Stoichiometric Flame Research Articles

Flame Structure and Propagation in Turbulent Flame-Droplet Interaction: A Direct Numerical Simulation Analysis

Three-dimensional Direct Numerical Simulations (DNS) in canonical configuration have been employed to study the combustion of mono-disperse droplet-mist under turbulent flow conditions. A parametric study has been performed for a range of values of droplet equivalence ratio ϕd, droplet diameter ad and root-mean-square value of turbulent velocity u′. The fuel is supplied entirely in liquid phase such that the evaporation of the droplets gives rise to gaseous fuel which then facilitates flame propagation into the droplet-mist. The combustion process in gaseous phase takes place predominantly in fuel-lean mode even for ϕd>1. The probability of finding fuel-lean mixture increases with increasing initial droplet diameter because of slower evaporation of larger droplets. The chemical reaction is found to take place under both premixed and non-premixed modes of combustion: the premixed mode ocurring mainly under fuel-lean conditions and the non-premixed mode under stoichiometric or fuel-rich conditions. The prevalence of premixed combustion was seen to decrease with increasing droplet size. Furthermore, droplet-fuelled turbulent flames have been found to be thicker than the corresponding turbulent stoichiometric premixed flames and this thickening increases with increasing droplet diameter. The flame thickening in droplet cases has been explained in terms of normal strain rate induced by fluid motion and due to flame normal propagation arising from different components of displacement speed. The statistical behaviours of the effective normal strain rate and flame stretching have been analysed in detail and detailed physical explanations have been provided for the observed behaviour. It has been found that the droplet cases show higher probability of finding positive effective normal strain rate (i.e. combined contribution of fluid motion and flame propagation), and negative values of stretch rate than in the stoichiometric premixed flame under similar flow conditions, which are responsible for higher flame thickness and smaller flame area generation in droplet cases.

Effects of Fuel Lewis Number on Localised Forced Ignition of Globally Stoichiometric Stratified Mixtures: a Numerical Investigation

The influences of fuel Lewis number L e F on localised forced ignition of globally stoichiometric stratified mixtures have been analysed using three-dimensional compressible Direct Numerical Simulations (DNS) for cases with L e F ranging from 0.8 to 1.2. The globally stoichiometric stratified mixtures with different values of root-mean-square (rms) equivalence ratio fluctuation (i.e. ϕ ′= 0.2, 0.4 and 0.6) and the Taylor micro-scale l ϕ of equivalence ratio ϕ variation (i.e. l ϕ /l f = 2.1, 5.5 and 8.3 with l f being the Zel’dovich flame thickness of the stoichiometric laminar premixed flame) have been considered for different initial rms values of turbulent velocity u ′. A pseudo-spectral method is used to initialise the equivalence ratio variation following a presumed bi-modal distribution for prescribed values of ϕ ′ and l ϕ /l f for global mean equivalence ratio 〈ϕ〉=1.0. The localised ignition is accounted for by a source term in the energy transport equation that deposits energy for a stipulated time interval. It has been observed that the maximum values of temperature and the fuel reaction rate magnitude increase with decreasing L e F during the period of external energy deposition. The initial values of L e F , u ′/S b(ϕ=1), ϕ ′ and l ϕ /l f have been found to have significant effects on the extent of burning of the stratified mixtures following localised ignition. For a given value of u ′/S b(ϕ=1), the extent of burning decreases with increasing L e F . An increase in u ′ leads to a monotonic reduction in the burned gas mass for all values of L e F in all stratified mixture cases but an opposite trend is observed for the L e F =0.8 homogeneous mixture. It has been found that an increase in ϕ ′ has adverse effects on the burned gas mass, whereas the effects of l ϕ /l f on the extent of burning are non-monotonic and dependent on ϕ ′ and L e F . Detailed physical explanations have been provided for the observed L e F , u ′/S b(ϕ=1), ϕ ′ and l ϕ /l f dependences.

