F. N. Egolfopoulos

University of Southern California | USC · Department of Aerospace and Mechanical Engineering

A computational investigation was carried out to assess the effects of highly energetic vortices on the local structure of laminar premixed flames. The study involved a lean atmospheric methane-air flame interacting with vortex sizes ranging from five times to half of the laminar flame thickness. The characteristic velocities of the vortices were c...

Intricacies associated with the estimation of laminar flame speed using the axisymmetric Bunsen flame technique were assessed, through parametric direct numerical simulations. The study involved methane-air mixtures at atmospheric pressure and temperature, and both the flame cone angle and flame surface area methods were utilized to estimate the la...

The influence of correlated scalar fluctuations on time-averaged laser absorption tomography measurements of temperature and species in a piloted turbulent premixed flame was examined using a coupled spectroscopic and fluid-dynamic analysis. To understand bias associated with turbulence, spatio-temporally resolved temperature and species mole fract...

An exploratory experimental and modeling investigation was performed to probe the effects of fuel and pressure on global observables of turbulent premixed methane-air, ethylene-air, and ethane-air jet flames. The study was carried out using a modified piloted premixed jet burner placed inside a variable pressure chamber. The experiments were conduc...

An experimental and numerical investigation of the thermochemical structure of piloted premixed jet flames was conducted, encompassing laser absorption tomography measurements and large-eddy simulations (LES). The investigation was performed holding laminar flame speed, jet Reynolds number, and surrounding flow conditions constant while considering...

The HyChem (hybrid chemistry) approach is utilized for modeling the combustion behaviors of gasoline fuels. The approach combines an experimentally constrained, lumped-step model for fuel pyrolysis under the high-temperature combustion condition and a detailed foundation fuel chemistry model to describe the subsequent oxidation of the pyrolysis pro...

Propagation of a confined spherically expanding flame induces isentropic compression that can culminate in autoignition and/or detonation under conducive thermodynamic conditions. This relatively simple technique measures a distinct ‘characteristic ignition delay time’ and complements other established approaches such as the rapid compression machi...

Radiation heat loss introduces one of the main uncertainties associated with the determination of laminar flame speeds from experiments using the spherically expanding flame constant volume method. In this study, a radiation model was developed to solve for the volumetric radiative power in spherical geometry using discrete transfer method accounti...

The laminar flame speed is an important input in turbulent premixed combustion modelling of spark ignition engines. At engine-relevant temperatures and pressures, its measurement is challenging or not possible and thereby it is usually obtained from simulations based on chemical models or power-law correlations. This work aims to investigate the pe...

The spherically expanding flame under constant volume method was introduced in 1934 by Lewis and von Elbe as a means to study laminar flame propagation at engine-relevant conditions. Despite its potential , this method has not been utilized extensively due to concerns regarding the underlying assumptions and data uncertainty. In the present study,...

The sensitivity coefficients of ignition delay time with respect to chemical kinetic rate parameters is traditionally calculated using a brute force approach wherein the number of initial value problems solved is no fewer than the number of rate parameters. By reformulating the underlying initial value problem as a boundary value problem, it is sho...

Unsteady premixed and non-premixed counterflow laminar flame simulations were conducted in order to investigate extinction effects on observables commonly used in turbulent combustion. CH4 and n-C12H26 were the fuels studied, with air as the oxidizer at pressures of 1, 5, and 10 bar. It was determined that CH2O persists, compared to all other react...

C1-C4 hydrocarbons are frequently referred to as foundational fuels, as their oxidation involves numerous rate-limiting steps that control the combustion characteristics of heavy practical fuels. The vast majority of the laminar flame speed data available in the literature have been determined at or near atmospheric conditions, and an extensive lit...

The isentropic compression that results from the propagation of a confined flame can lead to thermodynamic conditions favoring autoignition. First pointed out by Hu and Keck, this phenomenon serves as a technique to measure a well-defined characteristic ignition delay time (CIDT) and complement legacy approaches such as the rapid compression machin...

The Hybrid Chemistry (HyChem) approach has been proposed previously for combustion chemistry modeling of real, liquid fuels of a distillate origin. In this work, the applicability of the HyChem approach is tested for single-component fuels using JP10 as the model fuel. The method remains the same: an experimentally constrained, lumped single-fuel m...

