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Internal combustion engine deposits, and high molecular weight materials present in exhaust emissions, may be very difficult to characterise and analyse. This is because they are composed not only of complex molecules, but also of materials which are cross-linked to such an extent that they are insoluble and intractable to conventional methods of analysis. This paper discusses the scope of several approaches to studying such materials. The techniques used are: (I) heated probe mass spectrometry, (II) gas chromatography/mass spectrometry, (III) pyrolysis—gas chromatography/mass spectrometry, (IV) positive ion bombardment/mass spectrometry and (V) laser desorption/ionisation mass spectrometry. For the last of these techniques, an optical fibre method has been devised which permits the simple conversion of a conventional mass spectrometer to one with laser-desorption facilities. Examples of results are selected from those obtained by the authors in order to illustrate the strengths and limitations of each technique. The ultimate objectives in this work are to assess the extent to which the formation of such materials may be associated with particular fuels, oils, additives, or operating parameters of the engine.

While Homogeneous Charge Compression Ignition (HCCI) is a promising combustion mode with significant advantages in fuel economy improvement and emission reductions for vehicle engines, it is subject to a number of limitations, for example, hardware and control complexity, or NOx and NVH deterioration near its operating upper load boundary, diminishing its advantages. Conventional spark-ignition combustion mode is required for higher loads and speeds, thus the operating conditions near the HCCI boundaries and their corresponding alternatives in Sl mode must be studied carefully in order to identify practical strategies to minimise the impact of the combustion mode transition on the performance of the engine. This paper presents the results of an investigation of the combustion mode transitions between Sl and HCCI, using a combination of an engine cycle simulation code with a chemical kinetics based HCCI combustion code. It investigates and discusses the key issues concerning the combustion mode transition and its control. A new approach has been adopted in the modelling of the HCCI engine gas exchange and combustion, which allowed a parametric study of the transient process in the transition on a cycle-by-cycle basis and provided guidelines in the design of the engine hardware and its control strategies.