SUMMARY

Current diesel engine strategies are aimed at reducing emissions in-cylinder, rather than with aftertreatment, because aftertreatment use suffers from higher economic costs, durability issues, and fuel economy penalties. One potential approach for in-cylinder emissions reduction is to dynamically vary the fuel delivery rate during the injection period, referred to as injection rate-shaping. Injection rate-shaping offers a unique ability to control emissions because fuel-air mixing rates and combustion processes, which ultimately determine engine-out emissions, are governed by the fuel delivery rate. Widespread use of injection rate-shaping strategies in diesel engines has been limited, however, by the conflicting emissions results in engine literature. Recently, significant gains in diesel combustion knowledge for conventional injection rate shapes have been brought about by isolating the combusting spray from the rest of the engine suggesting that similar knowledge gains may also be possible for injection rate-shaping. To date though, very few studies have focused on the effects of isolated injection rate-shaped fuel sprays on emissions due to the technical difficulties in experimentally producing a range of desired injection rate shapes. This thesis aims to develop a fully-flexible experimental rate-shaping system and to study isolated injection rate-shaped fuel sprays in an optical chamber that mimics engine thermodynamic conditions. Using this approach, spray and combustion observables are measured to identify mechanisms responsible for the disparity in literature reported emissions using injection rate shaping. Towards this goal, a reduced-order model is developed to more concretely see the link between mixing and chemistry processes involving injection rate-shaped fuel sprays that might otherwise go unnoticed in experimental or higher fidelity computational approaches. Together, the proposed experimental and modeling techniques will probe a wide range of engine thermodynamic conditions and injection rate shapes to provide the engine community with the necessary tools to make informed decisions about how injection rate shaping should be employed for maximum emissions reduction.