New fuels, targets drive efficiency gains in two-stroke turbocharger segment

Advances in turbocharging technology and machinery will continue to play an important part in the industry’s efforts to meet challenging upcoming IMO greenhouse gas emission and carbon intensity targets.

“Everything is about reducing emissions at the moment,” Imhof said as the industry is focusing relentlessly on meeting upcoming IMO greenhouse gas emission and carbon intensity targets. “The [relative reduction of carbon intensity by 40% compared with 2008] 2030 target is just around the corner.”

The impact of energy efficiency design index (EEDI) requirements was also increasing shipowners focus on fuel efficiency.

Advances in turbocharger efficiency

ABB Turbocharging had responded to shipowner requirements by reducing the footprint and increasing the power density of its products.

Imhof gave the example of the company’s A255-L and A260-L turbochargers to demonstrate how these advances offered a solution for shipowners operating vessels below 40,000 dwt.

The turbochargers offered a 2% improvement in turbocharger efficiency, and a 30% reduction in space requirements and 50% in weight, compared with the preceding generation of turbochargers.

These efficiency savings were significant in themselves. “We estimate that every 1 percentage point increase in turbocharger efficiency is equivalent to a fuel efficiency improvement of 0.35g/kWh.”

Dual-fuel engine demands

The high efficiency of ABB Turbocharging’s A255-L and A260-L solutions also offered combustion optimisation and higher efficiency advantages for engine designers developing solutions for LNG and other new fuels, Imhof said.

Operating Otto Cycle low-pressure dual-fuel engines efficiently at high loads introduces high requirements for efficiency in scavenging air pressure, Imhof noted. The air-fuel mix can make it challenging to maintain combustion stability and avoiding knocking or excessively fast combustion. High-efficiency turbochargers help overcome these issues while contributing to higher break mean effective pressure needed to achieve efficient high-load operation.

Imhof noted that a key engine designer of 400mm and 500mm bore low-pressure dual-fuel low speed engines specified a minimum turbocharging efficiency of 69% for turbocharging solutions. “With our A255-L and A260-L turbochargers, we could already meet those requirements. In fact, we have proven on an engine that we can fulfil these requirements,” Imhof said.

However, the turbochargers also meet requirements for increased efficiency at low and partial loads. “We have made an improvement to turbocharger efficiency when the vessel is operating in diesel mode, at low to medium loads.”

The applicability to dual-fuel engines is important as LNG remains the most likely alternative fuel to HSFO and IMO 2020 fuels at present. This is particularly the case in the two-stroke segment, where LNG is steadily gaining market share.

One potential area of development focus is the further reduction of emissions from low-pressure dual-fuel two-stroke engine solutions. On the engine side, improvements such as reduced crevice volumes, have already led to reductions in methane slip. A further reduction through technical improvements will follow in turbocharging as well as in engine design, Imhof noted.

“A high turbocharging efficiency can ensure a high lambda is maintained in high-load operation, under any condition, thus minimizing the potential for fast combustion,” he explained. “As such, turbocharging can facilitate engine efficiency improvements, by supporting higher mean effective pressure. An improved engine efficiency directly reduces total GHG emissions.”

Looking ahead, Imhof stressed that the technological limits of single-stage turbocharging for two-stroke engines had not yet been reached.

“Turbocharger development is far from plateauing. We expect to see major steps in turbocharger technology for two-strokes in the coming years.”

Wider solutions

From a broader perspective, improving the overall efficiency of turbomachinery is just a part of one of three main routes to reducing greenhouse gas emission: power conversion technology improvements, hydrodynamic advances and better fleet utilisation.

Across all these routes, digital solutions are likely to play a role. ABB Turbocharging’s engine optimisation platform ABB Ability™ Tekomar XPERT is already well established and recent digital advances have focused on turbocharger service.

“These solutions include offering data-led intermediate inspections and introducing a fixed price for customers for complete overhaul at dry dock,” Imhof noted. These offerings represent a major step towards reducing lifecycle costs and enhanced ease of service.