Recent cpl items

A Generalized Pyrolysis Model for Combustible Solids

Wed, 23 Jul 2008 00:00:00 +0000

This dissertation presents the derivation, numerical implementation, and verification/validation of a generalized model that can be used to simulate the pyrolysis, gasification, and burning of a wide range of solid fuels encountered in fires. The model can be applied to noncharring and charring solids, composites, intumescent coatings, and smolder in porous media. Care is taken to make the model as general as possible, allowing the user to determine the appropriate level of complexity to include in a simulation. The model considers a user–specified number of gas phase and condensed phase species, each having its own temperature–dependent thermophysical properties. Any number of heterogeneous (gas–solid) or homogeneous (solid–solid or gas-gas) reactions can be specified. Both in–depth radiation transfer through semi–transparent media and radiation transport across pores are considered. Volume change (surface regression or swelling/intumescence) is handled by allowing the size...

Direct Use of Wet Ethanol in a Homogeneous Charge Compression Ignition (HCCI) Engine: Experimental and Numerical Results

Wed, 17 Oct 2007 00:00:00 +0000

Homogeneous Charge Compression Ignition (HCCI) engines are amenable to a large variety of fuels as long as the fuel can be fully vaporized, sufficiently mixed with air, and receive sufficient heat during the compression stroke to reach the autoignition conditions. This study investigates an HCCI engine fueled with ethanol-in-water mixtures, which we call “wet ethanol”. The motivation for using wet ethanol fuel is that significant energy is required for distillation and dehydration of fermented ethanol (from biosources, not from petroleum), thus direct use of wet ethanol could improve energy balance. Recent modeling studies have predicted that a HCCI engine can operate using fuel containing as little as 35% ethanol-in-water, with surprisingly good performance and emissions. With the previous modeling study suggesting feasibility of wet ethanol use in HCCI engines, this paper focuses on experimental operation wet ethanol in a 4-cylinder 1.9 liter engine running in HCCI mode....

A numerical investigation into the anomalous slight NOx increase when burning biodiesel; A new (old) theory

Wed, 25 Jul 2007 00:00:00 +0000

Biodiesel is a notable alternative to petroleum derived diesel fuel because it comes from natural domestic sources and thus reduces dependence on diminishing petroleum fuel from foreign sources, it likely lowers lifecycle greenhouse gas emissions, and it lowers an engine’s emission of most pollutants as compared to petroleum derived diesel. However, the use of biodiesel often slightly increases a diesel engine’s emission of smog forming nitrogen oxides (NOx) relative to petroleum diesel. In this paper, previously proposed theories for this slight NOx increase are reviewed, including theories based on biodiesel’s cetane number, which leads to differing amounts of charge preheating, and theories based on the fuel’s bulk modulus, which affects injection timing. This paper proposes an additional theory for the slight NOx increase of biodiesel. Biodiesel typically contains more double bonded molecules than petroleum derived diesel. These double bonded molecules have a slightly higher...

Flame Structure and Soot Formation in Inverse Diffusion Flames (Ph.D. Dissertation)

Wed, 16 May 2007 00:00:00 +0000

Flame structure and soot and carbon monoxide (CO) formation were studied in laminar co-flowing co-annular inverse diffusion flames (IDFs) in normal and microgravity. An IDF is a non-premixed flame that consists of an inner air flow surrounded by a fuel flow. Soot formation is important to understand because soot particles are a health concern and have a strong influence on flame radiation, while CO formation is important because of the role it plays in fire-related deaths. Soot formation in normal diffusion flames (NDFs) is difficult to study because soot forms in the center of the flame and is oxidized so that soot cannot be sampled easily. Soot formation can be studied more easily in IDFs because soot forms on the fuel side of the reaction zone, is convected away from the reaction zone without oxidizing, and cools quickly. Therefore, in IDFs, newly formed soot is easier to sample than in NDFs. Soot formation was studied in microgravity IDFs because buoyancy-induced...

Flame Height Measurement of Laminar Inverse Diffusion Flames

Mon, 2 Oct 2006 00:00:00 +0000

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be longer than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper’s analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper’s analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames.

