Experimental Study on Combustion Characteristics of Very Lean Propane-Air Mixtures Under Microgravity.

Abstract

Experiments have been carried out to examine the behavior of irregular flame propagation in a closed bomb, which appears in very lean propane-air mixtures, and to examine how the lean limits of flame propagation in a long tube are influenced by its diameter. The microgravity technique achieved in a freely falling chamber is employed because the realizations of symmetrical flame propagation in a closed bomb and in a long tube are possible. Experimental condition for the initial mixtures corresponds to room temperature and 0.1 MPa and the fuel used is propane of 99.9% purity. The experimental results show that (1) the flame propagation behavior of propane-air mixtures in a closed bomb close to lower flammability limit is irregular during the burning process and its irregularity occurs when Lewis number is larger than unity, (2) though the lean limit of the flame propagation in a long tube decreases with increasing its diameter, it holds constant when the tube diameter is more than 40 mm, and (3) under microgravity Its limit shifts to lower value more than that obtained under normal gravity.