Showing papers on "Autoignition temperature published in 1988"

Production of synthesis gas from hydrocarbonaceous feedstock

Abstract: Hydrocarbonaceous feedstocks are converted to synthesis gas by a catalytic partial oxidation process wherein a mixture of hydrocarbonaceous feedstock, oxygen or an oxygen-containing gas and, optionally, steam is provided to a catalytic partial oxidation zone at a temperature not lower than 93°C below its autoignition temperature and at an oxygen-to-carbon molar ratio from 0.3:1 to 0.8:1. The catalytic partial oxidation zone contains a catalyst having a geometric surface area-to-volume ratio of at least 5 cm²/cm³, preferably greater than 20 cm²/cm³. The catalyst volume requirements are comparatively low inasmuch as space velocities which are from about 20,000 hr.⁻¹ to 500,000 hr.⁻¹.

An Analytical Study on Knocking Heat Release and its Control in a Spark Ignition Engine

Abstract: In this study the relationship between the timing for the onset of autoignition and the amount of mixture fraction burned by autoignition and the resulting knock intensity is investigated using a combination of high-speed laser shadowgraphy and thermodynamic calculations. The experimental procedure is applied to examine the effect of a squish combustion chamber on suppressing knock. The results indicate that, when autoignition occurs in the squish area, an amount of mixture burned by autoignition is small, resulting in lower knock intensity

The autoignition chemistry of isobutane: a motored engine study

Abstract: Isobutane autoignition chemistry was examined in a motored, single-cylinder engine by measuring stable intermediate species, performing heat release analyses, and measuring visible emissions. Experimental measurements are compared with isobutane literature values, with previous n-butane results, and specific isobutane autoignition chemistry is discussed in light of the measurements

An Analytical Model for Knock in Dual Fuel Engines of the Compression Ignition Type

Abstract: The paper describes an attempt at developing an analytical method to provide a guideline for predicting the limit for acceptable power output of dual fuel engines due to the onset of autoignition and knock primarily through improved modeling of the chemical reaction rates of the charge during compression and subsequently following pilot ignition. Some performance results with methane as a fuel are presented

Thermal Autoignition Temperatures for Hydrogen-Air and Methane-Air Mixtures

Abstract: The autoignition temperature and ignition delay times for hydrogen-air mix tures and methane-air mixtures as a function of concentration were measured in the Bureau of Mines 1.2-L ignitability furnace. The data shows that the minimum autoignition temperature (MAIT) values obtained for hydrogen-air and methane-air mixtures are in excellent agreement with previously reported AIT values of other researchers. There is also good agreement in the gas con centrations at which the minimum AITs occurred.

Autoignition Chemistry of N-Butane in a Motored Engine:A Comparison of Experimental and Modeling Results

Abstract: A detailed chemical kinetic mechanism was used to simulate the oxidation of n-butane/air mixtures in a motored engine. The modeling results were compared to species measurements obtained from the exhaust of a CFR engine and to measured critical compression ratios

Photography of Combustion During Knocking Cycles in Disc and Compact Chambers

Abstract: Combustion during normal and knocking cycles has been observed in a single cylinder, spark ignition engine. Photographs of combustion in a disc chamber showed that autoignition of the end gas was the cause of knock. It was concluded that knock resulted from rapid entrainment and burning of reactants by the normal spark ignited flame

Ignition of steel alloys by impact of low-velocity iron/inert particles in gaseous oxygen

Abstract: The ignition of carbon steel and 316 and 304 stainless steels caused by the impact of low-velocity particles (a standard mixture consisting of 2 g of iron and 3 g of inert materials) in gaseous oxygen was investigated using NASA/White Sands Test Facility for the ignition test, and a subsonic particle impact chamber to accelerate the particles that were injected into flowing oxygen upstream of the target specimen It was found that the oxygen velocities required to ignite the three alloys were the same as that required to ignite the particle mixture Ignition occurred at oxygen velocities greater than 45 m/sec at 20 to 24 MPa and was found to be independent of pressure between 2 and 30 MPa Comparison of the present results and the past results from Wegener (1964) with the Compressed Gas Association (CGA) oxygen velocity limits for safe operations indicates that the CGA limits may be excessively conservative at high pressures and too liberal at low pressures

Evaluation of Hydroperoxide Concentrations During the Delay of Autoignition in an Experimental Four Stroke Engine: Comparison with Cool Flame Studies in a Flow System

Abstract: Organic peroxides were extracted in a flow system, from the combustion chamber of a motored C.F.R. engine operated as a compressor and running on n-heptane. The concentration of the only organic peroxide found before self ignition was estimated to be 6 x 1015 molecules cm−3. The decomposition rate was equal to 1018 molecules cm−3S−1. This value is the same as the rate of decomposition of organic peroxides found in the region before a stabilized cool flame of n-heptane in a flow reactor: these results illustrate the importance of low temperature oxidation during the delay of autoignition in spark ignition engines.

