Dimitrios Dardalis, a mechanical engineering graduate student at The University of Texas (UT), has patented a design that may bring about fuel savings in heavy-duty diesel engines.
His Rotating Liner Engine (RLE) is not yet in production. But Ph.D. candidate Dardalis predicts his concept could result in fuel savings of 4.5 percent to 5.5 percent for engines powering 18-wheel vehicles.
‘That may seem like a small number, but it’s actually huge,’ said Dr Ronald Matthews, professor of mechanical engineering and head of UT Austin’s Engines Research Program.
Matthews added that the fuel economy benefit could rise to as much as 27 percent at idle, which is a significant figure because cross-country truckers in the US often leave their engines idling all night.
A UT economic analysis looked at the potential benefit for a truck driven 120,000 miles per year that averages 6.5 miles per gallon of fuel at a cost of $1.40 per gallon. It showed that Dardalis’ design could yield annual fuel savings of up to $2,000 per truck per year.
Dardalis said his rotating liner technology can be used on any type of diesel engine, and that all engines using the technology will last longer and require less maintenance.
Dardalis’ design employs rotating liners: the metal cylinders in which an engine’s pistons move up and down. Typically, heavy-duty diesel engines have six fixed cylinders tightly pressed into pre-cast cavities within the engine block. A lubricated piston ring moving up and down inside each cylinder generates considerable friction.
This is particularly true when a piston ring approaches zero-velocity near the top of its cycle, a point where lubrication vanishes while the cylinder gas pressure is very high. Eventually, friction wears out the cylinder wall.
Dardalis developed a three-dimensional model, which shows a constant, evenly distributed lubrication film between the piston and inner cylinder wall will occur if the cylinders themselves are rotated throughout the entire cycle. Friction and its attendant wear are both said to be drastically reduced as fuel efficiency rises whilst harmful emissions decrease.
When he began his work several years ago, Dardalis recognised the value of incorporating the rotational feature into a diesel engine that would reduce fuel consumption.
The success of the rotating liner engine is said to depend on the ‘face seal’ between the rotating liner and the stationary cylinder head. His current prototype is made from a steel alloy, but he is continuing to test new materials.
Dardalis’ next step will be working with John Crane Packing Company, an international face seal technology producer with ultra-high precision manufacturing capabilities, to perfect the prototype.