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Deflagration to Detonation Transition in Chemical Rockets with Sudden Expansion/Divergence Regions

AIAA 2020-3520
Session: Innovative Propulsion Concepts
Published Online:

We discovered through theoretical studies that, at the creeping inflow conditions, any chemical rocket having port with the sudden expansion / divergent could predispose to deflagration-to-detonation-transition (DDT) at a critical total-to-static pressure ratio (TSPR) due to the phenomenon of Sanal flow choking. At the Sanal flow choking condition, the subsonic flow will get accelerated in the port of a rocket having uniform cross-sectional area due to the area blockage caused by the boundary layer displacement thickness (BLDT). At the Sanal flow choking condition, the lower critical detonation index (LCDI) is an exclusive function of the lowest heat capacity ratio (HCR) of the evolved gases; and the non-dimensional BLDT is an exclusive function of the HCR and the igniter/inflow Mach number. The mathematical model presented herein predicts the possibilities of DDT in all real-world fluid flow systems (continuum / non-continuum), at a critical TSPR, having port with sudden expansion and/or divergence regions or in constricted streamtubes. Note that when the pressure of the non-continuum fluid/nanofluid increases, average-mean-free-path decreases and thus, the Knudsen number reduces leading to a no-slip boundary condition with compressible viscous (CV) flow effect. The Sanal flow choking is a CV flow effect at which both the thermal choking and the wall-friction induced the flow choking converge at the sonic-fluid-throat creating the real-world fluid flow effect, which satisfies all the conservation laws of nature. The offshoot of this study reveals that the Sanal flow choking could lead to asymptomatic hemorrhage in biological systems, and susceptible to catastrophic failures of chemical energy systems including micro and nano thrusters due to the detonation. The risk of Sanal flow choking could be reduced by breaking the blockage, reducing the TSPR and/or increasing the HCR of the gases generating from the upstream region of the port of an internal flow system for keeping the TSPR always lower than LCDI.