Short-Duration Autoignition Temperature Measurements for Hydrocarbon Fuels

This study develops an experimental method for the reliable determination of auto ignition temperatures under a variety of conditions which involve short duration exposures of controlled fuelair mixtures on three metal surfaces. Over 1100 autoignition temperature determinations have been made for the ignition of 15 hydrocarbons on heated nickel, stainless steel, and titanium surfaces for three different fuelair mixtures. The measured autoignition temperatures generally decrease for the larger hydrocarbons and for richer mixtures, with the C2 hydrocarbons having particularly low values. The highest autoignition temperature are observed for nickel surfaces and the lowest for the stainless steel, with titanium being an intermediate case. Relationships between autoignition, radical-based chemical mechanisms and end-gas autoignition engine knock are discussed. Most of the previous autoignition data are unsatisfactory since measurements are typically carried out using ASTM E659 test. This test method attempts to measure the autoignition temperature of hydrocarbons fuels in the gas-phase under experimental conditions where it is more likely that ignition temperatures for a complex mixture of the products of fuel decomposition are being determined rather than those of the original fuel.