Europhysics Letters PREPRINT Coherence Resonances in an Autonomous Thermochemi- cal Model With Internal Fluctuations A. Lemarchand 1 and B. Nowakowski 2 1 Universit´ e Pierre et Marie Curie, Laboratoire de Physique Th´ eorique des Liquides, C.N.R.S. U.M.R. 7600, 4 place Jussieu, 75252 Paris Cedex 05, France 2 Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01- 224 Warsaw, Poland PACS. 05.40.-a – Fluctuation phenomena, random processes, noise, and Brownian motion. PACS. 82.33.Vx – Reactions in flames, combustion, and explosions. PACS. 82.40.Bj – Oscillations, chaos, and bifurcations. Abstract. – Direct simulations of the master equation associated with a two-variable ho- mogeneous thermochemical model are performed in order to analyze the effects of internal fluctuations on excitability and periodic oscillations. In both regimes, coherence resonances are observed in the absence of external noise and external forcing. These results suggest that the control of the combustion of lean premixed gas requires a stochastic description at a mesoscopic level. Short title: Coherence Resonances in Thermochemistry c EDP Sciences