Using Biofuel Tracers to Study Alternative Combustion Regimes

Mon, 18 Sep 2006 00:00:00 +0000

Interest in the use of alternative fuels and engines is increasing as the price of petroleum climbs. The inherently higher efficiency of Diesel engines has led to increased adoption of Diesels in Europe, capturing approximately 40% of the new passenger car market. Unfortunately, lower CO2 emissions are countered with higher nitrogen oxides (NOx) and particulate matter (PM) emissions, and higher noise. Noise and PM have traditionally been the obstacles toward consumer acceptance of Diesel passenger cars in North America, while NOx (a key component in photochemical smog) has been more of an engineering challenge. Diesels have non-premixed combustion with excess oxygen; reducing NOx to N2 in an oxygen rich environment is difficult. Adding oxygenated compounds to the fuel helps reduce PM emissions. However, relying on fuel alone to reduce PM is unrealistic due to economic constraints and difficult due to the emerging PM standards. Keeping peak combustion temperature below...

Landfill Gas Fueled HCCI Demonstration System

Mon, 18 Sep 2006 00:00:00 +0000

This demonstration system is intended to meet the California Energy Commission’s primary goal of improving California’s electric energy cost/value by providing a low-cost high-efficiency distributed power generation engine that runs on landfill gas. The project team led by Makel Engineering, Inc. includes UC Berkeley, CSU Chico and the Butte County Public Works Department.

The team has developed a reliable, multi-cylinder Homogeneous Charge Compression Ignition (HCCI) engine by converting a Caterpillar 3116, 6.6 liter diesel engine to operate in HCCI mode. This engine utilizes a simple and robust thermal control system. Typically, HCCI engines are based on standard diesel engine designs with reduced complexity and cost based on the well known principles of engine dynamics. Coupled to an induction generator, this HCCI genset allows for simplified power grid connection.

Testing with this HCCI genset allowed for the development of a control system to maintain optimal...

A Generalized Pyrolysis Model for Simulating Charring, Intumescent, Smoldering, and Noncharring Gasification

Mon, 28 Aug 2006 00:00:00 +0000

This paper presents a generalized pyrolysis model that can simulate the gasification of noncharring, charring, and intumescent materials, as well as smoldering in porous media. Separate conservation equations are solved for gaseous and condensed phase mass and species, solid phase energy, and gas-phase momentum. An arbitrary number of gas-phase and condensed-phase species can be accommodated, each having its own temperature-dependent thermophysical properties. The user may specify any number of solid to gas, solid to solid, or solid + gas to solid + gas reactions of any order. Both in-depth radiation transfer through a semi-transparent medium as well as radiation transport across pores are considered, and melting is modeled using an apparent specific heat. All volatiles generated inside the solid escape to the ambient with no resistance to flow unless the pressure solver is invoked to solve for the pressure distribution in the solid, with the resultant flow of volatiles calculated...

Application of Genetic Algorithms and Thermogravimetry to Determine the Kinetics of Polyurethane Foam in Smoldering Combustion

Tue, 25 Apr 2006 00:00:00 +0000

In this work, the kinetic parameters governing the thermal and oxidative degradation of flexible polyurethane foam are determined using thermogravimetric data and a genetic algorithm. These kinetic parameters are needed in the theoretical modeling of the foam’s smoldering behavior. Experimental thermogravimetric mass-loss data are used to explore the kinetics of polyurethane foam and to propose a mechanism consisting of five reactions. A lumped model of solid mass-loss based on Arrhenius-type reaction rates and the five-step mechanism is developed to predict the polyurethane thermal degradation. The predictions are compared to the thermogravimetric measurements, and using a genetic algorithm, the method finds the kinetic and stoichiometric parameters that provide the best agreement between the lumped model and the experiments. To date, no study has attempted to describe both forward and opposed smolder-propagation with the same kinetic mechanism. Thus, in order to verify that...

Field performance of a nephelometer in rural kitchens: effects of high humidity excursions and correlations to gravimetric analyses (Journal of Exposure Science and Environmental Epidemiology 2006)

Thu, 13 Apr 2006 00:00:00 +0000

Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Previous field validations of nephelometer performance in residential settings explore relatively low particle concentrations, with the vast majority of 24-hour average gravitational PM2.5 concentrations falling below 40 μg/m3. We investigate relationships between 24-hour gravitational particle measurements and nephelometric data logged by the personalDataRAM in highly polluted rural Chinese kitchens, where gravitationally determined 24-hour average...

