Increase In Initial Temperature Research Articles

Effect of ethanol on auto-ignition characteristics and laminar burning velocity of gasoline under elevated temperature and pressure

Gasoline and its surrogate fuels have developed rapidly in recent years, and the study of the theory of multi-fuel mixed combustion is vital to the improvement of power machines. On the basis of the important role of ethanol-gasoline mixtures in oxygenated alternative fuels, Cai and Pitsch’ s mechanism was selected for a numerical study to research the important role of ethanol with respect to combustion of gasoline from a chemical kinetic perspective. It is found that the addition of ethanol accelerates the LBV and shortens the IDTs of gasoline, and the LBV of ethanol-gasoline mixtures goes up as both the initial temperature and the ethanol ratio rise, while the LBV of ethanol-gasoline mixtures declines as the initial pressure increases. The IDTs of ethanol-gasoline mixtures tend to decrease as the initial temperature, ethanol ratio and initial pressure increase. The addition of ethanol increases the production of the intermediates CH3, HCO and CH2O, and the reactive radicals in the system increase with the addition of ethanol. In addition, the addition of ethanol can lead to an earlier surge of OH groups. This study is not only helpful for the design of ethanol-gasoline power engines, but also promotes the development of alternative fuels.

Study on Laminar Combustion Characteristics of Ammonia/ Hydrogen Premixed Based on Chemical Reaction Kinetics

The combustion characteristics of ammonia/hydrogen premixed laminar flow and the effect of hydrogen on the combustion performance of ammonia fuel were studied. First, the corresponding model of ammonia/ hydrogen premixed laminar combustion is established by using GRI3.0 mechanism, Konnov mechanism, Mei mechanism, Okafor mechanism, and Otomo mechanism respectively. Second, the simulation results are compared with the experimental results. It is found that the Mei mechanism and Okafor mechanism are more suitable for ammonia/ hydrogen premixed laminar combustion. On this basis, the effects of equivalent ratio, hydrogen ratio, and initial temperature on laminar flame velocity, maximum combustion temperature, and NO mole fraction were studied. The results show that the laminar flame velocity, the maximum combustion temperature, and the mole fraction of NO first increase and then decrease with the increase of the equivalent ratio, and the laminar flame velocity reaches the maximum when the equivalent ratio is 1.1. At the same time, with the increase of hydrogen ratio and initial temperature, the maximum combustion temperature increases first and then decreases. The mole fraction of NO increased with the increase of hydrogen ratio and initial temperature. The results show that mixing hydrogen in ammonia can improve the combustion characteristics of ammonia.

Exploring influence of MgO/CaO on crystallization characteristics to understand fluidity of synthetic coal slags

The crystallization has significant influence on fluidity of slag and slag discharge of entrained-flow-bed (EFB) gasifier. The crystallization characteristics and fluidity of five synthetic slags with different MgO/CaO ratios prepared on the basis of the range of oxide contents of Zhundong coal ash were investigated in this study. The results show that with the MgO/CaO ratio increase, the initial crystallization temperature increases, and the main temperature range of crystallization ratio growth moves to higher temperature range gradually which causes Tp25 (Tp25 is the temperature corresponding to the viscosity of 25 Pa·s) to increase. Mg-rich crystals are formed preferentially than Ca-rich crystals when adding the same amount of MgO and CaO during cooling. The effective slagging operating temperature range decrease from 217 °C for the slag with a 0:4 MgO/CaO ratio to 44 °C for the slag with a 4:0 MgO/CaO ratio with the MgO/CaO ratio increase. The slags with 2:2 and 1:3 MgO/CaO ratios show similar effective slagging operating temperature range, Tp25 and the temperature corresponding to the viscosity of 2 Pa·s. However, compared with the slag with a 1:3 MgO/CaO ratio, the crystallization ratio and rate of slag with a 2:2 MgO/CaO ratio are lower within lower temperature range (1300–1200 °C), causing its lower critical viscosity temperature and wider actual operating temperature range. Of the five slags, the widest effective slagging operating temperature range and the lowest Tp25 of the slag with a 0:4 MgO/CaO ratio due to its low crystallization ratio, and wider actual operating temperature range of the slag with a 2:2 MgO/CaO ratio make the two slags suitable for slag discharge of EFB gasifier.

