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Fast throttle opening in port-injected gasoline engines often results in a lean air-fuel ratio excursion lasting several engine cycles. Even when the engine is equipped with a three-way catalyst this lean excursion can lead to high tailpipe emissions. This paper will describe an in-cylinder method of measuring these air-fuel ratio excursions, using a fast flame ionisation detector. Examples will be given of air-fuel ratio excursions obtained on a four-valve-per-cylinder sequentially-injected gasoline engine equipped with a lambda sensor. The air-fuel ratio excursions together with measurements of the engine air flow are used to estimate me build up of the fuel film on the inlet manifold walls. Whilst air-fuel ratio excursions have been recorded previously by other investigators, their results were obtained from exhaust gas analysis using fast oxygen sensors.

Comparisons have been made between the ignition delay and combustion performance of sunflower oil and diesel fuel. The experimental results have been obtained in a naturally aspirated direct injection diesel engine, and particular attention has been given to the heat release analysis, ignition delay, combustion noise and lubricant degradation. The anomalous behaviour of sunflower oil is explained by reference to its physical properties and ignition quality, as reported in the literature from bomb tests. It is concluded that the power output and brake efficiency are largely unaffected by the use of the sunflower oil, and that lubricant degradation is not likely to be significant. However, the build up of combustion deposits already widely reported in the literature was observed. Suggestions are made as to how this might be ameliorated through modifications to the injection system.