Over the last two decades, gaseous and particle mass emissions of new diesel engines have been reduced effectively and progressively in response to the emissions legislation and due to the applied new technologies. There is, however, increasing concern about whether the engine modifications, while improving combustion and reducing emissions, have increased the number emissions of ultrafine and nanoparticles. So far, emissions regulations have solely been based on particulate matter (PM) mass measurements, not on particle number. Nanoparticles, however, form a major part of the PM emissions, but they do not considerably contribute to the PM mass and cannot be seen as a problem, if only PM mass is determined. Therefore, there is increasing interest in expanding the scope of the regulations to also include particle number emissions, e.g., Euro VI for on-road engines. The PM number limit will also be enforced for nonroad engines slightly later. Thus, more information is required about the particle number emissions themselves, but also about the effects of the engine technology on them. Wall-flow diesel particulate filters reduce the particle number very effectively within the entire particle size range. Nevertheless, in order to keep the filter as small as possible and to lessen the need for regeneration, the engine-out PM number should also be minimized. If the diesel particulate filters (DPFs) could be left out or replaced by a simpler filter, there would be greater freedom of space utilization or cost savings in many nonroad applications. This might be realized in installations where the engine is tuned at high raw NOx and a selective catalytic reduction (SCR) system is adopted for NOx reduction. However, it is not self-evident that new engine technologies would reduce the PM number emissions sufficiently. In this study, particle number emissions were analyzed in several nonroad diesel engines, representing different engine generations and exploiting different emissions reduction technologies: four- or two-valve heads, exhaust gas recirculation, different injection pressures and strategies, etc. All engines were turbocharged, intercooled, direct-injection nonroad diesel engines. Most engines used common-rail fuel injection technology. Comparisons were, however, also performed with engines utilizing either a distributor-type or an in-line fuel injection pump to see the long-term development of the particle number emissions. In this paper, the PM number emissions of nine nonroad diesel engines are presented and compared. Gaseous exhaust emissions and fuel consumption figures are also provided.

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