The effect of mixing and heat transfer on regression rate of TAGN-based fuel in a segregated AP/TAGN solid motor

The effect of mixing and heat transfer on regression rate of TAGN-based fuel of a segregated AP/TAGN solid motor is studied in the present study. A regression rate model of TAGN-based fuel under coupled combustion is developed and validated based on detailed reaction mechanism. The two-dimensional mixing characteristics in boundary layer and the effect on regression rate of TAGN-based fuel are analyzed in detail. The simulation results show that the increase of initial temperature of oxidizer gas leads to better mixing in the axial direction and higher temperature of burning surface. However, the mass concentration of O2 decreases greatly due to the increasing consumption by primary combustion reactions of AP-derived gaseous species. Therefore, the regression rate of burning surface decreases slightly. With inflow Mach number increasing from 0.32 to 0.75, mixing in the boundary layer is greatly enhanced. Therefore, both the temperature and regression rate increase with inflow Mach number. As pressure increases from 4 MPa to 10 MPa, the primary reactions of AP-derived gas species are also enhanced. Therefore, the mass concentration of O2 decreases rapidly, which leads to oxygen-lean combustion in the combustion chamber. Therefore, the temperature of burning surface decreases while the regression hardly varies despite of the better mixing near the burning surface at high pressure. The results show that the coupled combustion reactions between inflow oxidizer gas and fuel gas mainly occur in a narrow belt-like region of the boundary layer. The results show that the regression rate of solid fuel in the segregated solid motor is controlled by the competition between primary combustion and coupled combustion.

Numerical study of the effect of CO2/H2O dilution on the laminar burning velocity of methane/air flames under elevated initial temperature and pressure

AbstractDiluents have an essential effect during combustion. Discovering the influence of CO2 and H2O as diluents on laminar burning velocity (LBV) is helpful for combustion control and optimization. In this study, CH4/air/CO2/H2O mixtures were investigated and validated using the FFCM‐Mech 1.0 over extensive boundary conditions. The chemical effects of the diluents CO2 and H2O were separated using a decoupling method. It was found that an increase in initial temperature promotes the chemical effects, while an increase in initial pressure does the opposite. In addition, the inhibiting effect of CO2 on LBV is stronger than that of H2O. Sensitivity, mole fraction, and rate of production (ROP) analyses were used to reveal that the sum of the chemical effects of adding CO2 and H2O separately was greater than the chemical effects of adding equal amounts of CO2 and H2O simultaneously. This paper not only investigates the effect of CO2 and H2O on the LBV under wide boundary conditions, but also offers a valuable guide for studying the operating conditions and intensity settings of exhaust gas recirculation (EGR) and theoretical guidance for further research on the combination of EGR and in‐cylinder water injection technology.

EXERGY ANALYSIS OF AN OPEN-MODE ADSORPTIVE HEAT STORAGE UNIT BASED ON COMPOSITE ADSORBENT ‘SILICA GEL – CRYSTALLINE HYDRATE’

Exergy analysis of an open-mode adsorptive heat storage unit has been performed when a composite ‘silica gel – crystalline hydrate’ used as an adsorbent. The crucial factors affecting the exergy efficiency factor are stated to be temperature and initial humidity of airflow supplied to the inlet of adsorbent layer, temperature of external air and methods of air flow humidification. Procedure of calculation of the operating characteristics of an open-mode adsorptive heat storage device was further developed. The suggested procedure involves determination of adsorption, specific adsorption heat and final airflow temperature, useful heat, heat inputs for operating heat storage device and its efficiency factor, then exergy recovered, exergy supplied and exergy efficiency are calculated. Exergy efficiency depends on characteristics of flow of humid air fanned into the adsorbent layer such as temperature and initial absolute humidity which strongly affect the adsorption and final airflow temperatures. Increase of initial temperature of the humid air leads to decreasing of the exergy efficiency. Maximal values of exergy efficiency are determined at the absolute humidity and temperatures of initial airflow within the ranges of 0.03 – 0.04 kg/m3 and 20 – 30ºC, respectively. These characteristics are corresponded to the maximal airflow temperatures after passing through the adsorbent layer which meet to the Sanitary Regulations. Dependence of exergy efficiency vs. external air temperature and initial airflow temperature is shown. The exergy efficiencies of the open-mode adsorptive heat storage unit with steam and ultrasonic humidification were compared. Ultrasonic humidification is shown to allow increasing the exergy efficiency by 7 % against steam humidification. The obtained results can be used when energy-efficient heat and ventilation systems for residential premises developed.

