma

The effects of plasma on the combustion instability of a methane swirling premixed flame under acoustic excitation were investigated. The flame image of OH planar laser-induced fluorescence and the fluctuation of flame transfer function showed the mechanism of plasma in combustion instability. The results show that when the acoustic frequency is less than 100 Hz, the gain in flame transfer function gradually increases with the frequency; when the acoustic frequency is 100~220 Hz, the flame transfer function shows a trend of first decreasing and then increasing with acoustic frequency. When the acoustic frequency is greater than 220 Hz, the flame transfer function gradually decreases with acoustic frequency. When the voltage exceeds the critical discharge value of 5.3 kV, the premixed gas is ionized and the heat release rate increases significantly, thereby reducing the gain in flame transfer function and enhancing flame stability. Plasma causes changes in the internal recirculation zone, compression, and curling degree of the flame, and thereby accelerates the rate of chemical reaction and leads to an increase in flame heat release rate. Eventually, the concentration of OH radicals changes, and the heat release rate changes accordingly, which ultimately changes the combustion instability of the swirling flame.

Measurements and calculations of formaldehyde concentrations in a methane/N2/air, non-premixed flame: Implications for heat release rate

2009 ◽  
Vol 32 (1) ◽  
pp. 1311-1318 ◽  
Author(s):  
S.B. Dworkin ◽  
A.M. Schaffer ◽  
B.C. Connelly ◽  
M.B. Long ◽  
M.D. Smooke ◽  
...  
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Premixed Flame

Influence of the Spatial and Temporal Interaction Between Diesel Pilot and Directly Injected Natural Gas Jet on Ignition and Combustion Characteristics

2017 ◽  
Author(s):  
Georg Fink ◽  
Michael Jud ◽  
Thomas Sattelmayer
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Process ◽  
Gas Jet ◽  
Injection Timing ◽  
Release Rates ◽  
Temporal Interaction ◽  
The Impact

In this paper, pilot-ignited high pressure dual-fuel (HPDF) combustion of a natural gas jet is investigated on a fundamental basis by applying two separate single-hole injectors to a rapid compression expansion machine (RCEM). A Shadowgraphy system is used for optical observations, and the combustion progress is assessed in terms of heat release rates. The experiments focus on the combined influence of injection timing and geometrical jet arrangement on the jet interaction and the impact on the combustion process. In a first step, the operational range for successful pilot self-ignition and transition to natural gas jet combustion is determined, and the restricting phenomena are identified by analyzing the shadowgraph images. Within this range, the combustion process is assessed by evaluation of ignition delays and heat release rates. Strong interaction is found to delay or even prohibit pilot ignition, while it facilitates a fast and stable onset of the gas jet combustion. Furthermore, it is shown that the heat release rate is governed by the time of ignition with respect to the start of natural gas injection — as this parameter defines the level of premixing. Evaluation of the time of gas jet ignition within the operability map can therefore directly link a certain spatial and temporal interaction to the resulting heat release characteristics. It is finally shown that controlling the heat release rate through injection timing variation is limited for a certain angle between the two jets.

scholarly journals Effect of ratio between incoming cool air and outgoing hot gases on behaviour of compartment fire

2019 ◽  
pp. 326-326
Author(s):  
Olivier Zatao-Samedi ◽  
Abbo Oumarou ◽  
Jean M’Boliguipa ◽  
Mvogo Onguene ◽  
Ruben Mouangue
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Room Temperature ◽  
Data Acquisition System ◽  
Main Element ◽  
Compartment Fire ◽  
Release Rates ◽  
The Impact ◽  
Reduced Scale

Many factors have an influence on the development of compartment fire notably on its heat release rate as well as on its capability to propagate and become a flashover situation. The main element which rapidly conveys fire from a compartment to another is hot smoke flowing out through openings of the compartment source of fire. The present work aims to experiment the impact of the variation of heat release rate of the source on the behaviour of fire. So, five fire tests with different heat release rates were thus carried out in a reduced scale room. Temperature of burned gases inside the room, were measured during tests by sensors connected to a data acquisition system. Results revealed that temperature of burned gases as well as its content in carbon monoxide, evolves differently according to two ranges of the incoming air/outgoing gases ratio. The first range of which the ratio is lower than 2, corresponds to the case where both parameters decrease rapidly. The second range of which the ratio is higher than 2, corresponds to the case where both parameters decrease moderately. The transition from the first to the second range, points out the passing from the ventilation-controlled fire to the fuel-controlled fire. A relation expressing the variation of the mass flow rate of outgoing burned gases according to the heat release rate of the fire source has been given.