Computational Model of Forward and Opposed Smoldering Combustion with Improved Chemical Kinetics (PhD. Thesis)

Mon, 19 Dec 2005 00:00:00 +0000

A computational study has been carried out to investigate smoldering ignition and propagation in polyurethane foam. The one-dimensional, transient, governing equations for smoldering combustion in a porous fuel are solved accounting for improved solid-phase chemical kinetics. A systematic methodology for the determination of solid-phase kinetics suitable for numerical models has been developed and applied to the simulation of smoldering combustion. This methodology consists in the correlation of a mathematical representation of a reaction mechanism with data from previous thermogravimetric experiments. Genetic-algorithm and trail-and-error techniques are used as the optimization procedure. The corresponding kinetic parameters for two different mechanisms of polyurethane foam smoldering kinetics are quantified: a previously proposed 3-step mechanism and a new 5-step mechanism. These kinetic mechanisms are used to model one-dimensional smoldering combustion, numerically solving...

Field performance of a nephelometer in rural kitchens: effects of high humidity excursions and correlations to gravimetric analyses

Wed, 2 Nov 2005 00:00:00 +0000

Rural kitchens of solid-fuel burning households constitute the microenvironment responsible for the majority of human exposures to health-damaging air pollutants, particularly respirable particles and carbon monoxide. Portable nephelometers facilitate cheaper, more precise, time-resolved characterization of particles in rural homes than are attainable by gravitational methods alone. However, field performance of nephelometers must contend with aerosols that are highly variable in terms of chemical content, size, and relative humidity. Our investigation of relationships between 24-hour optical and gravitational particle measurements in rural Chinese kitchens depicts that where relative humidity remained below 95%, nephelometric response was strongly linear despite complex mixtures of aerosols. Where 95% relative humidity was exceeded for even a brief duration, nephelometric data were nonsystematically distorted, and neither concurrent relative humidity measurements nor use of...

Development of Isooctane Skeletal Mechanisms for Fast and Accurate Predictions of SOC and Emissions of HCCI Engines based on LLNL Detailed Mechanism

Thu, 27 Oct 2005 00:00:00 +0000

Fast and accurate numerical analysis is not only important for studying Homogeneous Charge Compression Ignition (HCCI) technology but also critical for designing HCCI engines. Chemistry plays the major role in determining Start of Combustion (SOC) and emissions of HCCI engines. The Lawrence Livermore National Laboratory (LLNL) detailed isooctane mechanism contains 857 species and 3,606 reaction steps making the calculation too expensive. This work describes a recent development of isooctane skeletal mechanisms for speeding up numerical simulations of HCCI. By using the rate analysis, two skeletal mechanisms were constructed: one with 258 species and the other with 291 species. The former was developed for accurate predictions of SOC and the latter is an expanded version of the one with 258 species aiming at accurate predictions of both SOC and emissions. Validations of the performances of these two skeletal mechanisms were conducted extensively for the operation regimes anticipated...

A Comparison of Infrared Light Emitting Diodes (IR-LED) versus Infrared

Thu, 27 Oct 2005 00:00:00 +0000

In lean premixed combustion systems, inadequate mixing of the fuel and air, prior to combustion can cause unnecessarily large pollutant emissions. Measuring the extent of mixing of fuel into air is often difficult, since combustion in lean premixed gas turbines takes place at high pressures, often making optical access to the combustion area limited. In addition, the pressure broadening of the molecular absorption lines renders the spectrally narrow line associated with a laser light source less useful. This paper studies some of the problems in determining the extent of mixing of the fuel into air in these lean premixed combustion systems. The focus of this paper is the use of an infrared light emitting diode (IR-LED) to quantitatively measure fuel concentration in a lean premixed gas turbine. The IR-LED emits radiation over a wide wavelength range compared to a laser, meaning that the development of an absorption coefficient to relate the fuel concentration to the absorption...

Ignition of Combustion Modified Polyurethane Foam

Thu, 27 Oct 2005 00:00:00 +0000

Results are presented from an experimental study on the ignition of the combustion modified (fire retarded) polyurethane foam Pyrell® (35.3 kg/m3 and 64.0 kg/m3) in elevated oxygen concentrations, ranging from 30% to 60%. The samples are exposed to an external flow and variable radiant heat flux on one face, and insulated on the other faces. The experiments show that Pyrell undergoes a weak smoldering reaction that requires significant assistance in the form of external heat input in order to propagate. The results also show that given sufficient oxygen and radiant heat flux, the smoldering reaction can produce enough volatile fuel and heat to trigger a gas phase ignition, i.e. a transition from smoldering to flaming, in pores in the char region. The experiments also indicate that high-density Pyrell is more ignitable than low-density Pyrell, which could be explained by the greater solid surface area for smoldering reactions to take place.

