The Influence of Noble Metals on Thermoacoustic Vibrations and Boundaries of the Region of a Negative Temperature Coefficient During Combustion of n-Pentane-Air Mixtures

The specific features of the ignition of premixed stoichiometric n -pentane–air mixtures are studied in the region of the negative temperature coefficient (NTC) of the reaction rate in a static fast puffing reactor in the presence of metallic platinum and palladium. It is shown that thermoacoustic oscillations occur in the NTC region in the absence of noble metals. However, in the presence of a platinum catalyst, which reacts with oxygen at the flame temperature and generates catalytic centers that propagate into the volume by convection/diffusion, thermoacoustic ignition modes disappear. In other words, the catalytic surface of platinum eliminates a certain stage of the kinetic mechanism: probably, the stage of inhibition after the appearance of a cold flame, while the NTC phenomenon disappears. In the presence of a palladium catalytic surface that does not generate catalytic centers propagating into the volume, the NTC phenomenon is observed. The discovered patterns should be taken into account when numerically simulating this phenomenon in the presence of a platinum surface; i.e., an acceptable chemical mechanism should describe thermoacoustic oscillations in the NTC region; and exclusion of a certain stage of the kinetic mechanism (probably of a surface nature) should cause the disappearance of the NTC reaction regime in the presence of a platinum catalyst. The stage should include a surface reaction of an active combustion intermediate on the platinum surface. In this reaction, the more active intermediates are formed from the less active product.