Initial Gas Temperature Research Articles

Laminar burning velocities of n-decane and binary kerosene surrogate mixture

Laminar burning velocities of n-decane and binary kerosene surrogate mixture consisting of n-decane (80%) and benzene (20%) by liquid volume were determined at atmospheric pressure and initial gas temperatures of 338 and 358K. The heat flux method was employed to measure the burning velocity in non-stretched flames and three kinetic mechanisms were used to simulate the results: JetSurF 2.0, and two models for kerosene developed at Politecnico di Milano: Skeletal Surrogate (121 species) and high-temperature detailed (ver. 1412). New measurements were compared with available literature results at 400K by extrapolation, which was performed using calculated temperature dependence of the laminar burning velocity. The data determined with the heat flux method agree with some previous counterflow burner measurements and disagree with the data from spherical flames. The detailed mechanism from PoliMi was able to reproduce the present experiments the best. The increase of the burning velocity in the surrogate mixture compared to n-decane was found to be insignificant.

Efficient in situ drying of low rank coal in a pressurized down-flow flash dryer

Flash drying of low rank coal with synthesis gas was addressed by using a pressurized down-flow dryer. The proposed method is a potential approach to secure gaseous water that is required in coal processing by utilizing moisture in the low rank coal. The drying process was promoted by increasing the initial temperature of the synthesis gas as a drying medium and decreasing the particle size of the coal. The moisture removal rate of the coal using synthesis gas at 9 bars and 500 °C reached up to 97% within ten seconds. Although it is a higher temperature than that of fixed bed or moving bed dryer, outlet moisture laden synthesis gas had the low level of tar enough to be a feedstock of downstream catalytic process due to the short residence time in the dryer. The chemical composition changes of the coal during the drying resulted in reducing oxygen content to the atomic ratio of oxygen to carbon as 0.1 and enhancing its calorific value. Disappearance of hydroxyl functional group from the surface and physical reduction of the surface area of the coal decreased the moisture re-adsorption capacity, which could prevent the spontaneous combustion of the low rank coal.

Экспериментальное исследование температурных следов капель воды, водных массивов и аэрозольных потоков, движущихся через высокотемпературные продукты сгорания

The experimental investigations of temperature, varying in a trace of water droplets, water flow masses and aerosol flows, moving through high-temperature combustion products, were conducted. The temperature values of vapor-gas mixture in an area, corresponding to the trace of water droplets, moving through high-temperature combustion products (initial temperature values were 450-950 K) were measured by quick-response thermocouples (time of thermal delay was less than 1 sec). The objects of investigations were aerosol flows with droplet sizes, equal to R d » 0.04÷0.40 mm, and droplet concentration, equal to g d » 3·10 -5 ÷12·10 -5 m 3 of droplets/m 3 of gas; single droplets with R d » 1.5÷2.5 mm, and significant water flow masses with characteristic size of 22-30 mm. Application of the quick-response thermocouples allowed defining the ranges of maximal reduction of gaseous medium temperature T g in a trace of extinguishing liquid according to a group of factors, such as a method of supplying of water into the combustion zone, characteristic size of the elements of liquid flow R d , droplet concentration in a water flow g d , temperature of the combustion products T g . The variation of combustion product temperature in a trace of motion of atomized flow, droplets and liquid flow masses was determined in the analysis of temperature trends, ranged from 15 K to 140 K. The values of preservation time t of low temperature of vapor-gas mixture in a trace of droplet flow, single droplets and significant liquid flow masses were determined relative to initial gas temperature: t » 4÷28 sec. It was experimentally defined that maximum values of time t correspond to supplying the atomized water, with characteristic sizes of elements, equal to R d » 0.15÷0.30 mm, and concentration, equal to g d » 3·10 -5 ÷12·10 -5 m 3 of droplets/m 3 of gas, into the standardized fire. The conditions when the characteristics of temperature and concentration traces have significant influence on processes of evaporation and heat exchange between gases and moving liquid (with accumulation of liquid energy) were determined. The ascertained experimental data prove the earlier made theoretical hypothesis about sufficiently long periods of preservation the temperature traces of water droplets, even if they are small. The obtained experimental information become the basis for developing the method of the effective reduction of fire temperature (flame and combustion products) in the technologies of polydisperse aerosol fire extinguishing.