Laser Extinction in Laminar Inverse Diffusion Flames

Tue, 18 Oct 2005 00:00:00 +0000

Measurements of line-of-sight laser extinction in a co-annular ethylene-air laminar inverse diffusion flame (IDF) were made to determine soot concentration. Extinction has frequently been used in the literature to measure soot concentration in normal diffusion flames (NDFs), but it has rarely been applied to IDFs. A coflow IDF contains a primary air flow surrounded by a fuel annulus. Soot particles form on the outside of IDFs, advect upward, and eventually quench without being oxidized. It has been proposed in the literature that IDFs will produce less near-flame soot than NDFs because, for flames of comparable fuel, size and flow rates, movement of soot outward into cool regions of an IDF limits its simultaneous exposure to the high temperatures and fuel pyrolysis products needed for soot growth. A two-dimensional soot concentration map of an IDF using experimental data confirms this hypothesis by showing integrated soot volume fractions to be an order of magnitude lower than...

LES of Sandia Flame D with Eulerian PDF and Finite-Rate Chemistry

Mon, 17 Oct 2005 00:00:00 +0000

Monte Carlo simulations of joint PDF approaches have been extensively developed in the past largely with Reynolds Averaged Navier Stokes (RANS) equations. Current interests are in the extension of PDF approaches to Large Eddy Simulation (LES). As LES allows to resolve the large scales of turbulence in time and space, a joint LESPDF approach holds the promise to ease the modelling requirements (e.g. mixing models). In the past we have implemented a joint scalar PDF approach into LES with the amelet model using an Eulerian approach. Our preliminary results demonstrated that careful implementation of the Eulerian approach can be fully consistent with the counterpart nite-volume method. In this paper, results of recent LES of a pilot CH4/Air ame (Sandia/TUD ame D) with realistic nite-rate chemistry will be reported using three di erent mixing models including modi ed Curl (MC), Interaction by Exchange with the Mean (IEM), and Eucledian Minimum Spanning Tree (EMST). The calculations...

Numerical Issues of Monte Carlo PDF for Large Eddy Simulations of Turbulent Flames

Tue, 11 Oct 2005 00:00:00 +0000

Monte Carlo simulations of joint PDF approaches have been extensively developed in the past largely with Reynolds Averaged Navier Stokes (RANS) equations. Current interests are in the extension of PDF approaches to Large Eddy Simulation (LES). As LES intends to resolve the large scales of turbulence in time, the coupling between Monte Carlo simulation and the flow field becomes an important issue. It is crucial to ensure some sort of coherency between the scalar field solution obtained via finite-volume methods and that from the stochastic solution of the PDF. In this paper, we first review the advantages and disadvantages of Eulerian and Lagrangian approaches. In order to clarify the coherency feature of a solution method, we introduce the concept of stochastic convergence for hybrid methods. Secondly, we present some preliminary results of an ongoing study with the Eulerian approach that reveals the numerical issues needing to be resolved. Results are presented for simulations...

SMOLDER IGNITION OF POLYURETHANE FOAM: EFFECT OF OXYGEN CONCENTRATION

Thu, 15 Sep 2005 00:00:00 +0000

Experiments have been conducted to study the ignition of both forward and opposed smolder of a high void fraction, flexible, polyurethane foam in a forced oxidizer flow. Tests are conducted in a small scale, vertically oriented, combustion chamber with supporting instrumentation. An electrically heated Nichrome wire heater placed between two porous ceramic disks, one of which is in complete contact with the foam surface, is used to supply the necessary power to ignite and sustain a smolder reaction. The gaseous oxidizer, metered via mass flow controllers, is forced through the foam and heater. A constant power is applied to the igniter for a given period of time and the resulting smolder is monitored to determine if smolder is sustained without the assistance of the heater, in which case smolder ignition is considered achieved. Reaction zone temperature and smolder propagation velocities are obtained from the temperature histories of thermocouples embedded at predetermined...

