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The mechanism of valve seat recession is well understood and a review of the existing literature shows that it consists of two processes - the generation of hard particles that then grind or abrade the valve seats. Metallic fuel additives can prevent recession by stopping the generation of these hard particles. Both new and previously published data are presented to demonstrate that low concentrations of all the commonly available additives provide adequate protection for most service applications. However, the data also show that severe testing with low treat rates will produce valve seat recession. The author argues that, if sufficient concentration of additive is used, the initiation of recession is stopped under extremely severe conditions and alternatives to lead can offer complete protection. The paper concludes that the use of lead replacement additives should be at the maximum possible level commensurate with all aspects of engine performance.

Six European vehicles fitted with carbon canisters have been tested under severe conditions to establish if evaporative losses of volatile organic compounds occur under European driving conditions - so-called “running losses”. The programme entailed the development of a point source measurement technique which has a number of advantages over other methods currently in use. Following the development and validation of the measurement technique, the six vehicles were tested at 28C over a range of driving cycles on a gasoline with a Reid vapour pressure of 90 kPa. None of the vehicles exhibited classical running losses, i.e. losses during higher-speed driving. This was due to the effectiveness of canister purging in these conditions. However, significant volatile organic compound (VOC) losses were observed for several vehicles during idle after a period of driving had heated the fuel. Substantial car-to-car variation was observed in the losses obtained.