Three-dimensional simulation of microwave-induced helium plasma under atmospheric pressure

A three-dimensional model is presented to investigate helium plasma generated by microwave under atmospheric pressure in this paper, which includes the physical processes of electromagnetic wave propagation, electron and heavy species transport, gas flow, and heat transfer. The model is based on the fluid approximation calculation and local thermodynamic equilibrium assumption. The simulation results demonstrate that the maxima of the electron density and gas temperature are 4.79 × 1017 m−3 and 1667 K, respectively, for the operating conditions with microwave power of 500 W, gas flow rate of 20 l/min, and initial gas temperature of 500 K. The electromagnetic field distribution in the plasma source is obtained by solving Helmholtz equation. Electric field strength of 2.97 × 104 V/m is obtained. There is a broad variation on microwave power, gas flow rate, and initial gas temperature to obtain deeper information about the changes of the electron density and gas temperature.

Combined cycle plants: Yesterday, today, and tomorrow (review)

Gas turbine plants (GTP) for a long time have been developed by means of increasing the initial gas temperature and improvement of the turbo-machines aerodynamics and the efficiency of the critical components air cooling within the framework of a simple thermodynamic cycle. The application of watercooling systems that were used in experimental turbines and studied approximately 50 years ago revealed the fundamental difficulties that prevented the practical implementation of such systems in the industrial GTPs. The steam cooling researches have developed more substantially. The 300 MW power GTPs with a closedloop steam cooling, connected in parallel with the intermediate steam heating line in the steam cycle of the combined cycle plant (CCP) have been built, tested, and put into operation. The designs and cycle arrangements of such GTPs and entire combined cycle steam plants have become substantially more complicated without significant economic benefits. As a result, the steam cooling of gas turbines has not become widespread. The cycles—complicated by the intermediate air cooling under compression and reheat of the combustion products under expansion and their heat recovery to raise the combustion chamber entry temperature of the air—were used, in particular, in the domestic power GTPs with a moderate (700–800°C) initial gas turbine entry temperature. At the temperatures being reached to date (1300–1450°C), only one company, Alstom, applies in their 240–300 MW GTPs the recycled fuel cycle under expansion of gases in the turbine. Although these GTPs are reliable, there are no significant advantages in terms of their economy. To make a forecast of the further improvement of power GTPs, a brief review and assessment of the water cooling and steam cooling of hot components and complication of the GTP cycle by the recycling of fuel under expansion of gases in the turbine has been made. It is quite likely in the long term to reach the efficiency for the traditional GTPs of approximately 43% and 63% for PGUs at the initial gas temperature of 1600°C and less likely to increase the efficiency of these plants up to 45% and 65% by increasing the gas temperature up to 1700°C or by application of the steam cooling in the recycled fuel cycle.

Experimental determination of the retention time of reduced temperature of gas–vapor mixture in trace of water droplets moving in counterflow of combustion products

We have experimentally studied temporal variation of the temperature of gas–vapor mixture in the trace of water droplets moving in the counterflow of high-temperature combustion products. The initial gas temperature was within 500–950 K. The water droplet radius in the aerosol flow varied from 40 to 400 μm. The motion of water droplets in the counterflow of combustion products in a 1-m-high hollow quartz cylinder with an internal diameter of 20 cm was visualized by optical flow imaging techniques (interferometric particle imaging, shadow photography, particle tracking velocimetry, and particle image velocimetry) with the aid of a cross-correlation complex setup. The scale of temperature decrease in the mixture of combustion products and water droplets was determined for a pulsed (within 1 s) and continuous supply of aerosol with various droplet sizes. Retention times of reduced temperature (relative to the initial level) in trace of water droplets (aerosol temperature trace) are determined. A hypothesis concerning factors responsible for the variation of temperature in the trace of droplets moving in the counterflow of combustion products is experimentally verified.

