Wärtsilä’s engine for the future

Robert Ollus: The Wärtsilä 31 features the technologies of the future
Robert Ollus: The Wärtsilä 31 features the technologies of the future
Designed for a multi-fuelled, hybrid-powered, digital age: The record-breaking Wärtsilä 31
Designed for a multi-fuelled, hybrid-powered, digital age: The record-breaking Wärtsilä 31

After developing a cutting-edge medium-speed platform, Finnish technology company Wärtsilä refuses to let unfortunate timing scupper the launch of its latest engine range. Gavin Lipsith reports from Vaasa.

Unveiled in June 2015 – just as the oil and gas sector stepped off a cliff – the Wärtsilä 31 has since garnered just six marine orders, for a total of nine engines. Given that the engine was designed primarily for the offshore market, the slow progress is not surprising and has done little to dent the company’s belief in its new product. As the market begins to  show signs of improvement, Wärtsilä hopes that increasing project numbers will translate into more encouraging order levels.

The development project behind Wärtsilä 31 transcends industry trends. As Robert Ollus, product manager for the series, explains: "The Wärtsilä 31 features the technologies of the future, which will also be used in our upcoming engines. It’s not just the two-stage turbocharging, or the increased capacity of the automation system, or the design of the engine block, combustion chamber, cylinder heads and bearings. It’s all of these coming together that we believe makes the 31 - and others to come - winners.”

The engine design is future-facing in many ways. Most notable is fuel flexibility. The engine is available as diesel, dual-fuel (LNG and diesel) or spark-ignited, pure gas versions - although the latter has yet to be released for marine applications. While Wärtsilä engineers note that the short life of spark plugs remains a challenge for pure-gas engines – particularly in marine applications with highly variable loads – the company is poised to offer the engines when demand emerges.

Patrik Wägar, product director, engines, says: “We are ready to supply spark-ignited engines. The question is when the market wants it. There has not yet been demand: it might be that LNG infrastructure has not been fully applied, or that people want to keep fuel strategies open - dual-fuel has been an obvious choice and will continue to be. But we can make it available.”

Fuel flexibility

Unusually, the Wärtsilä 31 features the same cylinder dimensions regardless of whether gas or diesel is used. This feature simplifies both construction and, should it be required, conversion of the engine. Conversion is further simplified by the modular construction of the engine – only the fuel injection piping (the common rail system) and piston crowns need be switched in the event of a retrofit. The fuel injection technology in the cylinder head remains the same for diesel and gas.

The Wärtsilä 31 holds the Guinness World Record for the world’s most efficient four-stroke engine, reaching an engine efficiency of more than 50%. This efficiency is the result of some key technologies, perhaps the most significant of which is two-stage turbocharging. This was a pre-requisite to the design of the new engine.

Ollus explains: “Modern turbochargers have a charging pressure ratio of six. Going down to simpler technology you can easily get a compression ratio of three. With two stages, that means a compression ratio of nine – we can get more boost using simpler technology by applying a low-pressure charger to feed a high-pressure charger.”

That extra boost, and the pressures it enables through the engine, are one reason why Wärtsilä had to redesign the engine block from scratch rather than using a similar base to its 32 and 34 ranges. Greater strength and stability was needed in the base to handle the power of the new engine.

Strong foundations

“Perhaps the optimum would have been to further develop the 32 and 34, which are excellent engines,” says Ollus. “But at some point, you need to make sure you that you have the reliability in the foundation to handle the bearing load stress and stress concentration. That’s the reason the 31 has different space between cylinders and bearing width.”

Two-stage turbocharging also gives room for manoeuvre when it comes to valve timings – allowing Wärtsilä to employ Miller timings on the inlet valve to improve efficiency. In this, the engine is aided by advances in common rail fuel injection and valve control. The common rail system enables greater control over the timing of fuel injection, while variable valve control (on both exhaust and inlet valves) means that users have even greater flexibility to meet their operational parameters.

Lars Anderson, vice president, four-stroke sales, explains that beyond a core audience of cruise/ferry and offshore vessels, this flexibility will make the engine attractive to specialist vessels including tugboats, construction vessels, dredgers and heavy lift ships. “These vessels often have requirements related to tough ambient conditions – extreme cold in the Arctic for example – or for load acceptance or load ramps,” he says. “The new features – two-stage turbocharging, digital fuel injection and variable valve timing – combined with improved automation give you great freedom to tune for any kind of installation.”

The UNIC automation system has been enhanced for the Wärtsilä 31 and the range of functions extended: Ollus lists a range of programmes including air-fuel ratio control, thermal management, start-stop management, knock control, valve control and ignition control. A self-tuning function means that operators can set a certain allowance for variance in cylinder pressure, enabling them to operate in a tighter window.

Updated automation

“The worst thing for reliability and availability is lack of capacity in your automation system,” says Ollus. “Our automation is much more robust, with increased data management and system capability. It is well adapted for the digital age and built for hybrid solutions.”

One hybrid solution is already being employed on one of four Wärtsilä 31 test engines running at the company’s headquarters in Vaasa: A 10 cylinder, dual-fuel engine is being tested with a permanent magnet shaft generator. “It’s a very short, compact engine and well suited for hybrid arrangements,” explains Ollus.

The automation system also has a role to play in the service and maintenance of the engine. For example, when one engine module is replaced there is no need to manually adjust many parameters – the new part can learn them from neighbouring modules. This contributes to what Ollus claims is a 50% reduction in maintenance compared with similar engines on the market today: Time between overhauls for pistons and cylinder heads is stated as 32,000 running hours – 60% longer than the best available counterparts.

Improved serviceability is supported by other component developments. One example is a cooling oil injection concept which means that oil doesn’t need to be piped through the connecting rod.

“The oil comes through the crankshaft up to the big end bearing,” explains Ollus. “This is the best for bearing behaviour because there are no grooves – there is a smooth surface for maximum time between overhauls. A lot of these details might not be seen but we think they will be visible in ship operators’ performance in the long term.”

In-house validation

The company is nearing 50,000 hours of running on the test engines and components – Wärtsilä has never done so much in-house validation on an engine range before, says Ollus. “So far components – pistons, liners, pumps and bearings – are looking great,” he adds.

The business case remains to be proven in the field – the first marine engines have been delivered but are not yet in service – but are encouraging on paper. Ollus suggests that the engine can perform at an average of 9g/kWh better than its predecessor engines.

Anderson uses the example of a 17MW ferry application to compare the 31 against the older (but still modern) 38 engine. “We can save 5% off the fuel bill - easily US$150,000 for a ferry of that size - and a further 20% off the maintenance bill thanks to longer intervals,” he says.

The company clearly believes that the Wärtsilä 31 sets a new benchmark for modern medium-speed engines. Ollus notes that the engine will be joined by a ‘bigger brother and smaller sister’ in due course, while technologies developed for the 31 will also be deployed in other Wärtsilä engines. It is a range that has been many years in the making, and one that is set to define Wärtsilä’s engine building business for years to come.

Wärtsilä 31 specifications



Spark-ignited gas

Cylinder bore (mm)


Piston stroke (mm)


Speed (rpm)


Cylinder output (kWh)




Bmep (bar)




Cylinders (no)

8, 10, 12, 14, 16, 20 (v-line only)

Wärtsilä 31 orderbook (as of June 2017)


Vessel type



FSUE Atomflot



3 x W8V31

Mols Linien



2 x W8V31

Peter Hepsö Rederi

Purse Seiner


1 x W8V31

Strand Senior

Purse Seiner


1 x W8V31

Research Fishing Co



1 x W12V31


Fishing Vessel


1 x W10V31



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