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In order to achieve ultra low emission levels with three-way catalysts, an early accurate air/fuel ratio control is essential. Positioning the oxygen sensor in the first part of the substrate helps to protect the oxygen sensor from being splashed by water during cold start, so that early heating and activation becomes a less limiting factor. For emission control purpose, a position of a rear sensor in the warm part of the catalyst gives improved possibilities for oxygen buffer control during catalyst warming up conditions. This enhances balancing HC and NOx in an early phase. In addition, for OBD reasons it is possible to locate the sensor in any axial position in the catalyst, which improves design possibilities for cold start detection, even for single brick catalyst systems. The paper describes the construction of the catalyst with an integrated oxygen sensor.

The formation of Nitrous Oxide (N2O) over an aged three way catalyst was analysed in a laboratory reactor for a variety of simulated Otto engine exhaust gas conditions. Nitrous Oxide formation was further analysed during FTP75 dynamometer test with a car. The car was equipped with either an aged catalyst or a fresh one. A fast response diode laser system was modified to enable detection of Nitrous Oxide and Carbon Monoxide simultaneously. From laboratory data the kinetics of Nitrous Oxide formation were evaluated with mathematical simulations and a mechanism was suggested. The results were compared to data from vehicle tests and the results were discussed in the light of the laboratory study. Two general trends were confirmed, i) N2O formation increases at slightly lean conditions: ii) catalysts with a low degree of deterioration gave lower N2O emissions, iii) the extent of N2O formation goes though a maximum with respect to dissociation rate of NO.

Cycle resolved fuel droplet dynamics measurements in the inlet port of an S.I. engine were performed under firing conditions in order to study real dynamic effects in the fuel flow to the engine. A Phase Doppler Particle Analyzer (PDPA) was used to detect the droplet size and velocity. The optical access was through a glass window in the bottom of the intake channel. The PDPA was synchronised with the engine combustion cycle in order to study the results in the engine frequency domain. The measurements were performed over the cross section of the channel. Different injection timing and engine running conditions were investigated, using standard unleaded gasoline. The results show that, during the camshaft's overlap period, there exists a “push-back” droplets effect, due to the pressure difference between the inlet manifold and the cylinder, that transports droplets far back in the inlet manifold.

The effect of various fuel-cut agings, on a Volvo Cars 4-cylinder gasoline engine, with bimetallic three-way catalysts (TWCs) was examined. Deactivation during retardation fuel-cut (low load) and acceleration fuel-cut (high load, e.g. gearshift or traction control) was compared to aging at λ=1. Three-way catalysts were aged on an engine bench comparing two fuel-cut strategies and their impact on of the life and performance of the catalysts. In greater detail, the catalytic activity, stability and selectivity were studied. Furthermore, the catalysts were thoroughly analyzed using light-off and oxygen storage capacity measurements. The emission conversion as a function of various lambda values and loads was also determined. Fresh and 40-hour aged samples showed that the acceleration fuel-cut was the strategy that had the highest contribution towards the total deactivation of the catalyst system.