Heavy-duty, off-road diesel engine low-load particle number emissions and particle control

Abstract

Exhaust gas particle and ion size distributions were measured from an off-road diesel engine complying with the European Stage IIIB emission standard. The measurements were performed at idling and low load conditions on an engine dynamometer. Nucleation-mode particles dominated the diesel exhaust particle number emissions at idle load. The nonvolatile nucleation-mode geometric mean diameter was detected at 10 nm or below. The nonvolatile nucleation-mode charge state implied that it has evolved through a highly ionizing environment before emission from the engine. The determined charging probabilities were 10.0 ± 2.2% for negative and 8.0 ± 2.0% for positive polarity particles. The nonvolatile nucleation particle concentration and size was also shown to be dependent on the lubricant oil composition. The particle emissions were efficiently controlled with a partial filter or with partial filter + selective catalytic reduction (SCR) combination. The particle number removal efficiencies of the aftertreatment systems were over 95% for wet total particle number (>3nm) and over 85% for dry particle total number. Nevertheless, the aftertreatment systems’ efficiencies were around 50% for the soot-mode particles. The low-load nonvolatile nucleation particle emissions were also dependent on the engine load, speed, and fuel injection pressure. The low load particle number emissions followed the soot-core trade-off, similar to medium or high operating loads.

Implications:

Idling and low-load diesel engine exhaust emissions affect harmfully the ambient air quality. The low-load particle number emissions are here shown to peak in the 10-nm size range for a modern off-road engine. The particles are electrically charged and nonvolatile and they originate from the combustion process. Tailpipe particle control by open channel filter can remove more than 85% of the nonvolatile 10-nm particles and about 50% of the soot-mode particles, while the fuel injection pressure increase can lead to particle number increase. The study provides a new viewpoint for low-load particle emissions and control.

Additional information

Notes on contributors

Tero Lähde

Tero Lähde is a patent examiner at Finnish Patent and Registration Office, Helsinki, Finland.

Annele Virtanen

Annele Virtanen is an associate professor at the University of Eastern Finland, Kuopio, Finland.

Matti Happonen

Matti Happonen is a research engineer at AGCO Power, Inc., Linnavuori, Finland.

Christer Söderström

Christer Söderström works as a research scientist and Matti Kytö is a principal scientist at VTT Technical Research Centre of Finland, VTT, Finland.

Matti Kytö

Christer Söderström works as a research scientist and Matti Kytö is a principal scientist at VTT Technical Research Centre of Finland, VTT, Finland.

Jorma Keskinen

Jorma Keskinen is a professor in the Department of Physics at Tampere University of Technology, Tampere, Finland.