Multiwalled Carbon Nanotubes (MWCNTs) as Ignition Agents for Air/Methane Mixtures

The possibility to ignite the single wall carbon nanotubes (SWCNTs) once exposed to the radiation of a flash camera, was observed for the first time in 2002. Subsequently, it was proposed to exploit this property in order to use nanostructured materials as ignition agents for fuel mixtures. Lastly, in 2011, it was shown that SWCNTs can be effectively used as ignition source for an air/ethylene mixture filling a constant volume combustion chamber; the observed combustion presented the characteristics of a homogeneous-like combustion. In the presented experimental activity, the potentiality of igniting an air/methane mixture by flashing multiwall carbon nanotubes (MWCNTs) has been exploited, and the results compared with those obtained igniting the mixture with a traditional spark plug. In detail, two types of tests have been carried out: the first, aiming at comparing the combustion process flashing a variable amount of nanoparticles introduced into the combustion chamber at fixed air/methane ratio; the second, at comparing the combustion process with the one obtained using a traditional engine spark plug, varying the air/methane ratio and at fixed amount of MWCNTs. During tests, the combustion process has been characterized measuring the pressure into the combustion chamber as well as acquiring images with a high-speed camera. The results confirm that the ignition triggered with MWCNTs leads to a faster combustion, without observing a well-defined flame front propagation, observed, as expected, with the spark assisted ignition. Moreover, dynamic pressure measurements show that the MWCNTs photo-ignition determines a more rapid pressure gradient and a higher heat release rate compared to spark assisted ignition.