In diesel engine development, NOx and particulate matter (PM) emissions have to be simultaneously reduced. Fuel consumption also has to be kept as low as possible. Today, exhaust PM is regulated based on particle mass. Ultra-fine particles are, however, known to be hazardous for human health but they do not very much affect the PM mass. Thus, the health effects of an engine can not be evaluated based only on PM mass.
To assess the adverse effects of particles, the particle number should also be examined. In this study, particle number emissions were therefore analyzed in several off-road diesel engines of different ages. The engines were developed for low emissions and fuel consumption experimentally, by usually running them according to the 8-mode ISO 8178-4 C1 off-road test cycle. Modern low-sulfur diesel fuel oil was burned, the sulfur content of the batches varying from 8 to 60 mg/kg. In addition to regulated gaseous emissions, the exhaust smoke and particle number concentrations were determined. An ELPI analyzer was adopted for PM number recordings.
The results showed that the number of hazardous particles may be almost equally low in engines of the early 1990s as in modern ones, although the older engines emit more visible smoke.