Experimental investigation on particulate filters for heavy-duty natural gas engines: Potentialities toward EURO VII regulation.

The urgent need to meet the stringent regulation requirements on sub-23 nm particles emissions is pushing the interest towards efficient strategies for their reduction, involving different propulsive technologies, including the Natural Gas engines. Although considered as particulate matter-free, the growing diffusion of Natural Gas Heavy-Duty engines as a key element in the low-term towards decarbonization, requires their compliance with upcoming regulations. The use of particulate filters, in combination with the Three-Way Catalyst (TWC), could represent a promising and viable solution to achieve high conversion of gas-phase criteria pollutants and high particles filtration efficiency. The present activity arose from a collaboration among research groups of CNR-STEMS, FPT Industrial and NGK Europe GmbH, two industrial companies leaders in the topics here addressed. Target of the work is the evaluation of the potentiality offered by the use of filters in the abatement of particles emitted by a Natural Gas engine. Particles number, mass and size distribution analysis have been performed over the World Harmonized Transient Cycles. The exhaust line was properly designed to foresee the installation of particulate filter downstream a conventional TWC, in a close-coupled configuration. The filtration efficiency of two filters, from hereon termed as CNG Particulate Filters (CPFs), with different wall thickness and cell structures and a filter with catalytic coating, was compared. High particle abatement efficiency was found for all the filters, with values close to 90%, without noticeable increases in backpressures. The CPF with standard porosity showed the best performance, while no further significant benefits were found with the addition of a catalytic coating. The performed analysis places in an important emphasis in view of the forthcoming EURO VII regulations on PN limits (PN) and sets the basis and direction for further optimization in filter material properties and catalyst coating in meeting stringent PN emission targets.