Ultrafine particle emission from combustion devices burning natural gas

New challenge in combustion is the extended use of "clean" fuels, such as methane, in "particle free" combustion devices. Although large efforts have been made, actual combustion systems burning methane are still source of particulate that might be emitted in the atmosphere. In this paper measurements of ultrafine particle emission from premixed laboratory flames and several practical combustion systems including domestic heaters and I.C. engines, all burning methane or natural gas are presented. A new diagnostic tool based on particle sampling and mobility size measurements has been used in order to evaluate total particulate concentrations and size distribution functions. The measuring apparatus, in the utilized configuration, allows detecting particle down to 2nm. An electrical low pressure impactor, much more sensible for particles larger then 20 nm, is instead used for the measurement of the larger particles. For all devices examined, experiments have shown that methane and natural gas combustion, even when it is conducted in overall lean premixed conditions, can produce particles with a mean size of 2-3nm and a very high number concentration, clearly higher than the ambient air background.