X-DF – low pressure dual fuel engines
Low-pressure dual-fuel engines operated according to the Otto cycle. In gas operation, the fuel-gas and air are homogeneously pre-mixed in the combustion chamber before ignition.
Together with the high amounts of air, this results in a lean homogeneous combustion with an equal temperature distribution throughout the entire combustion chamber. This is in contrast to engines following the diesel cycle where gas or liquid fuel is injected into the combustion chamber to flame and burn. The combustion in a flame is locally very rich, leading to local hotspots in which the nitrogen and oxygen content of the air react with each other, forming NOX. As low-pressure dual-fuel engines are able to avoid such hotspots*, the NOX emissions are approximately 50% of the set IMO Tier III limit.
(*In the pre-chamber diesel-fuel is injected as pilot fuel and burns according to the diesel process, i.e. the main diesel-typical emissions, such as NOX and particulate matter with low-pressure dual-fuel engines are related to the pilot fuel combustion. However, thanks to the extremely low pilot-fuel demand, those emissions can be kept at an absolute minimum.)
Consequently, X-DF engines require no further NOX reduction systems, such as exhaust gas recirculation (EGR) or selective catalytic reduction (SCR).
X-DF engines comply with IMO Tier III also during maneuvering, when starting and stopping.
In fact, the IGF code (International Code of Safety for Ships using Gases or other Low-flashpoint Fuels) and IACS (International Association of Classification Societies) rules require that maneuvering, including engine starting, stopping and reversing shall for safety reason carry out in diesel operating mode, even though gas operation is the intended IMO Tier III compliant operating mode.
Such a procedure will not violate the IMO Tier III rules since it is defined as part of the Auxiliary Control Devices (ACD) as described in the “IMO Guidance on the application of Regulation 13 of MARPOL Annex VI Tier III requirements to dual-fuel and gas-fueled engines”.
By definition, the ACDs are function or control strategies installed on a dual-fuel engine. The ACDs have to be identified, disclosed and declared in the engines’ Technical Files.
X-DF ready concept
Switching from liquid to gas fuel is a viable solution for dealing simultaneously with both the NOx and SOx requirements. Some X-engines have been designed to be X-DF ready, meaning that the standard diesel engine can be converted to a low-pressure X-DF engine by adding only the gas components.
X-Engines – Diesel Engines
Our X-engines are IMO Tier III ready as standard, through the designed interface with SCR systems.
SCR (Selective Catalytic Reduction)
The SCR reactor is put on the high-pressure side, before the turbine. Integrating the SCR reactor before the turbine allows the reactor to be designed in the most compact way due to the higher density of the exhaust gas. WinGD has developed and is systematically deploying high-pressure SCR solutions for the low-speed diesel engine portfolio with single and multi-turbocharger applications.
WinGD allows third-parties to supply high-pressure SCR systems in accordance with the interface specifications.
Typical high-pressure SCR arrangement.
Integrated SCR (iSCR)
WinGD has developed the first on-engine SCR for marine two-stroke engines. iSCR offers high-pressure catalytic reduction with greatly simplified installation and integration as well as significant savings in weight and required engine room space. It can be used for small- to medium-bore engines with one turbocharger that use low-sulphur fuels.
The SCR reactor is put on the low-pressure side, after the turbine. WinGD has developed an interface specification for low-pressure SCR applications for all low-speed engines which complies with the known low-pressure SCR system providers.
Low-pressure SCR is typically larger in volume and has the advantage of being less complicated to integrate into the exhaust stream.