Optically accessible engines

Regardless of whether they operate on conventional or renewable fuels, internal combustion engines rely on a complex interplay of fluid dynamics, thermodynamics, chemistry, and heat transfer. If we want to improve the efficiency and reduce emissions of these machines, we need to understand and model these processes. Simulations, in particular computational fluid dynamics, can be an important tool for that. We can also gain much insight by optical measurements in the engine. All the key phenomena – such as air flow, injection, fuel/air mixing, ignition, flame propagation, pollutant formation – can be visualized with appropriate lasers and cameras. These measurements have high resolution in time and space, but of course we need to be able to bring light into the engine and see into it with a camera.

Such optical access requires substantial modifications of the engine. The Imaging group at the EMPI-RF operates two single-cylinder research engines that are purpose-built for providing as much optical access as possible – that is, large windows – to the cylinder: A spark-ignition engine (SI, ’Otto‘), and a compression-ignition (CI, ’Diesel‘) engine. Both are passenger-car sized four-valve engines, with 0.5 and 0.4 liters displacement, respectively. They have optical access through both top 30 mm of the cylinder and through the piston, the latter via a mirror installed in the extended piston (‘Bowditch‘-type arrangement). Example projects using these engines are investigating the Diesel combustion of renewable ‘e-fuels‘, the soot formation from unwanted liquid fuel films in the cylinder, and the cyclic variability when running engine on hydrogen fuel.

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Photo of the EMPI-RF’s optically accessible spark ignition engine. The engine is running and the bright light from the combustion is clearly visible. ​