Showing papers on "Autoignition temperature published in 1981"

Autoignition characteristics of aircraft-type fuels

Abstract: An investigation was conducted of the ignition delay characteristics of five liquid hydrocarbon fuels in air. The test apparatus developed permitted independent variation and control of temperature, pressure, air flow rate, and fuel/air ratio in order that the effects of each parameter could be investigated independently. All of the fuels tested behaved in a predictable manner, that is, ignition delay time decreased as temperature, pressure, and fuel/air ratio increased. The results for the different fuels tested (Jet-A, MP-4, No. 2 diesel, ERBS, and cetane) were directly comparable, since it can be shown that the fuel spray characteristics from the multiple conical tube injector are relatively insensitive to small changes in fuel properties (viscosity, surface tension, and density).

Assessment of Diesel Particulate Control—Direct and Catalytic Oxidation

Abstract: The report discusses the technology and potential for disposal of diesel particulate by oxidation. Relevant properties of typical diesel particulate are given; note is taken of the small size (on the order of 0.1 micrometer diameter) and the presence of a portion extractable with an organic solvent. Available reaction rate data is used to derive particle lifetimes at various temperatures; these exceed likely exhaust system residence times. The use of catalysts to increase oxidation rates and lower ignition temperatures is discussed. Small amounts of many metals are effective in increasing the rate of oxidation by 2 to 5 orders of magnitude. Chemical reactor theory is used to derive ignition and operational characteristics of trap/oxidizers. Note is also taken of the tendency of these devices to go rapidly from a cold unignited state to an ignited state close to the adiabatic flame temperature of the fuel. Design techniques to ameliorate undesirable temperature excursions are presented.

Cellulosic Insulation Material III. Effects of Heat Flow Geometry on Smolder Initiation

Abstract: The variation with heat flow geometry of minimum heat source temperature which causes smolder initiation in cellulosic insulation has been examined for eight configurations. These configurations range from a wire-like source, to a flat planar source, to a corner formed by planar sources; they simulate such heat sources as electrical conductors and light fixtures and span the geometry range seen by insulation in practice. The ignition temperature for the same 20 cm deep insulation layer varies from 235°C (corner source) to 385°C (wire source). Other variables such as bulk density or the presence of smolder retardants have much less effect on ignition temperature. This behavior is rationalized in an approximate manner by simple heat generation/ heat flow arguments; it is predicted semi-quantitatively by a numerical model using reaction kinetics derived from thermal analysis. A smolder ignitability test for cellulosic insulations is suggested that simulates exposures to recessed light fixtures. The data here...

Sustained ignition secondary combustion unit

Abstract: A sustained ignition secondary combustion apparatus in a housing of refractory insulating material includes a first level for conducting secondary air through a secondary air inlet and channel, and a second level for conducting smoke products. A partition separates the levels or zones. Openings are provided in the partition between the levels bounded by a high temperature porous or fiberlike material in the form of igniter tube elements. Secondary air and smoke products diffuse into the interstices of the porous or fiberlike material where contact and combustion maintains the igniter tubes at or above the ignition temperature. Ignition and secondary combustion of smoke products in the second level is therefore sustained and secondary air is preheated as it passes through the openings. A secondary combustion zone is defined in the region of the openings between the levels and continues down stream through the exhaust outlet. The first and second levels of the secondary combustion unit may be arranged in a variety of configurations for preheating of secondary air and primary smoke by counterflow with high temperature end products of secondary combustion. Multiple or tortuous pathways may be provided for extended preheating. Primary smoke may also be preheated by smoke preheating tubes. The invention is also applied in a downdraft furnace.

