Multi-fuel and future-ready

New developments in fuel flexibility at the birthplace of the diesel engine.

Some are the size of an office block, and the smallest is the width of an index finger. They have been assembled in various wacky configurations; turned inside-out in an opposed piston engine; even a rotary one has been tried. To say the least, diesel engines are mature in 2023. Defying the usual expectations, it is ship engines which demonstrate some of the world’s most advanced technologies. A need to travel long distances between bunkering stops, and more liberal tolerances for weight and footprint, mean that ships can afford to support extremely sophisticated engines – though it is perhaps viewed in a less romantic aspect thanks to a focus on fuel efficiency, rather than speed, or noise.

MAN’s 49/60DF will burn methanol, LNG, marine diesel oil, HFO, and B40 biodiesel (Credit: MAN Energy Solutions)

For example, to great fanfare, computer-controlled valve timings have emerged in the automotive industry in the last few years through Freevalve AB, a project helmed by hypercar maker Koenigsegg. Freevalve controls valve timings using independent actuators, allowing them to stay open on close quickly depending on the driving condition. Though very much the preserve of supercars at present, Freevalve is hoping to filter down to more consumer-friendly models. 

In the maritime industry however, engines have been doing without cams for some time, and controlling valves and fuel injection via computer is practically old-hat. Recently though, MAN Energy Solutions released the 49/60 family of engines, which contain various updates including more advanced computer control, called Adaptive Combustion Control (ACC) 2.0, which the German machinery giant claims will make it the most fuel-flexible engine yet.

Cleaner and more efficient

MAN’s engine features updates to the common-rail injection system, now called the 2.2. This comprises a single length of reinforced piping, or rail, shared by all the fuel injectors. Keeping fuel pressure at 2,200 bar, a high-pressure pump coupled with computer-controlled injectors makes optimal fuel injection possible even at low loads -- something which, like Freevalve, would not be achievable with cams. This is crucial for reducing black carbon, also known as soot; a perennial problem for engines in the firing up stage, and during manoeuvring. “Please refer to our chimney – you will see there is no smoke,” said Stefan Terbeck, principal technical project manager at MAN, during a demonstration of a gas-only start demonstration of the 46/60DF.

Two-stage turbocharging has enabled ships to get huge efficiencies from their engines. In a configuration surprisingly reminiscent of shipping’s old steam piston engines, two-stage turbocharging features a small high-pressure turbine followed by a  larger low-pressure turbine, which can effectively double engine charge pressure. In early designs for MAN two-stage turbochargers, charge pressures reached around 6 bar. But a more compact and better-optimised design of two-stage turbocharger component on the 49/60 has now allowed this to increase to 10.5 bar. 

Not only is this useful for generating more power, it also works with the common rail system to optimise combustion. This has been particularly important when seeking to avoid the products of incomplete combustion, like NOx, which is more prevalent in diesel engines thanks to the high combustion heat. It also takes on a new degree of importance when burning LNG, which, if burned sub optimally, can result in emissions of unburned methane (methane slip).

Fuel flex

MAN boasts that the 49/60DF will be able to burn methanol, LNG (as well as its green variant bio-LNG and sometimes-green synthetic LNG), marine diesel oil, HFO, and B40 biodiesel. Being able to essentially control all aspects of what goes in and what comes out in a diesel engine’s combustion cycle makes it possible to address a huge number of potential problems with different future ship fuels, and during MAN’s programme of bench testing, the engine was frequently shown to have an efficiency exceeding 52%.

This means that the diesel has doubled in thermal efficiency in the 120 years since the Rudolf Diesel invention sharing its birthplace. It will be difficult to repeat this feat in the next century, as there are hard limits on the ability to convert heat into usable energy, beyond which even a nuclear reactor cannot go. But thanks to extraordinary strides made, it is difficult to imagine having abandoned the technology completely, a similar timespan into the future.

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Charlie Bartlett is a journalist specialising in maritime.