The main “Congress and Exposition” of the Society of Automotive Engineers (SAE) takes place in Detroit each Spring and smaller meetings are also held. One such meeting was the 1998 “International Fall Fuels and Lubricants Meeting and Exposition” held in San Francisco, October 19th to 22nd, 1998. Some 306 papers were presented to 1163 participants and a selection from sessions on the aftertreatment for petrol and diesel engines are reviewed here.

Plasma Technology Plasma is formed when very high voltage is applied across a zone through which exhaust gas flows. A variety of often novel chemical reactions is induced which might be useful in destroying pollutants. The papers presented probed fundamental questions. Siemens (982428) used dielectric barrier discharge devices in diesel exhaust gas to show that nonthermal plasma oxidation of NO to NO₂ is unfortunately favoured over dissociation to nitrogen and oxygen! Addition of ammonia in the presence of a Selective Catalytic Reduction catalyst brought about NOx reduction at 100°C. A related contribution from Lawrence Livermore National Laboratory, Northwestern University and Engelhard (982508) reported that SO₂ is not oxidised under conditions where NO₂ is formed. This could be useful in situations where sulfate formation is detrimental.

Three-Way Catalysts (TWCs) Ford (982549) reported on hydrocarbon (HC) conversion efficiencies over Pd-only, Pt/Pd/Rh, Pd/Rh and Pt/Rh formulations during stoichiometric and rich operation. Their Pd-only and Pt/Pt/Rh catalysts had higher HC efficiency than Pt/Rh or Pd/Rh catalysts, the conversion efficiency for ethyne was > 98% for Pd-based catalysts, and > 96% for methyl t -butyl ether (MTBE) with all catalysts. MTBE and formaldehyde emissions from a warm engine were concluded not to be environmentally significant. Concentrations were given for the ten most abundant HCs in fuel, exhaust gas and post-catalyst gas and, with the exception of methane, there was significant reduction of already low HC levels over the catalyst. This paper has data for conversions for 154 HCs over aged Pt/Pd/Rh catalyst. Toyota (982706) described work on thermal deterioration of Pt/Rh TWCs and found that oxygen storage capacity depends on Pt metal particle size.

The complexity in providing On-Board Diagnostics compliance and low emissions was evident in papers from Hyundai (982551) and Engelhard (982553). The former included evaporative and catalyst requirements, while the latter focused on development of ULEV catalysts, and included geometric surface area and heat capacity effects on catalyst light-off. The influences of substrate cell structure and catalyst configuration were emphasised by Corning, Johnson Matthey, Daimler Chrysler, and Southwest Research Institute (982634). There is advantage in having high cell density (high geometric surface area) during cold start; low thermal mass is important, and square cross-section cells are better than triangular ones. The viability of thin wall substrate in terms of processing necessary for incorporation into exhaust systems was confirmed by Corning (982635); thermal shock properties can be better than with conventional products. Emitec (982633) reported that conical metal substrates give enhanced gas flow over the main catalyst, and provide improved light-off due to heat cascade.