Smoldering combustion hazards of thermal insulation materials

Abstract: Work on the smolder ignitability in cellulosic insulation and on thermal analytical characterization of the oxidation of this material is presented. Thermal analysis (TGA and DSC) shows that both retarded and unretarded cellulosic insulation oxidizes in two overall stages, both of which are exothermic. The second stage (oxidation of the char left as a residue of the first stage) is much more energetic on a unit mass basis than the first. However, kinetics and a sufficient exothermicity make the first stage responsible for ignition in most realistic circumstances. Existing smolder retardants such as boric acid have their major effect on the kinetics of the second oxidation stage and thus produce only a rather small (20/sup 0/C) increase in smolder ignition temperature. Several simplified analogs of attic insulations have been tested to determine the variability of minimum smolder ignition temperature. These employed planar or tubular constant temperature heat sources in a thermal environment quite similar to a realistic attic application. Go/no-go tests provided the borderline (minimum) ignition temperature for each configuration. The wide range (150/sup 0/C) of minimum ignition temperatures confirmed the predominant dependence of smolder ignition on heat flow geometry. Other factors (bulk density, retardants) produced much less effect onmore » ignitability.« less

Time-resolved soot particulates in diesel spray combustion

Abstract: Experiments have been made to study the soot particulates formed at different stages of combustion of a simulated diesel spray by applying a newly developed laboratory combustor in which the following two essential characteristics of diesel spray combustion are reproduced: intermittency and autoignition. The combustor is designed so that the fuel is injected by using a diesel fuel injection system into a steadily flowing high temperature air stream resulting in autoignition and combustion. Soot particulates have been collected at different stages of combustion by applying an inert gas quenching technique. The mass concentration, diameter, number and carbon-to-hydrogen ratio of soot particulates, oxygen concentration and temperature in the flame as a function of the time from the start of fuel injection have been obtained. Mutagenic activity of the time-resolved soot particulates has been determined by using the bacterial mutagenesis test. Thus, some factors affecting time-resolved characteristics of soot particulates have been studied. Theoretical analysis is also made of the physical mechanism for soot particulates formation.

Catalytic Combustion of Hydrogen in Model Appliances

Abstract: Water-heater and space-heater designs were developed into working models that were laboratory-tested for performance in terms of self-starting capabilities for catalytic (Nameless) combustion; nearly complete combustion of the fuel gases (tank-grade hydrogen and reformed natural gas); efficient transfer of the heat of combustion to the fluid to be heated; and low or negligible pollutants in the products of combustion. The atmospheric catalytic-burner surfaces had to be designed so that the rate of heat generation is equal to the rate of heat dissipation when surface temperatures are below the autoignition temperature of H2 in air, 585°C (1085°F). This rate balance is accomplished by heat transfer to a heat sink (for example, water in a water heater or room air in a space heater). However, the heat-transfer rate to the heat sink from the combustion surface must be low enough during the low-temperature start-up period to allow the entire surface to reach its normal steady-state operating temperature. This must be accomplished in a relatively short period of time to avoid the release of significant amounts of unburned hydrogen during the start-up period. Measurements prove that, with proper catalyst loadings and burner configurations, over 91% of the fuel gas is reacted (catalytically combusted) to form water vapor. Thermal efficiencies exceeding 80% (based on the high heating value of hydrogen) were noted for water heating, and efficiencies exceeding 91% were noted for space heating with humidification. A major pollutant of general concern in combustion is N O X . Operating conditions permitted negligible addition of NOt to the ambient air, and in some cases, appliance operation reduced the level of NO_V in ambient air.

Autoignition in a free convection boundary layer

Abstract: The autoignition of premixed fuel/air mixtures at atmospheric pressure in the free convection boundary layer flow adjacent to a vertical isothermal hot plate has been investigated experimentally and theoretically. A flow rig is described that is used to simulate the free convection flow in free space of a fuel/air mixture over a vertical hot plate. Measurements of the reacting temperature field for a range of conditions up to the onset of ignition have been made in the rig using fine wire thermocouples. A mathematical model of this reacting free convection flow in which a one-step chemical reaction with Arrhenius kinetics is used to represent the exothermic oxidation chemistry is also described. Comparison of the experimental and theoretical results shows that this simple chemical model cannot yeild a satisfactory representation of the autoignition phenomenon. The experimental results are compatible with the cool-flame and two stage ignition behaviour observed in other experimental investigations. A more detailed representation of the oxidation chemistry is required for a satisfactory mathematical model.

