Diluent Air Research Articles

Effects of initial temperature and pressure on explosion characteristics of propane–diluent–air mixtures

The explosion characteristics of propane–diluent–air mixtures under various temperatures and pressures were investigated using a 20-L apparatus. The explosion limits of propane diluted with nitrogen or carbon dioxide were measured at high temperatures from 25 to 120 °C. The results showed that the upper explosion limit (UEL) increased, and the lower explosion limit (LEL) decreased with the rising temperature. The explosion limits of propane diluted with nitrogen or carbon dioxide were also measured at high pressures from 0.10 to 0.16 MPa. The results showed that the UEL increased, and the LEL almost remainedunchanged along with increased pressure. Under the same initial operating conditions, the concentration of nitrogen required to reach the minimum inerting concentration (MIC) point was higher than the concentration of carbon dioxide. Finally, the study investigated the limiting oxygen concentration (LOC) of propane under various initial temperatures, initial pressures, and inert gases. The LOC of propane decreased approximately linearly with increased temperature or pressure, and the LOC of propane dilution with carbon dioxide was greater than dilution with nitrogen from 25 to 120 °C or from 0.10 to 0.16 MPa, which indicated that the dilution effect of carbon dioxide was better than that of nitrogen.

Mixed Vapor Generation Device for delivery of homemade explosives vapor plumes

While there is a large body of research on the properties and detection of traditional military high explosives and propellant low explosives, there is a dearth of research on homemade explosive (HME) materials, though they are prevalent today. The safety of working with these materials in the laboratory is the greatest limiting factor preventing HME research. A vapor delivery tool, the Mixed Vapor Generation Device (MV-Gen), was designed to safely contain the individual solid or liquid components that often compose homemade explosives vapor plumes and deliver the mixed component vapors for instrumental sampling and analysis. Within the MV-Gen, each component is separated and only the vapors mix as they are carried through the device by flowing air. The resulting mixed vapor is representative of either mixed explosive material or bulk explosives. Component materials are held in up to four individual, removable vials with vapor concentrations controlled by vial orifice size, temperature, and diluent airflow. The total concentration can be adjusted by altering vial temperature via a thermal water jacket surrounding the entirety of the device, or by adjusting the flow rate of diluent air through the device. The MV-Gen was evaluated first with surrogate compounds, followed by two types of homemade explosives, to include a binary explosive mixture and a peroxide explosive. To evaluate the device, vapors were cold-trapped on an online sampling system and analyzed by gas chromatography/mass spectrometry. It was determined that the device yielded reproducible vapor concentrations of both single and mixed components, and the ratio of these vapors can be easily adjusted to mimic varying forms of homemade explosives.

Method for determination of flammability limits of gaseous compounds diluted with N2 and CO2 in air

The present work studies the flammability limits of combustible–diluent–air mixtures at 25 °C and 1 atm pressure. The diluent species, considered in this study, were nitrogen and carbon dioxide. A factor called kFL was obtained from mass and energy conservation, this factor relates the flammability limit of a combustible–air mixture to that of a combustible–diluent–air mixture. The factor kFL varies with diluent concentration. Nevertheless, it was shown that an average value of this factor (kFLav) can represent, with good accuracy, the variation of the flammability limits with diluent concentration.An empirical method to determine the flammability limits of combustible–diluent–air mixtures was developed. The method approximates kFLav by means of correlations. For the total set of experimental data, it was found that, for dilution with N2 and CO2 respectively: (a) at the LFL the Average of the relative errors (AARE) were 4.02% and 7.01%, the squared correlation coefficients (R2) were 0.9833 and 0.9660; and (b) at the UFL the AAREs were 3.91% and 5.57%, the R2 were 0.9920 and 0.9792.At the Fuel Inertization Point (FIP) there is an inert concentration above which the mixture is non-flammable. A method was developed to determine the diluent mole fraction in the combustible–inert mixture at the FIP. The AAREs of 0.82% and 1.95% were obtained for dilution with N2 and CO2, respectively.

