The core of turbocharger performance comes down to aerodynamics: the shapes and dimensions of the turbine and the impeller and their housings. A success factor for the new engines has therefore been the in-house team of aerodynamics specialists in Malmö, Sweden.
To meet tougher US emission standards, the new turbo compound engine has been developed as a cost-effective solution. It is especially favourable in North America where driving speeds are high. The new engine offers 6.5% reduction in fuel consumption, with the turbo compound unit as the major contributor.
“The turbo compound unit adds an extra turbine. It recovers energy in the exhaust gases and uses it to give extra power to the engine,” explains Per Andersson Specialist Aerodynamics, who has designed key parts of the unit.
An essential element in designing the turbo compound engine was engineering a highly optimised turbo that maximizes the efficiency of the entire system. Among many new features, the team in Malmö decided on a compressor diffuser with vanes.
“I think that is a first for the truck industry. It controls the flow better,” explains Magnus Ising, Specialist Aerodynamics.
Other design features include more blades in the compressor, a higher blade-outlet angle of the impeller wheel and a lower inlet blade height.
One of the main challenges was the extreme variation in pressure and speed of the exhaust flow.
“The turbo compound rotor reaches a spin-speed of 32 times the engine speed, and the speed will vary between 60,000 to 20,000 rotations per minute,” says Per Andersson.
Today, around 40 people work at Volvo Group turbo system development facility in Malmö. The site allows the engineers to design and test different systems entirely in-house, including prototype development and testing.
In the coming years, Volvo will continue to develop turbo compound technology to make engines more fuel efficient.
“Both the turbo unit and the turbo compound can be further refined,” says Magnus Ising.