1. Tampere University of Technology, Aerosol Physics Laboratory, P.O. Box 692 FIN-33101 Tampere, Finland, Aristotle University of Thessaloniki, Laboratory of Applied Thermodynamics, Aristotle University of Thessaloniki, GR 541 24 Thessaloniki, Greece, and VTT Technical Research Centre of Finland, Engines and Vehicles Research Group, P.O. Box 1000, FIN-02044 VTT, Finland