Exhaust inorganic nanoparticle emissions from internal combustion engines

Inorganic additives are used in internal combustion engine fuels and lubrication oils for several reasons. Some form deposits on engine internals and on exhaust emission control catalysts impairing the performance of either or both, and they can lead to significant numbers of potentially harmful tailpipe nanoparticle emissions. In this work we examined the fate of sulphur and metal derived from additives. A dichotomy between the amount of sulphate nanoparticles formed by sulphur from lubrication oil and from fuel is suggested to result from oxidised sulphur species in oil directly forming sulphate and thence nanoparticles. In contrast sulphur dioxide from combustion of fuel sulphur compounds does not form sulphate nanoparticles unless the exhaust temperature is high enough for formation of sulphate by oxidation over a downstream catalyst. These alternative pathways were demonstrated by measuring the size and number of particles formed in a pyrolysis reactor fed with low levels of sulphur dioxide, para-toluene sulphonic acid and sulphuric acid. The sulphonic acid and sulphuric acid formed similar amounts of similar sized nanoparticles (about 15 nm) whereas sulphur dioxide formed none unless it was passed over an oxidation catalyst above 200°C. Particle size measurements were also performed on the exhaust of a passenger car equipped with a gasoline engine operating on a chassis dynamometer. It was fuelled with standard gasoline and gasoline containing a low level of the octane enhancer methylcyclopentadienyl manganese tricarbonyl that produced a distinctive nucleation mode emission of extremely tiny, sub-10 nm nanoparticles. The implications of such solid inorganic particles on the European PMP particle number measurement protocol are discussed.