Full Pressure Range Research Articles

Assessing relative contributions of transport mechanisms and real gas properties to gas flow in nanoscale organic pores in shales by pore network modelling

It is well-known that the movement of gas in organic nanoscale pores of typical shales must be modelled by capturing real gas flow behaviours in the full range of flow regimes, gas ad-/de-sorption and its effect on the flow, and surface diffusion while properly accounting for real gas PVT and viscosity changes as affected by the confined pore space. So far, no comprehensive model has been developed to enable the evaluation of the relative contributions of each of these physical aspects in a realistic organic pore space. In this work, a steady-state pore-network gas flow model that accounts for all of the listed aspects is developed to allow an assessment of their flow contributions in organic pores. The gas flow model is applied to three pore/throat network models, which are constructed from the same realistic pore network but with different average pore radii at 15.6, 3.2 and 1.56 nanometres, respectively, to calculate apparent gas permeability for each model at gas pressures ranging from 5 to 70MPa. Analytical solution is applied to calculate the apparent gas permeability at the same gas pressures for three cylindrical pores with pore radii equal to the average pore radii of respective pore networks. For both the single pores and the pore networks, results show that when the average or single pore radius is larger than 10nm, there is little influence on apparent gas permeability no matter what gas property, either real or ideal gas, is considered, nor is the surface diffusion, in the full pressure range. However, when the pore radius is smaller than 5nm, the apparent gas permeability is notably influenced by the gas property and the surface diffusion. Furthermore when the pore radius is less than 2nm, the gas permeability will be significantly underestimated if the surface diffusion is neglected. It is found that the influence of both critical temperature and pressure in the confined pore space, which deviate from the expected values in wide space, is insignificant and negligible on shale gas permeability. The relative contributions of the gas property and the surface diffusion, respectively, are shown to follow different trends for the single pores and the pore networks within the range of the pressures. An analysis shows that the differences can be attributed to the mixture of large and small pores and throats in a pore network that effectively suppresses the stronger effects of the gas property and the surface diffusion in the smaller pores and throats. This indicates the importance to consider spatial pore size distribution and pore connectivity when seeking to estimate effective properties.

CH4/CO2 Mixture Adsorption on a Characterized Activated Carbon

The aim of this work is to provide new experimental data of the adsorption equilibria of CH4/CO2 binary mixtures on a microporous activated carbon Ecosorb. The mixtures studied were made for two nominal feed-gas compositions of 25 and 75 mol %. Adsorption isotherms were performed using a homemade manometric technique, combined with gas chromatographic analysis of the equilibrium gas-phase composition. Experimental isotherms are provided up to 3 MPa for three temperatures at 303.15 K, 323.15 K, and 353.15 K. The equimolar mixture was previously studied thus allowing a description of the CO2/CH4 mixture adsorption in a full range of pressure, temperature, and composition. As expected, the binary adsorption isotherms mixture reveals a preferential adsorption of CO2 compared to CH4 over the whole pressure and temperature range. Additionally, these adsorption data were used to check the capability of the ideal adsorbed solution (IAS) theory to estimate the mixture adsorption of CH4/CO2. At low pressures (up to...

Atmospheric Chemistry of Criegee Intermediates: Unimolecular Reactions and Reactions with Water.

Criegee intermediates are produced in the ozonolysis of unsaturated hydrocarbons in the troposphere, and understanding their fate is a prerequisite to modeling climate-controlling atmospheric aerosol formation. Although some experimental and theoretical rate data are available, they are incomplete and partially inconsistent, and they do not cover the tropospheric temperature range. Here, we report quantum chemical rate constants for the reactions of stabilized formaldehyde oxide (CH2OO) and acetaldehyde oxide (syn-CH3CHOO and anti-CH3CHOO) with H2O and for their unimolecular reactions. Our results are obtained by combining post-CCSD(T) electronic structure benchmarks, validated density functional theory potential energy surfaces, and multipath variational transition state theory with multidimensional tunneling, coupled-torsions anharmonicity, and high-frequency anharmonicity. We consider two different types of reaction mechanisms for the bimolecular reactions, namely, (i) addition-coupled hydrogen transfer and (ii) double hydrogen atom transfer (DHAT). First, we show that the MN15-L exchange-correlation functional has kJ/mol accuracy for the CH2OO + H2O and syn-CH3CHOO + H2O reactions. Then we show that, due to tunneling, the DHAT mechanism is especially important in the syn-CH3CHOO + H2O reaction. We show that the dominant pathways for reactions of Criegee intermediates depend on altitude. The results we obtain eliminate the discrepancy between experiment and theory under those conditions where experimental results are available, and we make predictions for the full range of temperatures and pressures encountered in the troposphere and stratosphere. The present results are an important cog in clarifying the atmospheric fate and oxidation processes of Criegee intermediates, and they also show how theoretical methods can provide reliable rate data for complex atmospheric processes.