Laminar burning velocity of acetic acid + air flames

Laminar burning velocities of acetic acid + air flames at 1 atm and initial gas temperatures of 338 K, 348 K, and 358 K were determined using the heat flux method. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions. Due to experimental problems related to the corrosiveness of acetic acid towards the burner material, the uncertainty of the burning velocities was relatively high up to ± 2 cm/s. Seventy reactions pertinent to acetic acid and ketene have been reviewed and detailed reaction mechanism for acetic acid combustion was developed. The model over-predicts measured burning velocities by about 3 cm/s. The mechanism was also tested comparing with flame structure of the low-pressure flame of acetic acid (Leplat and Vandooren, 2012). Good agreement with the concentration profiles of major products was found, however several minor intermediates were over- or under-predicted by the model. To elucidate reactions responsible for the differences observed, the sensitivity analysis was performed. It was found that the calculated burning velocities are insensitive to the reactions of acetic acid and mostly governed by C1 chemistry typical for all hydrocarbons and by reactions of ketene. Possible modifications of the rate constants within the evaluated uncertainty factors were discussed.

The role of initial tank temperature on refuelling of on-board hydrogen tanks

The influence of the initial tank temperature on the evolution of the internal gas temperature during the refuelling of on-board hydrogen tanks is investigated in this paper. Two different types of tanks, four different fuel delivery temperatures (from ambient temperature refuelling to a pre-cooled hydrogen at −40 °C), several filling rates and initial pressures are considered. It has been found that the final gas temperature increases linearly with the increase of the initial tank temperature while the temperature increase (ΔT) and the final state of charge (SOC) decrease linearly with increasing the initial temperature. This dependency has been found to be larger on type III than on type IV tank and larger the larger the initial pressure. Additionally CFD simulations are performed to better understand the role of the relevant phenomena on the gas temperature histories e.g. gas compression, gas mixing, and heat transfer. By comparing the results of calculations with adiabatic and diathermal tank walls, the effect of the initial gas temperature has been separated from the effect of the initial wall temperature on the process.

Fully coupled thermo-hydro-mechanical model for extraction of coal seam gas with slotted boreholes

China has abundant coal seams with high gas content and low matrix permeability, which is unfavorable for efficient gas extraction. Popular extraction technology that uses high-pressure water jet slotting can overcome this difficulty, increase the contact area of coal and air, and expand the influence radius of boreholes. Thus, this technology improves gas extraction rates and ensures mine safety. Although the high-pressure water jet slotting technology has been comprehensively investigated and tested, fewer studies have been conducted on coal seam gas extraction with slotted boreholes using a fully coupled thermo-hydro-mechanical model. Neglecting this coupled thermo-hydro-mechanical interaction may result in misleading estimates of the gas extraction effect, which could be detrimental to the production prediction, drainage optimization design and gas control.In this study, we first create a fully coupled thermo-hydro-mechanical (THM) model using a fully coupled finite element approach and a history data matching to ensure the reliability and validity of this model. Second, we perform simulation experiments to investigate the sensitivities of gas extraction with single slotted borehole to changes in the intrinsic and extrinsic factors (for example, permeability, gas pressure, temperature and radius of the slots). Finally, we examine the effect of the interaction of multi-boreholes on the optimization design of multi-boreholes in practical engineering applications. The results demonstrate that: (1) higher permeability, initial gas pressure, temperature and slot radius has an effect on the radius of a single slotted borehole. (2) For both conventional and slotted arrangements, the estimated completion time increases exponentially with an increase in the hole spacing. For the same hole spacing, the drainage time of the conventional arrangement is longer than that of the slotted arrangement. Thus, our fully coupled THM model can improve the current understanding of the gas drainage process with slotted boreholes and provide scientific guidelines to evaluate gas extraction and optimize the design of gas extraction systems.