Space shuttle based microgravity smoldering combustion experiments

Thu, 15 Sep 2005 00:00:00 +0000

Results from four microgravity smoldering combustion experiments conducted aboard the NASA Space Shuttle are presented in this work. The experiments are part of the NASA funded Microgravity Smoldering Combustion (MSC) research program, aimed to study the smolder characteristics of porous combustible materials in a microgravity environment. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder for the purpose of control and prevention, both in normal- and microgravity. The microgravity smolder experiments reported here have been conducted to investigate the propagation of smolder through a polyurethane foam sample under both diffusion driven and opposed forced flow driven smoldering. The present experiments, although limited, are unique in that they provide the only available information about smolder combustion in microgravity in sample sizes large enough to allow the self-propagation of the smolder reaction throughout...

An enthalpy-temperature hybrid method for solving phase change problems and its application to polymer pyrolysis and ignition

Thu, 15 Sep 2005 00:00:00 +0000

In this work, an enthalpy-temperature hybrid method is proposed for the numerical solution of generalized phase change problems, and applied to the prediction of polymer pyrolysis and ignition. The basic idea of this method is to treat both enthalpy and temperature as independent variables, and to solve the conservation equations and the constitutive equations (enthalpy-temperature relations) simultaneously. The formula of the enthalpy-temperature relations are not necessary the same for different phases, but can be chosen independently according to the characteristics of physical problems and the convenience of numerical analysis for each respective phase. Therefore this method applies to the problems regardless of the form of the constitutive equations. It overcomes the difficulty or even impossibility encountered in the traditional enthalpy-temperature method, of which either enthalpy or temperature must be consistently and explicitly expressed as a function of the other...

Microphones and Knock Sensors for Feedback Control of HCCI Engines

Thu, 8 Sep 2005 00:00:00 +0000

Homogeneous charge compression ignition (HCCI) engines lack direct in-cylinder mechanisms, such as spark plugs or direct fuel injection, for controlling the combustion timing. Many indirect methods have been used to control the combustion timing in an HCCI engine. With any indirect method, it is important to have a measure of the combustion timing so the control inputs can be adjusted for the next cycle. In this paper, it is shown that microphones and knock sensors can be used to detect combustion in HCCI engines. The output from various microphones and a knock sensor on an HCCI engine are measured at light and high loads. The combustion timing data obtained from the sensors are compared to the combustion timing data obtained from a piezoelectric cylinder pressure transducer. One of these sensors is selected and used for closed-loop control of the combustion timing in a single cylinder HCCI engine.

The Effect of the Di-Tertiary Butyl Peroxide (DTBP) additive on HCCI Combustion of Fuel Blends of Ethanol and Diethyl Ether

Thu, 8 Sep 2005 00:00:00 +0000

The influence of the small amounts (1-3%) of the additive di-tertiary butyl peroxide (DTBP) on the combustion event of Homogeneous Charge Compression Ignition (HCCI) engines was investigated using engine experiments, numerical modeling, and carbon-14 isotope tracing. DTBP was added to neat ethanol and diethyl ether (DEE) in ethanol fuel blends for a range of combustion timings and engine loads. The addition of DTBP to the fuel advanced combustion timing in each instance, with the DEE-in-ethanol mixture advancing more than the ethanol alone. A numerical model reproduced the experimental results. Carbon-14 isotope tracing showed that more ethanol burns to completion in DEE-in-ethanol blends with a DTBP additive when compared to results for DEE-in-ethanol without the additive. However, the addition of DTBP did not elongate the heat release in either case. The additive advances combustion timing for both pure ethanol and for DEE-in-ethanol mixtures, but the additive results in...

COSMIC: Carbon Monoxide and Soot in Microgravity Inverse Combustion

Fri, 26 Aug 2005 00:00:00 +0000

Almost seventy percent of fire related deaths are caused by the inhalation of toxins such as CO and soot that are produced when fires become underventilated.(1) Although studies have established the importance of CO formation during underventilated burning,(2) the formation processes of CO (and soot) in underventilated fires are not well understood. The goal of the COSMIC project is to study the formation processes of CO and soot in underventilated flames. A potential way to study CO and soot production in underventilated flames is the use of inverse diffusion flames (IDFs). An IDF forms between a central air jet and a surrounding fuel jet. IDFs are related to underventilated flames because they may allow CO and soot to escape unoxidized. Experiments and numerical simulations of laminar IDFs of CH4 and C2H4 were conducted in 1-g and µ-g to study CO and soot formation. Laminar flames were studied because turbulent models of underventilated fires are uncertain. Microgravity was...