An experimental study on the fuel type and attendant heat release effects on piloted turbulent premixed jet flames was carried out. The investigation focused on four fuels, namely methane, ethylene, n-heptane, and toluene, five lean to stoichiometric equivalence ratios, and two jet Reynolds numbers. The average flame height and the global turbulent...

The need for measuring laminar flame speeds for various fuels and blends is crucial for determining flame stabilization characteristics and design parameters for practical burner configurations. Various methodologies have been used over the years to estimate laminar flame speeds with axisymmetric Bunsen flames being one of the oldest and “simplest”...

A Hybrid Chemistry (HyChem) approach has been recently developed for the modeling of real fuels; it incorporates a basic understanding about the combustion chemistry of multicomponent liquid fuels that overcomes some of the limitations of the conventional surrogate fuel approach. The present work extends this approach to modeling the combustion beh...

Thermodynamic pressure rise during combustion is a key feature in internal combustion engines. Yet, hardly any studies have been conducted to investigate the effects of transient pressure rise on flame propagation as well as on the ignition of the unburned gas. In this study, the effects of unsteady pressure rise were parametrically studied using a...

Resistance to extinction by stretch is a key property of any flame, and recent work has shown that this property controls the overall structure of several important types of turbulent flames. Multiple definitions of the critical strain rate at extinction (ESR) have been presented in the literature. However, even if the same definition is used, diff...

The goal of this research was to develop a model for a UV photodecomposition reactor (PhoR), which is used for the removal of trace siloxane impurities from biogas. The model properly accounts for the phenomena taking place inside the reactor, including fluid flow, mass and heat transfer, the transmission of UV radiation, and the photodecomposition...

The opposed-jet counterflow configuration is widely used to measure fundamental flame properties that are essential targets for validating chemical kinetic models. The main and key assumption of the counterflow configuration in laminar flame experiments is that the flow field is steady and quasi one-dimensional. In this study, experiments and numer...

A tomographic laser absorption spectroscopy technique, utilizing mid-infrared light sources, is presented as a quantitative method to spatially resolve species and temperature profiles in small-diameter reacting flows relevant to combustion systems. Here, tunable quantum and interband cascade lasers are used to spectrally resolve select rovibration...

The laminar flame speed is an important property of a reacting mixture and it is used extensively for the characterization of the combustion process in practical devices. However, under engine-relevant conditions, considerable reactivity may be present in the unburned mixture, introducing thus challenges due to couplings of auto-ignition and flame...

The goal of this study is to assess the technical feasibility of remediating siloxane contaminants in biogas via a photochemical process. Specifically, we studied in the laboratory a process that involves the use of an ultraviolet (UV) photodecomposition reactor (PhoR) to convert siloxane trace impurities, commonly found in biogas produced in water...

The effect of fuel decomposition on fundamental flame properties was investigated computationally for atmospheric-pressure n-dodecane/air mixtures. The fuel decomposition was modeled under isobaric and adiabatic conditions for initial temperatures of 1100, 1200 and 1300 K, and equivalence ratios of 0.7, 1.0, and 1.4. For various extents of n-dodeca...

We propose and test an alternative approach to modeling high-temperature combustion chemistry of multicomponent real fuels. The hybrid chemistry (HyChem) approach decouples fuel pyrolysis from the oxidation of fuel pyrolysis products. The pyrolysis (or oxidative pyrolysis) process is modeled by seven lumped reaction steps in which the stoichiometri...

Real distillate fuels usually contain thousands of hydrocarbon components. Over a wide range of combustion conditions, large hydrocarbon molecules undergo thermal decomposition to form a small set of low molecular weight fragments. In the case of conventional petroleum-derived fuels, the composition variation of the decomposition products is washed...

Measurements of flame propagation velocities and extinction states in counterflow provide a valuable source of flame data that contain information about fundamental combustion physics. The approach to properly account for stretch effects in counterflow flame measurements through non-intrusive laser-based local velocity characterization was advanced...

Laminar flame speeds of methyl formate/air mixtures were measured at sub-atmospheric pressures for which limited data exist. The experiments were carried out in the counterflow configuration at an unburned mixture temperature of 333 K. The flow velocities were measured using particle image velocimetry. Particle phase slip correction was applied to...

