The Volvo Group’s new truck engines are more fuel efficient as a result of their new piston design which adds waves to the piston crown to improve the use of oxygen. (Earlier post.) The engineers (John Gibble, Frank Löfskog, Michael Balthasar, and Jan Eismark) behind the innovation have now received the Volvo Technology Award 2017. The new wave design has now been patented.
In the case of a standard piston, the injector is located at the top of the cylinder and the fuel is sprayed toward the sides of the cylinder through a number of orifices in the injector. The combination of heat and pressure causes the fuel to ignite before it reaches the cylinder wall.
|Left: conventional piston. Right: wave piston. Click to enlarge.|
The flame hits the wall of the combustion chamber at a speed of up to 50 meters per second, spreads along the piston bowl wall and then collides with adjacent flames at an angle of 180 degrees, while still traveling at a high speed.
When the flames collide, they compete for the available oxygen. At the same time, the oxygen in the center of the combustion chamber is never fully used.
For this reason, we wanted to identify a method of leading the flames into the center of the combustion chamber to make better use of the oxygen there.—Jan Eismark
The result of their work was the inclusion of ridges or waves in the piston crown. The piston has six of these ridges and the injector, which is located in the center of the cylinder at the top of the piston, has six orifices to ensure the fuel is sprayed between the ridges that lead the flames into the center.
|Spray-chamber results with a 2-hole nozzle and interacting walls showing a snapshot of 500 bar injection pressure, soot laser extinction images during late-cycle oxidation after end of injection. The wave-profile (right) creates a more effective oxidation resulting in a faster burn-out. Red lines are iso-contours of a fixed soot shadow pixel threshold value. White line is symmetry axis between the two sprays. Source: Chalmers. Click to enlarge.|
It must be possible to manufacture any new design cost-effectively in order for it to be used in production vehicles. A large amount of work has gone into developing the piston manufacturing methods to achieve the right balance between the cost of the parts and the benefits for customers. This was followed by thousands of hours of testing to refine the design and verify the durability of the new concept.
This solution is now in use in the latest engines from the Volvo Group and brings advantages for both customers and the environment. The more efficient combustion process it delivers has halved the quantity of soot particles emitted by the engine and has also reduced fuel consumption by an average of two percent.