Effect of Varied Air Flow on Flame Structure of Laminar Inverse Diffusion Flames

Fri, 26 Aug 2005 00:00:00 +0000

The structure of laminar inverse diffusion flames (IDFs) of methane and ethylene was studied using a cylindrical co-flowing burner. Several flames of the same fuel flow-rate yet various air flow-rates were examined. Heights of visible flames were obtained using measurements of hydroxyl (OH) laser-induced fluorescence (LIF) and visible images. Polycyclic aromatic hydrocarbon (PAH) LIF and soot laser-induced incandescence (LII) were also measured. In visible images, radiating soot masks the blue region typically associated with the flame height in normal diffusion flames (NDFs). Increased air flow-rates resulted in longer flames. PAH LIF and soot LII indicated that PAH and soot are present on the fuel side of the flame and that soot is located closer to the reaction zone than PAH. Ethylene flames produced significantly higher PAH LIF and soot LII signals than methane flames, which is consistent with the sooting propensity of

Bidimensional Numerical Model for Polyurethane Smoldering in a Fixed Bed

Fri, 26 Aug 2005 00:00:00 +0000

Smoldering combustion is described as an exothermic superficial heterogeneous-reaction that can propagate in the interior of porous fuels. Smoldering is generally an incomplete combustion reaction, which leaves behind a porous char that contains significant amounts of unburned fuel. If compared to flaming combustion, the heat release and the temperature characteristics of smoldering are low and its propagation is a slow process. Besides its characteristics of a weak combustion process, smoldering poses serious risk to fire safety; it is a common fire initiation scenario, because it is difficult to detect as, it can go unnoticed for long periods of time, It yields a high conversion of fuel to toxic products, and it can suddenly switch to flaming combustion. The propagation of the smoldering front is usually controlled by two factors: oxygen availability and heat losses. However it’s the result of several interacting mechanisms, such as chemical reactions (pyrolysis and oxidation),...

Flow-Assisted Flame Propagation Through a Porous Combustible in Microgravity

Wed, 24 Aug 2005 00:00:00 +0000

Experiments were conducted to measure the flame propagation rate of a plug-flow flame through a combustible matrix of randomly oriented cubes of polyurethane foam in microgravity and normal gravity as a function of the forced air flow. The experiments in microgravity were conducted at the Japan Microgravity Center (JAMIC) drop tower, which provides 10s of microgravity. The normal gravity experiments were simulations of the microgravity experiments, and by comparison, were used to determine the effect of gravity on the flame propagation process. The experiment was conducted in a cylindrical geometry. Ignition was accomplished by means of a hot-surface igniter brought into direct contact with the foam at one end of the sample holder. The other end of the sample was sealed to a fan drawing air through the sample, which was adjustable using a variable DC power supply. In this configuration the flame propagation is flow-assisted. The flame propagation rate was determined...

Investigation of HCCI Combustion of Diethyl Ether and Ethanol Mixtures Using Carbon 14 Tracing and Numerical Simulations

Wed, 24 Aug 2005 00:00:00 +0000

Despite the rapid combustion typically experienced in Homogeneous Charge Compression Ignition (HCCI), components in fuel mixtures do not ignite in unison or burn equally. In our experiments and modeling of blends of diethyl ether (DEE) and ethanol (EtOH), the DEE led combustion and proceeded further toward completion, as indicated by 14C isotope tracing. A numerical model of HCCI combustion of DEE and EtOH mixtures supports the isotopic findings. Although both approaches lacked information on incompletely combusted intermediates plentiful in HCCI emissions, the numerical model and 14C tracing data agreed within the limitations of the single zone model. Despite the fact that DEE is more reactive than EtOH in HCCI engines, they are sufficiently similar that we did not observe a large elongation of energy release or significant reduction in inlet temperature required for light-off, both desired effects for the combustion event. This finding suggests that, in general, HCCI combustion...