Hot Surface Ignition Tests of Aircraft Fluids

Abstract: : Five fluids commonly found in aircraft engine components, JP-4 and JP-8 fuels, Mil-H-5606 and Mil-H-83282 hydraulic fluids and Mil-L-7808 lubricating oil, were tested in the Aircraft Engine Nacelle Fire Test simulator (AENFTS) to define their Minimum Hot Surface Ignition Temperature (MHSIT's) when introduced as a spray or stream onto a hot engine bleed duct. The test employed a simple, uncluttered test section and a realistically simulated portion of the F-16 engine compartment. MHSIT's for all but Mil-H-83282 were consistently found to be higher than the fluids autoignition temperature. Keywords: Combustion; Jet fuels.

Burner for combustible gases

Abstract: A combustible gas burner having simple, effective safety features. The burner head is made of ceramic to provide insulation between the flame and the gas inlet, thereby preventing autoignition. The ceramic head is formed with a multiplicity of passages therethrough, which are sufficiently small to function as a flame arrester. This multiple passage structure also functions to reduce flame-out when a lean combustible gas mixture is subject to external dilution air. The ceramic burner head is secured to the gas inlet opening by means of a bonding agent which expands as it cures, thereby providing a positive mounting.

Catalytic ignition of hydrogen and oxygen propellants

Abstract: An experimental program was conducted to evaluate the catalytic ignition of gaseous hydrogen and oxygen propellants. Shell 405 granular catalyst and a monolithic sponge catalyst were tested. Mixture ratio, mass flow rate, propellant temperature, and back pressure were varied parametrically in testing to determine the operational limits of the catalytic igniter. The test results show that the gaseous hydrogen and oxygen propellant combination can be ignited catalytically using Shell 405 catalyst over a wide range of mixture ratios, mass flow rates, and propellant injection temperatures. These operating conditions must be optimized to ensure reliable ignition for an extended period of time. A cyclic life of nearly 2000, 2 sec pulses at nominal operating conditions was demonstrated with the catalytic igniter. The results of the experimental program and the established operational limits for a catalytic igniter using the Shell 405 catalyst are presented.

Kinetics of combustion of petroleum coke and sub-bituminous coal char: Results of ignition and steady-state techniques

Abstract: This paper presents kinetic data on the combustion of ≈90 μm particles of petroleum coke and a low-temperature char made from a subbituminous coal. The results were determined using a critical ignition technique, and are shown to compare well with measurements on the same materials using a steady-state flow reactor. The apparent activation energies were in the range 62 to 82 kJ/mol. The agreement between the results of the two techniques was best taking the reaction to be half order in oxygen: agreement was notably less good assuming orders of 0.75 and 1.0. The presence of volatile matter in the char lowered the measured ignition temperature, and it was necessary to devolatilize the char in order to make the conditions and results of the ignition and flow techniques comparable.

Hot pipe radiating device capable of preventing autoignition and self-heating

Abstract: The utility model discloses a hot pipe radiating device capable of preventing autoignition and self-heating, comprising a heat pipe evaporating section and a condensing section. The heat pipe evaporating section comprises a metal heat pipe poured by working substances (such as methanol, acetone, distilled water, etc.) (4). The condensing section comprises radiating pipes (2) and radiating fins (3) interconnected. The heat pipe (1) is communicated with the radiating pipe (2). After the heat pipe (1) is embedded into the hypergolic self-heating substances, the working substance (4) in the pipe absorbs heat and is vaporized to rise to the radiating pipe (2). The heat is emitted through the radiating fins. Thus, the working substance is cooled and flows back for vaporization and rise for the second time. Thus, cyclical operation is implemented continuously. The autoignition and the self-heating of the substance are avoided.

Modeling of the transient ignition of a nonmetal/oxygen system by heterogeneous reaction - Effects of oxygen pressure

Abstract: A theoretical model of the transient ignition of a nonmetallic polymer in a pure oxygen environment was developed and used to assess the safety of an oxygen system under elevated pressure. Results demonstrated that, for a general oxygen system, the ignition temperautre is sensitive to the external heating rate as well as such system parameters as the minimum ignition heat flux and the corresponding minimum ignition temperature. As the oxygen pressure increases, the minimum ignition temperature decreases, until, at a sufficiently high oxygen pressure, spontaneous ignition occurs. Numerical results generated by the model were correlated with the reported ignition data for polyethylene, Teflon, and nylon.

