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«Title of Document: MEASUREMENTS AND ANALYSIS OF EXTINCTION IN VITIATED FLAME SHEETS Justin Wade Williamson, Doctor of Philosophy, Directed By: ...»

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ABSTRACT

Title of Document: MEASUREMENTS AND ANALYSIS OF

EXTINCTION IN VITIATED FLAME

SHEETS

Justin Wade Williamson, Doctor of Philosophy,

Directed By: Professor André Marshall, Department of Fire

Protection Engineering

Accidental fires present many challenging hazards to people and property.

The thermal and toxic effects of fires are significantly affected by the ventilation conditions supplied to the fire. Vitiation is a consequence of limited ventilation, where the products of combustion mix with the unburned reactants prior to reaction.

Vitiation results in diluting and preheating the reactants, significantly enhancing the behavior of the fire. An interesting effect of vitiation is the increased propensity of the flame to experience extinction, either locally or globally. Likewise, there are other factors that can increase the propensity for extinction, including losses due to incomplete chemical kinetics, radiation, and conduction. These extinction events have a direct impact on the thermal and toxic hazards associated with accidental fires by creating holes in the reaction surface. This research provides a detailed analysis of local flame extinction by examining the behavior of counterflow flames undergoing kinetic losses, radiation losses, and vitiation. A thorough review of flame extinction theory was conducted to determine the appropriate parameters necessary for characterizing local flame extinction conditions. Simple scaling arguments are presented to demonstrate that each of these parameters is significant in accidental fires. Counterflow methane-air diffusion flames have been studied experimentally and numerically with OPPDIF to systematically examine the effects of each parameter on local flame extinction. Furthermore, a model is presented, which uses reactant composition and temperature in the vicinity of the flame, net radiation losses from the flame, and the local scalar dissipation rate as inputs to model local extinction conditions. The proposed model is suitable for integration into Computational Fluid Dynamics (CFD) codes used to predict the hazards associated with accidental fires.

MEASUREMENTS AND ANALYSIS OF EXTINCTION IN VITIATED FLAME

SHEETS

By Justin Wade Williamson Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy

Advisory Committee:

Associate Professor André Marshall, Chair Associate Professor Christopher Cadou, Dean’s Representative J.L. Bryan Professor James Quintiere Assistant Professor Peter Sunderland Associate Professor Arnaud Trouvé © Copyright by Justin Wade Williamson Acknowledgements This work was supported by the National Institute of Standards and Technology (Grant 70NANB4H1089) and managed by Dr. Jiann Yang, Fire Metrology Group Leader of the NIST Building and Fire Research Laboratory. I would also like to acknowledge Dr. Filippo Gavelli from Exponent for the internship opportunity they provided.

Many people have directly contributed to the success of this work. I would like to thank the professors and staff of the Department of Fire Protection Engineering for their varied contributions to this research. Primarily among them, I would like to acknowledge my advisors Professors André Marshall, Arnaud Trouvé, James Quintiere, and Peter Sunderland for their valued guidance in all stages of my research and professional development. Mr. Sigfried Dobrotka deserves accolades for the work done to develop the counterflow burner used in this study. This research was also a product of the collaborative efforts of the ventilation limited compartment fire research group, including substantial contributions from Dr. Yunyong Utiskul, Mr.

Zhixin Hu, Mr. Vivien Lecoustre, and Mr. Mizukami Tensei. I would also like to thank Dr. Xiaobo Yao, Dr. Carlos Cruz and Mr. Praveen Narayanan for the productive and insightful discussions we have shared.

Finally, I must acknowledge my wife, Marjorie Williamson, for her patience, dedication and support throughout. Her contributions are immeasurable.

–  –  –

Acknowledgements

Table of Contents

List of Tables

List of Figures

Nomenclature

Chapter 1: Introduction

1.1 Background and Motivation

1.1.1 Accidental Fires

1.1.2 Flame Vitiation

1.1.3 Flame Extinction

1.2 Literature Review

1.2.1 Extinction in Compartment Fires

1.2.2 Extinction in Unconfined Fires

1.2.3 Extinction in Counterflow Flames

1.2.4 Extinction in Combustion Systems

1.2.5 Numerical Simulation of Extinction

1.3 Objectives

1.3.1 Identify Physical Parameters that Govern Extinction

1.3.2 Determine the Most Significant Parameters Governing Extinction.......... 21 1.3.3 Develop an Approach to Identify Extinction Conditions

