Three steps to turbocharge shipping’s efficiency

As I research this year’s World Turbocharger Guide, there is a sense of urgency among technology companies. With energy efficiency rising ever higher on shipping’s agenda, one interviewee talked of an approaching “golden age” when turbochargers will be critical to meeting the industry’s emission targets. Three factors stand out as most likely to influence their future development.

Two-stage turbocharging is already making an impact on the marine four-stroke market, offering dramatic upgrades in efficiency to modern engines. But to date the technology – which uses low-pressure and then high-pressure turbocharging stages to deliver charge air to cylinders at much higher pressures – has not been deployed on two-stroke engines. That is due the different air outlet/inlet configurations that mean efficiency gains are not inherently of the same scale as for four-stroke engines.

There is a difference of opinion emerging as to whether two-stroke engines will ever be able to take advantage of two-stage turbocharging. On the one hand advocates argue that the energy efficiency demanded by new regulations, particularly IMO’s greenhouse gas emission reduction targets, will make the substantial engine redesigns required economically viable. They also point to the improving power density of modern turbochargers, which will reduce the scale of these changes.

On the other hand, opponents say that the cost and scale of such adaptions will negate any gains and that other efficiency steps will always be more cost effective. But given the demands that will soon be placed on shipping to reduce greenhouse gas emissions, turbochargers will have to find efficiency gains from somewhere. If two-stage turbocharging is not a solution, an entirely new approach will be needed.

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The answer, for some vessels, may lie in harnessing electrical power. The usefulness of starting turbochargers with a motor rather than a blower has been debated since long before Rolls-Royce acquired an electric starter patent in 2017. So far, the majority view has been that the size of turbochargers deployed in shipping would have too high an energy demand to make electrical starting worthwhile. That may change as more ships use energy storage, as turbocharger power density improves and as turbochargers themselves are harnessed for electricity generation – an innovation under investigation by more than one major turbocharger manufacturer.

Another major shift is likely to emerge in how turbochargers are integrated with engine auxiliaries. Turbochargers are central to the engine air system. As emissions regulations demand aftertreatment in many cases, the engine’s air supply and exhaust system is becoming increasingly complex. When targeting NOx emissions for example, turbocharger operation must be adapted to accommodate exhaust gas recirculation of selective catalytic reduction. A more integrated or holistic approach to designing the wider engine air management system could offer big benefits both to shipyards by reducing installation complexity, and to shipowners by simplifying operations and squeezing out extra efficiency.

There will be many other influences on the evolution of turbochargers including alternative fuels, new materials and the shifting practices of ship operators. But the adoption of multi-stage turbocharging, hybrid technologies and integrated air management will be critical as developments are driven by stricter energy efficiency requirements.