Quantitative analyses of NO formations from different reaction pathways in methane-air combustion at various pressures and temperatures

Numerical calculations of the laminar counterflow diffusion flames of methane-air are conducted to quantitatively study NO formations from different reaction pathways (mechanisms) at various pressures and/or initial air temperatures. A modified method, which deactivates the initiating reactions in a specific reaction pathway only for NO production while maintaining interactions with other pathways, is developed to calculate NO formation in each mechanism. Results indicate that in the thermal, prompt, N2O, and NNH reaction mechanisms, the NO production rate largely increases as the pressure or the initial air temperature increases, and in particular, as these two parameters are increased together as in a practical combustion system. In the thermal pathway, as the pressure is increased to 15 atm, NO is produced almost entirely on the fuel-lean side. In the prompt pathway, NO production generally occurs in regions with the progress variable ranging from 0.8 to 0.95; the maximum NO production rate moves from the fuel-rich towards the stoichiometric region as the pressure is increased. NO formation from the N2O or NNH mechanism occurs mainly at high pressures, but the corresponding production rate is an order of magnitude smaller than that from the thermal or prompt mechanism, respectively. In all the reaction mechanisms, NO consumption occurs through the reburn mechanism on the fuel-rich side, and the consumption rate significantly increases as the pressure and initial air temperature increase. Results herein provide a quantitative understanding of the effects of pressure and temperature on NO formations from different reaction mechanisms.

Experimental study on energy transformation of static liquid pool during flash evaporation

Energy transformation during static liquid pool flash evaporation of pure water is examined on the basis of flashing experiments with superheats between 2 and 38 °C, initial water height ranging from 50 to 170 mm, and an initial liquid pool temperature from 50 to 85 °C. Energy balance link the flashed mass with the liquid pool temperature and then measure the variable parameters influence on several quantities: cooling rate, flashing time, and liquid mass evaporated. The non-dimensional numbers, Jakob number (Ja) and Non-Equilibrium Fraction (NEF) are applied to evaluate the heat transfer process. In addition, parametric study is performed to address the effect of superheat, initial temperature, and depressurization on the flashing phenomenon. Finally, a comparison of energy transformation during normal cooling and flash cooling is proposed. Results suggested that at higher initial temperature and lower initial pressure, a lower value of the equilibrium temperature obtained, and a more rapid temperature drop occurs. The maximum deviation obtained between the experimental and calculated ones is 11 % for larger vacuum tank pressure. The cooling rate and the flashing time also affected by these flashing parameters. With the increase of initial temperature by 15 °C, the cooling rate is enhanced by 41 %, and by dropping the vacuum tank initial pressure by 34.4 kPa, the cooling rate is improved by 56 %. A combined effect of different initial conditions on the flashing process has been shown to better understand their impact on evaporated mass. The present procedure is useful in designing the flashing system for a variety of thermal applications.

Experimental and numerical study of the effect of initial temperature on the combustion characteristics of premixed syngas/air flame

The effects of different initial temperatures (T = 300–500 K) and different hydrogen volume fractions (5%–20%) on the combustion characteristics of premixed syngas/air flames in rectangular tubes were investigated experimentally. A high-speed camera and pressure sensor were used to obtain flame propagation images and overpressure dynamics. The CHEMKIN-PRO model and GRI Mech 3.0 mechanism were used for simulation. The results show that the flame propagation speed increases with the initial temperature before the flame touches the wall, while the opposite is true after the flame touches the wall. The increase in initial temperature leads to the increase in overpressure rise rate in the early flame propagation process, but the peak overpressure is reduced. The laminar burning velocity (LBV) and adiabatic flame temperature (AFT) increase with increasing initial temperature. The increase in initial temperature makes the peaks of H, O, and OH radicals increase.

