scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures III—Hexane- and isobutane-air mixtures

1934 ◽  
Vol 146 (856) ◽  
pp. 113-129 ◽  
Keyword(s):  
Critical Pressure ◽  
High Pressures ◽  
Initial Pressure ◽  
Liquid Fuels ◽  
Spontaneous Ignition ◽  
Lower Range ◽  
Ignition Point ◽  
Wide Range ◽  
Temperature Ranges ◽  
Low Pressures

In two recent communications we described the results of investigations into the influence of varying initial pressure up to 15 atmospheres on the spontaneous ignition of butane- and pentane-air mixtures, showing that in each case the ignition were located in two distinct and widely separated temperature ranges, location in the higher range occurring at low pressures and in the lower range at high pressures. Transference of an ignition point from the higher to the lower range occurred sharply, at a critical pressure, which depended upon the hydrocarbon concerned and the composition of its mixture with air. The bearing of these observations upon the problem of knock was also discussed. A wide range of explosive media, comprising mainly the higher hydrocarbons contained in liquid fuels, is now being systematically studied, and the present paper summarizes the results obtained for hexane- and isobutane-air mixtures. So far, our results support the view (also recently endorsed by Neumann and Estrovitch) that the lower group of ignition points is the outcome of the survival and further rapid oxidation of certain intermediate bodies, a process favoured by high pressure. whereas the higher group results from ignitions mainly of the products of their thermal decompositions which are favoured by low pressure.

scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures - IV—methane-, ethane-, and propane-air mixtures

1936 ◽  
Vol 154 (881) ◽  
pp. 95-112 ◽  
Keyword(s):  
Critical Pressure ◽  
Spontaneous Ignition ◽  
Lower Range ◽  
Experimental Conditions ◽  
Temperature Range ◽  
Limited Temperature ◽  
Tentative Hypothesis ◽  
Temperature Ranges ◽  
Higher Temperature ◽  
Temperature And Pressure

In previous papers the results of investigations into the influence of varying initial pressures up to 15-20 atmospheres on the spontaneous ignition of mixtures with air of butane, iso -butane, pentane, and hexane were described. On the attainment of a critical pressure, which varied both with the hydrocarbon concerned and the composition of its mixture with air, the ignition points were always found to fall sharply from a higher temperature range above 500°C to a lower range at about 300°C. At pressures just exceeding the critical transition pressures ignition occurred at first only within limited temperature ranges which widened and ultimately merged with increasing pressure. The striking relationship between the behaviours of the hydrocarbons referred to under the experimental conditions and their “knocking” propensities in an engine was also indicated. While the data available were inadequate for drawing any final con­clusion as to the character of the phenomena referred to, a tentative hypothesis was advanced that while ignition in the higher temperature range pertains mainly to the thermal decomponents of intermedially formed compounds, ignition in the lower system occurs when temperature and pressure conditions favour the survival and further oxidation of such bodies, particularly aldehydes.

scholarly journals The influence of pressure on the spontaneous ignition of inflammable gas-air mixtures. II.—Pentane-air mixtures

1933 ◽  
Vol 143 (848) ◽  
pp. 168-176 ◽  
Keyword(s):  
Atmospheric Pressure ◽  
Internal Combustion Engines ◽  
Critical Pressure ◽  
Initial Pressure ◽  
Spontaneous Ignition ◽  
Combustion Engines ◽  
Compression Method ◽  
Ignition Point ◽  
Hydrocarbon Combustion ◽  
The One

In a recent communication an account was given of an investigation into the influence of varying initial pressure on the spontaneous ignition of butane-air mixtures. Whereas at atmospheric pressure the known values of ignition temperatures for these mixtures were between circa 550 and 600°C. at higher pressures as, for example, those employed in the adiabatic compression method they had been located at circa 300°C. By progressively increasing the pressure from atmospheric to 15 atmospheres we were able to show that the ignition points actually fell into two well-defined groups the one above 450° C. for pressures not exceeding about 3 atmospheres and the other below 370°C. for higher pressures. Transference of an ignition point from the higher to the lower group occurred at a definite critical pressure which depended upon the composition of the mixture. This new features of hydrocarbon combustion seemed of undoubted importance in regard to the phenomenon of "knock" in internal combustion engines, the more so when it was discovered that the presence of 0·05% of lead tetraethyl was capable at pressure near the critical transition pressure of raising the ignition point from the lower to the higher group. On this account we have been determining the critical pressure regions in other explosive media and our results for pentane-air mixtures are incorporated in this paper.

scholarly journals The thermal decomposition of acetaldehyde and the existence of different activated states

1933 ◽  
Vol 141 (843) ◽  
pp. 41-55 ◽  
Keyword(s):  
High Pressures ◽  
Initial Pressure ◽  
Bimolecular Reaction ◽  
Bimolecular Reactions ◽  
First Order ◽  
Straight Line ◽  
Gas Reactions ◽  
Pass Through ◽  
Low Pressures ◽  
Kinetics Of

