Electro-Oxidation of Borohydride on Rhodium, Iridium, and Rhodium-Iridium Bimetallic Nanoparticles with Implications to Direct Borohydride Fuel Cells

Electrochemical oxidation of borohydride is studied on nanosized rhodium, iridium, and bimetallic rhodium-iridium catalysts supported onto Vulcan XC72R carbon. The catalysts are characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy in conjunction with cyclic voltammetry and polarization studies. The studies reveal that a 20 wt % bimetallic Rh-Ir catalyst supported onto carbon (Rh-Ir/C) is quite effective for the oxidation of borohydride. Direct borohydride fuel cell with Rh-Ir/C as the anode catalyst and Pt/C as the cathode catalyst exhibits a peak power density of 270 mW/cm(2) at a load current density of 290 mA/cm(2) as against 200 mW/cm(2) at 225 mA/cm(2) for Rh/C and 140 mW/cm(2) at 165 mA/cm(2) for Ir/C while operating at 80 degrees C. The synergistic catalytic activity for the bimetallic Rh-Ir nanoparticles toward borohydride oxidation is corroborated by density-functional theory calculations using electron-localization function. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3442372] All rights reserved.

Nonlinear Sliding Mode Control Design for an Air-breathing Engine with State Estimation

A modern system theory based nonlinear control design is discussed in this paper for successful operation of an air-breathing engine operating at supersonic speed. The primary objective of the control design of such an air-breathing engine is to ensure that the engine dynamically produces the thrust that tracks a commanded value of thrust as closely as possible by regulating the fuel flow to the combustion system. However, since the engine operates in the supersonic range, an important secondary objective is to manage the shock wave configuration in the intake section of the engine which is manipulated by varying the throat area of the nozzle. A nonlinear sliding mode control technique has been successfully used to achieve both of the above objectives. In this problem, since the process is faster than the actuators, independent control designs are also carried out for the actuators as well to assure the satisfactory performance of the system. Moreover, to filter out the sensor and process noises and to estimate the states for making the control design operate based on output feedback, an Extended Kalman Filter based state estimation design is also carried out. The promising simulation results suggest that the proposed control design approach is quite successful in obtaining robust performance of the air-breathing engine.

Synthesis of Poly(1,4-Divinylbenzene Peroxide)

Polymeric peroxides have received renewed attention in the recent past, in view of some significant explorations of their physical and chemical properties. The potential of polymeric peroxides as a class, as specialized fuel, and the need to synthesize such new materials have been reported in the literature. So far, this class of polymers is constituted only by a dozen or so polyperoxides. From the point of view of their use in propellant applications, the importance lies in making materials which are easy to handle etc., unlike the earlier reported poly(styrene peroxide) (PSP), a sticky semi-solid mass. However, judging from the better combustion characteristics, exploring aromatic monomers was thought worthwhile. In this preliminary communication, the synthesis of a new polymeric peroxide made from 1,4-divinylbenzene is reported. The polymer obtained was in powder form and had an exothermic heat of degradation approximately equal to that of PSP. 4 ref.--AA

Nonlinear intrinsic instability of solid propellant combustion including gas-phase thermal inertia

The problem of homogeneous solid propellant combustion instability is studied with a one-dimensional flame model, including the effects of gas-phase thermal inertia and nonlinearity. Computational results presented in this paper show nonlinear instabilities inherent in the equations, due to which periodic burning is found even under steady ambient conditions such as pressure. The stability boundary is obtained in terms of Denison-Baum parameters. It is found that inclusion of gas-phase thermal inertia stabilizes the combustion. Also, the effect of a distributed heat release in the gas phase, compared to the flame sheet model, is to destabilize the burning. Direct calculations for finite amplitude pressure disturbances show that two distinct resonant modes exist, the first one near the natural frequency as obtained from intrinsic instability analysis and a second mode occurring at a much higher driving frequency. It is found that er rn in the low frequency region, the response of the propellant is significantly affected by the specific type of gas-phase chemical heat-release model employed. Examination of frequency response function reveals that the role of gas-phase thermal inertia is to stabilize the burning near the first resonant mode. Calculations made for different amplitudes of driving pressure show that the mean burning rate decreases with increasing amplitude. Also, with an increase in the driving amplitude, higher harmonics are generated in the burning rate.

Leaching behavior of Indian fly ashes by an oedometer method

Thermal power stations use pulverized coal as fuel, producing enormous quantities of ash as a by-product of combustion. Currently, with very low utilization of the ash produced, the ash deposits at the thermal power stations are increasing rapidly. The disposal problem is expected to become alarming due to the limited space available for ash disposal near most thermal power stations. Among the various applications available for the use of fly ash, geotechnical application offers opportunity for its bulk utilization. However, the possibility of ground and surface water contamination due to the leaching of toxic elements present in the fly ash needs to be addressed. This paper describes a study carried out on two Indian fly ashes. It is found that pH is the controlling factor in the leaching behavior of fly ashes.

Photocatalytic degradation of nitrobenzenes with combustion synthesized nano-TiO2

The photocatalytic degradation of nitrobenzene and substituted nitrobenzenes under UV exposure was investigated with combustion synthesized nano-TiO2 and commercial TiO2 catalyst, Degussa P-25. The experimental data indicated that the photodegradation kinetics was first order. The photocatalytic degradation rates were considerably higher when catalyzed with combustion synthesized TiO2 compared to that of Degussa P-25. The degradation rate coefficients followed the order: 1-chloro,14-dinitrobenzene similar or equal to 4-nitrophenot > 2-nitrophenol > 1-chloro.4-nitrobenzene > 3-niti-ophenol > 2,4-dinitrophenol > 1-chloro,2-nitrobenzene > nitrobenzene > 1,3-dinitrobenzene. Plausible mechanisms and reasons for the observation of the above order are discussed.

