Wärtsilä move widens choice in mid-size engine market

31 Oct 2011
The new-generation Wärtsilä 620mm-bore engine, in seven-cylinder configuration

The new-generation Wärtsilä 620mm-bore engine, in seven-cylinder configuration

Through a major initiative to swell its range of low-speed, two-stroke marine diesels, Wärtsilä is set to provide owners, shipyards and designers with greater choice in the mid-size engine category, writes David Tinsley.

The planned introduction of new designs in the 620mm and 720mm cylinder bore sizes will intensify competition with arch-rival MAN, whose portfolio includes a broad and flexible offering in the 600mm-700mm-bore segment of the business. Common to both nascent types will be electronically-controlled common rail technology.

The new prime movers will cater to a wide swath of the mercantile fleet. The 620mm-bore engine has been designated the Wärtsilä X62, and is mainly intended for Panamax and Kamsarmax bulk carriers, the smaller types of Capesize bulker, Aframax tankers and also handysize containerships. The 720mm-bore design, to be known as the X72, will be suited to Capesize bulkers, Suezmax tankers, Panamax and sub-Panamax boxships. IMO Tier 2-compatible at launch, the new engines will be available with an SCR catalyst to meet Tier 3I NOx criteria.

Due to be available for delivery from September 2013 onwards, the 620mm-bore X62 diesel has a piston stroke of 2658mm, and will cover applications in the 8,000kW to 21,280kW band at running speeds of 80rpm to 103rpm. It is claimed to be the most compact engine in its speed class, incorporating limited physical width so as to help facilitate slimmer aft vessel design, in the interests of hydrodynamic efficiency.

The first examples of the 720mm-bore design are expected to be rolled-out approximately one year after the X62, and the various cylinder configurations make for maximum continuous ratings in the 14,440kW to 28,880kW range. Like the X62, it will offer scope for derating to meet specific requirements.

Testament to the fundamental and undiminished importance to the Finnish group of its two-stroke technology resources in Switzerland, rooted in the 1997 assimilation of New Sulzer Diesel, development work on the new engines is being undertaken at Wärtsilä’s low-speed competence centre in Winterthur. Input from licensees in Asia will ensure that the designs reflect the latest production requirements and associated know-how.

Both series of engines will be released in four-, five-, six-, seven- and eight-cylinder configurations, and will resume a Wärtsilä production presence in the 620mm- and 720mm-bore sizes previously vested in the Sulzer RTA62U-B and RTA72U-B types. The new, more powerful and more efficient X62 engine will yield 2,660kW/cylinder at 97/103 rpm. The 720mm-bore design will be rated for 3,610kW/cyl at 84-89 rpm. Wärtsilä anticipates a fuel consumption rate of 167-168g/kWh at 100% load for both series.

Besides the efficiency advantages conferred by the derating possibilities, one of the most significant features of the new generation of mid-size engines is the extended layout field, to the R1+ rating. This confers greater flexibility in selecting the most efficient propeller speed for the lowest daily fuel consumption according to specific vessel type and propeller diameter. The new engines will accordingly be equally suitable as installations in containerships as in bulkers and tankers. The concept was first applied successfully to the current family of 820mm-bore designs.

In the latest Wärtsilä catalogue, the engine models closest in bore size to the upcoming generation of 620mm and 720mm designs are the IMO Tier 2I-compatible RT-flex60C and RT-flex68/RTA68 types.

The 600mm-bore RT-flex60C, crafted for the economical propulsion of smaller container vessels and feederships, delivers a maximum 2,420kW/cyl at 114rpm, covering the 12,100kW to 21,760kW power band at the R1 rating. The 680mm-bore RT-flex68/RTA68 series has been developed for tankers and bulkers from about 20,000dwt up to Capesize and Suezmax applications, and produces 3,130kW/cyl at 95rpm. This results in a maximum power range of 15,650kW to 25,040kW at R1 MCR across the various configurations.

The current MAN offering in the 600-700mm-bore category is substantial, and has this year been augmented by the 2,680kW/cyl G60ME-C9 type and 3,640kW/cyl G70ME-C9 design.

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