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A systematic survey of chemical kinetic mechanisms (both simplified and global) shows an absence of a robust kinetic mechanism that can accurately predict characteristics of syngas-air nonpremixed ...

In this paper the phenomenon of flame jump vis-a-vis steady propagation in biomass packed beds in counter-current mode is discussed. By analyzing the fuel flux and propagation rate data from experi...

In this paper, experimental and theoretical investigations on the stability of coal-air flames in high-speed jets stabilized recirculating flow are presented. The current work reports the operation...

Mechanisms governing the gasification to combustion regime transition in counter-current packed bed biomass systems are investigated in the current work. Single-particle experiments are performed w...

In this paper, the Heterogeneous Quasi 1-D model for steady combustion of AP–HTPB propellants is extended to the unsteady regime. The extended model is used to calculate the pressure-coupled freque...

The present study focuses on the experimental determination of the global extinction strain rate ( a g ) for different syngas-air combinations using the Tsuji type configuration. To study the effect of porous burner diameter (D), a g values were obtained for four values of D at atmospheric pressure. The experimentally obtained a g for a given fuel-oxidizer combination decreases with an increase in burner diameter (D). This trend is consistent with the limited data available in the literature for hydrocarbon fuels. Other geometric and flow-field effects namely, (1) plug flow, (2) flow-field blocking by the burner, and (3) heat loss by the flame to sidewalls that can affect a g were also experimentally quantified. The results from this study show that the plug flow boundary condition is always satisfied for oxidizer inlet distance > 2 times the largest porous burner diameter. Burner diameter less than 1/4 times side wall length (as is the case for all burners used in this study) does not significantly modify the flow. Hence, these two flow-field modifications do not affect a g . However, heat loss from the flame to the ambient through the side walls can cause a 4–9 % decrease in a g . Experiments showed that, CO/H2 mixtures diluted with N2 yield 1.6–2.25 times higher a g in comparison to CO/H2 mixtures diluted with CO2. Increasing H2 from 1 to 5 % leads to 2.5–3.8 times increase in a g , compared to 5 to 10 % increase in H2 which leads to only 1.3–1.7 times increase in a g for 70 % of N2 (v/v) in fuel mixture. Global extinction strain rate ( a g ) increases by 1.5–2.4 times with 10 % increase in CO for fuel mixtures consisting of H2 (1 and 5 % by v/v), CO2 (50, 60 and 70 % by v/v) and N2 (50, 60, 70 and 80 % by v/v). The change in overall reactivity ( ω o ) due to different diluents is used to quantitatively explain the variation of a g for different fuel compositions. These effects are also qualitatively explained using OH radical concentration change with H2 % in the fuel mixtures.

In this paper, experimental investigations on oxy-steam gasification of biomass in downdraft packed bed reactor are presented; propagation regimes and the associated hydrogen yield will be the focus of the current work. Steady flame propagation is shown to be established for a range of oxygen mass flux (16–120 g/m2s) covering ‘gasification’ and ‘combustion’ regimes with O2 fractions of 23, 30 and 40% by mass (rest steam). By restricting the upstream bed temperatures between 120 °C (to avoid steam condensation) and 150 °C (to prevent bulk devolatilization of bed), the intrinsic H2 yield from biomass is determined over an equivalence ratio ( Φ ) range of 3.5 to 1.2. This is shown to correspond to a ‘volatiles’ based equivalence ratio ( ϕ v ) of 2.2 to 1. Interestingly, the H2 yield over this entire range is within 30–40 g/kg of biomass. Using equilibrium calculations, it is shown that the ‘unburnt volatiles’ is the major H2 source when ϕ v > 2 and as ϕ v → 1, ‘volatiles’ H2 drops close to zero and the major contribution is through the reaction, C + H2O → CO + H2. Increase in char conversion from about 20% at ϕ v ∼2.1 to almost 100% as ϕ v → 1, the corresponding increase in peak bed temperature and decrease in ‘higher hydrocarbons’ are consistent with the observed H2 yield. The important insight is, operating close to ϕ v = 1, under slightly rich condition, leads to tar free exit gas with little or no compromise on H2 yield. This hitherto unknown result is perhaps the reason why all earlier works focused only on highly fuel rich conditions and/or very high steam temperatures ( ∼ 800 °C), tolerating higher tar content.