scholarly journals Use of the cone calorimeter to detect seasonal differences in selected combustion characteristics of ornamental vegetation

2005 ◽  
Vol 14 (3) ◽  
pp. 321 ◽  
Author(s):  
David R. Weise ◽  
Robert H. White ◽  
Frank C. Beall ◽  
Matt Etlinger
Keyword(s):  
Moisture Content ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Cone Calorimeter ◽  
Mass Loss Rate ◽  
Combustion Characteristics ◽  
Release Rates ◽  
Intermediate Scale ◽  
Time To Ignition

The flammability of living vegetation is influenced by a variety of factors, including moisture content, physical structure and chemical composition. The relative flammability of ornamental vegetation is of interest to homeowners seeking to make their homes ‘fire safe’. The relative importance of the factors influencing fire behaviour characteristics, such as flammability, is unknown. In the present study, oxygen consumption calorimetry was used to obtain selected combustion characteristics of ornamental vegetation. Peak heat release rate, mass loss rate, time to ignition and effective heat of combustion of 100 × 100-mm samples of foliage and small branches were measured using a bench-scale cone calorimeter. Green and oven-dry samples of 10 species were collected and tested seasonally for a period of 1 year. Similar measurements were made on whole shrubs in an intermediate-scale calorimeter. The range of cone calorimeter peak heat release rates for green and oven-dry samples was 1–176 and 49–331 kW m−2, respectively. Moisture content significantly reduced heat release rates and increased time to ignition. Peak heat release rates for Olea europea and Adenostoma fasciculatum were consistently highest over the year of testing; Aloe sp. consistently had the lowest heat release rate. The correlation of peak heat release rates measured by the cone calorimeter and an intermediate-scale calorimeter was statistically significant yet low (0.51). The use of the cone calorimeter as a tool to establish the relative flammability rating for landscape vegetation requires additional investigation.

scholarly journals The Effects of CO2 Additional on Flame Characteristics in the CH4/N2/O2 Counterflow Diffusion Flame

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2905
Author(s):  
Ying Chen ◽  
Jingfu Wang ◽  
Xiaolei Zhang ◽  
Conghao Li
Keyword(s):  
Thermal Properties ◽  
Heat Release ◽  
Flame Front ◽  
Release Rate ◽  
Diffusion Flame ◽  
Flame Temperature ◽  
Radiative Properties ◽  
One Dimensional ◽  
Negative Effect ◽  
Counterflow Diffusion Flame

The effects (chemical, thermal, transport, and radiative) of CO2 added to the fuel side and oxidizer side on the flame temperature and the position of the flame front in a one-dimensional laminar counterflow diffusion flame of methane/N2/O2 were studied. Overall CO2 resulted in a decrease in flame temperature whether on the fuel side or on the oxidizer side, with the negative effect being more obvious on the latter side. The prominent effects of CO2 on the flame temperature were derived from its thermal properties on the fuel side and its radiative properties on the oxidizer side. The results also highlighted the differences in the four effects of CO2 on the position of the flame front on different sides. In addition, an analysis of OH and H radicals and the heat release rate of the main reactions illustrated how CO2 affects the flame temperature.

Flame Retardancy of Laponite- and Montmorillonite-Based Nylon 6 Nanocomposites

2003 ◽  
Vol 788 ◽  
Author(s):  
Gunes Inan ◽  
Prabir K. Patra ◽  
Yong K. Kim ◽  
Steven B. Warner
Keyword(s):  
Mass Loss ◽  
Heat Release ◽  
Heating Rate ◽  
Heat Release Rate ◽  
Flame Retardancy ◽  
Release Rate ◽  
Barrier Properties ◽  
Nylon 6 ◽  
Release Rates ◽  
Peak Heat Release Rate

