Flammability of complex hydrocarbon mixtures in air and nitrogen diluted atmosphere at ambient conditions and at elevated pressures

Abstract

An innovative experimental method was introduced to study flammability limits and limiting oxygen concentration of complex hydrocarbon mixtures simulating crude oil vapour composition. Flammability experiments were conducted in a 10L spherical vessel at 25 °C and initial pressures of 100 kPa, 1100 kPa and 2600 kPa in air with additional nitrogen. Based on the experimental data, applicability of selected empirical methods and two calculated adiabatic flame temperature based methods was validated for ambient initial conditions. The experimental results confirmed relative decrease below 6.5% for lower flammability limit and below 3% for limiting oxygen concentration with increasing pressure within the examined range. The upper flammability limit increased with initial pressure. Vapour-liquid equilibrium was found to be a constraint in the fuel-rich region at elevated pressures to keep the constant initial composition of the vapour phase. At ambient conditions the calculated adiabatic flame temperature based methods were able to approximate the experimental data well. Empirical mixing rules showed accuracy highly dependent on source literature data.