Autoignition characteristics of no. 2 diesel fuel

Abstract: Parametric tests to map the ignition delay characteristics were conducted at pressures of 3, 4, and 5 atm, inlet air temperatures up to 1150 K and fuel air equivalence ratios ranging from 02 to 10 Ignition delay times in the range of 6 msec to 60 msec at freestream flow velocities ranging from 10 m/sec to 40 m/sec were obtained The ignition delay times appeared to correlate with the inverse of pressure and the inverse exponent of temperature

Space heating stove

Abstract: An efficient space heating stove having a combustion chamber substantially completely enclosed with insulating firebrick whereby the operating temperatures within the combustion chamber can be maintained above the ignition temperature of the fuel being consumed. Combustible gases liberated by the wood fuel are burned as they pass through a perforated, hollow, tubular member located within the combustion chamber and through which the combustible gases must pass before they are exhausted from the stove. Fuel within the combustion chamber is efficiently burned before useful heat energy is extracted.

Combustion characteristics of hydrogen. Carbon monoxide based gaseous fuels

Abstract: The results of trials with a staged combustor designed to use coal-derived gaseous fuels and reduce the NO(x) emissions from nitrogen-bound fuels to 75 ppm and 37 ppm without bound nitrogen in 15% O2 are reported. The combustor was outfitted with primary zone regenerative cooling, wherein the air cooling the primary zone was passed into the combustor at 900 F and mixed with the fuel. The increase in the primary air inlet temperature eliminated flashback and autoignition, lowered the levels of CO, unburned hydrocarbons, and smoke, and kept combustion efficiencies to the 99% level. The combustor was also equipped with dual fuel injection to test various combinations of liquid/gas fuel mixtures. Low NO(x) emissions were produced burning both Lurgi and Winkler gases, regardless of the inlet pressure and temperature conditions. Evaluation of methanation of medium energy gases is recommended for providing a fuel with low NO(x) characteristics.

Time resolved soot particulates in autoignited intermittent spray flames

Abstract: An attempt has been made to study soot particulates formation at different stages of combustion of simulated diesel sprays by using a new laboratory combustor in which the following two essential characteristics of diesel spray are reproduced: intermittency and autoignition. The combustor is designed so that the fuel is injected by using a diesel fuel injection system into a steadily flowing high temperature air stream resulting in autoignition and combustion. Soot particulates have been collected at different stages of combustion by applying an inert gas quenching technique. The mass of soot particulates, C/H ratio, the microscopic diameter of each particle, the flame temperature and the oxygen concentration in the flame have been obtained. The results indicate that this new technique is a useful tool to obtain the time resolved characteristics of soot particulates in intermittent spray flames. The mass concentration of soot particulates increases during the early stages of combustion, reaches a maximum, after which it decreases near the end of the combustion process. The diameter and C/H ratio of the soot particulates increase with time while their number decreases. The mass concentration rates of formation and oxidation of soot particulates increase with the increase in flame temperature. Adding methanol to diesel fuel has a definite effect on reducing the soot particulates in the flame.

Combustion experiments in space

Abstract: Pivotal areas for needed combustion observations (available through space shuttle experimentation) include: (1) single- and two-phase premixed flame propagation and extinction limits; (2) noncoherent flame propagation and extinction; (3) autoignition of premixed single-phase and two-phase combustible reactants; (4) upper pressure limit combustion phenomena and ignition, propagation, and extinction processes in the neighborhood of such limits; (5) oscillatory combustion associated with the hydrocarbon-oxygen and with the carbon monoxide-oxygen systems; (6) two-phase flame spread and extinction involving lage liquid-gas or solid-gas interfaces; (7) radiative ignition of solids and liquids; (8) pool burning; (9) smoldering of solid combustibles and the associated transition to flaming or extinction; (10) laminar gas jet combustion; and (11) transient responses of combustible systems to time variation in gravitational field strengths. A number of these may be impacted by undesirably high g-jitter effects.