The primary objective of this study was to determine the capability of a CAT engine controlled by an advanced combustion emission reduction technology (ACERT) electronic control module to operate in a dual fuel mode. A CAT 6.6-liter ACERT test engine was outfitted to operate on a hydrogen-diesel fuel mixture. A continuous stream of hydrogen was infused into the intake air charge after the turbocharger. At 50% of rated load, the addition of hydrogen, at three different speeds (1300, 1800, and 2100 RPM), was examined. The hydrogen addition varied from 0-60% of input energy. The maximum amount of hydrogen added before knock occurred, for 1300, 1800, and 2100 RPM, was 54%, 46%, and 55%, respectively. At 1300 RPM, the addition of hydrogen resulted in a decrease in specific energy consumption (SEC) for all levels of hydrogen. For 1800 and 2100 RPM, the SEC improved only when hydrogen was added beyond 46% and 55%, respectively. Emissions testing, while using hydrogen, showed a consistent decrease in carbon dioxide (CO2) emissions and an increase in nitrogen oxides (NOx) emissions for all test speeds. The carbon monoxide (CO) emissions showed improvement at levels of hydrogen exceeding 40% for all test speeds. The hydrocarbon (HC) emission did not vary during the addition of hydrogen.