Lift-off and blow-off of methane and propane subsonic vertical jet flames, with and without diluent air

The paper seeks to increase understanding of subsonic jet flame blow-off phenomena, through experimental studies that include the controlled introduction of air into the fuel jet. As the molar concentration of air in the jet flame gas, Aj, is increased the reaction zone becomes leaner, and the flame lift-off distance increases. Eventually, flame oscillations develop and are followed by flame blow-off. A jet mixing analysis enables the extent of the leaning-off of the mixture to be estimated. From this, the reduced mean flamelet burning velocity, ua, is found at the location of the pure fuel jet flame. The conditions for blow-off are correlated with the last measured stable values of the dimensionless flow number, Ub∗, for methane and propane jet flames, with and without added air. Values of Ub∗ decline as the proportion of added air increases, more markedly so with methane. This is attributed to the leaning-off of the flame, and the associated decrease in the flame extinction stretch rate. As Ub∗ declines in value, with increasing air dilution, the emissions of unburned hydrocarbons just prior to blow-off increase. An underlying generality of the findings is revealed when ua is introduced into the expression for Ub∗, and Aj is normalised by the moles of air required to burn a mole of fuel.

Trace Explosives Vapor Generation and Quantitation at Parts per Quadrillion Concentrations

The generation of trace 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN) vapors using a pneumatically modulated liquid delivery system (PMLDS) coupled to a polytetrafluoroethylene (PTFE) total-consumption micronebulizer is presented. The vapor generator operates in a continuous manner with final vapor concentrations proportional to the explosive concentration in aqueous solution delivered through the nebulizer and the diluent air flow rate. For quantitation of concentrations in the parts per billionvolume (ppbv) to parts per trillionvolume (pptrv) range, Tenax-TA thermal desorption tubes were used for vapor collection with subsequent analysis on a thermal-desorption system programmable-temperature vaporization gas chromatograph (TDS-PTV-GC) with a μ-ECD detector. With 30 min sample times and an average sampling rate of 100 mL min(-1), vapor concentrations of 38 pptrv for TNT, 25 pptrv for RDX, and 26 pptrv for PETN were determined. For parts per quadrillionvolume (ppqv) vapor quantitation of TNT and RDX, an online PTV-GC system with a negative-ion chemical ionization mass spectrometer (methane reagent gas) was used for direct sampling and capture of the vapor on the PTV inlet. Vapor concentrations as low as 160 ppqv and 710 ppqv for TNT and RDX were quantified, respectively, with an instrument duty cycle as low as 4 min.

Dynamic headspace generation and quantitation of triacetone triperoxide vapor

Two methods for quantitation of triacetone triperoxide (TATP) vapor using a programmable temperature vaporization (PTV) inlet coupled to a gas chromatography/mass spectrometer (GC/MS) have been demonstrated. The dynamic headspace of bulk TATP was mixed with clean humid air to produce a TATP vapor stream. Sampling via a heated transfer line to a PTV inlet with a Tenax-TA™ filled liner allowed for direct injection of the vapor stream to a GC/MS for vapor quantitation. TATP was extracted from the vapor stream and subsequently desorbed from the PTV liner for splitless injection on the GC column. Calibration curves were prepared using solution standards with a standard split/splitless GC inlet for quantitation of the TATP vapor. Alternatively, vapor was sampled onto a Tenax-TA™ sample tube and placed into a thermal desorption system. In this instance, vapor was desorbed from the tube and subsequently trapped on a liquid nitrogen cooled PTV inlet. Calibration curves for this method were prepared from direct liquid injection of standards onto samples tube with the caveat that a vacuum is applied to the tube during deposition to ensure that the volatile TATP penetrates into the tube. Vapor concentration measurements, as determined by either GC/MS analysis or mass gravimetry of the bulk TATP, were statistically indistinguishable. Different approaches to broaden the TATP vapor dynamic range, including diluent air flow, sample chamber temperature, sample vial orifice size, and sample size are discussed. Vapor concentrations between 50 and 5400ngL−1 are reported, with stable vapor generation observed for as long as 60 consecutive hours.