Particulate formation in fuel oil combustion

Abstract: In an attempt to develop a simple screening method to predict potential air pollution by particulate emissions from residual fuel oil burners, a comprehensive and detailed study of the combustion of single droplets of a wide range of oils suspended on a fine thermocouple was made, and compared with particulate emissions from a spray burner fired with identical fuels. Single droplet combustion parameters such as the pre-ignition time (ti), ignition temperature (Ti), flame time (tf), coke combustion time (ti) and temperature (Tc) were derived from temperature-time traces of the droplet and particle combustion. The following relationships were established between the combustion parameters and the original droplet diameter (do): where A, Ti Ki, Kf and Kc are constants dependent upon the fuel. The Conradson Carbon Residue of each fuel correlated with both Kc and particulate emissions. Other relationships between single droplet parameters, fuel composition and particulate emissions were evaluated. A st...

D3He fuels in a field-reversed configuration

Abstract: Favorable features of the D3He fuel cycle in a field-reversed configuration are described. Based on a theoretical analysis, we find that the estimated plant efficiency is more than 70% and the 14 MeV neutron power fraction is as small as 1%. To reach the D3He ignition temperature of 100 keV with a reasonable external power source, one can first ignite a DT configuration and then alter the fuel to D3He. Hesting of the plasma is attributed to energetic fusion of charged particles and no additional heating is necessary. The equilibrium of D3He ignited plasmas may be self-sustained due to the preferential trapping of fusion proton in a field-reversed configuration.

Burning characteristics of partially devolatilized coals

Abstract: Thermal and chemical coal-desulfurization processes designed to yield refinable petroleum substitutes and solid fuels for boilers reduce the fuel's volatile matter content This reduced volatility influences combustion characteristics such as ignition temperature, flame stability, and carbon burn-out A variety of studies has been conducted on the oxidation reactivity of coal char On the basis of information available from these studies, it can be concluded that the conditions under which a char is prepared influences its reactivity Some of the production parameters that affect the reactivity are processing gas, heating rate, maximum heat treatment temperature, soak time at peak temperature, and pressure These factors influence the pore structure and active surface area of the char as well as the accessibility of a reactant gas to the internal surface area of the fuel during combustion or gasification Recently it has been suggested that char formation conditions that result in a higher H/C ratio or hydrogen content favor reactivity The work presented in this paper is part of a larger study which was undertaken to determine combustion characteristics of partially devolatilized coals

The Development of Combustion from Quasi-Stable Temperatures for the Iron Based Alloy UNS S66286

Abstract: The development of ignition and subsequent combustion from quasi-stable temperatures was studied for several iron, nickel, and cobalt-based alloys. The quasi-stable temperature was produced by heating a specimen with a continuous wave carbon dioxide laser. Endothermic and exothermic transitions appear to play an important role in the development of thermal runaway, ignition, and combustion. The apparent effect of the endothermic transitions was to accelerate the rate of oxidation of the alloy, which produced abrupt changes in surface temperature as well as increasing the rate of increase in surface temperature. In the final stages of the thermal runaway phase, endothermic and exothermic events forced the alloy surface rapidly into combustion. Total destruction of the specimen followed immediately. The results for the iron-based alloy UNS S66286, which represent the phenomena observed, are presented. A spontaneous ignition temperature, enhanced oxidation temperature and ignition temperature for the solid alloy have been defined. Data are presented for the oxygen pressure range of 1.7 to 13.8 MPa.

Ignition characteristics of the iron-based alloy UNS S66286 in pressurized oxygen

Abstract: The development of ignition and combustion in pressurized oxygen atmospheres was studied for the iron based alloy UNS S66286. Ignition of the alloy was achieved by heating the top surface of a cylindrical specimen with a continuous-wave CO2 laser. Two heating procedures were used. In the first, laser power was adjusted to maintain an approximately linear increase in surface temperature. In the second, laser power was periodically increased until autoheating (self-heating) was established. It was found that the alloy would autoheat to destruction from temperatures below the solidus temperature. In addition endothermic events occurred as the alloy was heated, many at reproducible temperatures. Many endothermic events occurred prior to abrupt increases in surface temperature and appeared to accelerate the rate of increase in specimen temperature to rates greater than what would be expected from increased temperature alone. It is suggested that the source of these endotherms may increase the oxidation rate of the alloy. Ignition parameters are defined and the temperatures at which these parameters occur are given for the oxygen pressure range of 1.72 to 13.8 MPa (25 to 2000 psia).