ABSTRACTThe flame retardancy of nylon 6/laponite and nylon 6/montmorillonite nanocomposites was investigated. The pronounced effect of layered silicates on heat release and mass loss rates of nylon 6 was examined. We found that nylon 6/laponite has 46 % and nylon 6/montmorillonite has 52.5 % lower peak heat release rates than that of neat nylon 6. The 6.5 % difference between the peak heat release rates of laponite- and montmorillonite-based nanocomposites was attributed to differences in aspect ratio and surface charge density of the nanoparticles.The barrier properties of nanocomposite chars was evaluated by examining the peak heat release and mass loss rate reductions of stacks of layers, with the bottom layer being neat nylon 6 polymer and the top layers being nanocomposites that formed chars during the experiments. We observed that the peak heat release rate of a 10×10×0.3 cm neat nylon 6 slab was reduced by about 45 % when protected with a char-forming nylon 6/montmorillonite slab of same dimensions. The dramatic reduction of the peak heat release rate of neat nylon 6 when covered with a nanocomposite char was consistent with the notion that the flame retardancy of polymer/clay nanocomposites is affected by the (thermal and/or mass) barrier properties of the char. In order to test the thermal insulation of the char, temperature profiles of the layered samples were measured during cone calorimeter experiments. We observed that the nanocomposite char that brought about a 44.5 % reduction in peak heat release and mass loss rates reduced the heating rate of the same neat nylon 6 by about 31.2 %. The reduction in the heating rate increased with the amount of nanocomposite char formed.

scholarly journals Numerical Study on the Effect of Tunnel Aspect Ratio on Evacuation with Unsteady Heat Release Rate Due to Fire in the Case of Two Vehicles

Energies ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 133 ◽  
Author(s):  
Younggi Park ◽  
Youngman Lee ◽  
Junyoung Na ◽  
Hong Sun Ryou
Keyword(s):  
Aspect Ratio ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Numerical Study ◽  
Longitudinal Direction ◽  
Release Rates ◽  
Aspect Ratios ◽  
Visibility Distance ◽  
Computational Fluid Dynamics Analysis

In this study, the characteristics of fires in case of two vehicles in a tunnel are analyzed by Computational Fluid Dynamics analysis for varying tunnel aspect ratios. Unsteady heat release rates over time are set as the input conditions of fire sources considering real phenomena. Unsteady heat release rate values are obtained from experiments. As a result, the smoke velocities above the fire source appear faster in the case of tunnels with a large aspect ratio because the higher the height of the tunnel, the faster the smoke velocity caused by buoyancy forces. The smoke velocity in the longitudinal direction increases quickly. However, the temperature distribution in the vicinity of the ceiling is low when the tunnel aspect ratio is large because the height of the tunnel is not directly affected by the flames. Also, the higher the height of the tunnel, the lower the visibility distance due to the heat and smoke coming down along the wall surface. However, in the tunnels represented in this study, it is considered that the visibility of evacuees is sufficiently secured.

Experimental and Numerical Studies of Ethanol Flames

2006 ◽  
Author(s):  
Priyank Saxena ◽  
Forman A. Williams
Keyword(s):  
Diffusion Flame ◽  
Radiation Effects ◽  
Diffusion Flames ◽  
Premixed Flames ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Detailed Chemistry ◽  
Partially Premixed ◽  
Partially Premixed Flame ◽  
Fuel Stream

This paper reports results of experimental and numerical investigations of ethanol-air diffusion flames and partially premixed flames at an air-side strain rate of 100 s−1, in a counterflow geometry. The diffusion flame consists of prevaporized fuel, with mole fraction of 0.3, diluted with nitrogen in the fuel stream, and plant air as the oxidizer stream. The partially premixed flame includes prevaporized fuel in air partially premixed to an equivalence ratio of 2.3 in the fuel stream, and plant air as the oxidizer stream. Temperature profiles were measured by thermocouple, and concentration profiles of the stable species C2H5OH, CO, CO2, H2, H2O, O2, N2, CH4, C2H6, and C2H2+C2H4 were measured by gas chromatography of samples withdrawn by a fine probe. Computational studies involved numerical integration of the conservation equations, with detailed chemistry, transport and radiation effects included, to calculate the structures of the counterflow flames. A chemical-kinetic mechanism consisting of 235 elementary steps and 46 species with recently published reaction-rate parameters was developed and tested for these flames. The proposed mechanism, which produces reasonable agreement with previous measurements of ignition, freely propagating premixed flames and diffusion-flame extinction, also yields good agreement with much of the present data, although there are quite noticeable differences between predicted and measured peak C2H6 concentrations. These differences and the desirability of additional tests of other predictions and of tests under other conditions motivate further research.

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