Failure pressures after repairs of 2-cm × 2.5-cm rhinologic dural defects in a porcine ex vivo model.

The objective of this study was to determine failure pressures of 6 rhinologic repair techniques of large skull base/dural defects in a controlled, ex vivo model. Failure pressures of 6 dural repairs in a porcine model were studied using a closed testing apparatus; 24-mm × 19-mm dural defects were created; 40-mm × 34-mm grafts composed of porcine Duragen (Integra), fascia lata, and Biodesign (Cook) were used either with or without Tisseel (Baxter International Inc.) to create 6 repairs: Duragen/no glue (D/NG), Duragen/Tisseel (D/T), fascia lata/no glue (FL/NG), fascia lata/Tisseel (FL/T), Biodesign/no glue (B/NG), and Biodesign/Tisseel (B/T). Saline was infused at 30 mL/hour, applying even force to the underside of the graft until repair failure. Five trials were performed per repair type for a total of 30 repairs. Mean failure pressures were as follows: D/NG 1.361 ± 0.169 cmH2 O; D/T 9.127 ± 1.805 cmH2 O; FL/NG 0.200 ± 0.109 cmH2 O; FL/T 7.833 ± 2.657 cmH2 O; B/NG 0.299 ± 0.109 cmH2 O; and B/T 2.67 ± 0.619 cmH2 O. There were statistically significant differences between glued (Tisseel) and non-glued repairs for each repair category (p < 0.05). All glued repairs performed better than non-glued repairs. Both D/T and FL/T repairs performed better than B/T repairs. No repair tolerated pressures throughout the full range of adult supine intracranial pressure.

Determination of the Dominant Species and Reactions in Non-equilibrium CO2 Thermal Plasmas with a Two-Temperature Chemical Kinetic Model

It has become increasingly clear that deviations from local thermodynamic equilibrium occur in thermal plasmas. This paper is devoted to investigating the non-equilibrium characteristics of CO2 thermal plasmas, which have wide application in industry. A two-temperature chemical kinetic model with a comprehensive chemical system is developed to calculate the non-equilibrium characteristics of CO2 thermal plasmas for a wide temperature range, from 12,000 to 500 K, at atmospheric pressure. The non-equilibrium results are compared to the equilibrium composition obtained by Gibbs free energy minimization, and significant deviations are found at lower temperatures. Based on the dependence of molar fractions on temperature, the dominant species are determined in three temperature ranges. The dominant reactions are then obtained by considering their contribution to the generation and loss of the dominant species. Using the dominant species and reactions, the full model is simplified into three simpler models and the accuracy of the simplified models is evaluated. It is shown that this approach greatly reduces the number of species and reactions considered, while showing good agreement with the full model, with a root-mean-square error of no more than 4 %. Thus, the complicated physicochemical processes in non-equilibrium CO2 thermal plasmas can be characterized by relatively few species and reactions. It is suggested that the two-temperature chemical kinetic model developed in this paper can be applied to the full range of pressures that occur in arc welding, arc quenching and other industrial applications. In addition, the simplified methods can be applied in multi-dimensional models to reduce the chemical complexity and computing time while capturing the main physicochemical processes in non-equilibrium CO2 thermal plasmas.

Strong enhancement of superconductivity at high pressures within the charge-density-wave states of2H−TaS2and2H−TaSe2

We present measurements of the superconducting and charge density wave critical temperatures (Tc and TCDW) as a function of pressure in the transition metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility measurements show that Tc increases from temperatures below 1 K up to 8.5 K at 9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in transition from incommensurate CDW to commensurate CDW. Above this pressure, the commensurate TCDW slowly decreases coexisting with superconductivity within our full pressure range.

