Numerical Investigation of Engine Performance and Emission Characteristics of an Ammonia/Hydrogen/n-Heptane Engine Under RCCI Operating Conditions
Leilei Xu, Xue‐Song Bai
Abstract
Abstract This paper examines the potential of using ammonia (NH $$_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mn>3</mml:mn> </mml:msub> </mml:math> ) as a primary fuel in heavy-duty engines for decarbonization, with some challenges yet to be addressed. It presents a numerical study of a Reactivity Controlled Compression Ignition engine, where pilot diesel is used to ignite the premixed ammonia/air mixture. The numerical model and combustion mechanism are validated against engine experimental results using methanol and iso-octane fuels and ignition delay times of ammonia/n-heptane mixtures measured in a rapid compression machine. The findings show that the engine can effectively operate with up to 50% of the total energy supplied by premixed ammonia, albeit with slightly elevated NO emissions compared to a diesel-fueled engine. Increasing ammonia further leads to lower combustion efficiency. Hydrogen can be utilized in the ammonia engine to enhance ammonia combustion; however, NO emissions increase further. Ammonia leakage primarily originates from regions near the cold wall, the center of the cylinder, and the crevice. N $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> O mainly forms at the ammonia flame front. Emission of N $$_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> O is therefore mainly due to flame front quenching near the wall.