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Bosch and Weichai Power boost diesel engine thermal efficiency




The Bosch modular commonrail system (Credit: Bosch)
The Bosch modular commonrail system (Credit: Bosch)


The path has now been set for passenger vehicles.

The shift to electric has started and by 2030 – in the UK at least – new petrol and diesel passenger vehicle and van sales will be banned. But that doesn’t tell the whole story. 

While smaller vehicles will need to be electric, the fate of larger commercial vehicle powertrains is yet to be made concrete. That’s why firms continue to make diesel engines as efficient as possible. Because, as much as there are those that dislike compression ignition technology, it remains one of the most efficient ways to power larger vehicles. 

Development milestone

Tier One supplier Bosch, working with Chinese commercial vehicle diesel engine manufacturer Weichai Power, has increased the technology’s thermal efficiency from 46% to 50%. This achievement shows just how much more is possible with the technology.

Weichai has invested a huge amount of research time and money into thermal efficiency improvement, an area of development that suffers from ever-decreasing gains. In 2015, Weichai established a special technical research team to conduct thousands of repeatable tests looking at how different approaches could improve diesel efficiency.

Achieving 50% thermal efficiency was difficult, but reaching it was accelerated over the past two years. Bosch and Weichai started the project in 2018. Bosch provided its modular commonrail system for the 12.9-litre six-cylinder diesel engine. It’s a critical part of the combustion process, guaranteeing efficient fuel supply and injection.

High injector flow rates make it possible to optimise the combustion strategy and achieve high engine performance. Depending on the demands it’s subject to, the system can last for up to 1.6 million kilometres. That means much-needed durability in a commercial vehicle application.

Changes to the combustion technology optimised the design of the air passage, fuel injection, combustion chamber profile and other systems to make the air-fuel mix in the combustion chamber more refined.

Exhaust energy distribution was also looked at in response to the increased difficulty of pollutant emission control caused by improved combustion, leading to a redesign of the exhaust system. The system adapts to the demand for exhaust gas recirculation, while ensuring the efficiency of turbines, achieving a 1% increase in brake thermal efficiency. Meanwhile lubrication technology is key to reducing overall system friction by 20%.

Precise control

Weichai also developed its own engine control unit to give more precise control of the engine and the combustion process. And it’s the combination of these points that helped Weichai, with its partner Bosch, to achieve the final goal of 50% thermal efficiency. At the same time the unit met China VI and Euro VI emission requirements.

Dr Volkmar Denner, chairman of the board at Bosch, said: “In increasing the efficiency by four percentage points, we have reached a new milestone. Even though the diesel engine is nearly 130 years old, its development continues.”

And that’s important, because, although there is a great deal of fever to move on to the next powertrain technology, diesel is likely to have a lot of life left in it, especially in commercial vehicle applications. Few other fuels offer the benefits that diesel does in this sector.

And Weichai is already looking to what it can achieve next. It plans to work with partners on future projects to reach a target of 55% thermal efficiency.


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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.



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