Effects of in-cylinder non-uniformities on mixture preparation in a light-duty Diesel engine operating a light-load Partially Premixed Combustion strategy.

The emissions, performance, and control of advanced combustion strategies such as Partially Premixed Combustion (PPC) is strongly affected by local fuel-air mixture preparation. In this work, we combine computational and experimental approaches to study the effects of combustion chamber geometric details and intake-induced non-uniformities in the temperature and velocity fields on the operation of a single cylinder, light-duty diesel engine operating in a slightly boosted, light-load partially-premixed compression ignition (PPCI) mode. A comprehensive computational model of the single-cylinder research engine was developed considering the complete intake and exhaust ducts and the plenums’ geometries, as well as adjustable throttling devices used to obtain different swirl ratios. The in-cylinder flow predictions were validated against PIV measurements at different swirl ratio configurations, confirming the reliability of the RANS turbulence modeling approach in capturing ensemble-averaged flow field properties. A batch of multidimensional simulations was then set up to model corresponding mixture preparation experiments, faturing a non-reactive charge and a single, early injection pulse, under different swirl ratio and injection pressure conditions. Finally, the effects of geometric details on velocity field non-uniformity were studied, showing that, even if it is not possible to simulate differences arising from deposits or injector nozzle-by-nozzle non-uniformities, detailed multidimensional modeling can noticeably improve the predictability of local mixture quantities that affect ignition and pollutant formation.

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