Turbocharger technology is helping new engines and fuels meet stringent environmental performance requirements
As engines and fuels develop to meet strict new environmental demands, the impact on turbocharger technology will be pronounced. There is a growing push to extract more power from smaller units, with lower noise and emissions; turbochargers will play a key role in achieving these goals. But as a panel of industry experts explained during a recent Riviera Maritime Media webinar, the current lack of clarity over future fuel types and availability is adding to the challenge of extracting greater performance from marine turbochargers.
“If you look at the development needs of engines over the next five years, there will be a shift towards increased power density and lower emissions,” explained GasKraft Engineering owner Professor Dr Hinrich Mohr.
These units will also need to demonstrate high fuel flexibility and be able to operate on fuel types ranging from high-sulphur heavy fuel and methanol, all the way up to urea. Hybrid systems will place greater demands on four-strokes, with increased start/stop and power take-off/power take-in (PTO/PTI) requirements. Exhaust aftertreatment equipment will also need to be integrated and optimised.
Dr Mohr said exhaust gas aftertreatment would lead to increased exhaust back pressure and noted that as hybrid systems are integrated into vessels, even existing engines will need to deal with increased operational demands. “For NOx reduction, exhaust gases might be recirculated, passing through the compressor and the speed profile will see high fluctuations because of engine start/stop using hybrid systems,” he said.
With this in mind, he said turbochargers must evolve to cope with the growing demands of smaller engine units. “Higher boost pressure will be needed as the engine inlet time slot will be reduced – a result of Miller timing. This will reduce NOx emissions and decrease knock tendency,” he added.
Complexity outweighs benefits?
How then will turbocharger manufacturers adapt their technology to cope with these growing demands? KBB Turbochargers key account manager Florian Hermann explained that while three-stage turbocharging remains a somewhat distant goal, existing single- and two-stage units still have scope for performance-related development. “For single-stage turbocharging, we currently require a ratio of about 5.5-1; seven years ago the mean value of our matched, single-stage turbocharging was about 4.7-1. For two-stage turbocharging the ratio is now above 10.”
In many instances, it is the application of the technology that determines the operating profile. As Dr Mohr noted “If you are operating a lot in part load, then two-stage turbocharging might not make sense. But if you operate on really high loads or constant high loads, then two-stage turbocharging might be helpful.” He also pointed to the advantages of two-stage turbocharging when engines are required to peak up to high loads often and quickly, explaining “Two-stage turbocharging with smaller turbochargers instead of one big one might be positive in terms of reaction time.”
Returning to the subject of the ever-growing demands placed on turbochargers, Mr Hermann explained that at present, for dual-fuel engines and dual-fuel turbocharger compressors, the highest power output still comes from diesel mode, which results in higher air flow rates and the highest pressure rates.
“Those effects are challenging turbochargers,” he said. “There is an effect on the compressor wheel, which is responsible for offering the pressure ratio and the flow rate and on the turbine. Both the compressor housing and the turbine housing have a major impact on the flow rate. And if we are talking about higher pressure ratios, there is also more heat which must be extracted from the turbocharger, requiring improved turbine management.”
Mr Hermann also flagged the issue of sealant damage around the shaft. “The shaft sealing is the only sealing between the exhaust gases, the pressure gases and the engine oil, so there is always a high risk of contamination. Further, if you have a high-pressure ratio and high flow rate, it can result in more torque being introduced in the shaft bearing system, which must also be factored into turbocharger designs.”
But Mr Hermann explained that too often, significant alterations and improvements in turbocharger technology were considered as mere ‘updates’ among end users. “The outline dimensions are the same; the maintenance is the same; it even looks the same. Customers struggle to understand the advances we have introduced.”
By way of example, Mr Hermann compared the KBB ST27 unit to the new ST27-EP turbochargers. “If we compare the standard map with the EP map there is an increased pressure ratio, from 5.5 to 6. We can also extend the range of maximum efficiency to introduce a higher pressure ratio, which pays off in terms of fuel consumption.”
And for emissions, he noted “We can optimise and reduce the weight and inertia of the rotor, which is crucial to reducing emissions and black smoke.”