Effect of Oxycombustion Diluents on the Extinction of Nonpremixed Methane Opposed-Jet Flames

ABSTRACTThis study investigates the differences between oxycombustion and conventional air combustion through methane flame extinction measurements and calculations. We report global extinction strain rates for methane with O2/N2, O2/CO2, and O2/CO2/H2O flames for a range of calculated stoichiometric adiabatic flame temperatures. Tests were performed in a subatmospheric opposed-jet burner, with pre-vaporized water. For a given oxidant diluent, global extinction strain rates increase strongly with increasing flame temperature and with pressure. At a given temperature, the effect of oxidant composition depends on whether dissociation is included in computing the stoichiometric adiabatic flame temperature. When dissociation is included, O2/CO2 and O2/CO2/H2O flames are roughly 30% harder to extinguish than O2/N2 flames. When dissociation is not included, the oxidant composition has a minimal effect. Calculations with the CHEMKIN suite of programs yield the same ranking of extinction strain rate for the different additives, when stoichiometric adiabatic flame temperature is matched with dissociation included.

Experimental and kinetic modeling study of a rich and a stoichiometric low-pressure premixed laminar 2,5-dimethylfuran/oxygen/argon flames

2,5-Dimethylfuran (DMF) is a promising biofuel and can be used as an alternative for or additive to gasoline. In this work, two low-pressure (30 Torr) premixed laminar DMF/oxygen/argon flames at the equivalence ratios of 1.0 and 1.5 were investigated using synchrotron vacuum ultraviolet photoionization mass spectrometry. Mole fraction profiles of the major species and the intermediates were measured. Especially, key species such as 2-(5-methyl)furylmethyl radical, 2,5-dimethylene-2,5-dihydrofuran, 1-oxo-1,3,4-pentatriene, 2-furylmethyl radical, fulvene, and cyclopentadienyl radical were quantified. A revised DMF model based on Somers model (Somers et al., 2013) was developed, including the addition of the fulvene kinetics and the development of the 2,5-dimethylene-2,5-dihydrofuran kinetics. The revised model, Somers model, and Togbé model (Togbé et al., 2014) were used to simulate the experimental results of this work. In general, the predicted mole fraction profiles are in reasonable agreement with the experimental results. The addition of the fulvene kinetics well predicts the mole fraction profiles of fulvene but over-predicts that of benzene. The formation of 2,5-dimethylene-2,5-dihydrofuran from 2-(5-methyl)furylmethyl radical becomes important in the stoichiometric DMF flame. The three models underestimate the mole fraction profile of 2-furylmethyl radical.

Experimental Investigation on the Influence of Simulated EGR Addition on Swirl-Stabilized CH4 Flames

AbstractLow-temperature combustion concepts for transport and power generation employ mixture dilution techniques, such as exhaust gas recirculation (EGR), that offer the potential of fuel flexibility, reduced pollutant emissions, and improved efficiency. These combustion modes, however, display a higher sensitivity to the compositional changes brought about by dilution, which in turn may have an adverse influence on the overall system performance. A fundamental study on the interactions between methane and simulated EGR was carried out on a swirl-stabilized, stoichiometric flame. The effects of varying levels and composition of diluents and preheating temperatures on flame structure and exhaust emissions, were experimentally investigated. Reductions of up to 90% and over 95% in NOx and CO emissions, respectively, where observed for higher levels of added diluents, whereas an increase in preheating temperature resulted in the opposite trends. It has been further demonstrated that, depending on fuel and th...

