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The Fast-response Flame Ionisation Detector is used to measure levels of un-burnt hydrocarbons in the cylinder and exhaust of engines. Its fast response allows uHC emission processes to be resolved within an engine cycle. This paper describes a method for obtaining even greater detail by post-processing the output of the device using a Finite-Impulse Response (FIR) digital filter. The specification of the filter can be obtained by understanding the flow regimes within the sampling system. Examples from in-cylinder and exhaust sampling are presented with suggestions for implementation and further improvement.

Fast Response Flame Ionisation Detectors can be used to observe events within the combustion chamber of engines to help understand the processes by which hydrocarbons escape combustion. In order to understand the timing of events it is necessary to establish the transit time of the measuring system, in particular the times associated with gas transport through the sampling capillaries. To this end, a quasi steady state flow model has been developed to evaluate the transit time for all parts of the cycle. These predictions can deviate significantly from those using steady-state assumptions. Experimental validation is presented.