In-cylinder fuel blending of gasoline with diesel fuel is investigated on a multi-cylinder light-duty diesel engine as a strategy to control in-cylinder fuel reactivity for improved efficiency and lowest possible emissions. This approach was developed and demonstrated at the University of Wisconsin through modeling and single-cylinder engine experiments. The objective of this study is to better understand the potential and challenges of this method on a multi-cylinder engine. More specifically, the effect of cylinder-to-cylinder imbalances and in-cylinder charge motion as well as the potential limitations imposed by real-world turbo-machinery were investigated on a 1.9-liter four-cylinder engine. This investigation focused on one engine condition, 2300 rpm, 5.5 bar net mean effective pressure (NMEP). Gasoline was introduced with a port-fuel-injection system. Parameter sweeps included gasoline-to-diesel fuel ratio, intake charge mixture temperature, in-cylinder swirl level, and diesel start-of-injection timing. In addition, engine parameters were trimmed for each cylinder to balance the combustion process for maximum efficiency and lowest emissions. An important observation was the strong influence of intake charge temperature on cylinder pressure rise rate. Experiments were able to show increased thermal efficiency along with greater than 90% decreases in oxides of nitrogen (NOX) and particulate matter (PM). However, indicated thermal efficiency for the multi-cylinder experiments were less than expected based on modeling and single-cylinder results. The lower indicated thermal efficiency as compared to the model predictions suggests a need for improved cylinder-to-cylinder control and further optimization within dual-fuel operation.