Frederick W. Williams

Heterogeneous catalytic CO2 conversion to value-added hydrocarbons

The impact that anthropogenic CO2 is having on the environment has been thoroughly documented over the last 20 years. Many different technologies have been proposed to reduce its impact on global warming such as geological sequestration. However, an interesting and attractive alternative would be the recycling of the gas into energy-rich molecules. Iron rather than cobalt catalysts, based on the Fischer–Tropsch technology, have shown the greatest promise in converting CO2 to value-added hydrocarbons. The addition of co-catalysts is, however, essential to fine tune the product distribution to the more desired alkene products. The role that both the promoter and support play on the catalysts activity is reviewed.

Chemiluminescence spectra from cool and blue flames: Electronically excited formaldehyde

Resolved emission spectra of electronically excited formaldehyde (1A2 → 1A1) have been obtained from two-stage ignition in a Vertical Tube Reactor combustion flow system, using acetaldehyde and n-butane as fuels. The very low intensity UV-visible emission from both the cool flame reaction zone (200–400°C) and blue flame reaction zone (400–800°C) is due to formaldehyde chemiluminescence. The “continuum” observed by previous researchers is due to formaldehyde band overlap, with typical hot flame emission from radicals, CO flame bands and continuum, and black body radiation being absent except for minor contributions in the acetaldehyde blue flame (800°C). Differences in the spectra band structure and underlying ‘continuum’ are due to the temperatures of the various flames. The cool flame formaldehyde emission yield per reacting fuel molecule is ∼10−8 for the fuels studied.

Multi-criteria fire detection systems using a probabilistic neural network

Abstract The Navy program, Damage Control Automation for Reduced Manning (DC-ARM), is focused on enhancing automation of ship functions and damage control systems. A key element to this objective is the improvement of current fire detection systems. As in many applications, it is desired to increase detection sensitivity and, more importantly, increase the reliability of the detection system through improved nuisance alarm immunity. Improved reliability is needed such that fire detection systems can automatically control fire suppression systems. The use of multi-criteria-based detection technology continues to offer the most promising means to achieve both improved sensitivity to real fires and reduced susceptibility to nuisance alarm sources. A multi-signature early warning fire detection system is being developed to provide reliable warning of actual fire conditions in less time with fewer nuisance alarms than can be achieved with commercially available smoke detection systems. In this study, a large database consisting of the responses of 20 sensors to several different types of fires and nuisance sources was generated and analyzed using a variety of multivariate methods. Three data matrices were developed at discrete times corresponding to the different alarm levels of a conventional photoelectric smoke detector. The alarm times represent 0.82%, 1.63% and 11% obscurations per meter. The datasets were organized into three classes representing the sensor responses for baseline (nonfire), fires and nuisance sources. A robust data analysis strategy for use with a sensor array consisting of four to five sensors for early fire detection and nuisance source rejection was developed using a probabilistic neural network (PNN) that was developed at the Naval Research Laboratory for chemical sensor arrays. The analysis algorithms described in this paper evaluate discrete samples and develop classification models that examine individual chemical signatures at discrete points.

Early warning fire detection system using a Probabilistic Neural Network

The Navy program, Damage Control-Automation for Reduced Manning is focused on enhancing automation of ship functions and damage control systems. A key element to this objective is the improvement of current fire detection systems. As in many applications, it is desired to increase detection sensitivity and,more importantly increase the reliability of the detection system through improved nuisance alarm immunity. Improved reliability is needed, such that fire detection systems can automatically control fire suppression systems. The use of multi-criteria based detection technology continues to offer the most promising means to achieve both improved sensitivity to real fires,and reduced susceptibility to nuisance alarm sources. A multi-criteria early warning fire detection system, has been developed to provide reliable warning of actual fire conditions, in less time, with fewer nuisance alarms,than can be achieved with commercially available smoke detection systems. In this study a four-sensor array and a Probabilistic Neural Network have been used to produce an early warning fire detection system. A prototype early warning fire detector was built and tested in a shipboard environment. The current alarm algorithm resulted in better overall performance than the commercial smoke detectors, by providing both improved nuisance source immunity with generally equivalent or faster response times.

The development and mitigation of backdraft: a real-scale shipboard study

This paper presents the results of a real-scale experimental test series to study the development and mitigation of backdrafts. Experiments consisted of creating backdrafts onboard a US Navy test ship, ex-USS SHADWELL. This study has shown that the key parameter for backdraft development is the fuel mass fraction. The results show that the critical fuel mass fraction, Yf, required for the development of diesel fuel backdraft is 0.16 for fully vitiated conditions. The effects of varying adjacent room boundaries and ventilation conditions are discussed. In general, the intensity of a backdraft is more dependent on the adjacent boundaries than on the ventilation conditions. The injection of water spray into the fire compartment was shown to be an effective mitigating tactic that was able to completely suppress backdrafts primarily by means of diluting the atmosphere and reducing the fuel mass fraction, rather than by a thermal mechanism of cooling.