Biomass thermo-chemical conversion under O2/CO2 conditions is experimentally investigated to establish its CO2 conversion potential. Packed bed configuration with counter-current flame propagation is chosen for this purpose and three different fuels are used (agro-residue pellets, coconut shells and wood pellets). For oxidizer streams containing 20, 25, 30, 40 and 50% O2 (v/v) (rest CO2) steady flame propagation is established at different superficial velocities and the following quantities are measured – temperature along the reactor, mass consumption rate and exit gas composition. Corresponding reference experiments with O2/N2 mixtures are performed for comparing the net CO2 conversion. The propagation regimes, similar to earlier studies with air, fall under the following two categories – (1) gasification – volatile oxidation accompanied by char reduction and (2) char oxidation dominated – simultaneous char and volatile combustion. Invoking equilibration of volatile oxidation under gasification conditions, a new procedure is established to estimate the net CO2 conversion (NCC). In general, NCC is significant around the volatile stoichiometric point ( ϕ v = 1 ) and falls off on either side as the oxygen mass flux is decreased or increased. NCC is zero in very rich regime i.e. when ϕ v ≫ 1 due to low bed temperatures and also when ϕ v 1 due to char oxidation. Maximum NCC of 627 g/kg of biomass is observed with 30% O2/70% CO2 (v/v) case at ϕ v = 0.96 for agro residue pellets. Cold gas efficiency ( η g ) is as high as 85% for the maximum NCC case. Enhanced gasification efficiencies of O2/CO2 cases as compared to corresponding air cases is due to the additional conversion of CO2 to CO (predominantly C + CO2 → 2CO). The difference in the fraction of char left over with CO2 and N2 cases is consistent with this observation. Corrected fuel flux (CFF), proposed to address these variations in fuel heating value, oxygen fraction in the oxidizer etc., is shown to exhibit universality with respect to oxygen mass flux and fuel type.

The Heterogeneous Quasi One-dimensional (HeQu1-D) model for AP/HTPB composite propellant combustion is extended to aluminized propellants. Following the serial burning approach of HeQu1-D, a statistical particle path through an aluminized propellant is taken to consist of aluminized binder-matrix coated AP particles of various sizes. Extending the idea of homogenization of fine-AP particles, aluminum particles are assumed to be homogenized with the binder-matrix. Large Al particles (nominal size ≥ 15 µm) in the binder-matrix are assumed to get ejected into the gas phase and hence do not contribute to heat feedback to the burning surface. With these modifications, the model is shown to accurately predict the burn rate variation with pressure and initial temperature of propellants using Al of nominal sizes in the range of 15–50 µm (termed conventional aluminum, CAl). The experimentally observed reduction in propellant burn rate with substitution of AP by CAl is shown to be due to the increase in fuel richness and energy sink effect of melting of Al. Catalytic effects due to addition of burn rate modifiers (Fe2O3 in space shuttle booster propellant, for instance) are also accounted for by modifications to gas phase rate parameters. Increase in burn rate up to 25% with Al particles of a few µm (3–6 µm) in comparison with non-aluminized propellant is explained by recognizing that there will be non-negligible fraction of sub-micron Al due to the associated particle size distribution. This leads to heat release by sub-micron Al combustion close to the surface and an enhancement in the heat feedback, by a combination of convective and radiative mechanisms. Dramatic increase in burn rate with sub-micron Al (a factor of 4–5 as compared to CAl) is captured by invoking radiation from fine-Al/Al2O3 particles to propellant surface. Agglomeration of sub-micron Al particles is invoked to explain the saturation of burn rate enhancement with reduction in Al particle size and the effectiveness of sub-micron Al substitution in smaller fractions (bi-modal Al). Predictions for over fifteen different propellants with varying fractions of fine and coarse aluminum from earlier literature have been presented. Comparisons of the predictions from the model with experimental results from different sources is shown to be excellent-to-good for most cases. The hitherto unknown radiation dominated ablation ( r ˙ > 50 mm/s ) of coarse AP particles and the effect of Al particle size on propellant temperature sensitivity are brought out. The MATLAB® code based on the model offers opportunity for design of AP-HTPB composite propellants with combination of fine and coarse aluminum with confidence.

This paper is concerned with a new and novel approach to modeling composite propellant burn rate behavior. It is founded on the fact that composite propellant combustion is largely boxed between the premixed limits - of pure AP and fine AP-binder (HTPB, here) whose burn behaviors are taken as known. The current strategy accounts for particle size distribution using the burn time averaging approach. The diffusional effects are accounted for through a calibrated heterogeneous quasi-one-dimensional model (HeQu1-D for short) that allows for the flame temperature dependence on the local AP size-binder thickness geometry. Fine AP-binder homogenization is adopted as in recent models with refinement on the particle size as a function of pressure. The specialty of the present approach is that it invokes local extinction for fuel rich conditions for specific particle sizes when the heat balance causes the surface temperature to drop below the low pressure deflagration limit of AP; this feature allows for the prediction of extinction of propellant combustion. Combining these ideas into a MATLAB((R)) calculation framework that uses a single dataset on properties of AP and binder consistent with burn rate vs. pressure of pure AP and fine AP-binder system allows for making the predictions of propellants with multiple particle sizes and different fractions. Comparisons of burn rate data over nearly thirty compositions from different sources appear excellent to good. It is found that it is important to treat the full particle size distribution to achieve better predictions. Low burn rate index (similar to 0.25) observed with addition of SrCO3 is captured by extending the model to include the effect of binder melt; the gas phase effect is accounted for by calibration against catalytic effect on the fine AP-binder propellant. An interesting deduction from the model is that the temperature sensitivity of propellants should not exceed that of AP. The robustness of the current model and speed of determining the burn rate behavior allow for the possibility of determining the particle size distribution required to meet the burn rate specifications of a specific propellant for practical applications before actually embarking on making the propellant. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A gasification-based single step process is reported for synthesizing moderately activated char (surface area in the range of 100–600 m2/g) from ligno-cellulosic biomass. The novelty of the process lies in the use of mixtures of O2-CO2 and O2-steam as gasification agents to obtain significantly higher activation in a single-step as compared to gasification with air (

In a rapidly changing world new technological advancements and improvements are a constant need and in the field of communication and data transmission the necessity of a new technology is a need of the hour. The Power Line Communications (PLC) is one such technology described in this paper which allows transmission of data over existing power lines. Since power lines are almost ubiquitous this technology could have a rapidly emerging market, utilizing existing electricity power lines for high speed transmission of data and voice servers. This method could possibly be seen as a new approach for home automation and for data transmission within industries internally and externally.

