Impact of Engine Operating Conditions on Particle Number and Size from a Small Displacement Automotive Diesel Engine

Particulate Matter (PM) particles number and size distribution emitted from a small displacement automotive Common-Rail Diesel engine were analyzed in order to evaluate the impact of different engine operating parameters, such as engine load, EGR rate and injection pattern during DPF regeneration. The engine was equipped with a close coupled aftertreatment system, featuring a Diesel Oxidation Catalyst (DOC) and a Diesel Particulate Filter (DPF) integrated in a single canning. The pollutant emissions were sampled at two locations along the exhaust system: at the engine outlet and downstream of the diesel oxidation catalyst, in order to characterize particles entering the DOC and the DPF respectively. Particle size distributions were measured by means of a two stage dilution system coupled with a downstream Scanning Mobility Particle Sizer (SMPS). Particles number were found to increase for increasing load and EGR rates, the latter being the dominant factor, with no significant impact of the DOC, showing also good correlation with conventional smoke opacity measurements. On the other hand, tests performed with post-injections for DPF regeneration showed dramatic increases (up to one order of magnitude) in particle numbers for large post-injected quantities, along with a significant shift towards smaller values (below 50) of the peak of particle number distribution. These increases in engine-out peak particles number values during regeneration were not detectable with standard FSN measurements, thus suggesting an increased importance of semivolatile components in the nanoparticles range. Moreover, under the same operating conditions, noteworthy reductions of particle numbers across the DOC were observed, thus providing further evidence of the importance of semivolatile components during post-injections.