NO reduction, CO and hydrocarbon oxidation over combustion synthesized Ag/CeO2 catalyst

The combustion technique produces ionically dispersed Ag on a nano-crystalline CeO2 surface. The catalysts thus produced were characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Catalytic properties towards NO reduction, CO and hydrocarbon oxidation have been investigated using the temperature programmed reaction technique in a packed bed tubular reactor. These results are compared with alpha-Al2O3 supported finely divided Ag metal particles synthesized by the same method. Both oxidation and reduction reactions over Ag/CeO2 have been observed to occur at lower temperatures compared to Ag/Al2O3. The rate and turnover frequency of the NO+CO reaction over 1% Ag/CeO2 are 56.3 mu mol g(-1) s(-1) and 0.97 s(-1) at 225 degrees C respectively. Activation energy (E-a) values are 71 and 67 kJ mol(-1) for CO+O-2 and NO+CO reactions, respectively, over 1% Ag/CeO2 catalyst.

Fractional-factorial design of a porous-carbon fuel-cell electrode

The use of fractional-factorial methods in the optimization of porous-carbon electrode structure is discussed with respect to weight-loss of carbon during gas treatment, weight and mixing time of binder, compaction temperature, time and pressure, and pressure of feed gas. The experimental optimization of an air electrode in alkaline solution is described.

Combustion of ammonium perchlorate-based composite propellants in presence of methylammonium perchlorates

The effect of tri- and tetramethylammonium perchlorates (MAP-3 and MAP-4) on the burning rate of ammonium perchlorate (AP) based propellants has been determined at various pressures. Both additives increase the burning rate; however, MAP-3 has a moderate effect, whereas MAP-4 has a rather large effect. To explain the results, the thermal decomposition and calorimetric values of the propellants having these additives have been examined. Compound MAP-3 affects the thermal decomposition rate considerably, whereas MAP-4 has virtually no effect on the decomposition rate. The contrasting effects of MAP-4 on decomposition and burning rate suggest that the enhancement of burning rate may be due to the catalysis of gas-phase reactions. Further, detailed differences between behaviour of MAP-3, and MAP-4 appear to be attributable to the melting and low-temperature exotherm of MAP-3 and nonmelting and high-temperature exotherm of MAP-4.

Flow structure and heat transfer characteristics behind a diaphragm in the presence of a diffusion flame

The characteristics of the separated flow behind a diaphragm over a burning surface are investigated experimentally. This complex problem of practical significance involving recirculation, blowing and combustion reactions is studied in a two-dimensional combustion tunnel. The flame structure, recirculation patterns and heat transfer to the surface are presented for a range of values of free stream and fuel injection velocities as well as for different heights of the diaphragm. The trends of heat transfer vs axial distance are shown to be similar to those resulting from a non-reactive heated stream with a diaphragm. Treating the case of a boundary layer diffusion flame as that corresponding to the zero height of the diaphragm, the heat transfer augmentation due to recirculation is estimated. It is found that at considerable downstream distances (xfh > 3), the heat transfer rates with diaphragm overtake the rates from a developing boundary layer case. Flow visualization studies with particle track photography show that there are many similarities between the reactive and the non-reactive cases.

Effect of trimethylammonium perchlorate on the decomposition and combustion of potassium perchlorate and potassium perchlorate-polyurethane propellants

Addition of trimethylammonium perchlorate to potassium perchlorate (KP) catalyzes its thermal decomposition. However, although the additive sensitises KP-PU propellant decomposition, its combustion is desensitised. The observed effects have been explained in terms of the role played by the early formation of potassium chloride.

Mesoporous Carbon and Poly(3,4-ethylenedioxythiophene) Composite as Catalyst Support for Polymer Electrolyte Fuel Cells

In situ polymerization of 3,4-ethylenedioxythiophene with sol-gel-derived mesoporous carbon (MC) leading to a new composite and its subsequent impregnation with Pt nanoparticles for application in polymer electrolyte fuel cells (PEFCs) is reported. The composite exhibits good dispersion and utilization of platinum nanoparticles akin to other commonly used microporous carbon materials, such as carbon black. Pt-supported MC-poly(3,4-ethylenedioxythiophene) (PEDOT) composite also exhibits promising electrocatalytic activity toward oxygen reduction reaction, which is central to PEFCs. The PEFC with Pt-loaded MC-PEDOT support exhibits 75% of enhancement in its power density in relation to the PEFC with Pt-loaded pristine MC support while operating under identical conditions. It is conjectured that Pt-supported MC-PEDOT composite ameliorates PEFC performance/durability on repetitive potential cycling. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3486172] All rights reserved.

Computational Fluid Dynamics in Combustion

Computational fluid dynamics has reached a stage where flow field in practical situation can be predicted to aid the design and to probe into the fundamental flow physics to understand and resolve the issues in fundamental fluid mechanics The study examines the computation of reacting flows After exploring the conservation equations for species and energy, the methods of closing the reaction rate terms in turbulent flow have been examined briefly Two cases of computation where combustion-flow interaction plays important role, have been discussed to illustrate the computational aspects and the physical insight that can be gained by the reacting flow computation