This article is concerned with a study of an unusual effect due to density of biomass pellets in modern stoves based on close-coupled gasification-combustion process. The two processes, namely, flaming with volatiles and glowing of the char show different effects. The mass flux of the fuel bears a constant ratio with the air flow rate of gasification during the flaming process and is independent of particle density; char glowing process shows a distinct effect of density. The bed temperatures also have similar features: during flaming, they are identical, but distinct in the char burn (gasification) regime. For the cases, wood char and pellet char, the densities are 350, 990 kg/m(3), and the burn rates are 2.5 and 3.5 g/min with the bed temperatures being 1380 and 1502 K, respectively. A number of experiments on practical stoves showed wood char combustion rates of 2.5 +/- 0.5 g/min and pellet char burn rates of 3.5 +/- 0.5 g/min. In pursuit of the resolution of the differences, experimental data on single particle combustion for forced convection and ambient temperatures effects have been obtained. Single particle char combustion rate with air show a near-d(2) law and surface and core temperatures are identical for both wood and pellet char. A model based on diffusion controlled heat release-radiation-convection balance is set up. Explanation of the observed results needs to include the ash build-up over the char. This model is then used to explain observed behavior in the packed bed; the different packing densities of the biomass chars leading to different heat release rates per unit bed volume are deduced as the cause of the differences in burn rate and bed temperatures.

Forest are the basis for sustaining the ecosystem and helps cleanse the environment and provides shelter food for life dependent on it. Humans owe a great responsibility in preserving the remaining forests and take preventive steps towards the destruction of forest. One of the major cause for forest destruction are forest fires. So this project deals with the development of an intelligent real time and automatic early warning system for forest fire. It enables remote monitoring of conditions inside the forest regions and creates an alert when an forest fire is detected by unique mail and sms, the sensor data are constantly monitored along with a gps location for each sensor node which are connected together by Zigbee modules capable of long range transmission, the simple battery monitoring system allows constant monitoring of power usage of the entire setup. On the whole this prototype model when implemented will be a cost effective way for preventing forest fires.

This article aims at seeking the universal behavior of propagation rate variation with air superficial velocity (V-s) in a packed bed of a range of biomass particles in reverse downdraft mode while also resolving the differing and conflicting explanations in the literature. Toward this, measurements are made of exit gas composition, gas phase and condensed phase surface temperature (T-g and T-s), and reaction zone thickness for a number of biomass with a range of properties. Based on these data, two regimes are identified: gasificationvolatile oxidation accompanied by char reduction reactions up to 16 +/- 1cm/s of V-s and above this, and char oxidationsimultaneous char oxidation and gas phase combustion. In the gasification regime, the measured T-s is less than T-g; a surface heat balance incorporating a diffusion controlled model for flaming combustion gives and matches with the experimental results to within 5%. In the char oxidation regime, T-g and T-s are nearly equal and match with the equilibrium temperature at that equivalence ratio. Drawing from a recent study of the authors, the ash layer over the oxidizing char particle is shown to play a critical role in regulating the radiation heat transfer to fresh biomass in this regime and is shown to be crucial in explaining the observed propagation behavior. A simple model based on radiation-convection balance that tracks the temperature-time evolution of a fresh biomass particle is shown to support the universal behavior of the experimental data on reaction front propagation rate from earlier literature and the present work for biomass with ash content up to 10% and moisture fraction up to 10%. Upstream radiant heat transfer from the ash-laden hot char modulated by the air flow is shown to be the dominant feature of this model.

The work reported here is concerned with a detailed thermochemical evaluation of the flaming mode behaviour of a gasifier based stove. Determination of the gas composition over the fuel bed, surface and gas temperatures in the gasification process constitute principal experimental features. A simple atomic balance for the gasification reaction combined with the gas composition from the experiments is used to determine the CH(4) equivalent of higher hydrocarbons and the gasification efficiency (eta g). The components of utilization efficiency, namely, gasification-combustion and heat transfer are explored. Reactive flow computational studies using the measured gas composition over the fuel bed are used to simulate the thermochemical flow field and heat transfer to the vessel; hither-to-ignored vessel size effects in the extraction of heat from the stove are established clearly. The overall flaming mode efficiency of the stove is 50-54%; the convective and radiative components of heat transfer are established to be 45-47 and 5-7% respectively. The efficiency estimates from reacting computational fluid dynamics (RCFD) compare well with experiments. (C) 2011 Elsevier Ltd. All rights reserved.