Systems and methods for removal of gas phase contaminants may utilize catalytic oxidation. For example, a method may include passing a gas that includes a gas phase contaminant through a catalytic membrane reactor at a temperature of about 150° C. to about 300° C., wherein the catalytic membrane reactor includes a bundle of tubular inorganic membra...

Systems and methods for removal of gas phase contaminants may utilize catalytic oxidation. For example, a method may include passing a gas that includes a gas phase contaminant through a catalytic membrane reactor at a temperature of about 150° C. to about 300° C., wherein the catalytic membrane reactor includes a bundle of tubular inorganic membra...

An exploratory study was performed on highly turbulent piloted premixed jet flames of straight chain (paraffin and olefin), branched, cyclo, and aromatic C1-C8 hydrocarbons. The goal was to investigate fuel effects on global and local flame observables under flow conditions corresponding to the transition from the thin to the broken reaction zone r...

Real fuels may contain thousands of hydrocarbon components. This paper examines how nature simplifies the problem. We will discuss the internal structure of the fuel oxidation process at high temperatures. Over a wide range of conditions, large hydrocarbon molecules undergo thermal decomposition to form a small set of low-molecular weight fragments...

In this work we introduce an unconventional approach to modeling the high-temperature combustion chemistry of multicomponent real fuels. The hybrid chemistry (HyChem) approach decouples fuel pyrolysis from the oxidation of fuel decomposition intermediates. The thermal decomposition and oxidative thermal decomposition processes are modeled by seven...

With increasing use of alternative fuels, approaches that can efficiently model their combustion chemistry are essential to facilitate their utilization. The hybrid chemistry (HyChem) method incorporates a basic understanding about the combustion chemistry of multicomponent liquid fuels that overcomes some of the limitations of the surrogate fuel a...

Laminar flame speed measurements were carried for mixture of air with eight C 3-4 hydrocarbons (propene, propane, 1,3-butadiene, 1-butene, 2-butene, iso-butene, n-butane, and iso-butane) at the room temperature and ambient pressure. Along with C 1-2 hydrocarbon data reported in a recent study, the entire dataset was used to demonstrate how laminar...

An experimental and numerical investigation of fuel and hydrodynamic effects is performed on piloted pre-mixed jet flames. The investigation is carried out at a constant laminar flame speed, varying heat losses, jet Reynolds number, fuel molecular weight, and fuel chemical classification. Large Eddy Simulations are performed in an attempt to reprod...

The counterflow configuration is widely used to study experimentally premixed and non-premixed flame ignition, with the advantage being that the data can be modeled using quasi one-dimensional codes. In this study, experiments and direct numerical simulations were carried out in order to assess the validity of the assumptions of the one-dimensional...

The effects of transient plasma discharge on the autoignition characteristics of dimethyl ether and propane mixtures with oxygen and argon were investigated computationally in a zero-dimensional constant pressure environment. A simple model of hydrocarbon decomposition by electron collisions was superimposed on detailed chemical kinetic models that...

The current study aims to resolve the experimental and modeling discrepancies previously observed for the extinction strain rates of counterflow, non-premixed n-decane and n-dodecane/nitrogen mixture versus oxygen. To achieve this goal, a recently developed transport theory of cylindrical molecular structure in dilute gases is used to model the bin...

The autoignition behavior is key towards providing insight into a fuel's behavior and performance and equally important towards developing kinetic models. However, there has been evidence in past literature that under certain conditions legacy reactor experiments may exhibit inhomogeneities that could potentially reduce the scientific value of the...

The effect of flowfield geometry on flame propagation and extinction of atmospheric CH4/N2/air flames was studied in the counterflow configuration. Laminar flame speeds and extinction strain rates for lean premixed and non-premixed flames were measured in axisymmetric burners producing either uniform or non-uniform axial velocity exit profiles. Par...

A model was developed to describe the dynamic performance of a flow-through catalytic membrane reactor (FTCMR) used for the destruction of a chemical warfare agent (CWA) simulant, specifically dimethyl methylphosphonate (DMMP). For such a reactor, after a certain time period during which it provides full protection, its performance begins to declin...

Spherically expanding and counterflow flame configurations are used extensively to determine laminar flame speeds. Significant advances have been made over the years with both the theoretical and experimental aspects of these standard experiments. However, discrepancies still persist in reported laminar flame speed data raising the question of accu...