Laminar burning velocities of benzene + air flames at room and elevated temperatures

Laminar burning velocities, SL, of benzene+air flames were determined at atmospheric pressure and initial gas temperatures, T, of 298, 318, 338 and 358K. Non-stretched flames were stabilized on a perforated plate burner using the heat flux method. New measurements were compared with available literature results obtained in spherical and counterflow flames at room and elevated temperatures. Data consistency was assessed with the help of analysis of the temperature dependence of the laminar burning velocity, which was interpreted using an empirical expression SL=SL0(T/T0)α. Both the laminar burning velocities and the power exponents, α, were compared with predictions of three kinetic mechanisms: JetSurF 2.0, and two models for kerosene developed at Politecnico di Milano: Skeletal Surrogate (121 species) and high-temperature detailed (ver. 1412). The last model demonstrated the best performance over the range of conditions studied.

SO2 removal by seawater in a spray tower: Experimental study and mathematical modeling

In this article, the reactive absorption of SO2 by seawater is studied in a spray tower experimentally and mathematically. The liquid film formation on the tower wall is implemented in the model and measured experimentally at different operating conditions. The effect of liquid to gas flow rate, initial SO2 concentration in gas phase and initial gas temperature on SO2 removal efficiency is examined. Regarding the importance of liquid droplets hydrodynamics and its effect on the performance of the equipment, the required differential equations for predicting the trajectory and local velocity of droplets are also developed based on the nozzle and spray characteristics and solved simultaneously with other governing equations. In order to survey the effect of nozzle type on removal efficiency, two different types of nozzles are examined. Semi-empirical correlations are proposed for two different nozzles by using experimental data and droplets hydrodynamics model, to predict the amount and the variation of liquid film mass flow rate on the spray tower wall. Results indicate that neglecting the liquid film formation leads to an average of 23% error in predicting the removal efficiency when nozzle type 1 is used, while the calculated error of model by considering the film formation is reduced to 4%. By implementation of droplets hydrodynamics model and applying a modified thermodynamics model for predicting the behavior of the existing chemical reactions, the capability of the spray tower model in predicting the SO2 removal efficiency is enhanced.

Temperature and Concentration Traces of Spray Flows During Motion in a Flame

Heat and mass transfer models are developed on the base of experimental data and using Ansys Fluent software. These models allow prediction of the temperature and concentration traces of droplets. Transfer mechanisms of water droplets from different flames of flammable liquid (ethanol, kerosene И benzine) with temperature gases 450–850 К are analyzed. The paper considers aerosol flows with droplets sizes of 0.04–0.4 mm and concentration of 3.8·10 -5 –10.3·10 -5 m 3 of droplets/m 3 of gas. The maximum gas temperature reduction in the trace of a moving liquid is ranged from 850 K to 600 K. The times of keeping the low temperature of the gas-vapor mixture in the droplets trace are from 13 s to 25 s relative to the initial gas temperature.

Experimental and modelling study of the effect of elevated pressure on ethane and propane flames

Laminar burning velocities, SL, of ethane+air and propane+air flames within an equivalence ratio range between 0.8 and 1.3 were determined at atmospheric and elevated pressures up to 4atm. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions, created using the heat flux method. Initial unburnt gas temperature was 298K. These new experimental results were compared with available literature data and predictions using three kinetic schemes: USC Mech II, San Diego mechanism and Aramco Mech 1.3. The models behave differently in reproducing SL of ethane and propane flames with closer agreement between Aramco Mech 1.3 and the present measurements. The pressure dependence of the laminar burning velocities was analysed using the expression SL=SL0(P/P0)β. Large deviations of the derived power exponent, β, were observed for different experimental datasets and between model predictions and the measurements. To elucidate these differences in the performance of the three mechanisms, sensitivity analyses of the burning velocity and of the power exponent β were performed. It was demonstrated that the power exponent β may serve as an independent target for model validation and improvement. When comparing β coefficients derived from the present and previous measurements of SL in methane, ethane, propane and n-pentane flames using the heat flux method, important similarities were found at lean conditions with large disparity in rich mixtures. Neither experiments nor modelling support the linear dependence of the power exponent β with equivalence ratio for flames of alkanes.

