The use of gas dynamics to link in-cylinder and exhaust system unburnt hydrocarbon measurements on a spark ignition engine

The paper reviews the ideas on the sources of unburnt hydrocarbons in spark ignition engines. Time resolved measurements made in-cylinder and in the exhaust system in previous investigations have revealed large differences between the cylinder and the exhaust system. It is not possible to distinguish between reductions by mixing and oxidation. The object of the present paper is to investigate the links between the two sets of measurements using a new development of engine gas dynamics. An outline is given of the authors' measurements and the new aspects of the gas dynamics model. The key idea of the latter is the introduction of "the path line streams". A recent study using this method is described and the results discussed. It explains the role of mixing at entry to the exhaust valve annulus and the post flame oxidation process. It is concluded that the new technique has extensive possibilities in the understanding of the problem of unburnt hydrocarbons from reciprocating engines.