Length Experimental and numerical study on the explosion suppression of hydrogen/dimethyl ether/methane/air mixtures by water mist containing NaHCO3

The explosion suppression effect of NaHCO3 water mist on the H-2/DME/CH4/air mixtures was experimentally investigated. Pressure data and flame images were recorded by a pressure sensor and a high-speed camera, respectively. The suppression mechanism of NaHCO3 water mist was further studied using a developed kinetic model. Results showed that the normalized laminar flame speed calculated by kinetic model agreed well with the experimental data. The suppression effect of NaHCO3 water mist on the H-2/DME/CH4/air mixtures explosion was significantly affected by fuel compositions, equivalence ratios and NaHCO3 concentrations. For stoichio-metric mixtures (phi = 1.0), the decreasing rate of the average flame propagation speed of CH4-enriched flames can be up to 84.9%, which is higher than that of DME-enriched flames and the H2-enriched flames. For DME-enriched flames, the decreasing rate of the average flame propagation speed of fuel-lean flames can also be up to 70%. Meanwhile, the maximum explosion pressure of the CH4-enriched flames and fuel-lean flames are more sensitive to the NaHCO3 water mist. The NaHCO3 water mist can suppress hydrodynamic instability while it has little effect on diffusional-thermal instability. The chemical kinetic model revealed that both the adiabatic flame temperature and the maximum mole fraction of (H + OH) can be decreased noticeably by NaHCO3 water mist. Sensitivity analysis indicated that NaOH + H = Na + H2O and Na + OH + M = NaOH + M are the dominant reactions of sodium-containing species for suppressing laminar flame speed. Reaction pathway analysis indicated that Na <=> NaOH suppression cycle is effective to reduce H and OH free radicals.