Aspects of retrofitting a compression ignition engine to direct injection of liquid ammonia

Ammonia has gained a substantial interest in the automotive industry as being carbon free fuel that can contribute to the reduction of greenhouse effect. However, its application in existing combustion engines, requires their prior adaptation. In this work we present retrofitting technology of an existing compression ignition (CI) engine to ammonia powered engine with direct injection of liquid ammonia. The work carried out results from the cooperation between Polish and Norwegian research groups within the project ACTIVATE (Ammonia as carbon free fuel for internal combustion engine driven agricultural vehicle). The technology developed steams from experimental and numerical studies conducted on a single-cylinder CI engine. installed on a small agriculture tractor. Directly injected biodiesel has been applied as an ignition promoter for ammonia. The experimental works were carried out on engine test benches and chassis dyno. They were supported by 0D and 3D simulations using stochastic reactor model (SRM) and CFD code Converge, respectively. An extensive matrix of engine operating points and fuel injection strategies was investigated experimentally and numerically to show possible advantages and disadvantages of different designs. Part of the research was devoted to the analysis of nitrous oxide formation due to its high global warming potential. The works have led to a technology of burning ammonia with biodiesel as ignition promoter of ammonia. The energy share of ammonia in the fuel that ensures stable engine operation in tractor application under actual driving conditions is estimated to 47%. Most efficient engine operation is ensured if ammonia and biodiesel are injected towards the end of the compression phase. Fuel that acts as an ignition promoter is injected shortly, usually a few crank angles, before ammonia. Too long delay between the two fuels deteriorates the combustion process and increases ammonia out emission. The combined numerical and experimental works resulted in a demo tractor powered with directly injected biodiesel and ammonia.