A Computer-Controlled Whole-Body Inhalation Exposure System for the Oil Dispersant COREXIT EC9500A

An automated whole-body inhalation exposure system capable of exposing 12 individually housed rats was designed to examine the potential adverse health effects of the oil dispersant COREXIT EC9500A, used extensively during the Deepwater Horizon oil spill. A computer-controlled syringe pump injected the COREXIT EC9500A into an atomizer where droplets and vapor were formed and mixed with diluent air. The aerosolized COREXIT EC9500A was passed into a customized exposure chamber where a calibrated light-scattering instrument estimated the real-time particle mass concentration of the aerosol in the chamber. Software feedback loops controlled the chamber aerosol concentration and pressure throughout each exposure. The particle size distribution of the dispersant aerosol was measured and shown to have a count median aerodynamic diameter of 285 nm with a geometric standard deviation of 1.7. The total chamber concentration (particulate + vapor) was determined using a modification of the acidified methylene blue spectrophotometric assay for anionic surfactants. Tests were conducted to show the effectiveness of closed loop control of chamber concentration and to verify chamber concentration homogeneity. Five automated 5-h animal exposures were performed that produced controlled and consistent COREXIT EC9500A concentrations (27.1 ± 2.9 mg/m3, mean ± SD).

An Inhalation Exposure System for the Oil Dispersant COREXIT® EC9500A

An automated whole body inhalation exposure system capable of exposing 12 rats was designed to examine the potential health effects of the oil dispersant (COREXIT® EC9500A [CE]) used during the Deepwater Horizon oil spill. A computer‐controlled syringe pump injected the CE into an atomizer where droplets and vapor were formed and mixed with diluent air. The aerosolized CE was passed into a customized exposure chamber where a calibrated light scattering instrument estimated the real‐time particle mass concentration of the aerosol in the chamber. A custom software GUI was developed to record and control parameters during the exposures. Software feedback loops controlled the chamber aerosol concentration and pressure throughout each exposure. Particle size of the dispersant aerosol was measured and shown to have a number peak at 271 nm and a mass peak at 961 nm. The method used to determine the chamber concentration was a modification of the acidified methylene blue spectrophotometric assay for anionic surfactants. Filter samples were extracted in 5 mL water/filter using sonication for 30 min and diluted 1/10 for analyses. CE filter content was extrapolated from a standard plot using the original CE (4–130 nL/mL water) material and adjusted for density. Five automated 5 hour animal exposures were performed that produced controlled and consistent CE concentrations (27.1 ± 2.9 mg/m3).

Conversion of NOAA atmospheric dry air CH4 mole fractions to a gravimetrically prepared standard scale

Sixteen mixtures of methane (CH4) in dry air were prepared using a gravimetric technique to define a CH4 standard gas scale covering the nominal range 300–2600 nmol mol−1. It is designed to be suitable for measurements of methane in air ranging from those extracted from glacial ice to contemporary background atmospheric conditions. All standards were prepared in passivated, 5.9 L high‐pressure aluminum cylinders. Methane dry air mole fractions were determined by gas chromatography with flame ionization detection, where the repeatability of the measurement is typically better than 0.1% (≤1.5 nmol mol−1) for ambient CH4 levels. Once a correction was made for 5 nmol mol−1 CH4 in the diluent air, the scale was used to verify the linearity of our analytical system over the nominal range 300–2600 nmol mol−1. The gravimetrically prepared standards were analyzed against CH4 in air standards that define the Climate Monitoring and Diagnostics Laboratory (CMDL) CMDL83 CH4 in air scale, showing that CH4 mole fractions in the new scale are a factor of (1.0124 ± 0.0007) greater than those expressed in the CMDL83 scale. All CMDL measurements of atmospheric CH4 have been adjusted to this new scale, which has also been accepted as the World Meteorological Organization (WMO) CH4 standard scale; all laboratories participating in the WMO Global Atmosphere Watch program should report atmospheric CH4 measurements to the world data center on this scale.