Effects of oxygen index on soot production and temperature in an ethylene inverse diffusion flame

An experimental study was conducted to investigate the effects of the Oxygen Index (OI) in an ethylene laminar inverse diffusion flame (IDF). The OI was varied from 21% to 37% and its influence was measured in terms of the flame height, soot volume fraction, soot temperature and radiant fraction. The stoichiometric flame height was measured by the spontaneous emission of CH∗ radicals and was found to decrease when the OI increases. In contrast, the luminous flame height increases with OI because soot can still form and grow beyond the reaction zone. Radial profiles of soot volume fraction and soot temperature were obtained by means of a Modulated Absorption/Emission (MAE) technique. The line-of-sight intensities, integrated along the optical path and captured by ECCD camera at two wavelengths were inverted using deconvolution and regularization techniques in order to obtain radial profiles of soot volume fraction and temperature. The increase in OI enhances soot volume fraction due to higher temperatures and soot formation rates. Both the local and integrated soot quantities increase with OI. The radiant fraction of IDF increases with the OI in a similar way to the integrated soot volume fraction.

A Study on Laminar Lifted Jet Flames for Diluted Methane in Co-flow Air

The laminar lifted jet flames for methane diluted with helium and nitrogen in co-flow air have been investigated experimentally. Such jet flames could be lifted in both buoyancy-dominated and jet momentum dominated regimes (even at nozzle exit velocities much higher than stoichiometric laminar flame speed) despite the Schmidt number less than unity. Chemiluminescence intensities of OH* radical (good indicators of heat release rate) and the radius of curvature for tri-brachial flame were measured using an intensified charge coupled device (ICCD) camera and digital video camera at various conditions. It was shown that, an increase in OH * concentration causes increase of edge flame speed via enhanced chemical reaction in buoyancy dominated regime. In jet momentum dominated regime, an increase in radius of curvature in addition to the increased OH * concentration stabilizes such lifted flames. Stabilization of such lifted flames is discussed based on the stabilization mechanism.

Combustion characteristic and heating performance of stoichiometric biogas–hydrogen–air flame

An experimental study has been conducted to investigate stoichiometric biogas–hydrogen mixed fuel flames and the combustion characteristic and heating performance of three biogases enriched with hydrogen were examined. Both similar flame behavior and new finding are reported with reference to the literature.The dependence of flame stability on the fraction of hydrogen and the CO2 concentration was analyzed in the aspects of fuel property alteration and flow aerodynamics variation. The experiments showed a favorable effect of hydrogen and detrimental effect of CO2 on flame stability. Examination of flame cone height showed that under constant Re and Ф, the cone height is longer at either higher hydrogen fraction or higher CO2 concentration. In addition, at higher fraction of hydrogen in the mixed fuel, flame flammability strengthens, flame temperature enhances and CO emission reduces. Further, polyhedral reaction cone was detected for stoichiometric flames under high hydrogen concentration conditions.Great care was paid to the heat transfer behavior of stoichiometric biogas–hydrogen flames. First, when the cone tip touches the copper plate, the stagnation point heat flux is not the maximum peak when compared to heat flux peaks at other nozzle-to-plate distance. Comparison between two flames of identical cone height indicated that higher flame temperature is a dominant factor influencing heat transfer. Further, longer flame height tends favor heat transfer only at large nozzle-to-plate distances.

Intracavity Laser Absorption Spectroscopy Study of HCO Radicals during Methane to Hydrogen Conversion in Very Rich Flames

Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser diagnostics. Absolute concentration profiles of HCO were measured by intracavity laser absorption spectroscopy, and temperature profiles were obtained with laser-induced fluorescence of OH. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. These new experimental data were compared with predictions of two models: GRI-mech. 3.0 and Aramco mech. 1.3. GRI-mech. performs better in a stoichiometric flame, whereas Aramco mech. is in better agreement with experiments in the rich flames. Detailed analysis of the behavior of these two models revealed that similar performance is essentially fortuitous and explained by balancing of different reactions involved in HCO formation and consumption.

