Low-emission operation of an NH ₃ -diesel dual-fuel 4-stroke engine targeting EU Stage V performance via combined combustion control and exhaust gas aftertreatment

Internal combustion engines operated in combined heat and power generation applications can achieve high overall efficiencies by utilizing both electrical output and exhaust heat, while also offering rapid load flexibility for grid support. However, engines fueled with conventional diesel or natural gas contribute significantly to greenhouse gas emissions. To mitigate CO 2 emissions, engines operated with hydrogen admixture to natural gas or in pure hydrogen mode are under development. Nevertheless, the high reactivity of hydrogen and the associated risk of knocking combustion posing challenges for engine operation and can limit thermal efficiency. In addition, the low volumetric energy density of hydrogen complicates fuel transport and storage, particularly in applications lacking direct access to gas or hydrogen infrastructure. In this context, ammonia (NH 3 ) represents a promising alternative due to its higher volumetric energy density and established transport and storage infrastructure. Direct combustion of ammonia in internal combustion engines, however, introduces several technical challenges. While ammonia combustion is CO 2 -free, the formation of nitrous oxide (N 2 O), a potent greenhouse gas, can occur. Additionally, compliance with stringent emission regulations requires effective control of nitrogen oxides (NO x ) emissions and unburned ammonia (NH 3 slip). Moreover, emissions of carbon monoxide (CO) and unburned hydrocarbons (HC), originating from small quantities of diesel pilot fuel used for ignition support, must also be minimized. To fully realize the greenhouse gas reduction potential of ammonia-fueled engines while meeting modern emission limits, an integrated optimization of combustion and exhaust gas aftertreatment (EAT) is essential. In this study, an ammonia-diesel dual-fuel combustion concept was investigated using a single-cylinder research engine (SCE). A coupled approach was applied, combining targeted adjustments of engine operating parameters to shape the raw exhaust gas composition with a systematic evaluation of two different exhaust aftertreatment catalyst configurations on the SCE.