HIGH-PRESSURE COMBUSTION - IGNITION TEMPERATURES TO 1000 BAR

Ignition temperatures of gaseous mixtures of methane with oxygen or air at initial pressures between 50 and 1000 bar been been measured. Two cylindrical reaction vessels of 4 and 10 cm(3) and one spherical vessel with 21 cm(3) volume were applied which withstand dynamic pressures up to 6000 bar at 900 K (600 degrees C). Most experiments used the ''heat-up'' method with a high pressure gas mixture heated up inside and together with the reaction vessel until spontaneous rapid reaction began, Additional experiments were made with preheated empty vessels and with forced ignition by hot wires. Spontaneous ignition temperatures for stoichiometric methane-air mixtures are around 870 K (600 degrees C) at atmospheric pressure and decrease to 660 K (390 degrees C) at 1100 bar ignition pressure. Semenov plots give straight lines for various reaction conditions. Effective activation energies could be derived. With the assumption of a global reaction order of 2, the activation energy for stoichiometric methane-air is 359+/-4 kJ/mole, for stoichiometric methane-oxygen it is 253+/-10 kJ/mol. Considering earlier experiments with ''hydrothermal'' supercritical flames, ignition with added high pressure steam were made.