Deflagration to Detonation Transition with Increased Reactivity of Iso-octane and Ethane Mixtures

The deflagration to detonation transition (DDT) represents the most catastrophic explosion scenario, characterized by supersonic flame propagation, overpressure, and shock waves. This phenomenon poses significant safety risks to human safety and property damage particularly in fuel storage facilities. In combustion engines, DDT events are abnormal occurrences that can damage engine components, obstructing the progression toward engines with higher compression ratios and thermal efficiency. In the face of pressing demands for energy conservation and carbon emission reductions, a thorough understanding of DDT, especially within combustion engine environments, is essential for the innovation of advanced engines. Furthermore, the increasing reliance on ethane, both as an essential feedstock for ethylene production in the petrochemical industry and as a potential source for power generation, underscores the need to understand its combustion characteristics. This includes a particular focus on the risks of explosion associated with DDT in open environments. Such understanding is crucial for mitigating DDT-related risks and for the advancement of safer and more efficient combustion technologies.
This research firstly investigates and analyze the different ignition modes including deflagration, autoignition and transition to detonation inside an optical Rapid Compression Machine (RCM), aiming to have a comprehensive understanding of the DDT mechanism and the phenomenon of super-knock in compressed engine conditions. Concurrently, to understand the laminar and turbulent characteristics of ethane-air flames and effects of hydrogen on laminar ethane flames, measurements were taken in a fan-stirred spherical combustion vessel, and specific correlations were proposed to align with the measured data. These measurements are valuable for the application of ethane-hydrogen-air mixtures in engines, gas turbines, burners, and serve as a critical database for simulation purposes. Additionally, the specialized finite volume computational fluid dynamics (CFD) code, MG, incorporates the compressible Navier-Stokes equation, progress variable and k-ε turbulence model, along with a correlation of measured turbulent burning velocities, to enable simulations of large-scale ethane-air DDT.
The experiments conducted in the RCM indicated that the transition to detonation occurs when the velocity of the autoignitive reaction wave matches the acoustic velocity, coupled with rapid heat release from a hot spot. This phenomenon was analysed by monitoring changes in two dimensionless parameters ξ the ratio of autoignition velocity to acoustic velocity, and ε, representing the rate of heat release in hot spots. In terms of ethane-air combustion characteristics, the knowledge gap of the Markstein length/number, flame instability, and the effects of hydrogen addition on ethane-air laminar flame characteristics and turbulent flame characteristics of ethane-air are filled. The large-scale ethane-air DDT simulation demonstrated that the process unfolds in four phases: laminar propagation, turbulent flame acceleration, transition to detonation, and detonation propagation. The simulation highlighted that turbulence generated from the flame's interaction with baffles plays a crucial role in accelerating the flame, thereby facilitating the DDT.