ABSTRACT A variable pressure, counterflow combustion chamber has been built for the experimental investigation of ignition in a convective-diffusive system. In this paper we present our results on ignition of nonpremixed, counterflowing jets of 20% H2 in N2 versus heated air, within a wide range of pressures and flow strain rates. The system was brought to ignition by increasing gradually the temperature of the air stream. Each steady-state situation just prior to ignition was characterized by measuring detailed centerline axial flow velocity and temperature distributions, for ambient pressures between 0.1-6.0 atm and pressure-weighted strain rates between 50-400 s−1. The ignition temperature, defined as the maximum temperature of the air jet just prior to ignition, was found to increase with increasing flow strain rate at all pressures. Furthermore, its sensitivity to strain-rate variations was found to be much higher at elevated and reduced pressures (above ∼ 2 atm and below ∼ 0.5 atm) than it was at at...