Initial investigations into ammonia combustion at conditions relevant for marine engines

Abstract

The greenhouse gas reduction targets set out by the International Maritime Organisation (IMO) in their initial strategy will not be achievable without the adoption of fuels associated with a significantly lower net carbon footprint than the traditional marine fuels. Among the potential alternatives to current fuels,including liquified natural gas (LNG), ammonia is often considered to be the most promising candidate, for a variety of reasons, but first and foremost due to its carbon-free nature. However, the application of ammonia as fuel in marine transport is not without challenges, not only in terms of bunkering, storage and handling on board that require appropriate measures for ensuring safe operation at all times. The chemical properties of ammonia governing its ignition and combustion characteristics also require proper consideration in the specification of the combustion system layout. In this context, a good understanding of the actual combustion behaviour at relevant conditions is imperative. Therefore, a novel “optical engine” test facility (Flex-OeCoS) has been used to perform initial investigations to that end.The Flex-OeCoS has been specifically designed to allow applying optical measurement methods for acquiring ignition and flame propagation data at a wide range of operational parameters. It is capable of achieving engine relevant compression/combustion pressures and temperatures at variable speeds and its very elaborate operating concept allows adjusting the main parameters such as pressure, temperature and turbulence intensity at start of combustion individually and with a high level of accuracy and reproducibility. The present paper starts from a fundamental description of the Flex-OeCoS and its main features, including an overview of the extensive validation performed to demonstrate the relevance for a wide range of engine applications. The extensions of the test facility for enabling the operation on ammonia are then outlined before presenting the results obtained during an initial test series: Ignition and combustion characteristics of ammonia are illustrated by means of high-speed imaging data as well as thermodynamic analysis results for a variety of conditions. The results of these investigations are expected to serve as an excellent basis for the selection, initial specification, and further optimisation of ammonia combustion systems on large marine engines and to thus contribute to achieving the IMO’s decarbonisation targets.