Showing papers on "Autoignition temperature published in 1977"

Autoignition Characteristics of Hydrocarbon Fuels at Elevated Temperatures and Pressures

Abstract: A problem to be treated in the design of prevaporizing/premixing combustors for use in advanced air-breathing engines is autoignition of the fuel-air mixture prior to injection into the primary combustion zone. The high combustor inlet temperatures and pressures of these engines can promote preignition and flame stabilization in premixing passages. However, data regarding the ignition delay characteristics of hydrocarbon fuels of interest, e.g., JP-type fuels and fuel oils, under conditions representative of those encountered in operating engines are not presently available in the literature. Therefore, a research program was undertaken to develop design data and criteria which will permit evaluation of the autoignition characteristics of hydrocarbon fuel-air mixtures at elevated pressures and temperatures. Measurements of the autoignition characteristics of JP-4, No. 2 fuel oil, and No. 6 fuel oil were made in dry air at temperatures in the range 750°F (400°C) to 1100°F (593°C) and at pressures in the range 100 psia (6.8 atm) to 240 psia (16.3 atm). Tests were performed in a steady-flow apparatus in which the pressure, temperature, and mixture flow rate were adjusted to induce autoignition and maintain a stationary flame front. The ignition delay time was considered equivalent to the residence time of the fuel-air mixture between the point of injection and the axial position of the flame, and it was computed from the average flow velocity. The effects of a number of physical factors, including air pressure and temperature, fuel temperature and concentration, and initial spray characteristics (e.g., droplet size and size distribution), upon the ignition characteristics were evaluated.

Method and apparatus for conservation of energy in a thermal oxidation system for use with a printing press

Abstract: Solvents evaporated from ink solutions in the drying sections of a multi-station printing press are converted into harmless gases by heating in an oxidation chamber. The amount of energy required to maintain the oxidation temperature is substantially reduced by preheating the exhaust by passing same through a previously heated bed of ceramic heat exchanger elements prior to introduction into the oxidation chamber. At high solvent concentration levels, preheating to the ignition temperature may result in excess heat of combustion being generated which is detrimental to the oxidation chamber structure. In order to regulate the heat generated, a portion of the heat exchanger bed is bypassed by a regulated amount of exhaust. Alternatively, the solvent concentration level of the exhaust can be lowered by mixing same with the floor sweep exhaust (of substantially lower solvent concentration) in regulated proportions in order to control the amount of heat of combustion generated during preheating. The latter method has the advantage of providing floor sweep capability without increased cost.

Preliminary studies of autoignition and flashback in a premixing-prevaporizing flame tube using Jet-A fuel at lean equivalence ratios

Abstract: Lean equivalence ratios from 0.3 to 0.7 were observed. Combustor inlet air pressures were varied from 0.54 to 2.5 MPa, combustor inlet air temperatures from 550 to 700 K, and reference velocities from 8 to 35 meters per second. Autoignition delay times ranged from 15 to 100 milliseconds and varied inversely with pressure. The Arrhenius activation energy was 41,840 joules per mole. Temperature rise data were obtained in a long premixing-prevaporizing tube at a pressure of 0.56 MPa. Preflame temperature rise data were a function of equivalence ratio, inlet air temperature, and tube residence time. Significant temperature rise occurred above temperatures of 760 K, with autoignition occurring at 775 K for equivalence ratios greater than 0.47. The reactions were similar to cool-flame phenomena. Flashback velocities were measured at temperatures of 610 and 700 K, pressure of 0.56 MPa, and equivalence ratios from 0.6 to 1. Flashback velocities varied from 30 to 65 meters per second.

Experimental evaluation of fuel preparation systems for an automotive gas turbine catalytic combustor

Abstract: Spatial fuel distributions, degree of vaporization, pressure drop and air velocity profiles were measured. Three airblast injectors and an air-assist nozzle were tested. Air swirlers were used to improve the spatial fuel-air distribution. The work was done in a 12 cm tubular duct. Test conditions were: a pressure of 0.3 and 0.5 MPa, inlet air temperatures up to 800 K, air velocities of 10 20 m/s and fuel-air ratios up to 0.020. The fuel was Jet A. The best results were obtained with an airblast configuration that used multiple cones to provide high velocity air for atomization and also straightened the inlet airflow. With this configuration, uniform spatial fuel-air distributions were obtained with mixing lengths greater than 17.8 cm. In this length, vaporization of the fuel was 98.5 percent complete at an inlet air temperature of 700 K. The total pressure loss was 1.0 percent with a reference velocity of 20 m/s and 0.25 percent at 10m/s. The air velocity was uniform across the duct and no autoignition reactions were observed.