1.3.4 Formulate an Extinction Model

Chapter 2: Approach

2.1 Flame Theory

2.1.1 Vitiation

2.1.2 Incomplete Chemistry

2.1.3 Radiation Losses





2.1.4 Extinction Physics

2.1.4.1 Detailed Chemistry

2.1.4.2 Activation Energy Asymptotics

2.1.4.3 Simplified Critical Damköhler Number

2.1.4.4 Critical Flame Temperature

2.2 Experimental Methodology

2.2.1 Counterflow Burner Design

2.2.2 Controls

2.2.3 Diagnostics

2.2.4 Error Analysis

2.3 Computational Methodology

2.3.1 Counterflow Flame Solver

2.3.2 Controls

2.3.3 Diagnostics

2.3.4 Error Analysis

2.4 Summary

iii Chapter 3: Results

3.1 Extinction of Flames with Pure Air and Pure Fuel

3.1.1 Kinetic Limit

3.1.2 Radiative Limit

3.1.3 Additional Significant Observations

3.2 Extinction with Vitiation Effects

3.2.1 Oxidizer Vitiation

3.2.2 Fuel Vitiation

3.3 Extinction with Scalar Dissipation Rate Effects

3.3.1 Oxidizer Vitiation

3.3.2 Fuel Vitiation

3.3.3 Activation Temperature

3.3.3.1 Detailed Chemistry

3.3.3.2 Activation Energy Asymptotics

3.3.3.3 Simplified Critical Damköhler Number

3.4 Extinction with Radiative Loss Effects

3.4.1 Oxidizer Vitiation

3.4.2 Fuel Vitiation

3.4.3 Approximating Radiation Losses from Sooty Flames

3.5 Evaluating the Extinction Models

3.5.1 Detailed Chemistry

3.5.2 Activation Energy Asymptotics

3.5.3 Simplified Critical Damköhler Number

3.5.4 Critical Flame Temperature

3.6 Two-Parameter Extinction Effects

3.6.1 Oxidizer Vitiation

3.6.2 Fuel Vitiation

Chapter 4: Conclusions

Appendix A

Bibliography

–  –  –

Table 1: Operation procedure for conducting extinction experiments with the counterflow burner.

Table 2: Experimental uncertainty of selected quantities calculated for oxidizer and fuel vitiation.

–  –  –

Figure 1: Compartment fire with air vitiation effects and the association between 1-D flamelet studies and local flame behavior. Local reactants are affected by ∞ ∞ dilution ( YO2 ≤ YOamb ) and preheating ( TO2 ≥ TOamb ).

Figure 2: Compartment fire with fuel vitiation effects and the association between 1D flamelet studies and local flame behavior. Local reactants are affected by dilution ( YF∞ ≤ YFamb ) and preheating ( TF∞ ≥ TFamb )

Figure 3: The mean scalar dissipation rate at the flame tip for heptane pool fires as a function of pool diameter from the scaling analysis. The flame energy release rate is provided for reference.

Figure 4: Top injector of the Opposed Flow Slot burner. Oxidizer is injected along the central axis surrounded by N2 co-flow. An identical injector assembly is used for fuel.

Figure 5: Diagram of experimental flow control and reactant heating system for oxidizer vitiation.

Figure 6: Summary of burner operating capabilities and sample flame images for oxidizer vitiation between pure air and extinction at χ st = 0.49 s -1................... 60 Figure 7: OPPDIF output of flame energy generation per unit volume versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞........ 67 Figure 8: OPPDIF output of local temperature versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞.

Figure 9: OPPDIF output of local velocity versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞.

Figure 10: OPPDIF output of local thermal diffusivity versus local temperature for several simulations. Thermal diffusivity is a non-standard output and a commonly used model is illustrated as a simplification.

Figure 11: Calculation of scalar dissipation rate from OPPDIF output from Equation (5) versus location (a) and mixture fraction (b) and (c). Arrows indicate solutions of decreasing YO∞.