The spherically expanding flame method is the only approach for measuring laminar flame speeds at thermodynamic states that are relevant to engines. In the present study, a comprehensive evaluation of data obtained under constant pressure and constant volume conditions was carried out through experiments, development of a mathematically rigorous me...

The potential for the use of chemical weapons has increased in recent times. The successful use of a flow-through catalytic membrane reactor (FTCMR) as a protection system against a chemical warfare agent (CWA) was recently reported by this group. This FTCMR, employing a single catalytically active mesoporous membrane, was applied for the destructi...

Ignition temperatures of non-premixed flames of ethylene/n-dodecane blends were measured and modeled in the counterflow configuration at atmospheric pressure and an unburned fuel-carrying stream temperature of 453 K. Ethylene is an important product of the thermal decomposition of large molecular weight n-alkanes such as n-dodecane that produces et...

The possibility of use of chemical weapons has increased in recent years, both as a result of potential terrorist attacks as well as of ongoing international conflicts. The successful application of a flow-through catalytic membrane reactor (FTCMR) as an individual protection (IP) system for the destruction of dimethyl methylphosphonate (DMMP), whi...

The hydrogen oxidation chemistry constitutes the foundation of the kinetics of all carbon- and hydrogen-containing fuels. The validation of rate constants of hydrogen-related reactions can be complicated by uncertainties associated with experimental data caused by the high reactivity and diffusivity of hydrogen. In the present investigation accurat...

The uncertainties associated with the extraction of laminar flame speeds through extrapolations from directly measured experimental data were assessed using one-dimensional direct numerical simulations with focus on the effects of molecular transport and thermal radiation loss. The simulations were carried out for counterflow and spherically expand...

The decomposition of silane (SiH4), as a model silicon-containing trace compound in renewable natural gas (RNG), has been studied during RNG combustion at ambient pressure conditions, using the opposed-jet, flat-flame experimental configuration. Silane flame concentration profiles were obtained, which indicate that complete Sill, oxidation occurs i...

The extinction characteristics of non-premixed iso-cetane and decalin flames were investigated in the counterflow configuration at atmospheric pressure and a fuel-carrying stream temperature of 443 K. The flow velocities were measured using particle image velocimetry and the local pre-flame strain rate was determined at extinction. Two recently dev...

Speciation studies of low-pressure flames using intrusive sampling and molecular beam mass spectrometry analysis are essential towards developing and validating combustion models. In order to assess potential probe-induced effects, direct numerical simulations of a realistic experimental configuration were carried out using a finite-volume fully co...

The extinction strain rates of the non-premixed iso-cetane and decaline flames were experimentally investigated in the counterflow configuration at atmospheric pressure and a fuel-carrying stream temperature of 443 K. The results were compared with the previously determined extinction limits of n-hexadecane flames. It was found that as the fuel mas...

An experimental study was performed for piloted turbulent jet flames at high turbulence levels, and using for the first time fuels with relatively large molecular weights, between C6and C8, including linear, branched, alpha, cyclo, and aromatic hydrocarbons. The experiments aim to investigate the effects of the fuel chemistry on the flame structure...

The oxidation characteristics of several small methyl and ethyl esters with carbon number less than six were investigated in laminar flames. The kinetics of such fuels are subsets of those of larger alkyl esters that are constituents of practical biodiesel fuels. A total of seven fuels, namely methyl formate, methyl acetate, methyl propionate, meth...

Laminar flame speeds of iso-cetane/air and decalin/air mixtures were measured in the counterflow configuration at atmospheric pressure and an elevated unburned mixture temperature of 443 K. Axial flow velocities were measured along the stagnation streamline using the digital particle image velocimetry. The laminar flame speeds were determined by de...

Industries such as aviation and consumer electronics are currently being challenged to reduce and eventually eliminate their reliance on halogenated flame retardants because they are environmentally persistent and have the potential to generate highly toxic compounds during their oxidation. Phosphorus-based flame retardants have been proposed as al...

An experimental and computational investigation was conducted on the propagation of butanol/air flames. The butanol isomers have attracted interest as potential candidates for large-scale use in the transportation sector as next generation biofuels. Furthermore, the accurate description of the high-temperature oxidation chemistry of these fuels, wh...

Tabulated chemistry methods are used extensively in large eddy simulations of turbulent flames due to their computational efficiency. However, there is no universal choice of laminar flame configuration to represent a flamelet, and both twin counterflow flames and counterflow reactant to product flames have been utilized in previous work. A detaile...

