A new single-cylinder optically accessible heavy duty diesel engine has been conceived and constructed at the Institut fu¨r Kolbenmaschinen. Rather than being made from a quartz glass cylinder, the cylinder liner of this engine is modified with three round, flat optical access ports to facilitate laser-optical measurements within the combustion chamber. The flat optical surfaces prove less problematic than a quartz glass cylinder in terms of internal reflections, cleaning procedures, cost, and robustness. A specially adapted piston facilitates the passage of the laser sheet into the piston bowl and provides a view into the bowl at top dead center. Computational fluid dynamics (CFD) simulations were performed in order to estimate the effects of the optically necessary piston and cylinder liner modifications on in-cylinder flow and to compare the flow characteristics with those simulated for a non-modified engine. Emphasis is placed on turbulence behavior before top dead center. The trade-offs and limitations inherent in the modified piston design are discussed in this context. Further optical investigations with this engine will provide insight into the mixture formation and combustion processes. In particular, the soot formation and oxidation processes will be studied under realistic engine operating conditions.

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