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A method for non-intrusive measurement of spark plug fouling, burn quality, pre-ignition and spark characteristics is described. The technique relies on a continuous monitoring of the leakage current to the spark plug centre electrode, via a high voltage diode stand off arrangement. By way of demonstration, the system operation is reported for investigations of cold start plug fouling.

The transport of fuel during cold start in the intake of a port-injected engine has been investigated using a standard engine with very little modification. A fast response FID sampling from the intake manifold is used to measure the instantaneous vapor concentration during the start. At short times after the start, the engine is stopped, and the port under investigation isolated. The engine is then warmed up by passing hot water through it and at the same time is flushed with hot air, in the port and the cylinder. This evaporates the liquid fuel, and by integrating the vapor concentration multiplied by mass flow of the displaced gas, the fuel mass in the isolated port and cylinder is measured. It is shown how the mass of liquid in the port at the time at which the engine is stopped can reliably be related to the concentration measurement. By stopping the engine at different times after the start, detailed accounting of the fuel transport as a function of time since start can be made.

Understanding mixture formation phenomena during the first few cycles of an engine cold start is extremely important for achieving the minimum engine-out emission levels at the time when the catalytic converter is not yet operational. Of special importance is the structure of the charge (film, droplets and vapour) which enters the cylinder during this time interval as well as its concentration profile. However, direct experimental studies of the fuel behaviour in the inlet port have so far been less than fully successful due to the brevity of the process and lack of a suitable experimental technique. We present measurements of the hydrocarbon (HC) concentration in the manifold and port of a production SI engine using the Fast Response Flame Ionisation Detector (FRFID).