The vortex-flame interaction has been studied extensively in the past in order to provide insight into turbulent combustion phenomena. However, most of the studies have been conducted in the wrinkled flamelet or corrugated flamelet regime using small molecular weight hydrocarbons. In the current work, the interaction of Zimont scale vortex/vortices...

The oxidation characteristics of C2 hydrocarbons were revisited in flames established in the counterflow configuration. Laminar flame speeds of ethane/air, ethylene/air, and acetylene/oxygen/nitrogen mixtures as well as extinction strain rates of non-premixed ethane/air flames were measured using digital particle image velocimetry. The experiments...

There is a strong drive towards utilizing oxygenated biofuels in blends with existing fossil fuels. Improving the kinetic modeling of the oxidation of these bio-derived oxygenates requires further investigation of their key stable intermediates such as the aldehydes. In this study, an experimental and chemical kinetic modeling investigation of prop...

Ignition temperatures of non-premixed flames of octane and decane isomers were determined in the counterflow configuration at atmospheric pressure, a free-stream fuel/N2 mixture temperature of 401 K, a local strain rate of 130 s−1, and fuel mole fractions ranging from 1% to 6%. The experiments were modeled using detailed chemical kinetic mechanisms...

Laminar flame speeds of mixtures of air with n-C14H30, n-C16H34, a petroleum-derived JP-5 jet fuel, a camelina-derived hydrotreated renewable JP-5 jet fuel, a petroleum-derived F-76 diesel fuel, and an algae-derived hydrotreated renewable F-76 diesel fuel, were measured in the counterflow configuration at atmospheric pressure and elevated unburned...

Ignition temperatures of non-premixed cyclohexane, methylcyclohexane, ethylcyclohexane, n-propylcyclohexane, and n-butylcyclohexane flames were measured in the counterflow configuration at atmospheric pressure, a free-stream fuel/N2 mixture temperature of 373 K, a local strain rate of 120 s−1, and fuel mole fractions ranging from 1% to 10%. Using t...

Laminar flame speeds and extinction strain rates of cyclopentadiene/air mixture were determined in the counterflow configuration at atmospheric pressure, unburned mixture temperature of 353 K, and for a wide range of equivalence ratios. The experiments were modeled using recently developed kinetic models. Sensitivity analyses showed that both flame...

Biofuels are considered as potentially attractive alternative fuels that can reduce greenhouse gas and pollutant emissions. iso-Pentanol is one of several next-generation biofuels that can be used as an alternative fuel in combustion engines. In the present study, new experimental data for iso-pentanol in shock tube, rapid compression machine, jet...

The combustion characteristics of promising alternative fuels have been studied extensively in the recent years. Nevertheless, the pyrolysis and oxidation kinetics for many oxygenated fuels are not well characterized compared to those of hydrocarbons. In the present investigation, the first chemical kinetic study of a long-chain linear symmetric et...

Understanding the kinetics of large molecular weight aldehydes is essential in the context of both conventional and alternative fuels. For example, they are key intermediates formed during the low-temperature oxidation of hydrocarbons as well as during the high-temperature oxidation of oxygenated fuels such as alcohols. In this study, an experiment...

The extinction characteristics of near-limit premixed flames were studied experimentally and theoretically under microgravity conditions in the opposed-jet counterflow configuration, to detemine the synergistic effects of heat loss and strain rate on flame extinction, and their implications on the existence of fundamental flammability limits. Exper...

The effect of O2 composition modulation on the dynamics and structure of lean CH4/air premixed flames was computationally and experimentally investigated, in light of its relevance to oxygen-enhanced combustion (OEC). OEC can result in conditions of stable combustion with reduced NOx emissions. Experiments were conducted in the stagnation flow conf...

The possibility of use of chemical weapons has increased in recent years, both as a result of potential terrorist attacks as well as of ongoing international conflicts. The successful application of a flow-through catalytic membrane reactor (FTCMR) as an individual protection (IP) system for the destruction of dimethyl methylphosphonate (DMMP), whi...

The fate of siloxane impurities during the combustion of renewable natural gas has been investigated experimentally in the counter-flow configuration. These impurities were shown to decompose completely within the pre-flame and luminous regions, and to form silica layers on metal surfaces in contact with the flame environment. It was determined tha...