Two new turbochargers have been designed to push performance limits in response to shipowners’ operating demands
Changes in the design focus at ABB Turbocharging over the past decade offer an interesting perspective of how shipowner needs have shifted in that time. And its latest launches show where the company believes shipping is headed. Perhaps not surprisingly, getting more power from less steel – as opposed to more power whatever the size – remains the focus.
When the group launched its A100-L for two-stroke engines in 2009, the product was designed to address an industry-wide increase in sailing speeds that had been triggered by cheap fuel. The demand was for greater engine power, which meant higher pressure ratios were needed from turbochargers, as more air crammed into the same cylinder offers better combustion. The A100-L duly met that demand with a pressure ratio of 5.0 and a turbocharger efficiency of 75%.
By 2013, shipping’s needs had changed. Higher fuel prices led to the introduction of slow steaming. Power was no longer the priority and engines were being de-rated to improve fuel economy. For fuel efficiency, one of the biggest design demands on turbochargers is increasing air flow volume, meaning that smaller units can meet the intake air demands of bigger cylinders, or the same engine needs smaller turbochargers.
The A200 series was introduced in 2013 as a response to slow steaming, explains ABB Turbocharging head of global sales low-speed turbochargers Alexandros Karamitsos. A higher volume flow contributed to fuel efficiency, as opposed to the higher-pressure ratios and power outputs sought by the earlier A100 versions.
ABB Turbocharging’s A255-L and A260-L, unveiled at CIMAC World Congress, build on the turbocharger platform first developed in 2009 with the A100 model. While the design approach has been adapted to reflect ship operation trends, the focus on improving power density has remained a steady focus for all turbocharger companies. This contributes to the Energy Efficiency Design Index – allowing more power to be squeezed from smaller engines – and offers greater flexibility in engineroom design.
High turbocharging efficiency has been retained while size, weight and service costs have been cut. While the A165-L cut service costs by 10% and weight by 28% compared to the previous TPL73-B model (launched in 1999), the A255 and A260 reduce service costs by 30% and weight by 50%.
Mr Karamitsos says: “Further focus will be placed on turbocharger efficiency in the future, alongside higher compressor pressure ratio demands, to enable two-stroke engines to reach their full potential. Our new turbochargers will deliver the highest levels of turbocharger efficiency and power density while enabling small-bore two-stroke engines to achieve lower fuel consumption and comply with emissions regulations.”
"Fuel diversity is interesting [as] you need high pressure ratios and turbocharger efficiency even more if you are using gas"
The two new frame sizes are suitable for two-stroke engines typically used on vessels up to 10,000-40,000 dwt including bulk carriers, tankers, container feeders and car carriers. They can be used with either diesel or dual-fuel engines, and in conjunction with NOx or SOx aftertreatment.
A range of matching components will be available to fit specific enginebuilder requirements and the new units fit into ABB Turbocharging’s ‘drydock-to-drydock’ service approach, which aims to minimise intermediate turbocharger inspection between overhauls.
If the demand for power density – as Mr Karamitsos describes it “more power from less steel” – is one defining trend for today’s two-stroke engines, another is the emergence of gas fuels. So the launch of a turbocharger designed for the biggest segment to take up gas fuels – high-speed, lean-burn engines – is a sensible move.
According to ABB Turbocharging managing director Oliver Riemenschneider, gas engines demand more from turbochargers, giving the company an opportunity to test its performance limits.
“Fuel diversity is interesting for us,” he says. “You need high-pressure ratios and turbocharger efficiency even more if you are using gas. The sensitivity of LNG to temperature and humidity for example, means that you need a more stable combustion, which pressure and efficiency help maintain.”
ABB Turbocharging is preparing to launch a further development of its A100-H turbocharger. While that product has met the demands of gas engines operating at a brake mean effective pressure (bmep) of 22 bar, there are some engines that require a higher range but do not need the pressures that two-stage turbocharging can provide.
When it is launched (before late 2021) the A200-H will push single-stage turbocharging pressure ratios up to 6.5, while maintaining high turbocharging efficiency of more than 69% – 3% more than the A100-H.
According to ABB Turbocharging general manager for high-speed sales Gerald Müller, compressor technology is a critical element in this design. ABB aimed for a wide compressor map – 70% wider than the A100-H – to ensure surge margins and allow stable engine operation on gas. There is also a new turbine stage developed to enable the compressor to be driven to the levels required to achieve high-pressure ratios.
Improving maintenance has remained a priority for the new products. The A200-H series will use sensors and engine data to offer life assessments and maintenance recommendations to operators. Online analysis will allow assessment of the shaft and rotor components at every inspection interval. This will mean that, subject to condition, rotor lifetime can be extended rather than the more rigid, time-based replacement of parts.
Given the timing of its launch, the A200-H series is likely to benefit from recent investments in digitalisation. Last year the company launched Digital SIKO, an advisory system that uses operational data to predict the remaining lifetime of rotating parts.
Mr Riemenschneider explains: “Cloud-to-cloud data exchange provides us with the operational database. Combining that with visual inspection in the workshop we can recommend whether the components are good until another drydock or need to be exchanged.”
So far, the company is tracking its products on seven vessels using the cloud-to-cloud exchange and the system will become part of its standard offering for two-stroke engines. Mr Reimenschneider confirms that the company will develop a digital monitoring system for its four-stoke turbochargers by next year. Monitoring four-stroke units is more complex because of those engines’ higher temperatures and more varied operating requirements, he explains.
The A200-H will be offered in three frame sizes: A230-H, A235-H and A240-H. Two rotor sizes will be available for each frame, along with matching components, to allow a wide range of volume flows within each frame. Both rotors use a standard bearing housing arrangement and customers will have the choice of two bearing concepts for the same turbocharger. An ABB-patented bearing module design supports robust plain bearings, but a newly developed ball bearing system is also available. This offers increased mechanical efficiency, particularly at part load.
This reduction enables more rapid turbocharger and engine start times to be achieved. Both bearing types operate with standard engine oil, but oil consumption is lower for the ball bearing system. Upgrading to the ball bearing system can also be carried out with module exchange, with no other changes required.
The first pre-series prototypes will be tested in Q4 2019. It is just one example of how, as shipping prepares to enter unchartered territory regarding its fuels, ABB is pushing its own boundaries to make engines ready for the challenge.