Flammability Limits: A Comprehensive Review of Theory, Experiments, and Estimation Methods

Flammability limits play an important role in combustion research, industrial applications, and fire safety. This article provides a comprehensive review of recent developments in the fundamental understanding of flammability limits and their experimental determination as well as estimation methods for pure fuels and fuel mixtures. The article begins with a discussion of the importance and challenges of determining flammability limits. It then presents the theoretical, computational, and experimental methods available to understand the mechanism of flammability limits and to quantify them. The experimental setups using cylindrical and spherical vessels to determine the flammability limits are discussed. The effects of buoyancy, thermal radiation, and flame stretch are examined. The relationship between the fundamental flammability limits and the extinction limits of stretched flames via strain and radiation is presented. The effects of initial temperature, pressure, mixtures of different fuels, and diluents are examined, and available estimation methods are presented. Finally, the flammability limits of renewable and alternative fuels are addressed and strategies for estimating the flammability limits of these fuels are presented.