But he warned these developments also result in more complexity and increased maintenance, which could impact the independence of third-party providers and required the ’empowerment’ and understanding of suppliers and customers. “We are currently developing next-generation two-stage turbocharging and I could imagine three-stage turbocharging might be a solution for a limited application range.” But he suggested such developments required so much additional maintenance and costs that their roll-out would remain limited for many years to come. “The main market will remain single-stage turbocharging, but demand for two-stage turbocharging will grow, particularly for stationary engines because those engines are normally running on the same or similar high load profile where two-stage turbocharging really pays off.”
Balancing cost and efficiency
End-user requirements will dictate the pace and direction of any technology that is likely to remain on board a vessel for years, if not decades, to come. Tufton Asset Management Cyprus fleet efficiency and project manager Paul Morgan was keen to stress the importance of keeping the customer front and centre of mind.
“When we discuss multi-stage turbocharging for example, we are looking at a huge amount of time and energy going into development,” he said. “As an operator, I am looking at anything that is going to increase the efficiency of the engine, but there is also the issue of cost, maintenance and spares. For me, the benefits of this new technology in terms of efficiency must be balanced alongside the additional cost of employing it.”
Mr Morgan also queried whether the technology being developed now would be of any use to operators of older vessels, asking “Is this something only for modern engines, or is it applicable to all the 15- and 20-year-old vessels out there?”
KBB’s Mr Hermann offered an OEM take on this point. “We have to individually look at the engines because we receive a lot of enquiries for retrofits and it may be possible to compare an old turbocharger and replace it with a newer one. But you have to be careful because the compressor map will likely have a different shape, the pressure ratio will be higher and there is always the danger of damaging the engine with this approach.” As such, he explained “There is still a reason to keep standard turbocharged products in your portfolio.”
“In LNG we have very clean combustion; this is where we must head with all fuels”
Turning to the ever-present concern over fuel type and availability, the panel considered the impact of new blends, biofuels and LNG on turbocharger functionality.
“We supply a lot of turbochargers to stationary engines which are often run with biofuels and we have detected a glazing which affects the turbine housing,” said Mr Hermann. “If the fuel quality is very bad, it can also affect the shaft sealing, but in general this effect is quite low compared to [running] heavy fuel oil,” he added.
Citing LNG as a reference, Dr Mohr said “In LNG we have a very clean combustion and this is where we must head with all fuels, from methanol to urea, which is a carrier for hydrogen.”
But he questioned whether such fuels provided adequate combustion efficiency. “Do we have enough energy in the exhaust to drive the turbochargers? If you do not produce enough energy on turbine side, then you have a lack of air on the suction side. So we need a new thermodynamic arrangement for some of these fuels.”
Mr Hermann noted that compared to heavy fuel oil, LNG should result in less contamination in terms of turbine washing and oil leakage due to carbonisation. This can only be good news for operators, as reduced contamination should lead to less downtime for repairs and servicing, but it remains a concern as Mr Morgan noted, “We operate mainly mid to old tonnage and one of my biggest challenges in relation to the engines and the turbochargers is the quality of, and uncertainty over, the fuels that we are using.”
He went on to say the current crop of VLSFO is resulting in considerable fouling on the turbine side and some failures. “It is my opinion that this is down to low-sulphur fuels; the engines were not built to manage these fuels.”
It was a view that piqued the interest of Dr Mohr, who said “I have not seen this effect much in recent months, but it is interesting and clearly related to changing fuel compositions. When we change from high-sulphur heavy fuel oil to low-sulphur heavy fuel oil, we might have a lot of paraffins inside and this might cause this effect.” But he added “If we go for low-sulphur fuels independent of HFO, the combustion should be cleaner and should result in less fouling.”
Regulation drives development
With so much impacting the turbocharger sector – from hybrid engines to emissions, to fuel type – it is almost impossible to determine how the sector might evolve over the next five, let alone 25, years. But the webinar participants were unanimous in their belief that regulation, more than any other factor, would drive the direction of development.
“There is no doubt that [development] is going to be emissions-led and based on the availability of fuel and fuel type,” said Mr Morgan. But he warned that such developments must not render current vessels obsolete. “As an operator with older vessels in my fleet it comes down to maintenance costs and reliability. There are a lot of new vessels being built, but there are a lot more vessels already in service and we have a lot of vessels that we need to maintain.”
But as Dr Mohr concluded, there is already a clear goal in place from IMO to reduce CO2 emissions by 70% by 2050. With this in mind, he said “I believe turbocharger performance will therefore be key to engine development over the next two decades.”
Watch the Marine Turbochargers OEM Forum Webinar in our webinar library