Flammability Characteristics of Light Hydrocarbons and Their Mixtures at Elevated Conditions

Abstract

Accurate data of flammability limits for flammable gases and vapors are needed to prevent fires and explosions. The flammability limit is the maximum or minimum fuel concentration at which a gas mixture is flammable in a given atmosphere. Even though investigations of flammability limit have been carried out for decades, data are still scarce and sometimes unavailable. Through years of study, people have developed estimation and approximation methods for the prediction of flammability limit. However, these methods exhibit significant variations, especially at elevated temperatures and pressures. This research focuses on the flammability limits of light hydrocarbons (methane, propane, and ethylene) and their binary mixtures at normal and elevated conditions. The flammability limits of pure light hydrocarbons, and binary mixtures were determined experimentally at the temperature up to 300ºC and initial pressure up to 2atm. The experiments were conducted in a closed cylindrical stainless steel vessel with upward flame propagation. The combustion behavior and different flammability criteria were compared and the 7% pressure increment was determined as the most appropriate criterion for the test. Experimentally measured pure hydrocarbon flammability limits are compared with existing data in the literature to study the influence of temperature, pressure, and apparatus set. An estimation model was developed for the prediction of pure light hydrocarbon flammability limit at elevated conditions.

For binary mixtures, experiment data were compared with predictions from Le Chatelier’s Rule to validate its application at elevated conditions. It was discovered that Le Chatelier’s rule works fairly well for the lower flammability limit of mixtures only. The explanation of the difference between upper flammability limit predictions with experimental data was investigated through the reaction pathway analysis using ANSYS CHEMKIN software. It was proved that for the upper flammability limit test, ethylene was more reactive than methane and propane in the combustion process. Finally, a modified Le Chatelier’s rule model was developed and validated using experimental data.