Abstract

The transition to low-carbon fuels introduces new challenges for the design of energy systems based on internal combustion engines. This paper addresses the effects of ammonia as one of the prime fuels for highly efficient two-stroke engines, e.g., based on MAN high-pressure injection technology. Even if these prime movers can maintain a high effective efficiency over a wide load range, the thermodynamic features of the ammonia combustion have a strong impact on the waste heat pattern. The analysis indicates that the lower adiabatic flame temperature and the chemical composition of the exhaust gases reduce the exhaust temperature, while variations in the specific heat capacity of the exhaust mixture reduce the exergy. This phenomenon is directly related to a reduced potential of working fluid generation in waste heat recovery (WHR) systems. The paper concludes that to maintain high overall plant energy efficiency, advanced technologies, such as organic Rankine cycles (ORC), have to be applied to compensate for the loss of the thermal potential, especially at off-design load conditions.