All internal combustion piston engines emit nanoparticles. Part of them are soot particles as a results of incomplete combustion of fuels, or lube oil. Another part are metal particles, most probably oxides, commonly called ash. A major source of metal particles is engine wear and corrosion. The lube oil reentraines these abraded particles into the combustion zone. There they are partially vaporized and ultrafine oxide particles formed through nucleation [1]. Other sources are metallic additives to the lube oil, or the fuel, and debris from the catalytic coatings in the exhaust-gas after-treatment. The formation process results in extremely fine particles, typically smaller than 50 nm. Thus they can intrude through the alveolar membranes directly into the human organism and can even penetrate the cell nucleus [5]. The consequent health risk necessitates a careful investigation of these emissions and effective curtailment. Substantial information is available on Diesel engine particulate emissions, [2, 3, 4] but there are almost no results for SI engines reported. Beside an example of metal oxide particles from a Diesel engine, [2], the present paper shows some preliminary results of particle mass and nanoparticle emissions of SI engines. Four SI engines were investigated: two older and two newer engines, comprising two car engines and two motorbikes. The tests were done on standard transient driving cycles, and steady-state at constant 50 km/h and idling because prior to this study high concentrations of ash were observed with Diesels during idling, [2]. All tests were done with particle samples collected from the CVS tunnel, during long operating periods, to have sufficient material for analyzing. At the steady-state points, the particle size spectra were measured and based on this the source as “ash” postulated. The results show that the older engines emit high concentrations of both soot and ash particles. The size distribution is bimodal for soot and ash particles. The newer engines’ emission results are less uniform and the concentrations are lower, as expected. Altogether, the concentrations of these ash particles in the exhaust gas of Diesel and SI-engines can be so high, that more detailed investigations are requiredy.

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