Derating two-stroke engines

New system aims to extend the CII compliance lifetime of merchant vessels

Technology group Wärtsilä has introduced what it describes as a “new radical derating retrofit solution”. Wärtsilä Fit4Power is said to extend the Carbon Intensity Indicator (CII) compliance lifetime of an average ship by three to five years.

May 16, 2023

It says the retrofit solution enables shipowners to reduce the bore size of two-stroke engines by 25% while significantly improving combustion efficiency, which in turn reduces both fuel consumption and greenhouse gas emissions. Wärtsilä says this will improve the efficiency of their existing fleet, ensuring compliance with CII regulations and, it claims, future-proofing assets against future environmental measures.


As a pilot, Wärtsilä 2-Stroke Services installed Wärtsilä Fit4Power on a container ship with a large-bore two-stroke main engine last year.  According to Wärtsilä, the results proved that a vessel with this kind of main engine, that is now oversized for today’s operating patterns, can save 2,000 tonnes of fuel and reduce at least 6,000 tonnes of CO2 emissions annually thanks to this retrofit solution. Fit4Power received certificate of product design assessment from American Bureau of Shipping (ABS) in 2022.


Wärtsilä asserts that, while conventional derating merely tunes engines for operation at lower loads, its system involves reducing the bore diameter of engine cylinders and introducing a new combustion chamber design, enabling the engine to run at optimal loads and with state-of-the-art fuel efficiency. The higher compression ratios and firing pressure achieved mean that the modified engine offers far greater efficiency than either conventionally derated engines or unmodified engines run at much lower loads.


Without modification, according to Wärtsilä, more than 80% of the global merchant fleet could fall into the lowest CII rating by 2030. This would require mandatory corrective action and risking losing business to more efficient vessels. Improving engine efficiency and optimisation with solutions such as Fit4Power is one of the simplest and most cost-effective means of reducing emissions, according to Wärtsilä.


The new solution has been designed to be compatible with Wärtsilä Fit4Fuels (Wärtsilä’s Two-stroke future fuels conversion platform), that enables vessels to use LNG, methanol and ammonia fuels.

Injection systems for new fuels


German engine injection system manufacturer Woodward says it is developing a comprehensive new range of injection systems applicable for new and future-fuel powered engines, including engines running on methanol and ammonia.


According to Woodward, the new systems are being designed to support the global energy transition to low carbon fuels. The comprehensive portfolio of injection systems for P2X fuels in large engines will range from 100 kW/Cylinder to over 1000 kW/Cylinder – to enable all possible combustion concepts.


For applications that require the highest levels of power density and efficiency, Woodward is developing a High-Pressure Dual-Fuel (HPDF) platform for methanol and ammonia injection with full diesel backup capability.


 Woodward claims: “The new range of direct solenoid actuated injection systems is perfectly tailored to meet market requirements for simpler and retrofitted systems, including methanol injection systems for Port Fuel Injection (PFI) and Direct Injection (DI). The injectors are designed for optimal atomization of the fuel to enable good mixing and minimize wall wetting.”


For gas engines that are adapted to run on gaseous P2X fuels such as hydrogen and ammonia, Woodward’s SOGAV gas admission valves are also being optimised to withstand the properties of these fuels such as poor lubricity, corrosion behaviour and hydrogen embrittlement.

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