Study Of Autoignition Research Articles

Synthesis of La(Ca)CrO3 Powder by an Autoignition Process and Study of its Sintering Behaviour and Electrical Conductivity

Ultrafine powders of calcium substituted lanthanum chromite has been synthesized by a simple process of autoignition of citrate-nitrate gel followed by calcination of the ash in the temperature range 600--650 C. Average particle size can be varied between 0.38 to 1.2 {micro}m through changes in the experimental parameters. These powders can be sintered at relatively low temperatures (1,250--1,300 C) compared to those normally reported. In addition, Bi{sub 2}O{sub 3} is found to act as an effective sintering aid for this material. Sintered samples have been characterized in terms of their microstructure and electrical conductivity.

An Analytical Examination of Various Criteria for Defining Autoignition Within Heated Methane-Air Homogeneous Mixtures

Different criteria for establishing ignition within reactive methane-air mixtures are discussed. It is shown that for relatively low initial mixture temperature using the different ignition criteria tends to produce very small relative differences in the values of the ignition delay. These differences can become very significant at relatively high initial mixture temperatures. Criteria for ignition based on sudden changes in pressure and temperature are recommended for reliably establishing the onset of autoignition, both in modeling and experimental studies.

Experimental and modeling study of oxidation and autoignition of butane at high pressure

Oxidation and autoignition of stoichiometric, lean (ϕ = 0.8), and rich (ϕ = 1.2) butane-“air” mixtures are studied in a rapid compression machine between 700–900 K and 9–11 bar. Information is obtained concerning cool flames and ignition delays. Product profiles for selected major and minor species are measured during a two-stage ignition process. The presence of C 4 heterocycles may be connected to isomerization and decomposition of butylperoxy radicals. The experimental results are compared with numerical predictions of an homogeneous adiabatic model based on the Pitz-Westbrook comprehensive chemical mechanism of 1990. The experimental and predicted delays are in the same order of magnitude. A relatively good agreement is found for the major species profiles. Improvement of the mechanism is needed to account for the minor products. The different paths of OH formation are discussed.

An experimental and theoretical study of autoignition on a horizontal hot pipe

A mathematical model has been formulated which describes the initiation of acetaldehyde cool flames in the free convection boundary layer adjacent to a horizontal hot pipe. The model accurately predicts the experimentally determined boundary layer temperature profiles in the case of nonreacting flow and the cool flame initiation positions in case of reacting flow. No changes to the kinetic parameters of the model were required. The predicted minimum cool flame initiation temperatures were found to be similar to our experimemtal measurements of autoignition temperature; the model thus offers a method of predicting autoignition temperature in this situation.

Auto-ignition of hydrocarbons behind reflected shock waves

The paper reports on the study of auto-ignition of hydrocarbon-oxygen mixtures behind reflected shock waves. Because of their bearing on the problem of knock in internal combustion engines, n-heptane and iso-oc??ne were chosen as the combustible species. Their stoichiometric mixtures with oxygen had to be diluted with 70% argon to reduce the influence of the boundary layer. Photographic records demonstrated the existence of two different modes of ignition, as has been previously established for the hydrogen-oxygen system. One, called strong ignition, manifested itself by a shock wave generated in the immediate proximity of the back wall of the shock tube. The other, refered to as mild ignition, had chemical reactions starting at distinct points in the gaseous medium producing essentially constant pressure flames. The pressure-temperature limits between the regions of mild and strong ignition (strong ignition limit) were determined. From the same experimental tests, induction time data was obtained over the pressure range of 1–4 atm and the temperature interval of 1200–1700°K. The strong ignition limits were found to correlate best with the lines of constant partial derivatives of the logarithm of induction time with respect to temperature at constant pressure.

An analytical approach to auto‐ignition and knock in internal combustion engines

A simplified analytical approach to the problem of determining the conditions for the onset of knock in spark ignition engines is made, using a criterion for knock based on a hypothetical gross chemical reaction of the fuel-air mixture in the end gas. It is then applied to auto-ignition studies in motored engines. Parameters such as compression ratio, initial temperature and pressure, fuel properties, ignition timing, speed and mixture strength are considered. This simplified treatment may form a basis for interpolating data, particularly when few parameters are being varied at a time. Some aspects of the treatment are illustrated by experimental engine data, drawing whenever possible from already published results.

Studies of autoignition and knock with propane as an engine fuel

The mechanism of knock for both methane and propane is considered, with particular reference to the influence of the products of pre-flame oxidation on the knocking limit. The special problems of high temperature operation are dealt with in relation to knock-limited performance and the ability of the engine to operate using weak mixtures. Heat is added (a) by general heating of the whole charge, and (b) by local heating of part of the charge. Combustion is characterized (i) by knock-limited compression ratio in the fired engine, and (ii) by spontaneous ignition in the motored engine. It is concluded that propane is an excellent fuel for a high speed spark ignition engine, that a wide range of power output is available by quality control, and that compression ratios up to 10:1 can be used without knocking. Methane was less satisfactory in the engine tested.

Shock Tube Technique for Study of Autoignition of Liquid Fuel Sprays

Shock Tube Technique for Study of Autoignition of Liquid Fuel Sprays