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An approach to characterization and after-treatment of particulate emissions from gasoline engines

Abstract The growing importance of understanding and controlling particulate emissions from gasoline engines is outlined, and an experimental simulation approach is described which has the potential for exploring particle deposition/capture and oxidation phenomena under well-controlled conditions, thus avoiding some of the uncertainties involved in interpreting engine experiments. Artificially generated sub-100 nm carbon particles are introduced into a synthetic exhaust gas stream, simulating engine-out soot emissions. Initial experiments in insulated pipe flows have shown very little particle deposition or change in mean size for residence times up to 1–2 s at uniform temperatures up to 400°C and hydrocarbon concentrations up to 4000 ppm C1′ in line with the results of supporting analytical and computational studies. Further numerical predictions suggested that it might be possible to capture some 20–30 per cent of the particles by turbulent diffusion alone at higher gas flowrates more representative of those in engine exhaust pipes. The effect of two different catalysts and an uncoated monolith on particle size and concentration has been investigated at space velocities of 50000 and 100000 h−1, with an inlet gas temperature of 400°C. Particle penetration through the catalysts increased with particle size but in all cases exceeded 70 per cent, with no evidence of significant changes in particle mean size. In the next phase of experimental and modelling work, the contribution of thermophoresis to particle deposition in uninsulated pipes will be examined.