Abstract
Ammonia is garnering significant interest from the international maritime sector as an alternative fuel. It is attractive as a hydrogen carrier and as a fuel because it has a higher volumetric energy density compared with gaseous or liquid hydrogen, making it easier to store and transport without requiring high pressures or cryogenic storage. Ammonia has significant toxicity concerns, but safe handling procedures have already been established because it is one of the most widely produced chemicals worldwide for use as a fertilizer. Barriers to consuming NH3 as a fuel in engines include (1) less favorable ignition energy and flame speed compared with conventional fuels; (2) emissions challenges, including potentially high NH3, NOX, and N2O emissions; and (3) fuel delivery and handling challenges. Although NH3 has been used to fuel compression-ignition marine engines in limited demonstration projects, technical barriers still exist. The use of NH3 as a fuel in smaller-bore, high-speed auxiliary engines for large vessels and for smaller inland and coastal marine applications remains unaddressed. This work investigates a late-injection diesel pilot ignition dual-fuel NH3 strategy using a single-cylinder, high-speed Cummins four-stroke diesel engine platform with a 107 mm bore and 1.1 L displacement per cylinder. The engine was modified for port fuel injection of heated gaseous anhydrous NH3. The diesel fuel injection system and the combustion geometry were unmodified to represent a retrofit application, which would minimize additional hardware to maximize diesel fuel displacement with NH3. The results show the applicability of a late injection diesel pilot strategy to overcome the challenging fuel properties of NH3 over the engine operating envelope. Mapping results focusing on emissions are presented, and comparisons are made to a conventional diesel combustion baseline.