Multispectrum analysis of the oxygen A-band

Retrievals of atmospheric composition from near-infrared measurements require measurements of airmass to better than the desired precision of the composition. The oxygen bands are obvious choices to quantify airmass since the mixing ratio of oxygen is fixed over the full range of atmospheric conditions. The OCO-2 mission is currently retrieving carbon dioxide concentration using the oxygen A-band for airmass normalization. The 0.25% accuracy desired for the carbon dioxide concentration has pushed the required state-of-the-art for oxygen spectroscopy. To measure O2 A-band cross-sections with such accuracy through the full range of atmospheric pressure requires a sophisticated line-shape model (Rautian or Speed-Dependent Voigt) with line mixing (LM) and collision induced absorption (CIA). Models of each of these phenomena exist, however, this work presents an integrated self-consistent model developed to ensure the best accuracy.It is also important to consider multiple sources of spectroscopic data for such a study in order to improve the dynamic range of the model and to minimize effects of instrumentation and associated systematic errors. The techniques of Fourier Transform Spectroscopy (FTS) and Cavity Ring-Down Spectroscopy (CRDS) allow complimentary information for such an analysis. We utilize multispectrum fitting software to generate a comprehensive new database with improved accuracy based on these datasets. The extensive information will be made available as a multi-dimensional cross-section (ABSCO) table and the parameterization will be offered for inclusion in the HITRANonline database.

Experimental and numerical studies of pressure effects on syngas combustor emissions

Pressure effects on NOx and CO emissions of a model syngas combustor were experimentally and numerically studied. The validated numerical method was employed to analyze pressure effects on the combustor emissions such as different mixing levels and extra reactant addition. The model combustor, fueled with 10MJ/Nm3 coal-derived syngas, was installed in a pressurized test-rig, and emissions were measured within 0.1–0.35MPa. Based on the flow, temperature and species fields calculated by the CFD method, a chemical reactor network (CRN) model was established. With a detailed chemical scheme, the emissions calculated by the CRN model agreed well with experimental results. The model was then employed to calculate emissions within pressure range from 0.1 to 2.0MPa, with the adiabatic flame temperature in the primary zone varied from 1477 to 2317K. The calculated NOx and CO emissions generally showed exponential relationship with the operating pressure, except that the NOx emission decreased at higher pressure when the primary adiabatic flame temperature was lower than 1800K. Through the analyses of the NOx formation pathways, it was found that the higher pressure would generally enhance the N2O pathway, which dominated NOx formation at low temperature, but NOx emission concentration through N2O pathway decreased with pressure above 1.0MPa at low temperature, which could explain the NOx emission behavior. The CRN modeling method was applied to analyze the effects of pressure on emission behaviors under the different mixing modes and with the extra reactant such as H2O and NH3 in fuel. Premixed and steam dilution burning modes showed better performance on reducing emissions at elevated pressures. NH3 could obviously increase the emission levels, especially at low pressure. Comprehensive understanding of the relationship between the emissions and the operating pressure in full pressure range was obtained, which could be valuable for the predicting and analyzing the syngas combustor pollutant emissions.

Adsorption equilibria and kinetics of six pure gases on pelletized zeolite 13X up to 1.0 MPa: CO2, CO, N2, CH4, Ar and H2

The adsorption equilibria and kinetics of CO2, CO, N2, CH4, Ar and H2 on zeolite 13X were measured via the volumetric method at 293, 308 and 323K and up to 1.0MPa. Adsorption isotherms and the heat of adsorption were analyzed over a full range of pressures. Each experimental isotherm was correlated with Langmuir, Sips and temperature-dependent Sips models, with the deviations for each model being evaluated. The Sips model showed a smaller degree of deviation from the experimental data than the Langmuir model. The isosteric heat of adsorption sequence was H2<Ar<CH4≒N2<CO<CO2 along with surface loading. The experimental uptake curves were correlated with a non-isothermal kinetic model because the adsorption kinetics was controlled via heat generation and transfer. Adsorption rates of the gases on zeolite 13X were affected by the isosteric heat of adsorption, heat transfer rate and adsorption affinity. At the same temperature and pressure, the sequence of reciprocal of the effective diffusional time constant (D/RP2) revealed the following sequence: CH4≒N2<CO<CO2, showing pressure and temperature dependency. While the diffusion rates of CO and N2 were controlled via micropore diffusion, CO2 and CH4 were significantly affected by macropore diffusion due to high heat transfer resistance. Compared to experimental results between the powder and pellet forms of zeolite 13X, the zeolite pellet binders led to a reduction in adsorption capacity and heat of adsorption. However, the difference in adsorption kinetics was relatively minute.