Homogeneous thermal gas reactions were at one time tacitly assumed to possess a definite order, unimolecular and bimolecular reactions, for example, being sharply distinguished. The kinetics of the decomposition of acetalde­ hyde, CH 3 CHO = CH 4 + CO, over the pressure range of 100 to 400 mm. were found to satisfy the criterion of a bimolecular reaction, namely, that the reciprocal of the time for half change (1/ t 1/2 ) )plotted against the initial pressure ( p 0 ) gave a straight line inclined to the axes. The line, however, did not pass through the origin, as may be seen in fig. 1 of the present paper. This indicated the presence of some first order reaction, the nature of which was not determined. Subsequently, in accordance with the collision theory of activation and deactivation, it was shown that certain reactions, sometimes called quasiummolecular, change their order from the second at low pressures to the first at high pressures. This apparently was the reverse of the behaviour shown by acetaldehyde.

The Critical Pressure at the Onset of Flame Instability of Syngas/Air/Diluent Outwardly Expanding Flame at Different Initial Temperatures and Pressures

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ziyu Wang ◽  
Ziwei Bai ◽  
Guangying Yu ◽  
Sai Yelishala ◽  
Hameed Metghalchi
Keyword(s):  
High Speed ◽  
Critical Pressure ◽  
Hydrodynamic Instability ◽  
Experimental Studies ◽  
Initial Pressure ◽  
High Energy ◽  
Oxide Semiconductor ◽  
High Energy Density ◽  
Flame Instability ◽  
Wide Range

Syngas has gained attention recently due to its high energy density and environmentally friendly characteristics. Flame stability plays an important role in flame propagation in energy conversion devices. Experimental studies were performed in a cylindrical chamber to investigate flame instability of syngas/air/diluent mixture. A Z-shape Schlieren system coupled with a high-speed complementary metal–oxide–semiconductor camera was used to record flame pictures up to 40,000 frames per second. In this research, syngas is a mixture of hydrogen and carbon monoxide and diluent is a blend of 14% CO2 and 86% N2 with the same specific heat as the burned gases. Three main flame instabilities namely Rayleigh–Taylor (body force) instability, hydrodynamic instability, and thermal-diffusive instability have been studied. For the onset of flame instability, a power law correlation for the ratio of critical pressure to initial pressure of syngas/air/diluent flames over a wide range of initial temperatures (298–450 K), initial pressures (1.0–2.0 atm), equivalence ratios (0.6–3.0), diluent concentrations (0–10%), and hydrogen percentages (5–25%) in the fuel has been developed.

scholarly journals Numerical investigation of energy transfer efficiency from microwave radiation to plasma in a cylindrical resonant cavity

2021 ◽  
Vol 2119 (1) ◽  
pp. 012123
Author(s):  
M Y Hrebtov ◽  
M S Bobrov
Keyword(s):  
High Pressures ◽  
Hydrogen Plasma ◽  
Resonant Cavity ◽  
Computational Cost ◽  
Absorption Efficiency ◽  
Energy Transfer Efficiency ◽  
Generation Process ◽  
Plasma Generation ◽  
Wide Range ◽  
Low Pressures

Abstract The paper presents a simplified numerical model of the hydrogen plasma generation process in a microwave resonant cavity. The model assumes electroneutrality and the prescribed electron temperature of the plasma, thus significantly reducing the computational cost. This allows for the parametric study in a wide range of operating pressures end electric field magnitudes (at a frequency of 2.45GHz). The prescribed model allows finding the effective range of operating pressures for the plasma generation. At low pressures, the collision rate is too low to effectively absorb all the emitted energy while at high pressures the electron conductivity drops which also reduces the absorption efficiency.

THERMAL CONDUCTIVITY OF SOLIDS AT HIGH TEMPERATURES AND HIGH PRESSURES

2007 ◽  
Vol 21 (25) ◽  
pp. 4419-4427 ◽  
Author(s):  
S. K. SHARMA ◽  
S. K. SRIVASTAVA ◽  
B. S. SHARMA
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
High Temperatures ◽  
High Pressures ◽  
Equations Of State ◽  
Conductivity Equation ◽  
Thermoelastic Properties ◽  
Thermal Conductivity Equation ◽  
Wide Range ◽  
Low Pressures

In the present study, we have extended the model due to Tang1 based on the thermal conductivity equation due to Leibfried and Schlomann12 so as to make it applicable for a wide range of pressures and temperatures. We have used the Stacey14,15 equations of state (EOS) for determining the thermoelastic properties of NaCl , KCl and Al 2 O 3 at high pressures and high temperatures. These are used to estimate the variations of thermal conductivity with the change in pressure along different isotherms at selected temperatures. The results thus obtained are compared with the values derived from relations, which reproduced available experimental data well at low temperatures and low pressures. Experimental data at high temperatures and high pressures are not available. A close agreement between the two sets of data reveals the validity of the present work.

