Abstract: An approach for estimating the ignition temperature of adiabatic fixed-bed reactors is suggested. A phase plane of dimensionless temperature and dimensionless concentration is used to show both the ignition and extinction curves of a single catalyst pellet. The trajectory, i. e., the operating line of the reactor, which shows the progress of the chemical reaction, is always a straight line with a slope of —45°. Ignition occurs as the trajectory touches the ignition curve.A simple method is recommended to predict the critical gas inlet temperature which causes reactor ignition without recourse to determining the reaction kinetics. All reactions can be assumed to be of zeroorder.. This assumption introduces negligible error but considerably simplifies the experimental work.