Propagation characteristics and inherent instability of hydrogen-air premixed flame with inert gas dilution.

Hydrogen, which emits large amounts of heat and has harmless products, is considered a potential alternative fuel. However, its wide flammability range and low ignition energy make it hazardous during storage and transportation. Therefore, in the event of a hydrogen leak in a confined space, a certain amount of inert gas can be added to inhibit combustion. Nonetheless, the addition of inert gas can also lead to an increase in the initial pressure as well. The aim of this research is to analyze the characteristics of laminar flame propagation and the inherent instability of laminar flames composed of 30% H 2 -air under various initial pressures and different types or quantities of inert gas dilution. In the experimental setup, hydrogen and air are pressurized into a 20 L spherical chamber to create the required mixed gas, following which inert gases such as CO 2 , N 2 , and He are added to achieve the desired pressure levels. Initially, the study focuses on elucidating the impacts of different variables on parameters such as flame propagation speed, flame stretching rate, un-stretched flame propagation speed, Markstein Length, and un-stretched flame burning speed. Additionally, it delves into investigating the effective Lewis number, density ratio, and flame thickness under varying conditions to understand the mechanisms influencing inherent flame instability. The findings indicate that increasing p 0 or augmenting the amount of dilute gas mixing both exacerbate flame front instability and reduce the critical radius of the flame. Among the three admixed species, CO 2 addition exhibits the most significant effect. [Display omitted] • Experiments study on the inherent flame instability of H 2 -air with combined effects of p 0 and inert gas dilution. • For p 0 ≥ 150 kPa, CO 2 addition≥ 20%, or N 2 addition≥ 25%, the stretching rate enhances flame propagation speed. • Inert gas dilution alters the structure of the H 2 -air premixed flame front. [ABSTRACT FROM AUTHOR]