Energy Output of High‐speed Flowing Two‐phase IPN/Air in the Combustion Chamber

AbstractFuel‐air cloud explosions or detonations are often affected by initial ambient conditions. A two‐dimensional (2D) semi‐confined model was established to study the effects of the inflowing air temperature and initial temperature of the combustor on the explosion process of isopropyl nitrate (IPN)/air mixture. The results showed that at different initial temperatures (1000–3000 K), the first peak pressure (P1) and second peak pressure (P2) decreased with the increase in initial temperature; the maximum flame temperature (2338–3534 K) increased with the increasing initial temperature; the explosion pressure and temperature had the opposite trends with the initial temperature, indicating that the oxygen content in the combustor had a greater impact on the explosion pressure, while the initial temperature had a more significant effect on the flame temperature. Under different incoming air temperatures (1000–3000 K), the flame temperature (∼2700 K) of the two‐phase explosion had a small difference at the incoming temperature of≤2500 K, signifying that the airflow temperature (<3000 K) and the oxygen content in air jointly dominated the flame temperature; the flame temperature was 3100 K at the incoming temperature of 3000 K, which was about 300 K higher than other incoming flow temperatures, indicating that the flame temperature was more sensitive to the incoming air temperature (≥3000 K). At 600 m/s airflow, the explosion parameter curves at the inflow temperatures of 300 K and 600 K were compared, and the critical inflow temperature of the explosion process was also investigated.

Numerical evaluation of the influence of initial pressure/temperature on the explosion properties and soot formation of methane/coal volatiles mixtures

In this study, a model for describing both chain reactions and product growth for the explosions of methane/coal volatiles mixtures based on chemical reaction kinetics was established to calculate the impact of initial temperature and initial pressure on the deflagration features of the mixtures. The variation for the macroscopic explosion parameters and the microscopic reactions of methane/coal volatiles explosions under different conditions are investigated using reaction kinetics simulation. Results suggest that the Pmax increased by 64.496 %, 64.499 %, 64.502 %, and 64.504 % when the initial pressure changed from 0.8 to 1.3 atm. Whereas, under increasing initial temperature, the Pmax decreased by −18.167 %, −18.179 %, −18.190 %, and −18.200 % while the Tmax increased by 90.49 K, 90.07 K, 89.67 K, and 89.30 K, respectively. Meanwhile, the influence of initial temperature on the sensitivity of primary elementary reactions was more prominent than that of the initial pressure. The ROP of the key radicals H/O/OH unnecessarily presented an increasing tendency under the increasing initial temperature while the maximal molar fraction of each key radical increased. The increase in both initial pressure and initial temperature would greatly promote the growth of C(B), which in turn largely accelerated the formation of soot particles. This preliminary work would be beneficial for the preemptive precaution and effective control of the explosions in coal-derived industries.

Experimental study on the flammability limit parameters of premixed methanol-gasoline vapor-air mixtures

In this research, the fire and explosion risks of methanol-gasoline blended clean fuels are assessed in experimental studies of the flammability limit parameters of methanol-gasoline vapors at different methanol proportions (M0∼M100) and initial temperatures (313–393 K). The experimental results show that when the proportion of methanol in the methanol-gasoline mixture increases, both upper and lower flammability limits increase. When the initial temperature increases, the lower flammability limit of a methanol-gasoline blend decreases, and a higher methanol volume fraction in methanol-gasoline mixtures corresponds to a more obvious decrease in the lower flammability limit. When the temperature increases from 313 K to 393 K, the lower flammability limit of M75 drops by 11.86%. Under the condition of inert gas dilution, the limiting oxygen concentration gradually decreases with increasing proportion of methanol in methanol-gasoline mixtures. Additionally, the explosion triangle of methanol-gasoline vapor expands to the lower left corner, which increases the deflagration hazard of methanol-gasoline mixture under low oxygen content conditions. The results of this research will help researchers evaluate the fire and explosion risks of related processes and devices and establish a technical index for the application of blended methanol-gasoline clean fuels.

Experimental investigations on transient flow and heat transfer characteristics of RP-3 at supercritical pressure

Variable operation conditions due to the wide speed range of hypersonic vehicles are complicated and are often related to the heat load change of the chamber wall. Thermal and flow response characteristics during flight state change are investigated in this research experimentally by utilizing the electrically heating experiment system. It is revealed that the response time of flow and heat transfer due to step perturbation is longer than that of perturbation. The response time decreases as the initial temperature increases when the fuel temperature is lower than the critical temperature. Once the temperature is higher than critical temperature, the response time begins to increase as the initial temperature increases. A 3D transient model is adopted to help to explain this phenomenon. The results indicate that the reason for the characteristics is the weakening of heat diffusion near the wall due to heat transfer deterioration. This conclusion is beneficial to the regulation of the coolant.

