Marine engine-builders could employ the simulation tools used by use Formula One racing teams to develop and improve hard-working componentry
The buzzword in engine development these days is ‘virtual validation’. As the shipping industry, especially the high-speed sector, insists on diesel-powered engines that are faster, stronger, greener and ever more fuel-efficient, manufacturers are resorting to virtual – or simulation – technologies to develop, test and validate these increasingly advanced new power plants.
This is the approach taken by Liebherr Components in the case of its latest cylinder heads, by any measure vital elements in today’s crop of robust and durable engines. In a paper entitled Cylinder head development for high-speed diesel engines - methodology and challenges, Dr Bechir Mokdad of Liebherr Components’ mechanical simulation department told the International Council of Combustion Engines (Cimac) conference in Vancouver in June that “developing highly loaded internal combustion engines working on the edge of physical limits is an increasing demand of the market.”
He went on to cite all those things that shipowners have come to expect from engine suppliers – “low fuel consumption, high power density to fulfil emission legislation, long life of optimised components and, last but not least, reduced time to market.” Abbreviated work-up periods are particularly important in pricing – the faster the power plant can be developed, the less it will cost.
Hence, the adoption of virtual validation, which is used as standard in the design of Formula One (F1) racing cars and is being widely adopted in the oil and gas industry as a fast-track method for building giant structures, such as floating production storage and offloading vessels (FPSOs). But as Dr. Mokdad explains, the science of simulation applies equally well to a relatively small, if vital, component like a cylinder head.
A lot is asked of a cylinder head, especially in a marine engine. It must withstand great heat and constant mechanical stresses, including bolted connections, while also maintaining combustion and peak firing pressure. And that, as Liebherr’s engineer explains, is just the start: “The head has also to ensure cooling of its components like exhaust ports and injectors [while] routing air and exhaust gases in and out from the main engine body with minimum pumping losses and optimised flux motion.”
Most enginerooms take the reliability of cylinder heads for granted, but their development follows a multi-stage, normally time-consuming process. First, the component’s thermal boundary conditions are defined – that is, the temperatures it must withstand. Then the cylinder head is introduced into its working environment, which requires detailed analysis of the distribution of stress.
Next, assessments are performed on the component’s thermomechanical and high-cycle fatigue, the latter being particularly important in fast ferries or naval vessels. Along the way other residual stresses relating to the casting process and eventual heat treatments must be calculated, so that the integrity of the component can be guaranteed when under heavy load.
This is where an automated and simulated workflow can shave months and even years off the development process. Not only that, virtual validation provides engineers with more certainty about the integrity of the final product. Until simulated design was adopted, they felt obliged to be more conservative, leading to the over-building of components.
As Dr. Mokdad notes: “Traditionally, the simulation of the cylinder head relied on comfortable safety margins due to a lack of knowledge of numerous aspects such as loading mechanisms, materials properties, manufacturing processes etc. [But now] optimised designs and performances of mechanical components have been increasingly required.”
In short, engineers can proceed with the confidence that they can push the design further.
Along its simulation journey, Liebherr has also found that virtual validation and associated tools make it easier for engine manufacturers to fine-tune existing cylinder heads, as well develop other engine components such as turbochargers and pistons.
So what exactly are these virtual tools? Liebherr typically uses state-of-the-art finite element analysis for the structural and thermal work, and computational fluid dynamics – a standard tool in the F1 industry – for the calculation of fluid and gas exchange.
After-treatment for the future
In anticipation of the 2020 sulphur cap, a research and survey vessel in the North Sea has been field-testing MAN Energy Solutions’ latest scrubber, the SCR-LPH. Finally, after 5,000 operating hours in which the vessel satisfactorily met the IMO’s Tier 3 standards, it was decided to put the after-treatment system on the market, both for new builds and as a retrofit for existing vessels. That decision followed a series of rigorous runs on MAN’s test bed in Fredrikshavn, Denmark, followed by type approval by all major classification societies that came in late 2018.
The company is now booking sales of the scrubber, which is purpose-designed for its 175D family of high-performing engines. Parallel with the development of the engines first released in 2016, the exhaust after-treatment system is a future-proofed technology that, explains Thomas Seidl, head of the high-speed product line, is capable of fulfilling the IMO’s imminent Tier 3 emission limits as well as covering tougher regulations, such as for diesel particulate filters.
“In contrast to other state-of-the-art, selective catalytic reduction (SCR) systems, it consists of multiple smaller reactors, which can be mounted vertically or horizontally in the engineroom as close as 2 m apart from the engine, or dozens of metres apart in the stack,” he told the Cimac conference in a paper called MAN 175D – high-speed engine family.
Labelled MAN SCR-LPH (for low pressure, high speed), the fundamental principle behind the system is that it should cope with everything thrown at it, from regulations to customer requirements. “This gives the customer maximum flexibility regarding the integration of the after-treatment system into the vessel design,” he added. “MAN’s closed-loop SCR control is used to ensure the desired emissions regardless of the ambient condition, the fuel type or the case of operation.”
In a departure from normal practice, the system’s designers looked at the automotive sector, in which MAN has considerable experience and know-how, and opted to base it on that industry’s components, rather than carry over parts from the medium-speed sector. “The boundary conditions of a high-speed marine engine …. allow for the use of more sophisticated catalyst technologies as well as the implementation of after-treatment technologies known from on-road application,s such as diesel particulate filter technologies,” he explained.
The engineers were aiming to use standard components that allow the system to be scaled up relatively effortlessly. In the same vein, the design team also went for as compact a system as possible, fundamental in the quest for flexibility. “The SCR system covers the demands of high-speed markets such as tug boats, yachts and industrial applications,” says Mr. Seidl. “Compared to its big brother, the MAN SCR-LPC, the high-speed system turns out as the most compact of all [our after-treatment] systems.”
Looking to the future, the system can be fine-tuned to cope with new regulations and fuels. “Due to fuel being restricted to clean distillate fuels such as DMA (marine gas oil) and EN590 (an EU standard), the pitch of the SCR catalyst can be increased to finer mesh sizes, leading to smaller catalyst volume,” MAN’s engineer adds.