Равновесие водяного газа с углеродом

The calculated possible parameters of equilibrium of water gas with carbon are presented in the form of spatial (3-dimensional) diagram in coordinates “ xCO – xH2 – T ”,. It can be supplemented with a graph of isothermal projections of isothermal section surfaces onto the plane “ xCO – xH2 ”. Different ways of obtaining gas atmosphere with oxygen potential sufficient to reduce metal oxides are explored. The most technological method of obtaining gas mixture capable of reducing metal oxides is heating water vapour in contact with carbon. In this case the resulting water gas composition is determined by heating temperature only. Maximum concentration of hydrogen xH2 reaches 0.5 when “H2O – C” is heated to ~ 900 K, and heating to temperatures above 1100 K produces a mixture of reducing gas agents with equal concentrations xCO = xH2 = 0.5. Heating gas mixtures “H2O – CO2” in contact with carbon produces water gas with reduced concentration of H2 and increased concentration of CO. Gas atmosphere (H2 – H2O – CO – CO2) of any composition can be obtained by heating mixtures “H2 – CO” in contact with carbon. Formation of CO2 occurs as a result of the dissociation reaction of CO and water vapor by the reaction H2O + CO = H2 + CO2. A technique of quantification of the carbon gasification with water vapor H2O carbon dioxide CO2 is presented. Calculations showed that gasification reactions C + CO2 = 2CO and C + H2O = CO + H2 can occur both forth and back depending on the composition of the initial gas mixtures and temperature.

Numerical simulation of particle motion and heat transfer in a rotary kiln

A two-fluid approach and diverse heat transfer models are applied to a two-dimensional cross-section of a rotary kiln coupled with granular flow kinetic theory, which treats random granular motion as thermal molecular motion. The models are validated by comparison with the available experimental data. The results show that the bed surface velocity characteristic peak is located at the center and down the edges. The highest temperature is found at the bed surface and the temperature gradient in the bed is lower than that in the rotary kiln wall. The main factors that affect the temperature distribution are the initial gas temperature and rotational speed of the kiln.

A modified model of mode approximation for nitrogen plasma based on the state-to-state approach

This paper addresses the analysis of thermally nonequilibrium processes in nitrogen plasma initiated by fast heating of the gas in a shock wave and by its expansion in a supersonic nozzle flow. A novel model of mode approximation has been developed that treats rate constants of plasma-chemical processes and processes of vibrational–translational, electronic–translational and electronic–electronic exchange obtained via summation of level rate coefficients of elementary reaction channels for given vibrational states, while suggesting the existence of a local Boltzmann distribution over the vibrational levels in each electronic state , , , , , of the molecule. Despite the fact that this level-based mode model is much simpler than the state-to-state model, it makes it possible to reproduce with high accuracy the evolution of nonequilibrium parameters and species concentrations predicted by the accurate state-to-state model in the post-shock-front region. However, in the expanding supersonic flow, this model cannot describe properly the variation of nonequilibrium parameters and species concentrations of electronically excited molecules and N atoms. The inaccuracy rises on decreasing the initial temperature of preheated gas in the reservoir. The comprehensive analysis of different factors influencing the prediction ability of the developed level-based mode model is also reported.

Laminar burning velocity of nitromethane + air flames: A comparison of flat and spherical flames

Laminar burning velocities, SL, of nitromethane and air flames at 1 atm and initial gas temperatures, T, of 338 K, 348 K, and 358 K were determined using the heat flux method. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner under adiabatic conditions. The comparison of these new experimental data and recent literature results obtained in spherical flames at 423 K was guided by the analysis of the temperature dependence of SL using expression SL = SL0(T/T0)α, and also by kinetic modelling of premixed flames employing detailed mechanisms suggested in the literature. It was demonstrated that conventional recalculation of the flame front speed into the burning velocity using density ratio of the unburned and burned gases at equilibrium is inappropriate for spherical nitromethane flames. Both the laminar burning velocities and the power exponents, α, were compared with predictions of the kinetic mechanisms. Remaining discrepancies of the modelling and reconciled experimental data were highlighted.

