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To pinpoint the nature of the sawtooth wave, extensive experiments of methane-air continuous rotating detonation (CRD) are conducted in a hollow chamber around the boundary of the operating range. The time occupancy ratio and the increasing ratio of pressure rise (Δ t i / Δ T i and Δ P i / Δ t i) derived from high-frequency pressure data, and the integral of chemiluminescence intensity (ICI) based on self-luminescence images are proposed as quantitative parameters to distinguish the detonation wave and the sawtooth wave. The results show that the sawtooth wave is a critical unstable mode between conventional isobaric combustion and CRD, propagating with high Δ t i / Δ T i and low Δ P i / Δ t i. Meanwhile, the reaction zone of sawtooth wave is verified to be stabilized in the center of combustor through the self-luminescence observation. Especially, the multiple transition processes from the sawtooth wave to the CRD wave are accurately captured, and simultaneously represented as the change from single-peak waveform to double-peak waveform on ICI, the rise of Δ P i / Δ t i , and the reduction of Δ t i / Δ T i. The significant distinction of the sawtooth wave and the CRD wave in the coupling characteristics is confirmed through Short-Time Fourier Transform processes on ICI and high-frequency pressure. For the CRD wave, the propagation frequency of the reaction zone matches that of the pressure wave, whereas not for the sawtooth wave. It is ascertained that the reaction zone is decoupled with the pressure wave for the sawtooth wave, and the nature of the sawtooth wave is deflagration combined with a weak pressure wave. [ABSTRACT FROM AUTHOR]

Explosion venting offers overpressure protection from potential industrial explosion hazards. This work experimentally studied the non-equilibrium explosion venting of methane–air mixtures in 22L and 110L spherical vessels, under various venting areas and pressures. The results showed that venting area had an obvious influence on explosion venting pressure and the small venting area can hardly protect the vessel from the explosion hazards. When A/V 2/3 is less than 0.00855, pressure will rise after explosion venting and there is linear relationship between the maximum explosion venting pressure and venting pressure. When A/V 2/3 is bigger than 0.025, it is near to the equilibrium venting and independent on the venting pressure. When the A/V 2/3 is up to 0.016, abnormal overpressure occurs under 0.1353 MPa venting pressure. For unconstrained explosion venting, P red in 22L and 110L spherical vessels is equal and (dP/dt) max accords with Cube-Root law for venting in the same A/V 2/3 . The prediction curves of (dP/dt) max vs V 1/3 for unconfined vent different A/V 2/3 and the prediction curves of P red vs venting pressure under different A/V 2/3 are provided. [ABSTRACT FROM AUTHOR]

This paper presents a three dimensional numerical simulation of premixed methane-air low swirl stabilized flames. The computational domain has a simple geometry describing a LBS (low swirl burner) with 50mm of nozzle diameter. RANS Standard k - ε model to treat turbulence coupled with partially premixed combustion model are used. The purpose is to show the applicability limits and their capacities to predict governing flame parameters by varying swirl intensity and CH4 mass fraction at the inlet, which shows the optimum operating area of the burner in terms of generated energy and flame stability with a particular interest to thermal NOx apparitions. This work is compared and validated with experimental and LES numerical simulation works available in the literature. Results offered good similarity for all flame studied parameters. Swirl number was varied from 0.5 to 1.0 to ensure a wide operating range of the burner. From S=0.6, we observed the onset of recirculation zones, while for the inert flow the appearance of recirculation zones was observed for S=0.9. CH4 equivalence ratio was increased from 0.6 to 1.4. That showed apparition of zones with important NOx mass fraction due to the existence of zones with high temperature. Otherwise, the flow field wasn't disturbed in terms of recirculation zones apparitions who remained absent for all cases. Actual investigation works to find equilibrium between the maximum of generated temperature and the minimum of NOx emissions for swirled burners. Used models haven't showed applicability limits, results were clear and precise and offered a significantly gain in computing time and means. [ABSTRACT FROM AUTHOR]