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Crank-angle resolved, gas temperatures are determined in the combustion chamber of a Volkswagen (VW) standard-production, port-injected SI engine. During idle, two different methods are applied: (1) a direct spectroscopic emission-absorption technique at a resonance line of potassium, seeded to the air stream to generate sufficient spectral absorptance (‘colouring’ technique), and (2) a more standard, indirect method in which temperatures are derived from pressure recordings using a two-zone thermodynamic model. Combustion temperatures obtained during idle with both the spectroscopic (1) and ‘two-zone’ (2) methods are in good agreement. In addition, the spectroscopic technique is extended to transient operating conditions where the ‘two-zone’ method is not applicable. Combustion temperatures measured during cold-start and abrupt load alteration are in good agreement with former investigations.

A novel diagnostic method, termed laser tomography, is made feasible for application in automobile engine combustion studies, and sample results of temperature field measurements are presented. To investigate the potential of this method, data are taken in the visible region of the spectrum, where ‘coloring’ of the gas with potassium is required to overcome unsufficient spectral absorption. The research motor, a single-cylinder, BMW SI engine is controlled by a test stand. The tomographic method is based on the use of two known techniques: simultaneous measurement of the spectral absorption and emission data combined with tomographic recon-struction. Since optical access to the engine combustion chamber is limited, twelve laser beams are used for the probing, generated by beam splitters either from a single titan sapphire or dye laser.