The temperature dependence of the laminar burning velocities of methyl formate + air flames

Laminar burning velocities, SL, of methyl formate and air flames were determined at atmospheric pressure and initial gas temperatures, T, of 298, 318, 338 and 348 K. Measurements were performed in non-stretched flames, stabilized on a perforated plate burner at adiabatic conditions, generated using the heat flux method. These new experimental data shed light on discrepancies seen in previously published results, and the temperature dependence of the laminar burning velocity of methyl formate was analysed using expression SL = SL0(T/T0)α. It was found that the power exponent, α, has a minimum close to equivalence ratio, ϕ, of 1.0. Both the laminar burning velocities and alpha coefficient were compared with predictions of the mechanisms of Glaude et al. (2005), Dooley et al. (2010) and Dievart et al. (2013). While the two latter mechanisms are in generally good agreement in lean mixtures, the Glaude mechanism over predicts the experimental burning velocities over the entire range of equivalence ratios. The temperature dependences predicted by the Glaude and Dievart mechanisms, however, are rather close and agree well with the measurements. To elucidate these differences and similarities in the performance of two mechanisms, the sensitivity analysis of the power exponent α was performed for the first time. It was demonstrated that examination of the temperature dependence of the burning velocity provides an independent approach for analysis of experimental data consistency.

Spontaneous ignition of isolated n-heptane droplets at low, intermediate, and high ambient temperatures from a mixture-fraction perspective

Detailed numerical simulations of isolated n-heptane droplets autoignition have been conducted at pressures of 5 and 10atm for several values of the initial ambient gas temperature. The ignition modes considered included low-, intermediate-, and high-temperature ignition. The analysis was conducted from a mixture-fraction perspective. For sufficiently low values of the ambient gas temperature, two-stage ignition was observed. Under these conditions, low-temperature reactions played an important role in the transition of the system to a fully burning state. As the initial value of the ambient gas temperature increased, the influence of the low-temperature reactions on the ignition process decreased and eventually became marginal for temperatures above 900K. Comparisons against homogeneous reactor calculations showed that the ignition location in mixture fraction space could be reasonably predicted for the high-temperature case, whereas discrepancies occurred for the intermediate- and low-temperature ones due to the shift in the maximum reactivity of the system caused by the cool flame appearance. The dependence of the ignition process on the initial droplet diameter was also studied for different values of the initial ambient gas temperature. It was found that, for all cases investigated, a value of the droplet diameter existed for which ignition took the least time to occur. For smaller droplets, the ignition transient was longer and eventually a burning flame did no longer appear when the droplet was initially too small. For the low-temperature case, the minimum ignition delay time was determined by the competition between the quicker ignition of the cool flame and the longer second induction time resulting from the decrease in the droplet size; for the high-temperature case, it was the results of phenomena occurring early during the droplet lifetime.

Combustion characteristics of low concentration coal mine methane in divergent porous media burner

Low-concentration methane (LCM) has been one of the biggest difficulties in using coal mine methane. And previous studies found that premixed combustion in porous media is an effective method of low calorific gas utilization. This paper studied the combustion of LCM in a divergent porous medium burner (DPMB) by using computational fluid dynamics (CFD), and investigated the effect of gas initial temperature on combustion characteristic, the distribution of temperature and pollutant at different equivalence ratios in detail. Besides, the comparison of divergent and cylindrical burners was also performed in this paper. The results show that: the peak temperature in DPMB increases as the increasing of equivalence ratio, which is also suitable for the outlet NO discharge; the linear correlation is also discovered between peak temperature and equivalence ratios; NO emission at the initial temperature of 525K is 5.64times, larger than NO emission at the initial temperature of 300K. Thus, it is preferable to balance the effect of thermal efficiency and environment simultaneously when determining the optimal initial temperature range. The working parameter limits of divergent burner are wider than that of cylindrical one which contributes to reducing the influence of LCM concentration and volume fluctuation on combustion.