Anomalously high flammability of low volatility fuels due to anomalously low ignition temperatures

Abstract: Fuel flammability is usually predicated on flash points, resulting from exposure of fuel to flame. Low molecular weight (high volatility) fuels have lower flash points and thus are judged more flammable than low volatility fuels. A startling reversed relationship has been shown to exist, however, for lower members of the alkane series, between molecular weight and ignition temperature (IT), occasioned by contact with hot surfaces: up to a point, less volatile higher molecular weight fuels have lower IT's and are more easily ignited when exposed to hot surfaces. For higher members of the alkane family this trend reverses, resulting in minimum IT's for the C/sub 5/ - C/sub 9/ alkanes. Branched chain alkanes, arenes and olefins also have anomalously high IT's. Free radical effects are unimportant among factors influencing ignition temperature; ionic effects may be important, as is the case for fires involving active metal, phosphorus, thermite and similar inorganic incendiary agents. This may be useful in fuel selection, if fires are anticipated to result from contact with hot metal surfaces, as in aircraft crashes, fuel spills on hot engine surfaces, or similar effects, instead of by contact with flame. Molecular modelling considerations are discussed to explain the anomalous trends.

Liquid fuel combustion apparatus

Abstract: PURPOSE:To suppress generation of bad odor in a liquid fuel combustion apparatus, by providing a supersonic atomizer which atomizes liquid fuel and an ignitor which ignites the liquid fuel in a combustion chamber, and by refluxing unburned gas, which generated and flowed out of the combustion chamber at the time of ignition, into the combustion chamber to burn it. CONSTITUTION:A vibrator 20 is continuously vibrated by a supersonic vibration generating means, and liquid fuel is atomized at the edge 22 of a vibrator and is sprayed outwardly. When an ignitor 60 is actuated, the atomized fuel partially reaches the ignition temperature by the produced heat of the ignitor 60, and starts burning. Afterwards a flow of atomized stream around it is evaporated and is burned by self-combustion heat. At the time of ignition in the combustion device, a hot air fan 4, which is provided with a heating chamber 6, is rotated to the reverse direction of that at the time of a normal combustion, and by that operation, unburned gas discharged to the heating chamber 6 is mixed with combustion air by a combustion air fan 14 as shown by dotted arrows in the picture. The unburned gas fed back into the flame chamber 2 is completely burned by the flames in the flame cylinder 50 together with the combustion air.

Laser-heated rotating specimen autoignition test

Abstract: Specimens of 440 C steel were rotated in a chamber pressurized with oxygen gas and heated with a 5-kW CO2 laser to determine the temperature required for autoignition to occur. Tests included exposures of static and rotating (25,000 rpm) specimens in oxygen pressurized to 5.51 MPa, and with focused laser fluences of more than 3.5 billion W/sq m. Specimen surface temperatures were monitored with a scanning infrared camera. Temperature measurement difficulties were experienced due to a problem with internal reflection inside the test chamber; however, posttest specimen examinations confirmed that surface melt (1371 C) was achieved in several tests. No sustained combustion was initiated in any rotating specimen. One static specimen was ignited. Results indicated that conditions necessary for autoignition of 440 C steel are more dependent on specimen geometry and available heat removal mechanisms. Sustained combustion occurred in the ignited static specimen with an estimated 130 C/sec cooling rate due to conduction. The rotating specimens could not sustain combustion due to a greater conductive/convective cooling rate of about 4000 C/sec and ejection of molten material. These results were applied to the Space Shuttle Main Engine (SSME) oxygen turbopump bearings to conclude that the LOX-cooled 440 C steel bearings cannot sustain combustion initiated by skidding friction.

Computer modeling of engine knock chemistry

Abstract: The development of detailed chemical kinetic reaction mechanisms for analysis of autoignition and knocking of complex hydrocarbon fuels is described. The wide ranges of temperature and pressure encountered by end gases in automobile engine combustion chambers result in extreme demands on the reaction mechanisms intended to describe knocking conditions. The reactions and chemical species that are most important in each temperature and pressure regime are discussed, and the validation of these reaction mechanisms through comparison with idealized experimental results is described. The use of these mechanisms is illustrated through comparisons between computed results and experimental data obtained in actual knocking engines. >

Effects of a nonisothermal reactor on ignition and flame-propagation conditions

Abstract: The ignition mode is important in flame propagation [I, 2]; if the combustion wave is initiated in a hot reactor zone, one can derive the ignition temperature T i if one incorporates the spontaneous heating during the induction AT = T i -To, where To is the wall temperature in the hot zone AT with the other parameters predetermines whether a diffusion mechanism or a thermal one will predominate in flame propagation [1-4]