Influence of Jet on Aerosol Retention by Pool Scrubbing Under Multihole Injector

In severe nuclear power plant accidents, when the containment is in a serious challenging state, the gas mixture in the containment can be injected into the spent fuel pool through the multihole injector by the containment depressurization measure, to reduce the risk of containment overpressure failure and the release of radioactivity to the environment. The pool scrubbing efficiency of aerosol under the jet regime is studied on the small-scale aerosol pool scrubbing facility, focusing on the influence of mass flux, steam fraction, submergence, particle diameter, and pool initial temperature on the aerosol decontamination factor (DF). The results show that under the jet regime, the DF value is significantly greater than that in the bubble regime and the effect of jet flow on the mechanism of steam condensation and aerosol removal of the rising zone is weak under the conditions explored. DF increases with the increase of mass flux owing to the droplet interception and inertial collision aerosol removal mechanisms. Because the high pool temperature weakens the aerosol removal by steam condensation, DF decreases with the increase of initial pool temperature under the conditions explored. Based on the experimental data and the analysis of the removal mechanism under the jet regime, an empirical model of aerosol DF considering mass flux, steam fraction, pool temperature, submergence, and particle size is established and verified by the international experiments. The proposed model can be used to calculate DF in the process of containment overpressure discharge.

A general prediction model of minimum film boiling temperature during quenching propagation in narrow rectangular channel

During quenching, the Leidenfrost effect deteriorates the heat transfer at high temperatures before the arrival of the minimum film boiling point. Accurate prediction of the minimum film boiling temperature (Tmin) is significant in assessing cooling efficiency and providing a reference for optimization design. The experimental investigation on the Tmin is carried out in multi-narrow rectangular channels containing internal and external coolant channels. The effects of initial surface temperature and wall heat flux on Tmin are discussed in detail. The experimental results indicate that Tmin increases with the increase of initial wall temperature and wall heat flux, by an average of 6.5% and 7.7%, respectively. Under high wall temperature and heat flux conditions, the ratio of Tmin to the initial wall temperature at the inlet is much larger and then remains nearly constant with the propagation of the quench. Furthermore, an improved dimensionless prediction model of Tmin is proposed considering the effects of high initial wall temperature and wall heat flux. The comparison results illustrate good agreement with relative errors within ± 15%. Meanwhile, the current model predicts most of the published experimental data with an uncertainty of ± 15%.

The Effects of Temperature and Impact Velocity on the Shock Wave Response of Pore-Embedded Metallic Glasses

In this work, the shock wave response of a pore-embedded CuZr metallic glass (PEMG) under different impact velocities (0.5–1.5 km/s) and initial temperatures (300–600 K) was evaluated through the molecular dynamics (MD) simulation. The results indicated that the nucleation and growth of nanoscale shear events around the pore were the dominant mechanisms for plastic deformation under the shock wave. It was also found that the increase in the impact velocity led to the filling of pore, which was due to the structural softening and the local temperature increment in the vicinity of pore. Moreover, the spall event originated from the formation and coalescence of tension transformation zones, leading to the formation of nanovoids in the system. At higher velocities, the spallation was accompanied with the formation of more nanovoids with smaller sizes, inducing the brittle failure in the system. The MD outcomes also showed that the increase in initial temperature decreased the shock pressure and flow shear stress and led to the smoother spallation in the PEMG.

