The effect of thermodynamic and transport properties on the convective-to-absolute transition in heated round jets is investigated with the spatio-temporal linear stability theory, by considering three sets of properties with increasing complexity. Present models include (i) a constant property model often used in the literature, (ii) a simplified model with variable properties, and (iii) a more accurate equilibrium air mixture model, accounting for dissociation reactions in the flow. A family of arbitrary single-stream and dual-stream jet profiles, representative of typical configurations studied in the literature, is investigated and adapted to each model. Our results show that considering a variable viscosity and thermal conductivity has a destabilizing effect on absolute instabilities in the viscous regime. Furthermore, this destabilization is stronger for the outer mode in dual-stream jets than for the inner mode or the jet-column mode in single-stream jets. With sufficient heating (S < 0.3), results obtained with the equilibrium model strongly depart from those of calorically perfect gas models and display absolute domains deformed by the chemical activity. For absolute instabilities triggered by the baroclinic torque such as jet-column and inner modes, the convective-to-absolute transition is shifted toward thinner and hotter configurations, while the opposite is observed for the outer mode. Finally, we observe a dependence of the equilibrium model stability properties on the static pressure.

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