Experimental and Numerical Study of Ignition and Flame Propagation for Methane–Air Mixtures in Small Vessels

Maria Prodan,Emilian Ghicioi,Aurelian Nicola,Robert Laszlo,Irina Nalboc,Sonia Suvar

doi:10.3390/pr9060998

Abstract

Methane is one of the most common gaseous fuels that also exist in nature as the main part of the natural gas, the flammable part of biogas or as part of the reaction products from biomass pyrolysis. In this respect, the biogas and biomass installations are always subjected to explosion hazards due to methane. Simple methods for evaluating the explosion hazards are of great importance, at least in the preliminary stage. The paper describes such a method based on an elementary analysis of the cubic law of pressure rise during the early stages of flame propagation in a symmetrical cylindrical vessel of small volume (0.17 L). The pressure–time curves for lean, stoichiometric and rich methane–air mixtures were recorded and analyzed. From the early stages of pressure–time history, when the pressure increase is equal to or less than the initial pressure, normal burning velocities were evaluated and discussed. Qualitative experiments were performed in the presence of a radioactive source of 60Co in order to highlight its influence over the explosivity parameters, such as minimum ignition energy, maximum rate of pressure rise, maximum explosion pressure and normal burning velocity. The results are in agreement with the literature data.

Highlights

The explosion ignition and propagation in a closed space where a flammable mixture can be formed raises important safety issues for the fuel processing, storage or transport activities
The importance of studying the early stage of the closed vessel combustion process lies in the practical applicability of knowing the normal burning velocity
In this respect, there can be performed a greater number of experiments in a shorter time with a smaller quantity of flammable substances

Summary

Introduction

The explosion ignition and propagation in a closed space where a flammable mixture can be formed raises important safety issues for the fuel processing, storage or transport activities. The flame spreads throughout the confined space causing a rapid release of energy, accompanied by increased pressure and emissions of heat and light. The evolution of pressure during confined explosions is the most important information needed for risk assessment and for the design of pressure vessels and pressure relief systems [1]. The explosion properties (indices) are the maximum explosion pressure, the maximum pressure rise rate, the time required to reach the maximum explosion pressure, the minimum ignition energy and the burning velocity. Measurements of its flammability properties are periodically reported, following the update of experimental methods

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Results

Conclusion