Evaluation of Intumescent Coatings for Shipboard Fire Protection

In response to several claims from Manufacturers that intumescent coatings could be used in place of fire insulation and provide equal protection to shipboard structures during a fire, U.S. Navy conducted an extensive investigation of several fire protective coatings for use aboard ship. These fire protective coatings included water and solvent based coatings, insulative coatings, and foams. The objective of this program was to identify passive fire protection (PFP) coatings for shipboard interior applications capable of meeting U.S. Navy (USN) fire resistance requirements (DRAFT MIL-PRF-XX 381) of 30 min rating with backside average temperature rise less than 139 C using UL-1709 fire curve (post flashover fire). This evaluation consisted of small scale fire, adhesion, and impact tests; intermediate scale room corner fire tests, and full scale fire tests conducted aboard ex-USS SHADWELL. The test results with steel substrate show that all candidate coatings failed to meet minimum U.S. Navy fire resistance criteria when used as stand-alone coatings. Furthermore, many coatings demonstrated poor adhesion, and fell off from the substrate during the fire test. These data have led the Navy to conclude that intumescent coatings tested in this study are not sufficient to protect shipboard spaces during a fire and are not equivalent when used alone as direct replacement for batt or blanket type fibrous fire insulation (mineral wool, StructoGard) installed aboard U.S. Navy ships. However, U.S. Navy smallscale fire tests have also demonstrated that some of the intumescent coatings, when applied over substrates such as Glass Reinforced Plastic (GRP), did reduce flame spread and smoke generation.

FORMATION AND CHEMILUMINESCENT DECOMPOSITION OF DIOXETANES IN THE GAS PHASE

Abstract— High resolution chemiluminescence spectra have been obtained of the singlet electronically excited products of O2(1Δ) plus alkene, dioxetane forming, reactions. The experiments were conducted in a flow apparatus at pressures of 1–5 torr. The spectra are a measure of the unrelaxed initial distribution of energy in the excited product. Results are reported for ethylene, 1, 1‐difluoroethylene. methyl vinyl ether, ethyl vinyl ether, n‐butyl vinyl ether, ketene, ketene‐d2, allene, unsymdimethyl allene, dimethyl ketene, 2‐methoxy propene, 1‐ethoxy propene, 2‐bromo propene, and N, N‐dimethyl isobutenyl amine. Chemiluminescence activation energies, representing the cycloaddition process, and absolute quantum yields for singlet excited product, ranging from 10‐‐4 to 2.5 × 10‐‐2. are reported for 10 alkenes. Several of the reactions, 1,1‐difluoroethylene, ketene, ethylene and allene give formaldehyde 1nπ* product with excess vibrational‐rotational energy and a higher quantum yield than reactions not displaying this phenomenon. This is an indication of at least partially statistical partitioning of the energy in excess of that needed to electronically excite the formaldehyde. The experiments with ketene and ketene‐d2 provide the first evidence for the existence of unsubstituted 1,2‐dioxetanone. The results from several of the experiments, particularly those with 2‐methoxy propene and I‐ethoxy propene are consistent with the mechanism of Goddard, which predicts regioselective and stereoselective attack of O2(1Δ) upon alkoxy substituted alkenes having allylic hydrogen.

Mitigation of TNT and Destex explosion effects using water mist

The effects water mist has on the overpressures produced by the detonation of 50 lb equivalent of high explosives (HE) TNT and Destex in a chamber is reported. The overpressures for each charge density were measured with and without mist preemptively sprayed into the space. A droplet analyzer was placed in the chamber prior to the detonation experiments to characterize the water mist used to mitigate the explosion overpressures. The impulse, initial blast wave, and quasi-static overpressure measured in the blast mitigation experiments were reduced by as much as 40%, 36%, 35% for TNT and 43%, 25%, 33% for Destex when water mist was sprayed 60s prior to detonation at a concentration of 70 g/m(3) and droplet Sauter Mean Diameter (SMD) 54 microm. These results suggest that current water mist technology is a potentially promising concept for the mitigation of overpressure effects produced from the detonation of high explosives.

Investigation of Multi-Sensor Algorithms for Fire Detection

There is widespread interest in the development of advanced fire detectors. A primary objective of fire detection is to provide prompt indication of the presence of a fire, without responding to deceptive signatures from nuisance sources. The principal purpose of this project is to identify the characteristics of a discriminating fire detector for Naval shipboard applications incorporating ionization, photoelectric, carbon dioxide and carbon monoxide sensors. Test data from previously conducted full-scale tests involving fire and nuisance sources are being analyzed to develop an algorithm involving combinations of the magnitude or slope of the response signal from each sensor. Acceptability of a particular algorithm is judged based on the number of correct classifications (fire vs. nuisance) and response time to fire sources.

Modeling pool-like gas flames of propane

Abstract Turbulent, buoyant pool-like propane flames with heat release rates of 15.8, 22.9 and 37.9 kW are numerically modeled. The model assumes a parabolic flow field, α κ–ϵ turbulence model, and an eddy-dissipation concept for the interaction of the chemistry and turbulence. Radiative heat transfer is incorporated by the flux model with the absorption and emission coefficients evaluated using a temperature-weighted gray gas model. Predictions are made for the flame shapes, axial velocity, axial mean temperature and various scalar properties along the centerline, the radial distribution of temperature and velocity at various axial heights, and the air entrainment behavior. The overall agreement between the predicted and experimental flame behavior is seen to be good; however, the radial expansion of the flame is underestimated in the combustion zone.