–  –  –

Figure 13: OPPDIF output of local mass fraction of oxygen versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞

Figure 14: OPPDIF output of local mass fraction of water vapor versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞.............. 71 Figure 15: OPPDIF output of local mass fraction of carbon dioxide versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞.............. 71 Figure 16: OPPDIF output of local mass fraction of carbon monoxide versus location (a) and mixture fraction (b). Arrows indicate solutions of decreasing YO∞........ 72 Figure 17: Determination of the reference extinction condition by recreating the classical S-Shaped curve with TO∞ = TF∞ = 300 K, YO∞ = 0.23, YF∞ = 1 and χ st from Equation (5).

Figure 18: Stoichiometric flame temperature versus scalar dissipation rate for flames between the kinetic extinction limit and the radiative extinction limit with TO∞ = TF∞ = 300 K, YO∞ = 0.23, YF∞ = 1 and χ st from Equation (5)................... 78 Figure 19: (a) Flame energy generation and radiation losses per unit area, and (b) integral radiant fraction, versus local scalar dissipation rate between the kinetic and radiative extinction limits with TO∞ = TF∞ = 300 K, YO∞ = 0.23, YF∞ = 1 and χ st from Equation (5).

Figure 20: Scalar dissipation rate model from Equation (49) versus the direct calculation of the scalar dissipation rate from Equation (5), illustrating a nearly 1 to 1 relationship

Figure 21: Flame energy generation and radiation losses per unit area versus local scalar dissipation rate between the kinetic and radiative extinction limits with TO∞ = TF∞ = 300 K, YO∞ = 0.23, YF∞ = 1 and χ st from Equation (49).

–  –  –

Figure 22: (a) Illustration of a vitiated constant scalar dissipation rate pathway to extinction. (b) Description of flame energy production per unit area and stoichiometric temperature along the constant scalar dissipation rate pathway where TO∞ = TF∞ = 300 K, YO∞ = 0.23, YF∞ = 1 and χ st = 1.53 s-1 using Equation (5), Tst, 0 = 1980 K, and q 0′ = 2.06 × 105 W/m2 from OPPDIF.

′ vii Figure 23: Illustration of oxidizer vitiation effects on extinction flame temperature for detailed chemistry from OPPDIF (a) and the Burke-Schumann model (b). The linear fit lines in (a) are used to highlight data grouping and the arrows indicate groups of increasing TO∞. ( TF∞ = 300 K, YF∞ = 1)

Figure 24: Illustration of fuel vitiation effects on extinction flame temperature for detailed chemistry from OPPDIF (a) and the Burke-Schumann model (b). The lines in (a) are used to highlight data grouping and the arrows indicate groups of increasing TF∞. ( TO∞ = 300 K, YO∞ = 0.23)

Figure 25: Illustration of scalar dissipation rate effects on critical oxidizer concentrations for detailed chemistry from OPPDIF (a) and the Burke-Schumann model (b). The lines are used to highlight data grouping and the arrows indicate groups of increasing TO∞. ( TF∞ = 300 K, YF∞ = 1)

Figure 26: Illustration of scalar dissipation rate effects on critical fuel concentrations for detailed chemistry from OPPDIF (a) and the Burke-Schumann model (b).

The lines are used to highlight data grouping and the arrows indicate groups of increasing TF∞. ( TO∞ = 300 K, YO∞ = 0.23)

Figure 27: Activation temperature determination for detailed chemistry extinction from OPPDIF. Only oxidizer vitiated extinction conditions are included in the log fit with χ st determined from Equation (5). ( T a = 39980 K)

Figure 28: Activation temperature determination for the AEA model from experimentally and numerically determined extinction conditions, with χ st determined from Equation (37). ( Ta = 16394 K)

Figure 29: Activation temperature determination for the SCDN model from experimentally and numerically determined extinction conditions, with χ st determined from Equation (49). ( Ta = 24178 K)

Figure 30: Solutions for the critical flame temperature using the radiation corrected Burke-Schumann model from Equation (23) versus absorption coefficient, demonstrating that the critical flame temperature is always constant for a given scalar dissipation rate. The symbols are used to highlight solution grouping.... 99 Figure 31: Solutions and data of critical oxidizer concentrations with the combined effects of radiation losses and scalar dissipation rate. The arrow indicates solutions of increasing absorption coefficient. ( TO∞ = TF∞ = 300 K, YF∞ = 1).. 101 viii Figure 32: Solutions for the combined effect of radiation losses and scalar dissipation rate on critical fuel concentrations. The arrow in indicates solutions of increasing absorption coefficient. ( TO∞ = TF∞ = 300 K, YO∞ = 0.23 )



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