Methane standard gases for atmospheric measurements at the MRI and JMA and intercomparison experiments

A calibration system of standard gases for atmospheric methane measurements using a gas chromatograph equipped with a flame ionization detector was developed at the Meteorological Research Institute (MRI) in 1993 and later at the Japan Meteorological Agency (JMA) in 2000. Calibration results for the two systems exhibited good agreement. Although the primary standard gases of the MRI and JMA were prepared independently using the gravimetric method, their methane standard scales were quite similar, (a difference of less than 1 ppb). A comparison of gravimetric standards prepared by several Japanese gas companies showed a methane scale difference within ∼5 ppb relative to the primary standards of the MRI. These gravimetric-scale differences were primarily caused by methane impurities in the diluent air used for standard gas preparation. Long-term storage experiments indicated that the methane contents of standard gases were stable in high-pressure cylinders for 8-9 years. No significant drift of methane was found in any of the standard gases in the MRI; however, to evaluate the stability of the JMA standards, data collected over a longer period of time is required. We evaluated the differences between the methane scales of the MRI and other laboratories based on the previous intercomparison experiments. The differences found in the standard scales used by different laboratories were largely due to the diverse origins of the primary standard gases.

Effects of diluent admissions and intake air temperature in exhaust gas recirculation on the emissions of an indirect injection dual fuel engine

Effects of diluent admissions and intake air temperature in exhaust gas recirculation on the emissions of an indirect injection dual fuel engine

Water vapour and carbon dioxide decrease nitric oxide readings.

Measurement of nitric oxide levels in exhaled air is commonly performed using a chemiluminescence detector. However, water vapour and carbon dioxide affect the chemiluminescence process. The influence of these gases at the concentrations present in exhaled air, has not yet been studied. For this in vitro study, mixtures of 50, 100 and 200 parts per billion (ppb) NO in air were prepared and fed into the NO analyser either directly or bubbled through water. Mixtures with CO2 were prepared by adding 0-10% CO2 to the diluent air. We found a significant decrease in NO readings in the water-saturated samples compared to the dry gas (p < 0.001), strongly dependent on the partial pressure of water. NO levels in exhaled air (mean 10 +/- 2 ppb) showed a decrease of 17 +/- 3% when water vapour was not absorbed. From the experiments with CO2 we found a decrease in NO reading of 1.04 +/- 0.07% per volume CO2 (%). Presence of water vapour, thus, leads to a systematic underestimation of NO levels. Insertion of a water absorber might, therefore, be advantageous. The influence of CO2 concentrations in the normal respiratory range is negligible. With high expiratory CO2 levels as applied in permissive hypercapnia, the effects may be substantial.

Intercalibration experiment of methane standard gas scale between NOAA/CMDL and MRI/GRL.

We developed an automated GC/FID analysis system to determine methane mixing ratios of standard gases with a mean precision of ±0.12%. The GC/FID analysis of five gravimetric standards showed that their methane scale was stable and internally consistent. However, the diluent air for these standards had a small amount of methane, which was estimated to be 35.5 ppb. Thus, our MRI/GRL scale was corrected for methane impurity in the diluent air. The methane mixing ratio of dry natural air in an aluminum cylinder prepared for the intercalibration experiment was determined to be 1.7545±0.0015 ppm on the basis of the MRI/GRL scale. This mixing ratio was higher by 23.0 ppb than that assigned by NOAA/CMDL. This difference indicated that the offset of 23.0 ppb between NOAA/CMDL and MRI/GRL scales will need to be taken into account when methane data from both laboratories are compared.

Energy characteristics of a supersonic CO chemical laser

The specific characteristics of a cw supersonic CO chemical laser utilizing a nonequilibrium chemical source of atomic oxygen were studied experimentally and theoretically. It was found that fairly high energy characteristics may be achieved by scaling the source. An observed reduction in the output energy was attributed to an anomalously fast vibrational deactivation of the CO molecules by oxygen atoms and to a drop in the concentration of oxygen atoms due to recombination in three-body collisions. A theoretical analysis was made of the feasibility of an increase in the output power of this laser at high pressures in the resonator when the supply of diluent air was increased.