Experimental investigation of a swept-strut fuel-injector concept for scramjet application

Abstract: Results are presented of an experiment to investigate the behavior at Mach 4 flight conditions of the swept-strut fuel-injector concept employed in the Langley integrated modular scramjet engine design Autoignition of the hydrogen fuel was not achieved at stagnation temperatures corresponding to a flight Mach number of 4; however, once ignition was achieved, stable combustion was maintained Pressure disturbances upstream of the injector location, which were caused by fuel injection and combustion, were generally not observed; this indicates the absence of serious adverse combustor-inlet interactions Mixing performance and reaction performance determined from probe surveys and wall pressure data indicate that high combustion efficiency should be obtained with the combustor length provided in the scramjet engine design No adverse interaction between the perpendicular and parallel fuel-injection modes was observed

Surface Temperature Measurements in the Mevinq Wire Technique

Abstract: The surface temperature of a substrate at ignition is a sensitive measure of its ignitability and one which holds the promise of providing direct information about the fundamental chemistry and physics of ignition. Measurements were presented of the surface temperature of the substrate in the moving wire technique (MWT) for studying polymer combustion. In the MWT, the substrate is moved at a controlled speed through a stationary ignition source, with the result that combustion is held stationary in laboratory coordinates. The measurement of surface temperature is a vital part of the MWT and substantially clarifies the ignition process. The measurements were achieved by two methods. The first employs a null point method in which a thermocouple is in rubbing contact with the substrate; the thermocouple is surrounded by an oven whose temperature is adjusted to the null point. The second method makes use of thermal paints in the nonburning regimes. Results for teflon in the present study indicate that the surface temperature at ignition in an O/sub 2/-rich source flame is independent of the shape, temperature, flow speed and O/sub 2/-level of the source flame. It is also independent of the size and probably the geometry of the substrate. Hence,more » ignition temperature appears to be invariant, and information of direct applicability to real practical systems can thus be gathered in the scientifically simpler moving wire system.« less

Development of an experiment for determining the autoignition characteristics of aircraft-type fuels

Abstract: An experimental test apparatus was developed to determine the autoignition characteristics of aircraft-type fuels in premixing prevaporizing passages at elevated temperatures and pressures. The experiment was designed to permit independent variation and evaluation of the experimental variables of pressure, temperature, flow rate, and fuel-air ratio. A comprehensive review of the autoignition literature is presented. Performance verification tests consisting of measurements of the ignition delay times for several lean fuel-air mixture ratios were conducted using Jet-A fuel at inlet air temperatures in the range 600 K to 900 K and pressures in the range 9 atm to 30 atm.

The use of the high flux heater in the smoke chamber to measure ignitability and smoke evolution of composite panels

Abstract: Ten samples of composite panels were evaluated in the smoke chamber using a high flux heater to produce heat flux levels up to 9.5 watts per square cm. This study demonstrated the potential of the apparatus as a means of evaluating ignitability as well as smoke evolution. Depending on the material and the heat flux level, ignitability results ranged from ignition within 2 seconds to no ignition during the test period. Smoke density generally increased with increasing heat flux. A composite panel consisting of bismaleimide-fiberglass/bismaleimide honeycomb with carbon microballoons exhibited the lowest smoke density at high heat flux levels and the greatest resistance to autoignition.

Evaluation of a Premixed, Prevaporized Gas Turbine Combustor for No. 2 Distillate

Abstract: Results of a series of tests on a prevaporized, premixed combustor to evaluate its emissions control potential while operating on No. 2 distillate oil are presented. The concept utilized the heat capacity of the combustor inlet air to absorb the heat of vaporization of the fuel. Tests were conducted at combustor inlet temperatures and pressures characteristic of current generation electric utility gas turbines (345 C and 10 atm). NOx emissions in excess of proposed EPA gas turbine standards (75 ppm at 15 percent O) were observed at the 10 atm pressure condition and are believed to be the result of incomplete evaporation of the fuel Attempts to increase vaporization rates by increasing inlet air temperature were limited by autoignition of the mixture in the fuel preparation ports.Copyright © 1977 by ASME

Change in basic kinetic characteristics of oxidation near the first ignition boundary

Abstract: 1. On the example of the promoted burning of carbon monoxide it was shown that the character of all of the basic parameters of the branched chain process, including the chemiluminescence, as a function of the initial conditions experiences a sharp change when the branching factor has a zero value. 2. In contrast to the statements encountered in the literature, chemiluminescence is also observed below the autoignition boundary, i. e., at negative values of the branching factor.

An Application of Livengood-Wu Integral Method to Predict Time of Cool Flame Explosion During Piston Compression Process

Abstract: Livengood and Wu offered the following integration equation to predict the time of knock te, ∫te0 (1/τ)dt=1, along the end gas pressure time and temperature time histories, under the assumptions of zero order reaction and critical concentration of chain carriers, and showed that the agreement between the predicted and actual times of occurrence of autoignition is reasonable. An attempt is made in this paper to check on the utility of the integration procedure for cool flame explosions along the state time history of mixture during the motoring compression period. The pre-cool flame reaction which is primarily a degenerated branching reaction is taken to be similar to the zero order reaction and the critical concentration of active intermediate products is supposed to give rise to cool flame. Empirical coefficient and exponent in the general Arrhenius equation for the cool flame ignition delay τ1 are found by the results obtained using a rapid compression machine developed here. Experimental results verify that this integration procedure is valid in the limited range of motoring compression temperatures where cool flame explosions occur Tc no more than the temperature at the end of the compression stroke of the rapid compression machine TE, but falls over in the range of TE≠Tc, especially TE