Flat-plate boiloff calorimeters for testing of thermal insulation systems

Cryostats have been developed and standardized for laboratory testing of thermal insulation systems in a flat-plate configuration. Boiloff calorimetry is the measurement principle for determining the effective thermal conductivity (ke) and heat flux (q) of test specimens under a wide range of actual conditions. Cryostat-500 is thermally guarded to measure absolute thermal performance when calibrated with a known reference via an adjustable-edge guard ring. With liquid nitrogen as the energy meter, the cold boundary temperature can be adjusted to any temperature between 77 K and approximately 300 K by the interposition of a thermal resistance layer between the cold mass and the specimen. A low thermal conductivity suspension system has compliance rods that adjust for specimen thickness and compression force. Material type, thickness, density, flatness, compliance, outgassing, and temperature sensor placement are important test considerations, and edge effects and calibration techniques for the apparatus are crucial. Over the full vacuum pressure range, the thermal performance capability is nearly four orders of magnitude. The horizontal configuration provides key advantages over the vertical cylindrical cryostats for testing at ambient pressure conditions. Cryostat-500’s design and test methods, other flat-plate boiloff calorimeters, and results for select thermal insulation materials (composites, foams, aerogels) are discussed.

Abstracts From the 36th Annual Scientific Meeting of the HBPRCA

### CONTRIBUTION OF THE AREA POSTREMA TO THE INCREASED CARDIAC SYMPATHETIC NERVE ACTIVITY IN OVINE HEART FAILURE Abukar Y, Ramchandra R, May CN The Florey Institute of Neuroscience and Mental Health, Melbourne, Victoria, Australia Background : Heart failure (HF) is associated with an increase in cardiac sympathetic nerve activity (CSNA), which is directly linked to mortality in HF patients. The mechanisms responsible for the elevated CSNA remain unclear. Previous studies indicate that the area postrema (AP), a circumventricular organ in the brainstem, plays a role in the control of sympathetic nerve activity. We hypothesized that the elevated CSNA in HF is mediated by the AP and lesioning this region would reduce the increased CSNA in sheep with HF. Aims : To determine the effect of sham lesion or lesion of the AP on CSNA and hemodynamics in conscious sheep with HF. Methods : Studies were conducted in 2 groups of sheep with pacing-induced HF: sham (n=6) and AP lesion (n=6) sheep. Mean arterial blood pressure (MAP), heart rate (HR) and CSNA were recorded simultaneously in conscious sheep at least 4 days after surgery. Results : Heart failure was associated with a significant decrease in ejection fraction (from 74±2 % to 38±1 %; P<0.001), which was similar in both groups. There was a significant reduction in CSNA burst incidence in the AP lesion group compared with the sham group (45±10 and 89±3 bursts/100 heartbeats, respectively; P<0.01). Conclusions : In sheep with HF, the group with lesion of the AP had a significantly lower CSNA compared with the sham group. These data suggest that the AP plays a role in setting the detrimental high levels of CSNA in HF. ### G PROTEIN-COUPLED ESTROGEN RECEPTOR SIGNALING IMPROVES STROKE OUTCOME IN FEMALE MICE Broughton BRS, Jansen GL, Sobey CG Department of Pharmacology, Monash University, Clayton, Victoria, Australia Background: Estrogen has been assumed to provide neuroprotection following stroke entirely via classical estrogen receptors. Interestingly, there is recent evidence that activation of a novel G …

Solubility of Methane in Propylene Carbonate

The solubility of methane in propylene carbonate was measured at the temperatures (244.26, 248.14, 255.37.37, 266.48, 273.15, 298.15, 333.15, and 373.15) K. Pressures ranged from (101 to 11200) kPa. The Peng–Robinson equation of state was used to correlate the data over the full temperature and pressure range. A linearly temperature dependent binary interaction parameter was found to correlate the experimental data the best. The correlation reproduces the experimental data with an overall average percent deviation in the mole fraction of 6.9 %. The Krichevsky–Ilinskaya equation combined with the Peng–Robinson equation of state was used to obtain Henry’s constants of methane in propylene carbonate.

Lattice solution model for order-disorder transitions in membranes and Langmuir monolayers.