An improved generator for the production of metal oxide fume

An improved generator is described for the production of atmospheres of metal oxide fume by the pyrolysis of a suitable metal salt aerosol. The effect of various operating parameters, including the concentration of the metal salt solution and its injection rate, and the flow rate of the diluent air, on the concentration of the generated atmosphere has been investigated for cadmium oxide fume. Data are presented to illustrate the stability of the generated atmosphere for both cadmium and lead oxides.

A method for continuous measurement of ammonia in respiratory airways

A method has been developed that can continuously measure respiratory NH3 with a detection limit of 30 parts per billion by volume (ppbv) at an averaging time of 1 s. The method is based on the chemiluminescent detection of NO, which is produced by oxidizing NH3 at 850 degrees C. A polyethylene sampling probe, incorporating a heated capillary tip bathed in dry, NH3-free diluent air, minimizes NH3 losses due to absorption in breath condensate. In one subject, flow and tidal volume were monitored during quiet mouth breathing while NH3 and CO2 were sampled at the lips. In 10 subjects, NH3, and CO2 were sampled at the lips during quiet mouth breathing ranged from 280 to 1,280 ppbv (mean plus or minus SE, 540 PLUS OR MINUS 85 PPBV).

Pollution Measurements of a Swirl-Can Combustor

Pollutant levels of oxides of nitrogen, unburned hydrocarbons, and carbon monoxide were measured for an experimental, annular, swirl can combustor. The combustor was 42 inches in diameter, incorporated 120 modules, and was specifically designed for elevated exit temperature performance. Test conditions included combustor inlet temperatures of 600, 900 and 1050 F, inlet pressures of 5 to 6 atmospheres, reference velocities of 69 to 120 feet per second and fuel-air ratios of 0.014 to 0.0695. Tests were also conducted at a simulated engine idle condition. Results demonstrated that swirl can combustors produce oxides of nitrogen levels substantially lower than conventional combustor designs. These reductions are attributed to reduced dwell times resulting from short combustor length, quick mixing of combustion gases with diluent air, and to uniform fuel distributions resulting from the swirl can approach. Radial staging of fuel at idle conditions resulted in increases in combustion efficiencies and corresponding reductions in pollutant levels.

Effect of Humidify on Light-Scattering Methods of Measuring Particle Concentration

An experimental investigation was undertaken to isolate and quantitatively determine the effect relative humidity has on the light-scattering ability of aerosols. Both the naturally-occurring ambient aerosol of State College, Pa., and several common test aerosols were used. A measured flow of aerosol was mixed with a measured flow of particle-free air to form a mixture of constant contaminant level; the humidity of this mixture was varied by controlling the moisture content of the clean diluent air. The total light scattered by a given aerosol sample, at various relative humidities, was measured with a Sinclair-Phoenix aerosol photometer (measures the total light scattered in the near forward direction). All measurements were carried out at atmospheric pressure, and after the particulates had an average of 1½ minutes to reach equilibrium with the water vapor. Natural and laboratory-generated aerosols were both tested in this manner.

CALIBRATION OF A FISSION GAS MONITOR.

Abstract-A method for calibrating beta-sensitive gas-monitoring equipment is presented which avoids precise mixing of concentrated active gases with diluent air This method depends upon ntutron activation of the argon in P- 10 proportional counting gas Ld passage ofthe active gas suevely through the monitor chamber and a proportional counter chamber. The latter serves for the determination of specific activity of the monitor gas. The method is satisfactory for specific activities corresponding approximately to maximum permissible concentration (MPC) levels. INTRODUCTION IN MONITORING for gross airborne activities, the separate determination of particulate and gaseous activities is frequently desirable. The particulates can be determined by conventional filter techniques, which in conjunction with suitable detectors serve for the separate deter- mination of gross alpha, beta and gamma activities. In most situations, true gaseous alpha contaminants are not ofinterest. Because of these considerations, the calibration method discussed herein is limited to gaseous beta-gamma activi- ties. The monitor chambers discussed employ a chamber volume of roughly 1 ft3 and thin window