Structure of CH4/O2/Ar flames at elevated pressures studied by flame sampling molecular beam mass spectrometry and numerical simulation

Experimental data are reported on the structure of laminar premixed methane/oxygen/argon flames stabilized over a flat burner at 1, 3, and 5 atm with different equivalence ratios ϕ (0.8–1.2). Mole fraction profiles of the reactants (CH4, O2), major stable products (CO2, H2O, H2, CO) and intermediates such as H, OH, CH3 radicals, as well as ethylene and acetylene, were measured by molecular-beam mass spectrometry. The temperature profiles in the flames were measured by thermocouples in the presence of a sampling probe to take into account the flame cooling effect due to the probe. The structures of stoichiometric flames at 1, 3 and 5 atm were compared to elucidate the effect of pressure on the mole fractions of the flame species. Fuel-lean (ϕ = 0.8) and fuel-rich (ϕ = 1.2) flames at 5 atm were also investigated in this work. All the experimental data were compared with the numerical simulations using the Premix code and three detailed chemical kinetic mechanisms for methane combustion available in the literature: the GRI-Mech 3.0, AramcoMech 1.3 and USC Mech II. The absolute mole fractions of CH4, O2, H2O, CO, CO2, H2, H, OH, CH3 in the flames and their dependences on pressure were captured by both mechanisms reasonably well. An analysis of the reaction mechanisms was performed to gain insights into the kinetics of methane combustion in stoichiometric conditions in the range of pressures from 1 to 5 atm and to explain the observed pressure effects on peak mole fractions of flame radicals. The decrease of peak mole fractions of acetylene and ethylene with pressure increase, which was observed in the experiments, was not reproduced by the mechanisms. Both mechanisms predicted the increase in their peak mole fractions with pressure (in the range from 1 to 3 atm). The kinetic analysis indicated the need to revise the pressure-dependent chemistry of acetylene and ethylene formation in the mechanisms.

Near-Field Characteristics of a Rectangular Jet and Its Effect on the Liftoff of Turbulent Methane Flame

Understanding the stability of turbulent flames is a key for the design of efficient combustion systems. The present paper reports an experimental study on the effect of the internal geometry of a rectangular orifice on the characteristics/stability of a turbulent methane flame. Three rectangular nozzles with different orifice lengths having an identical exit aspect ratio (AR) of 2 were used. The co-airflow strength was also varied to evaluate its effect on the jet flow emerging from the rectangular nozzle. The experimental data revealed that the jet initial conditions affect both the flow characteristics and the liftoff of turbulent diffusion methane flame. That is, increasing the orifice length of the rectangular nozzle resulted in delaying the occurrence of the axis-switching phenomenon, reducing the length of the jet potential core, and accelerating the liftoff transition of the attached flame. The co-airflow was found to reduce the velocity strain rate in the shear layer, displace the occurrence of axis-switching farther downstream of the jet, and delay flame detachment. The results revealed also that there is a clear interplay between the flame liftoff and the jet near-field molecular mixing and flow characteristics. That is, a rectangular jet which spreads faster and generates higher near-field velocity strain and turbulence intensity causes flame detachment at a lower fuel jet velocity. Based on this, a correlation was found between the flame liftoff velocity, the fuel molecular thermal diffusivity, the stoichiometric laminar flame speed, and the fuel jet strain rate at the nozzle exit. This relationship was shown to successfully predict the liftoff velocity of methane flame as well as other common gaseous hydrocarbons and hydrogen flames.

Assessment of an Equivalent Reaction Networks Approach for Premixed Combustion

The pollutants produced by the burning of fossil fuels have a severe impact on the environment and on mankind. Computational fluid dynamics (CFD) is a powerful tool, which is widely used to predict the emission of these pollutants from industrial combustion systems. Nevertheless, to predict these emissions the chemical reaction must be represented by a detailed mechanism, which includes pollutant formation pathways. Thus, using a complex mechanism, especially in 3D simulations with a realistic geometry is prohibitively expensive computationally. In this article, the equivalent reaction networks (ERN) method is used in conjunction with a Reynolds-averaged Navier Stokes (RANS) approach to reduce the cost of these computations. For this purpose, a pilot stabilized stoichiometric methane-air flame is chosen with a specific interest in species with slow time scales, such as CO and NOx. The Favre averaged CFD results are then compared to previously-reported experimental measurements and earlier computations using conditional moment closure (CMC) at five axial locations within the flame. Despite the simplicity of the ERN method in contrast with other more complex combustion models, the comparison of the CFD results with the experimental measurements for the prediction of CO are extremely encouraging.

