The world’s first 14-cylinder low-speed engine entered service on 1 September 2006 in a large, fast container vessel. Developed by Wärtsilä Corporation, the 14-cylinder Wärtsilä RT-flex96C engine is also the world’s most powerful engine with an output of 80,080 kW (108,920 bhp) at 102 rpm.
The 14-cylinder Wärtsilä RT-flex96C engine is a major breakthrough for ship propulsion. It extends the power available to suit the new generation of large containerships while combining the benefits of proven, reliable engine designs with the complete flexibility of RT-flex common-rail technology.
Traditionally low-speed marine engines have been built with a maximum of 12 cylinders. However, when it was recognised some years ago that envisaged container ships would need more than was available from existing RTA96C and RT-flex96C low-speed engines, a solution was found to extend the engine power range to 80,080 kW by offering also 13- and 14-cylinder engines.
The 14-cylinder RT-flex96C is thus based on an already well-established 12-cylinder RT-flex96C design, which itself was developed from the RTA96C engine type widely applied in container ships since 1998. It thus benefits from the wealth of service experience with engines of the same type. To date there are more than 300 RT-flex96C and RTA96C engines in service or on order worldwide.
Adaptation for 14 cylinders
Extensive consideration was nevertheless given to the practicality of the increased numbers of cylinders and to ensure that the engines match everyone’s expectations in terms of safety, reliability and durability.
With regard to the engine structure, the opportunity had already been taken when adapting the RTA96C engine type to accommodate the RT-flex common-rail system to introduce certain modifications in all cylinder numbers for better manufacture. These changes also resulted in greater stiffness and reduced stresses in the structure. The revision also took into account the 14-cylinder engines to ensure that they had adequate structural strength and rigidity without further modification.
The crankshaft of the RT-flex96C has sufficient torque capacity for 14 cylinders, the material having been upgraded to enable an increased shrink fit for a greater design margin. The thrust bearing structure in RT-flex96C engines with a mid-gear drive has been revised to reduce deformations and stresses even with the increased thrust in the 14-cylinder engine when the vessel is equipped with a shaft motor.
Wärtsilä RT-flex common-rail system
The fully electronically-controlled Wärtsilä RT-flex common-rail system of the 14-cylinder engine brings important benefits to shipowners. It gives unrivalled flexibility in the way the engines operate, resulting in smokeless operation at all operating speeds, lower fuel consumption, reduced maintenance costs and lower steady operating speeds for better manoeuvring. The RT-flex system also has the potential for adaptation to future needs.
A visual feature of the 14-cylinder RT-flex96C is the modest size of the compact supply unit compared with the overall dimensions of the engine, and the absence of the full-length camshaft usual in mechanically-controlled engines. The supply unit with its fuel and servo oil supply pumps is on the engine side, at the mid length on a mid gear drive. There are two identical rail units, each for seven cylinders, along the side of the cylinder tops.
High-efficiency waste heat recovery
An important feature of the first ship installation of the 14RT-flex96C is the high-efficiency waste heat recovery system. It contributes major savings in fuel consumption and reductions in exhaust gas emissions.
Exhaust gases of the ship’s main engine pass through an exhaust-gas economiser to generate steam for a turbine-driven generator. The turbogenerator set also includes an exhaust-gas power turbine driven by a portion of the exhaust gases diverted from the main flow through the engine’s turbochargers.
This high-efficiency waste heat recovery plant can provide an electrical output of up to about 12% of the main engine power. The generated electricity is supplied to the ship’s main switchboard and employed in a shaft motor to assist in ship propulsion. A portion of the steam from the exhaust economiser is utilised in shipboard heating services.
Energy recovery is maximised by adapting the engine to the lower air intake temperatures that are available by drawing intake air from outside the ship (ambient air) instead of from the ship’s engine room. The engine turbochargers are matched for the lower air intake temperatures thereby increasing the exhaust energy without affecting the air flow through the engine. There is thus no increase in the thermal loading of the engine and there is no adverse effect on engine reliability.
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Notes to the editor:
Wärtsilä enhances the business of its customers by providing them with complete lifecycle power solutions. When creating better and environmentally compatible technologies, Wärtsilä focuses on the marine and energy markets with products and solutions as well as services. Through innovative products and services, Wärtsilä sets out to be the most valued business partner of all its customers. This is achieved by the dedication of more than 12.000 professionals manning 130 Wärtsilä offices in over 60 countries around the world.