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Is it 'game over' for the diesel engine?

The diesel engine has become a highly efficient power source – but how much further does it have to go? Dr Staffan Lundgren discusses the engine’s development and what its future may look like.

Despite being developed continuously over the 20th century to become a highly fuel-efficient power unit, the diesel engine is now considered by some to be in danger of becoming obsolete.

However, there is someone who is more optimistic about the engine’s longevity and its ability to continue as a cost-efficient solution for creating mechanical energy: Dr Staffan Lundgren, who is a lead strategist at the Volvo Group, in Gothenburg, Sweden.

He has worked in the automotive industry, principally for the Volvo group of companies, for more than three decades, specialising in evaluating new technologies for the future of propulsion, including highly efficient diesel engine technology.

“The diesel engine has a theoretical system efficiency of between 55 and 60 per cent,” Lundgren said. “For reference, the best power stations operate at 50 to 55 per cent efficiency, and fuel cells are also around 50- plus per cent efficient – so diesel engines can be incredibly efficient.”

He says the reason diesel has remained such a popular power source globally is because its diffusion combustion – where the combustion is concentrated around the ignition and oxygen is diffused around the combustion area – is very efficient.

"Making diesel engines very clean is possible and that is something the heavy-duty industry has made greater progress on than the light-duty sector"
Dr Staffan Lundgren, lead strategist at the Volvo Group

“It has minimal energy losses to the walls of the engine through radiation or convection – much lower than a gasoline engine,” Lundgren said. “The basic diesel engine is very strong and can withstand very high pressures.”

In terms of its efficiency, he said there had been big improvements over the diesel engine’s journey – ranging from about 35 per cent efficiency in the 1980s to about 50 per cent today.

“That means half of the fuel is now being put into useful mechanical work,” he added. “For reference, a gasoline engine is around 35 per cent efficient.

“These gains have come from high pressure common rail fuel injection systems, turbo-charging and the introduction of computing power to control precisely the combustion and the after-treatment management systems.”

While acknowledging that good fuel efficiency is increasingly every customer’s number one demand, Lundgren says engines also require good engine performance and durability, especially in relation to meeting emissions requirements – which puts these elements sometimes in competition with one another.

However, even allowing for the fact businesses require greater engine power to move larger loads (Volvo Group’s largest engine output is about 745kW), he says that compared to passenger cars, all heavy-duty applications remain “relatively” underpowered.

Alternative fuels

The diesel engine is frequently accused of being environmentally unfriendly, but Lundgren says the engine can “clean up its act”.

“Making diesel engines very clean is possible and that is something the heavy-duty industry has made greater progress on than the light-duty sector,” he said.

“Part of the reason for this is that the efficiency demanded by customers in the heavy-duty sector is much higher.”

Lundgren concedes that increasing efficiency while simultaneously lowering emissions is a conundrum.

“It has been a challenge to refine the thermodynamic process to compensate for the burden of having added the selective catalytic reduction after-treatment system. But now we are back on track to increase efficiency step by step.”

He says the drive towards zero emissions is dependent on a range of factors, including the definition of emissions.

Fuel efficiency is a key concern for construction machine owners.
Fuel efficiency is a key concern for construction machine owners.

“If you propel the engine with fuel that has no carbon and couple it with an efficient combustion process that creates no soot, then zero emissions is possible,” Lundgren said. “We have been working on using methane and dimethyl ether as clean alternatives to diesel. This is not a new idea.

“In 1900, the diesel engine was successfully run on peanut oil. The problem isn’t with the technology of making the clean fuels work, but rather their availability.

“But if the supply issue of renewable fuels can be solved, then it is possible for diesel engines to run 100 per cent CO2-free.”

As a result, Lundgren said, it’s quite feasible that “cleaner” fuels could be run through a typical combustion engine.

“From an efficiency point of view the engine doesn’t care if the fuel molecule comes from a fossil or a renewable source,” he said. “So with investment in the right type of renewable fuels, the transition to renewables should be straightforward.

“Electro-fuels (or e-fuels) use solar or wind power to ‘crack’ water and combine it with CO2 from methane, and these fuels feature quite high efficiency – up to 80 per cent claimed. This could be an interesting complement to electrification.”

Next big step

To lower fuel consumption further and increase engine efficiency, Lundgren said the next big step would be to encourage electromobility.

“The demand on engines in the future will not be so varied as it is today,” he predicted. “There is a difference between how efficient an engine is at its ‘sweet spot’ and how efficient across the whole real world operating range.

“Partnering engines with electric motors, as in parallel hybrids, allows the engine to run at its most efficient level. Without doubt, electrification will form part of the future combustion driveline solution.”

Other advancements, Lundgren added, may help reduce fuel expenses such as stop/ start technology and 48V electric systems (that power ancillaries electrically, rather than mechanically).

However, he said a more important source of greater efficiency, and potential commercial viability, could be heat recovery, which is not simple to achieve on heavy-duty engines that run relatively cold exhausts.

Lundgren is optimistic that the diesel combustion engine will remain a “very cost-efficient solution for creating mechanical energy” for the foreseeable future.

“That said, legislation, especially in Europe, is pushing towards electrification quite strongly, and that may impact directly on the combustion engine’s longevity,” he said. “Our feeling is that its use will be application-based, and that it will continue for a considerable time in long distance uses, such as ships and long haul trucks. But even here there will probably be a blend of technologies in use.

“The diesel engine – in a modified form – can be very clean and efficient. It also plays well with electrification. As a manufacturer, we need to find the best solution, based on the decisions society makes. Whatever they are, we need to be prepared.”

Source: Volvo Construction Equipment/SE10

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Wednesday, 18 September, 2019 9:04am
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