Lipid monolayers and bilayers have been used as experimental models for the investigation of membrane thermal transitions. The main transition takes place near ambient temperatures for several lipids and reflects the order-disorder transition of lipid hydrocarbonic chains, which is accompanied by a surface density gap. Equivalence between the transitions in the two systems has been argued by several authors. The two-state statistical model adopted by numerous authors for different properties of the membrane, such as permeability, diffusion, and mixture or insertion of cholesterol or protein, is inadequate for the description of charged membranes, since it lacks a proper description of surface density. We propose a lattice solution model which adds interactions with water molecules to lipid-lipid interactions and obtain its thermal properties under a mean-field approach. Density variations, although concomitant with chain order variations, are independent of the latter. The model presents both chain order and gas-liquid transitions, and extends the range of applicability of previous models, yielding Langmuir isotherms in the full range of pressures and areas.

Underwater blast wave pressure sensor based on polymer film fiber Fabry-Perot cavity.

This paper describes the theoretical and experimental aspects of an optical underwater shock wave sensor based on a polymer film optical fiber Fabry-Perot cavity manufactured by vacuum deposition technology. The transduction mechanism of the sensor involves a normally incident acoustic stress wave that changes the thickness of the polymer film, thereby giving rise to a phase shift. This transient interferometric phase is interrogated by a three-phase-step algorithm. Theoretically, the sensor-acoustic-field interaction principle is analyzed, and the phase modulation sensitivity based on the theory of waves in the layered media is calculated. Experimentally, a static calibration test and a dynamic calibration test are conducted using a piston-type pressure calibration machine and a focusing-type electromagnetic shock wave. Results indicate that the repeatability, hysteresis, nonlinearity, and the overall measurement accuracy of the sensor within the full pressure range of 55MPa are 1.82%, 0.86%, 1.81%, and 4.49%, respectively. The dynamic response time is less than 0.767μs. Finally, three aspects that need further study for practical use are pointed out.

Relaxor ferroelectrics materials under high pressure

The rich phase diagrams from both relaxor and normal ferroelectrics under high pressure, stimulate us to study the pressure effect on the relaxor-PbTiO3 (PT) systems, to check whether the high pressure cubic structure will turn to low symmetry structure upon strong compression is the common behaviors for relaxor ferroelectrics materials. Furthermore, a complete phase diagram study of pressure-temperature effect on structure will allow us to explore the limitation on applications of relaxor-PT material devices under harsh environment involving in high pressure and high temperature conditions. Structure evolution and phase transition of several solid solution ferroelectrics, such as Pb(YbNb)O3-PT (PYN-PT), have been studied using in situ synchrotron X-ray diffraction (XRD) and Raman spectroscopy techniques under high pressure and high temperature conditions. XRD results show pressure induced phase transitions to a cubic phase, while the persistence of Raman spectroscopy in the full pressure range indicates its local distortion. A pressure-temperature phase diagram is further constructed to determine the stability region of the ferroelectric phase. The results provide useful guidance for the applications of this kind of high Curie temperature ferroelectric crystal under extreme conditions, and extra clue to synthesis of ferroelectric materials with tailored properties.

Pressure dependence of mass burning rates in diluent premixed flames of H2/O2 at high pressures

Pressure dependence of mass burning of diluted hydrogen premixed flames is studied numerically over a full range of pressure. Mass burning rate is selected to be a parameter for burning capability of flames. First, positive linear dependence of mass burning rate has been confirmed at low pressures and negative pressure dependence has appeared in the medium range of pressure, which complies with the results reported in previous experimental works. And then, when the pressure range is extended more, positive pressure dependence is recovered or shows up again at high pressures. The flame structures of temperature and species profiles in each pressure regime are demonstrated. They show that the latter two dependences of negative and positive can be explained by enhanced recombination reactions producing HO2 at high pressures and chain re-branching to OH production via H2O2, respectively. There are three distinct dependences of mass burning or global chemistry in hydrogen flames. Two onset pressures, at which pressure dependence changes, depend on equivalence ratio, degree of dilution, diluent species, and unburned-gas temperature. Accordingly, the onset pressure can be used as a parameter characterizing burning of premixed flames.