Some aspects of stabilization and structure of laminar premixed hydrogen-air flames in a microchannel

In the present paper, flame stabilization and structure are investigated numerically for non-adiabatic hydrogen-air flames at different equivalence ratios and inlet velocities. A cylindrical microcombustor in which combustion occurs in the annular region between two concentric tubes is investigated. The inner hollow tube contains static nitrogen gas and this combination acts as a thermal reservoir that stores and recirculates heat to the incoming mixture. Investigations are carried out using detailed numerical model incorporating two-dimensional transport, thermal radiation, multi-step kinetics, and conjugate heat transfer. Flame is sustained by the continuous ignition mechanism activated by an uninterrupted temperature field between gas mixture and wall developing at steady state. Heat losses from flame resulted in a crossover temperature higher than that of the lean-limit and stoichiometric free flames due to slow radical build-up. Thermal diffusion of hydrogen is shown to be responsible for enhancing the burning intensity of leading edge. Diffusion and reaction kinetics at the flame tip result in twin-peaked heat release rate distribution, most prominently for fuel rich flame (ϕ = 1.7).

Effect of piston shapes and fuel injection strategies on stoichiometric stratified flame ignition (SFI) hybrid combustion in a PFI/DI gasoline engine by numerical simulations

In this research, the stratified flame ignition (SFI) hybrid combustion process was proposed to enhance the control of SI–CAI hybrid combustion and moderate the maximum pressure rise rate (PRRmax) by the combination of port fuel injection (PFI) and direct injection (DI). The effect of the stratified flame formed by different piston shapes, start of direct injection (SOI) timings and direct injection ratios (rDI) on the stoichiometric SFI hybrid combustion and heat release process was studied using the three-dimensional computational fluid dynamics (3-D CFD) simulations. The spark ignited flame propagation near the spark plug and the auto-ignition heat release process of the diluted mixture were modelled in the framework of 3-Zones Extended Coherent Flame Model (ECFM3Z) by the extended coherent flame model and tabulated auto-ignition chemistry of a 4-component gasoline surrogate, respectively. The operating load of indicated mean effective pressure (IMEP) 3.6bar was selected to represent a typical part-load operation. The sweep of the spark timing (ST) was performed for different pistons, SOI timings and direct injection ratios. The SFI hybrid combustion process with the same combustion phasing was investigated in details. The optimal stratified mixture pattern, characterized with the central rich mixture around spark plug and stratified lean mixture at the peripheral region, formed by the newly designed Piston A and B effectively lowers the PRRmax with a slight deterioration of IMEP. The later SOI timing advances the crank angle of 50% total heat release (CA50) and significantly reduces the PRRmax with a little deterioration of IMEP. As the direct injection ratio is increased, both the PRRmax and IMEP decrease. During the SFI hybrid heat release process, spark timing is effective to control CA50, IMEP and PRRmax regardless the piston shapes, SOI timings and direct injection ratios. However, the sensitivity of SFI hybrid combustion to the stratified mixture varies with the spark timing. The reduction of the PRRmax caused by the stratified flame enables the advance of spark timing to achieve maximum IMEP.

