Full operational map of a spark-ignited medium-duty single-cylinder 100% ammonia-fueled engine

Abstract

Anhydrous ammonia (NH₃) is a zero-carbon fuel that has a higher volumetric energy density and can be more easily transported and stored than gaseous or liquid hydrogen. Challenges associated with ammonia’s low laminar flame speed and high ignition energy have limited its use in the past. Many experimental efforts have attempted to overcome these limitations in internal combustion engines by blending ammonia with hydrogen or another higher reactivity fuel; however, reducing complexity by enabling pure ammonia fueling is desirable from the perspective of widespread implementation. This experimental study investigates the full operating map of a single-cylinder version of a 6.7-L displacement diesel engine retrofitted for 100% ammonia spark ignition (SI) operation. Performance and emissions measurements were completed across the full operational map with additional sweeps of spark timing and equivalence ratio conducted at selected conditions. The engine maintained stable operation above 4 bar IMEP_g across the entire tested map and maintained gross fuel consumption values of 250 g/kWh diesel equivalent or less when above idle speed and 50% load. Slightly rich (φ = 1.025 ± 0.015) operation was maintained across the test conditions to minimize the three emissions of interest (NH₃, NO_x, and N₂O) and was controlled using the measured raw NO_x concentration. Emissions control using exhaust NO_x concentration, as opposed to O₂, proved to be a promising approach to maintain constant NH₃/NO_x ratios across a large portion of the operational map.