Pd–V–Pd composite membranes: Hydrogen transport in a wide pressure range and mechanical stability

The composite membranes based on group 5 metals are capable of H2 separation with high speed and infinite selectivity. Hydrogen transport through Pd–V–Pd composite membranes of planar and tubular shape was investigated in the pressure range of (1×10−8–6×10−1)MPa at 400°C. Due to the wide pressure range both the diffusion rate limited regime of hydrogen permeation and the regime limited by the H2 molecule dissociation were observed in one experiment. The density of flux permeating through the 100µm-membrane reached 2.4scc/(cm2s) that seems to be one of highest ever achieved in the membranes based on group 5 metals as well as in any other unsupported metallic membranes. The concentration of dissolved hydrogen сН/сV reached 0.42 but no noticeable reduction in hydrogen diffusivity was found. The constant value of sticking probability of H2 molecules (4×10−4) that was observed over full range of pressures used in this study indicates that the surface saturation has insignificant influence on the kinetics of boundary processes. The 100-fold cycling of hydrogen pressure from 0 to 0.6MPa did not result in any loss of tubular membrane integrity and change of its shape despite the fact that the ductile-to-brittle transition occurred in each cycle. The operation with samples of planar and tubular shape demonstrated that V-based composite membranes can be used at least for laboratory studies. Further work to improve the long-term stability is necessary for their practical applications.

A Micromachined Pressure Sensor with Integrated Resonator Operating at Atmospheric Pressure

A novel resonant pressure sensor with an improved micromechanical double-ended tuning fork resonator packaged in dry air at atmospheric pressure is presented. The resonator is electrostatically driven and capacitively detected, and the sensor is designed to realize a low cost resonant pressure sensor with medium accuracy. Various damping mechanisms in a resonator that is vibrating at atmospheric pressure are analyzed in detail, and a formula is developed to predict the overall quality factor. A trade-off has been reached between the quality factor, stress sensitivity and drive capability of the resonator. Furthermore, differential sense elements and the method of electromechanical amplitude modulation are used for capacitive detection to obtain a large signal-to-noise ratio. The prototype sensor chip is successfully fabricated using a micromachining process based on a commercially available silicon-on-insulator wafer and is hermetically encapsulated in a custom 16-pin Kovar package. Preliminary measurements show that the fundamental frequency of the resonant pressure sensor is approximately 34.55 kHz with a pressure sensitivity of 20.77 Hz/kPa. Over the full scale pressure range of 100–400 kPa and the whole temperature range of −20–60 °C, high quality factors from 1,146 to 1,772 are obtained. The characterization of the prototype sensor reveals the feasibility of a resonant pressure sensor packaged at atmospheric pressure.

Wide-Ranging Viscosity Measurements of Rocket Propellant RP-2

Expanding on earlier viscosity measurements of rocket propellants from 293 to 373 K at atmospheric pressure, the viscosity of rocket propellant RP-2 was measured from 270 to 425 K with pressures to 137 MPa. The instrument was an oscillating-piston viscometer, modified and recalibrated at the National Institute of Standards and Technology with dodecane as a reference fluid over the full temperature and pressure range. Based on the recalibrations, the repeatability of the measurements was found to be approximately 3%, whereas the uncertainty of the instrument is estimated at 5%. The measured viscosities of RP-2 were compared with values calculated with a five-component surrogate mixture model developed at the National Institute of Standards and Technology. The experimental data have a stronger pressure dependence than the mixture model and are up to 29% higher at high compressions.

The effect of pressure and oxygen concentration on the combustion of PMMA

An experimental study of the flammability properties of PMMA at low pressures and oxygen concentrations was performed. The work was motivated by the importance of these effects on fire safety in the aviation industry. Measurements were obtained in a mass loss calorimeter inside a large 10m3 pressure vessel capable of reaching pressures as low as 0.1atm. The PMMA flammability was characterized by measuring the burning rate and the time to ignition of small test samples. These were ignited and burned under different external heat fluxes, total pressures and oxygen concentrations. The combined effects of pressure and oxygen concentration on the burning rate, combustion flow field, and ignition were evaluated. Results showed that at low pressure, the burning rate was less intense with a decrease in the mass loss rate. However, the reduction in pressure caused a shortened ignition delay time. Experimental measurements were compared with a simple analytical model showing good agreement. The results also show how pressure and oxygen concentration contributed to the heat transfer from the flame. The model revealed that a single function in oxygen and pressure could account for both flame radiative and convective effects. As a result, a power law fit was obtained for the relation of the combined pressure and oxygen effect on the burning rate. This correlation shows a good agreement with the measurements and predicts the burning rate behavior for the full range of pressure and oxygen tests.