Initial Temperature Effects on the Combustion Characteristics of Al

AbstractThe combustion of aluminium in propellants plays an important role in the energy release of propellants, and investigations of the combustion mechanism of aluminium can help to further improve the energy release characteristics of propellants. The changes in reaction temperature and product content over time during the reaction of Al(l)/O2 and Al(l)/AP systems at different initial temperatures were calculated using the Closed Homogeneous Batch Reactor in CHEMKIN‐PRO, and a sensitivity analysis was performed for the Al(l)/AP system. The results showed that with increases in the initial temperature, the heat storage time and combustion time of the Al(l)/O2 system were shortened and the equilibrium temperature increased, which was also true for the Al(l)/AP system. Moreover, the increase of initial temperature was favourable to the decomposition of O2 and the formation of AlO in Al(l)/O2 system but had little effect on the Al/AP system. The main reaction path of the Al(l)/AP system changed with increases of initial temperature, although , , , and are common elementary reactions with high temperature sensitivity and thus play a decisive role in the change of H2, AlCl, AlO and O contents as well as the changes of the reaction temperature of the system. In this paper, the combustion characteristics of an Al/AP system were investigated in depth, and the results can provide a theoretical basis for revealing the combustion mechanism and improving the energy release characteristics of aluminium‐based AP‐containing solid propellants.

Experimental study on the explosion characteristic and flame propagation of methanol spray at different injection pressures

The risk of methanol spray explosion increased under negative pressure. And the explosion characteristics and flame propagation of methanol spray at different injection pressures under negative pressure have been further investigated in this paper. Experiments were carried out by varying the injection pressure (13–21 bar) to study effects of different turbulence intensities on spray explosion. The effect of different concentrations (198–514.8 g/m3) and initial temperatures (303.15–323.15 K) on the explosion of methanol sprays (308.15 K) was also explored. At different injection pressures, decreasing concentrations and increasing initial temperatures promoted a reduction of particle size linearly. The effect of initial turbulence on the combustion and explosion regions was not remarkable. However, the increasing injection pressures facilitated the pmax, (dp/dt)max, and Tmax of methanol spray. The excessive methanol concentration inhibited the explosion characteristics. The increase of initial temperature significantly increased the risk of spray explosion. However, when the initial temperature was above 313.15 K, the particle size of methanol spray was less than 10 μm. The expansion rate of the combustion region remained stable. And the spray explosion was close to the vapor-phase methanol explosion.

Modeling the Process and Properties of Ash Formation during Pulverized Biomass Combustion

The present work mainly developed a mathematical model based on the plug flow model and coarse fly ash particles’ fragmentation model to describe the behavior and evolution of ash formation and the influence of the biomass feeding rate and flue gas cooling rate on ash properties, which is validated by literature data. The model considers homogeneous nucleation of alkali vapors, heterogeneous condensation of vapors on newly formed particles and fly ash particles, and collision-coagulation between aerosol particles, which is also applied to numerically study and analyze the ash formation characteristics in the cases of practical boiler pulverized fuel combustion and SO2 sulfation. The results show that the mathematical model can reasonably describe the ash formation and the influence of the biomass feeding rate and the flue gas cooling rate on the mass PSDs of PM10 and its elements. The initial nucleation temperature and initial nucleation particle size increase with the biomass feeding rate, which is of great importance to the cooling rate on the initial nucleation number concentration and the initial nucleation particle size. Elements Na, K, and Cl are mainly concentrated in PM1, but rarely distributed in PM1–10. The condensation of Na, K, and Cl on coarse particles increases with the biomass feeding rate and decreases with the cooling rate. The ash characteristics obtained from the experiment condition with an ultra-high flue gas cooling rate and minimum biomass selected may have a large deviation from that of practical biomass combustion, and the sulfated reaction may reduce Cl corrosion rather than ash deposition.

Safe operating conditions of isoperibolic homogeneous semibatch reactions: Effect of mixing heat

The mixing heat in a semibatch reactor may lead to an increase or decrease of the reaction initial temperature, which has an impact on the safety of the reaction. In this paper, the effect of mixing heat on the safe operating conditions of isoperibolic homogeneous semibatch reactions was studied. Mass and energy balance models considering mixing heat were constructed. Based on the balance models, boundary diagrams and adiabatic temperature diagrams were compared under different mixing heat levels. The mixing heat and reaction heat of esterification reaction between propionic anhydride and sec-butanol were measured by EasyMax. According to the experimental results, the effect of mixing heat on the thermal runaway critical cooling temperature was investigated. The results indicated that the mixing heat had a significant effect on the thermal behavior state of the reaction. The critical criterion considering the mixing heat can more accurately predict the safe reaction operating conditions for the isoperibolic homogeneous semibatch reactions. This work provided helpful suggestions for predicting safe operating conditions of reactions at different mixing heat effect levels.