Silane Air Research Articles

Ignition Delay Time for Hydrogen–Silane–Air Mixtures at Low Temperatures

A modified physicomathematical model of ignition of hydrogen–silane–air mixtures is applied to calculate the ignition delay time for these mixtures at low initial temperatures (300–900 K) and pressures (0.4–1 atm) of the mixture. It is shown that the diagram of the ignition delay time as a function of temperature contains a region of the so-called negative temperature coefficient. The influence of the pressure in the mixture and of the silane fraction on the length of this region is studied. It is found that an increase in both factors (silane concentration and pressure in the mixture) leads to an increase in the length of the negative temperature coefficient region.

Physical and mathematical modeling of interaction of detonation waves in mixtures of hydrogen, methane, silane, and oxidizer with clouds of inert micro- and nanoparticles

ABSTRACTThe physical and mathematical models for the description of the detonation process in mixtures of hydrogen–oxygen, methane–oxygen, and silane–air in the presence of inert nanoparticles were proposed. On the basis of these models, the dependencies of detonation wave (DW) velocity deficit versus the size and concentration of inert nanoparticles were found. Three regimes of detonation flows in gas suspensions of reactive gases and inert nanoparticles were revealed: (1) stationary propagation of weak DW in the gas suspension, (2) galloping propagation of detonation, (3) destruction of the detonation process and transformation to wave of turbulent burning. It was determined that the mechanisms of detonation suppression by micro- and nanoparticles are closed and lie in the splitting of a DW to frozen shock wave and ignition and combustion wave. Concentration limits of detonation were calculated. It turned out that concentration limits (on particle volume concentration) of detonation are quite similar for particles with diameters ranging from 10 nm to 1 µm.

Attenuation and Suppression of Detonation Waves in Reacting Gas Mixtures by Clouds of Inert Micro- and Nanoparticles

Physicomathematical models are proposed to describe the processes of detonation propagation, attenuation, and suppression in hydrogen–oxygen, methane–oxygen, and silane–air mixtures with inert micro- and nanoparticles. Based on these models, the detonation velocity deficit is found as a function of the size and concentration of inert micro- and nanoparticles. Three types of detonation flows in gas suspensions of reacting gases and inert nanoparticles are observed: steady propagation of an attenuated detonation wave in the gas suspension, propagation of a galloping detonation wave near the flammability limit, and failure of the detonation process. The mechanisms of detonation suppression by microparticles and nanoparticles are found to be similar to each other. The essence of these mechanisms is decomposition of the detonation wave into an attenuated frozen shock wave and the front of ignition and combustion, which lags behind the shock wave. The concentration limits of detonation in the considered reacting gas mixtures with particles ranging from 10 nm to 1 μm in diameter are also comparable. It turns out that the detonation suppression efficiency does not increase after passing from microparticles to nanoparticles.

Assessment and Control of Detonation Hazard of Silane-Containing Mixtures

A formula for calculating the induction period of a silane–air gas mixture has been proposed. The dimension of a detonation cell and the energy of direct initiation of gaseous detonation were assessed. Consideration has been given to the issue of control of the parameters of detonation of silane-containing mixtures. The parameters of Chapman–Jouguet detonation, the relative dimension of the cell of a detonation wave, and also the parameters of explosion at constant pressure and volume in a stoichiometric silane–air gas mixture with additions of chemically inert microparticles (Al2O3) have been calculated. A series of experiments was conducted on measurement of the pressure profile resulting from the explosion of the silane–air mixture in a volume of cubic shape with the known average fuel–oxidant ratio. The distribution of the fuel during the silane jet flowing out into this volume was visualized. The distribution of silane in a cloud in its outflow into the cubically shaped volume and in a high-speed jet flowing out into an unbounded space was calculated. The performed investigations can be useful in evaluating the comparative efficiency of explosion of clouds of silane– and hydrocarbon–air mixtures.

Ignition of a two-fuel hydrogen–silane mixture in air

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen–air mixture in the temperature range from 1200 to 2500 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.