Detailed influences of chemical effects of hydrogen as fuel additive on methane flame

A detailed kinetic analysis of chemical effects of hydrogen addition on laminar premixed stoichiometric methane-air flames was conducted at atmospheric pressure. Flame structures and mole fraction profiles affected by chemical effects of hydrogen addition for major species, free radicals and intermediate species are analyzed with particular emphasis on the formations of soot precursor and oxygenated air pollutants. The results illustrate that chemical effects of hydrogen additive lead the methane profile to move towards the upstream side and suppress the formation of acetylene and ketene. The concentrations of free radical H, O and OH increase as methane is replaced by hydrogen mainly due to its chemical effects. In contrast, although the chemical effects of hydrogen addition facilitate the productions of formaldehyde and acetaldehyde, the hydrogen dilution and thermal effects on reducing mole fractions of both species are more significant. As a consequence, the total effects of hydrogen addition lead to a decrease in formaldehyde and acetaldehyde concentrations. Compared to formaldehyde and acetaldehyde, NO mole fraction diminishes in a similar fashion with increased hydrogen additive that the decrease of NO concentration caused by hydrogen dilution and thermal effects is larger than the increase due to its chemical effects.

Laminar burning velocities at elevated pressures for gasoline and gasoline surrogates associated with RON

The development and validation of a new gasoline surrogate using laminar flame speed as a target parameter is presented. Laminar burning velocities were measured using a constant-volume spherical vessel with ignition at the center of the vessel. Tested fuels included iso-octane, n-heptane, toluene, various mixtures of primary reference fuels (PRFs) and toluene reference fuels (TRFs) and three gasoline fuels of 70, 85 and 95 RON (FACE J, C and F) at the initial temperature of 358K and pressures up to 0.6MPa in the equivalence ratio ranging from 0.8 to 1.6. Normalized laminar burning velocity data were mapped into a tri-component mixture space at different experimental conditions to allocate different gasoline surrogates for different gasoline fuels, having RON of 70, 85 and 95. The surrogates of TRF-70-4 (17.94% iso-C8H18+42.06% n-C7H16+40% C7H8), TRF-85-1 (77.4% iso-C8H18+17.6% n-C7H16+5% C7H8), and TRF-95-1 (88.47% iso-C8H18+6.53% n-C7H16+5% C7H8) of RON 70, 85 and 95, respectively, are shown to successfully emulate the burning rate characteristics of the gasoline fuels associated with these RONs under the various experimental conditions investigated. An empirical correlation was derived to obtain laminar burning velocities at pressures that are experimentally unattainable as high as 3.0MPa. Laminar burning velocities were comparable to the simulated values for lean and stoichiometric flames but they were relatively higher than the simulated values for rich flames. A flame instability assessment was conducted by determining Markstein length, critical Pecklet number, and critical Karlovitz number at the onset of flame instability.

Oxy-combustion of Low-Volatility Liquid Fuel with High Water Content

Following our previous studies of swirl-stabilized spray combustion of fuels that have a high water content, in this work, we investigate low-volatility fuels, specifically glycerol. Results show that, to obtain a self-sustained flame, the concentration of glycerol in water is much higher than that of ethanol (a high-volatility fuel) in water. However, even for glycerol concentrations as high as 60 wt %, the self-sustained flame is lifted from the nozzle and not attached, as in the ethanol case. The calculated stoichiometric adiabatic flame temperature (Tad) for 60 wt % glycerol is 2602 °C, whereas for 15 wt % ethanol (which is a very stable flame), it is only 673 °C. The two systems differ in that ethanol is more volatile than water, whereas glycerol is less. Thus, in the former case, the fuel is preferentially vaporized, whereas in the latter case, water is preferentially vaporized. Thus, flame stabilization is particularly challenging for fuels where the volatility is less than that of water when the water content of the spray is high. To assist flame stability for glycerol–water solutions, tert-butanol and ethanol were added in low concentrations. Experimental results revealed that stable attached flames can be obtained for 30 wt % glycerol in water when 8.3 wt % tert-butanol (B8.3/G30) or 10 wt % ethanol (E10/G30) is added under oxy-fired conditions. Both tert-butanol and ethanol have been shown to be particularly volatile in water when present at low concentrations because of their high vapor pressures and very high activity coefficients. The flame stability for B8.3/G30 and E10/G30 was characterized under 100 and 85% swirl flow conditions. Temperature measurements were conducted for four stable flames, and temperature contours were generated. For the stable flames, a hot zone exists in the near burner region, because of the preferential vaporization of the high-volatility fuel component, which provides heat to robustly vaporize the fuel and stabilize the flame.

