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New European motor vehicles must comply with emissions regulations which will soon include the exhaust produced during cranking and warm-up, when a catalyst is not active. This paper describes a technique of using rapid acting sampling valves to take measurements from the combustion chamber and exhaust pipe of a spark ignition engine during this period. The samples were analysed for both total hydrocarbons and individual species. Results obtained from an engine operating on propane fuel are presented. The concept of a storage parameter, developed previously from tests on an engine operating at the cyclic repeating condition (CRC) is used to help interpret the measurements. The total hydrocarbons readings show the behaviour of the engine to resemble that of the fully warmed state 15 seconds after start. Using the storage parameter indicates this similarity occurs closer to 50 seconds from start.

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.

Computer simulations of internal combustion engine cycles utilize empirical information, such as the flow characteristics of valves. This paper presents comprehensive data on the flow area of piston controlled ports. Detailed results of systematic steady flow tests on both inlet and exhaust ports are presented. New aspects of the work are that it covers a wide range of pressure ratios for normal and reverse flow directions and that comparative results, with and without the restrictions of an exhaust belt, are included. The concept of effective flow area is briefly discussed and relevant equations given. Previous experimental work is reviewed.