Calculation of flammability limits of silane–oxygen and silane–air mixtures

The upper and lower flammability limits of silane–oxygen and silane–air mixtures at pressures of 0.05–1.1 atm and temperatures of 350–640 K are found on the basis of Westbrook’s detailed chemical kinetics. It is demonstrated that the death of OH radicals has a minor effect on these limits (their stability) within the framework of the Arrhenius kinetic model. The effect of the silane–air mixture composition on the flammability limits is found. It is shown that the behavior of the ultimate temperature of ignition is nonmonotonic as the fraction of silane increases.

CGA G-13 large-scale silane release test – Part II. Unconfined silane–air explosions

A series of large-scale field trials to better understand the explosion characteristics of silane–air was conducted by the G-13 Silane Task Group under the direction of the Compressed Gas Association (CGA) and its guidelines. Silane was released from a high-pressure source into the open atmosphere, and overpressure measurements of unconfined silane–air explosions were taken at different locations away from the explosion centre. It was found that significant blast effects can result from relatively small releases of silane (around 0.1kg). It is possible to achieve these small releases during an accidental discharge from a “pigtail” connection (a small-diameter coiled tube that connects a silane tube trailer to a process). Therefore, accidental silane explosions should be recognized as significant and possible events when handling silane. These results were also used in the proposed revision of ANSI/CGA G-13 Storage and Handling of Silane and Silane Mixtures.

Combustion Reactions in Silane–Air Flames II. Counterflow Diffusion Flame

Abstract A detailed chemical reaction scheme and a full set of governing equations for fluid dynamics were used to elucidate the chemical and physical phenomena involved in a silane–air counterflow diffusion flame, where the fuel and air issue from the lower and upper nozzles, respectively. It was found that a stagnation surface, where the axial velocities fall down to zero, is kept in a position slightly shifted to the upper side, dividing the system into two zones: the upper air side and the lower fuel side; after leaving the nozzle silane begins to dissociate itself into SiH2 and H2 when it reaches the region of rising temperature; oxygen penetrates into the fuel side by diffusion and reacts with H2 forming OH radicals and H atoms. The produced SiH2 is further dehydrogenated to SiO via HSiO; comparing with premixed flames, the diffusion flames have large local equivalence ratios, so that the combustion reactions in the latter flames occur through a different mechanism.

Combustion Reactions in Silane–Air Flames I. Flat Premixed Flames

Abstract In this work the combustion mechanism of silane–air flames is elucidated through a simulation employing a detailed chemical scheme. Two different pathways for the consumption of silane were found: SiH4→SiH3→SiH2O→HSiO, which proceeds in low-temperature regions, and SiH4→SiH2→HSiO, occurring at high temperatures; this supports results previously reported in the literature. It was also found that some reactions occur over wide ranges of temperature and that the governing step for the whole silane combustion is the reaction of silane with hydroxyl radicals. A least square fitting to the burning velocities and adiabatic flame temperatures obtained for the four investigated mixtures, with equivalence ratios of 2.0, 1.43, 1.0, and 0.5, indicated that a mixture with equivalence ratio of about 1.2 would have the largest burning velocity and the highest flame temperature.

Premixed silaneoxygennitrogen flames

The burning velocities of lean premixed silaneoxygennitrogen flames were measured in the silane and oxygen concentration ranges from 1.6% to 2.9% and from 4% to 24%, respectively. Combustion product analyses and flame temperature measurements were also carried out. The burning velocity of a silaneair flame is around 55 cm/s at a silane concentration of 2%. For lean mixtures, when the oxygen concentration is reduced, dependence of burning velocity upon silane concentration decreases but does not significantly affect the flame temperature. For extremely lean flames, the degree of hydrogen production increases with decreasing silane, although silane is consumed almost completely. On the other hand, if the silane concentration exceeds stoichiometric, the burning velocity increases gradually with increasing silane concentration. In that case, silane as well as oxygen are consumed completely and, at the same time, hydrogen rather than water production becomes dominant. The mechanism of silane combustion is discussed, based on numerical calculations, where the mechanism used in the calculation is assembled by analogy of silane to methane combustion.