Effects of hydrogen addition on propagation characteristics of premixed methane/air flames

An experimental study has been conducted to investigate the effects of hydrogen addition on the fundamental propagation characteristics of methane/air premixed flames at different equivalence ratios in a venting duct. The hydrogen fraction in the methane–hydrogen mixture was varied from 0 to 1 at equivalence ratios of 0.8, 1.0 and 1.2. The results indicate that the tendency towards flame instability increased with the fraction of hydrogen, and the premixed hydrogen/methane flame underwent a complex shape change with the increasing hydrogen fraction. The tulip flame only formed when the fraction of hydrogen ranged from 0 to 50% at an equivalence ratio of 0.8. It was also found that the flame front speed and the overpressure increased significantly with the hydrogen fraction. For all equivalence ratios, the stoichiometric flame (Φ = 1.0) has the shortest time of flame propagation and the maximum overpressure.

An Experimental and Kinetic Modeling Study of Premixed Laminar Flames of Methyl Pentanoate and Methyl Hexanoate

Abstract Detailed chemical structures of stoichiometric and rich premixed laminar flames of methyl pentanoate and methyl hexanoate were investigated over a flat burner at 20 Torr and for methyl pentanoate at 1 atm. Molecular beam mass spectrometry was used with tunable synchrotron vacuum ultraviolet (VUV) photoionization for low pressure flames of both methyl pentanoate and methyl hexanoate, and soft electron-impact ionization was used for atmospheric pressure flames of methyl pentanoate. Mole fraction profiles of stable and intermediate species, as well as temperature profiles, were measured in the flames. A detailed chemical kinetic high temperature reaction mechanism for small alkyl ester oxidation was extended to include combustion of methyl pentanoate and methyl hexanoate, and the resulting model was used to compare computed values with experimentally measured values. Reaction pathways for both fuels were identified, with good agreement between measured and computed species profiles. Implications of these results for future studies of larger alkyl ester fuels are discussed.

Experimental and kinetic modeling study of styrene combustion

The aim of this work is to report new experimental data on styrene combustion and develop a kinetic model for styrene combustion. Three laminar premixed flames of styrene with equivalence ratios of 0.75, 1.00 and 1.70 were studied at low pressure (0.0395atm) using synchrotron vacuum ultraviolet photoionization mass spectrometry. The JSR oxidation of styrene/benzene mixtures with three equivalence ratios of 0.50, 1.00, and 1.50 was studied at atmospheric pressure using gas chromatography. The mole fraction profiles of flame species and oxidation species were measured. A kinetic model of styrene combustion with 290 species and 1786 reactions was developed from our recently reported toluene model, and was validated on the new experimental data from this work and previous ignition delay time data. The O-atom attack reactions, H-atom abstraction reactions and other H-atom attack reactions were found to dominate the consumption of styrene. In particular, the O-atom attack reactions on the double bond of styrene play an important role in the JSR oxidation and the lean and stoichiometric flames, while the pyrolytic reactions have increasing contributions as the equivalence ratio increases. The phenyl radical plays a crucial role in the decomposition of styrene since it affords most of the reaction fluxes from styrene. In the aromatics growth process, phenylacetylene, the 1-phenylvinyl radical, the phenyl radical, and styrene serve as major precursors of polycyclic aromatic hydrocarbons (PAHs), leading to the high sooting tendency of styrene compared to toluene and ethylbenzene.