The Short-Time Compressibility of Elastohydrodynamic Lubricants

1991 ◽  
Vol 113 (2) ◽  
pp. 361-370 ◽  
Author(s):  
K. T. Ramesh
Keyword(s):  
High Pressures ◽  
Elastohydrodynamic Lubrication ◽  
Deformation Analysis ◽  
Plate Impact ◽  
Wide Range ◽  
Density Relationship ◽  
Short Time ◽  
Impact Experiments ◽  
Low Pressures ◽  
Short Times

Elastohydrodynamic (EHD) lubricants are subjected to very large pressures (several GPa) for very short times (10−4 seconds) in typical EHD contacts. However, measurements of EHD lubricant compressibilities to date have primarily been made for quasistatic deformations and only for relatively low pressures. This paper presents some experimental results on the variation of the density of the lubricant 5P4E over a very wide range of pressures and over two distinct timescales, from 10−6 seconds to 10−4 seconds. The very short time (10−6 seconds) data are obtained from plate-impact experiments, and the data near 10−4 seconds are obtained with a new experimental technique using the compression Kolsky bar. It is observed that the commonly used Dowson-Higginson relationship represents too stiff a response at the high pressures for these short times, at least for this synthetic lubricant. A full finite deformation analysis of the plate impact problem is used to obtain the material response function for the large compressibilities observed. On the basis of these results, we suggest a new form of the pressure-density relationship for an elastohydrodynamic lubricant that appears to hold over the entire range of pressures and for time durations on the order of those actually occurring in elastohydrodynamic lubrication.

Untersuchungen am Elektronenstrahlplasma

1966 ◽  
Vol 21 (12) ◽  
pp. 2033-2039 ◽  
Author(s):  
Winfried Herrmann
Keyword(s):  
Beam Energy ◽  
Critical Pressure ◽  
High Pressures ◽  
Essential Feature ◽  
High Energy ◽  
Quiescent State ◽  
Neutral Gas ◽  
A Value ◽  
Hybrid Frequency ◽  
Low Pressures

The beam plasma exists in at least two states: The “quiescent” state with low pressures and the "turbulent" state with high pressures of the neutral gas (argon in most experiments). The quiescent state is described theoretically. It is shown that the system should transport growing waves with frequencies just below the upper hybrid frequency ωH2=ωp2+ωc2. These oscillations are found experimentally for ωp > k1 ωc, where k1 has a value of about 0.35 in the experiments described. Increasing the pressure and the plasma density as well raises the amplitude of the oscillations. Then at the critical pressure the turbulent state with high density is produced very abruptly. The essential feature of this second state is the high energy loss of the beam particles. The dependence of the losses on the parameters of the system is studied in detail. The maximum losses may attain 50% of the original beam energy. Some other properties of the system are described.

Wide-range equations of state for organic liquids

2007 ◽  
Vol 5 ◽  
pp. 113-120 ◽  
Author(s):  
R.Kh. Bolotnova
Keyword(s):  
High Pressures ◽  
Equations Of State ◽  
Organic Liquids ◽  
Liquid Phases ◽  
Wide Range ◽  
High Pressures And Temperatures

The method of construction the wide-range equations of state for organic liquids, describing the gas and liquid phases including dissociation and ionization which occurs during an intense collapse of steam bubbles and accompanied by ultra-high pressures and temperatures, is proposed.

scholarly journals Study and Assessment of Defect and Trap Effects on the Current Capabilities of a 4H-SiC-Based Power MOSFET

Electronics ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 735
Author(s):  
Fortunato Pezzimenti ◽  
Hichem Bencherif ◽  
Giuseppe De Martino ◽  
Lakhdar Dehimi ◽  
Riccardo Carotenuto ◽  
...  
Keyword(s):  
Drain Current ◽  
Oxide Semiconductor ◽  
Temperature Dependent ◽  
Channel Mobility ◽  
Blocking Voltage ◽  
Current Voltage ◽  
Wide Range ◽  
Temperature Ranges ◽  
Joint Contribution ◽  
State Resistance

A numerical simulation study accounting for trap and defect effects on the current-voltage characteristics of a 4H-SiC-based power metal-oxide-semiconductor field effect transistor (MOSFET) is performed in a wide range of temperatures and bias conditions. In particular, the most penalizing native defects in the starting substrate (i.e., EH6/7 and Z1/2) as well as the fixed oxide trap concentration and the density of states (DoS) at the 4H-SiC/SiO2 interface are carefully taken into account. The temperature-dependent physics of the interface traps are considered in detail. Scattering phenomena related to the joint contribution of defects and traps shift the MOSFET threshold voltage, reduce the channel mobility, and penalize the device current capabilities. However, while the MOSFET on-state resistance (RON) tends to increase with scattering centers, the sensitivity of the drain current to the temperature decreases especially when the device is operating at a high gate voltage (VGS). Assuming the temperature ranges from 300 K to 573 K, RON is about 2.5 MΩ·µm2 for VGS > 16 V with a percentage variation ΔRON lower than 20%. The device is rated to perform a blocking voltage of 650 V.

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