Hydrogen-assisted catalytic ignition characteristics of propane–air with a chemical kinetic model in a Pt/γ-Al2O3 micro-combustor in different feeding modes

Abstract

From ambient cold-start conditions, the hydrogen self-ignition and hydrogen-assisted ignition of propane–air mixtures with a chemical kinetic model in different feeding modes were investigated numerically in Pt/γ-Al₂O₃ catalytic micro-combustors. For the steady and transient state, the micro-combustion and self-ignition characteristics of lean hydrogen–air mixtures were presented, and the hydrogen-assisted combustion of propane–air mixtures was investigated numerically in the co-feed mode and the sequential feed mode. The computational results indicate the large thermal inertia of the micro-combustor solid structure leads to slow temperature dynamics, and the transient response is dominated by the thermal inertia. In general, the concentration of hydrogen required for propane ignition increased with increasing wall thermal conductivity, decreasing inlet velocity, and decreasing inlet equivalence ratio of propane–air mixtures. In the co-feed mode, the combustion characteristics of hydrogen-assisted propane qualitatively resemble the selectively preheating initial portion of the combustion chamber wall. In the sequential feed mode, the time taken to reach the steady state, the hydrogen cut-off time, the propane ignition time and the cumulative propane emissions increased with increasing wall thermal conductivity; the ignition characteristics are similar to partially preheating the initial segment of the micro-combustor for low and moderate wall thermal conductivity values (0.5 and 20 W m⁻¹ K⁻¹); however, the ignition characteristics are close to completely heating the micro-combustor wall for high wall thermal conductivity values (200 W m⁻¹ K⁻¹). The minimum cumulative amount of hydrogen usage and minimization of startup time are discussed.