Explosions of Gas/Carbon Black Nanoparticles Mixtures: an Approach to Assess the Role of Soot Formation

The influence of carbon blacks nanoparticles addition to methane/air mixture explosions has been studied. Low concentrations of carbon black nanoparticles ranging from 20 to 300 nm average diameter have been mixed with methane. Explosion tests have been performed in the 20 L sphere and in a flame propagation tube at different initial degrees of turbulence. The burnt gases have been analysed by micro gas-chromatography. The influence of carbon black nanoparticles on the explosion severity and on the velocity of the front flame has been appreciated by comparing the results obtained for pure methane explosions. It appears that the maximum explosion overpressure can slightly increase when a few percent of carbon blacks are introduced for lean mixtures but decrease for rich mixtures. This trend can be explained by using an analogy and assuming that carbon nanoparticles are soot nuclei, which enhance the physical and/or chemical condensation of combustion products. Furthermore, the explosion severity seems to decrease due to the increase of the radiation heat exchange with the introduction of low concentrations of nanoparticles. Finally, the front flame was modified from a semi-parabolic profile to a non-uniform profile, which was formed of multiple perturbations generated by the burnt particles (flamelets). These perturbations makes the flame front surface wrinkled, resulting in noticeable changes on the heat transfer, flame velocity and explosion properties.