A Comparison of Three Fire Models in the Simulation of Accidental Fires

Mon, 22 Aug 2005 00:00:00 +0000

The assumptions and the results of applying three fire modeling approaches to study three accidental fires that occurred in single-family dwellings, are presented in this work. The modeling approaches used are: a simplified analytical model of fire growth, a zone model (CFAST) and a field model (FDS). The fires predicted are: a house fire of suspected initial location but of unknown ignition source, a small-apartment fire initiated by the ignition of a sofa which extinguished due to oxygen depletion, and a one-story house fire started by a malfunctioning gas heater. The input to each model has been kept as independent as possible from the other models while consistent with the forensic evidences. The predictions from the models of the fires’ characteristics are analyzed in the context of the forensic evidences for each accidental fire to compare the models’ predictive capabilities. It is found that in spite of the differences in the sophistication of these three modeling approaches,...

Transition from Forward Smoldering to Flaming in Small Polyurethane Foam Samples

Sat, 23 Apr 2005 00:00:00 +0000

Experimental observations are presented of the effect of flow velocity, oxygen concentration, and a thermal radiant flux, on the transition from smoldering to flaming in forward smoldering of small samples of polyurethane foam with a gas/solid interface. The experiments are part of a project studying the transition from smoldering to flaming under conditions encountered in spacecraft facilities, i.e., microgravity, low velocity variable oxygen concentration flows. Because the microgravity experiments are planned for the International Space Station, the foam samples had to be limited in size for safety and launch mass reasons. The feasible sample size is too small for smolder to self propagate because of heat losses to the surroundings. Thus, the smolder propagation and the transition to flaming had to be assisted by reducing heat losses to the surroundings and increasing the oxygen concentration. The experiments are conducted with small parallelepiped samples vertically placed...

The effect of buoyancy on opposed smoldering

Thu, 10 Mar 2005 00:00:00 +0000

An experimental investigation on the effects of buoyancy on opposed-flow smolder is presented. Tests were conducted on cylindrical samples of open-cell, unretarded polyurethane foams at a range of ambient pressures using the Microgravity Smoldering Combustion (MSC) experimental apparatus. The samples were tested in the opposed configuration, in which the flow of oxidizer is induced in the opposite direction of the propagation of the Smolder front. These data were compared with opposed-forced-flow tests conducted aboard STS-69, STS-77, and STS-105 and their ground-based simulations. Thermal measurements were made of the smolder reaction to obtain peak reaction temperatures and smolder velocities as a function of the ambient pressure in the MSC chamber. The smolder reaction was also observed using high-frequency ultrasound pulses as part of the ultrasound imaging system (UIS). The UIS measurements were used Lis a second means of providing smolder propagation velocities Lis well...

Forced forward smoldering experiments in microgravity

Thu, 10 Mar 2005 00:00:00 +0000

Results from two forward forced-flow smolder tests on polyurethane foam using air as oxidizer conducted aboard the NASA Space Shuttle (STS-105 and STS-108 missions) are presented in this work. The two tests provide the only presently available forward smolder data in microgravity. A complimentary series of ground-based tests were also conducted to determine, by comparison with the microgravity data, the effect of gravity on the forward smolder propagation. The objective of the study is to provide a better understanding of the controlling mechanisms of smolder for the purpose of control and prevention, both in normal- and microgravity. The data consists of temperature histories from thermocouples placed at various axial locations along the fuel sample centerline, and of permeability histories obtained from ultrasonic transducer pairs also located at various axial positions in the fuel sample. A comparison of the tests conducted in normal- and microgravity indicates that smolder...

Modeling of One-Dimensional Smoldering of Polyurethane in Microgravity Conditions

Thu, 10 Mar 2005 00:00:00 +0000

Results are presented from a model of forward smoldering combustion of polyurethane foam in microgravity. The transient one-dimensional numerical-model is based on that developed at the University of Texas at Austin. The conservation equations of energy, species and mass in the porous solid and in the gas phases are numerically solved. The solid and the gas phase are not assumed to be in thermal or in chemical equilibrium. The chemical reactions modeled consist of foam oxidation and pyrolysis reactions, as well as char oxidation. The model has been modified to account for new polyurethane kinetics parameters and radial heat losses to the surrounding environment. The kinetics parameters are extracted from thermogravimetric analyses published in the literature and using Genetic Algorithms as the optimization technique. The model results are compared with previous tests of forward smoldering combustion in microgravity conducted aboard the NASA Space Shuttle. The model calculates...