Dimitrios Dardalis, a mechanical engineer at the University of Texas in Austin has patented a design that could mean massive fuel savings for diesel engines.
Although not yet in production, Dardalis predicts that his Rotating Liner Engine (RLE) could lead to fuel savings of 5.5% for engines powering today’s 18-wheel rigs.
While that may seem like a small number, Dr. Ronald Matthews, head of UT Austin’s Engines Research Program, explained that diesel engines consume vast quantities of fuel to begin with, so any gains in fuel efficiency quickly result in cost savings. He added that the fuel economy benefit rises to as much as 27% at idle – significant because truckers often leave their engines idling all night.
But the technology is not just for trucks. Dardalis says that the RLE could be used on any type of diesel engine to improve its lifetime by up to 300% and save fuel without compromising emission output.
Dardalis took his inspiration from the Sleeve Valve Engines used on aircraft during the Second World War. ‘I first read about it as a kid, in an encyclopedia my parents bought me,’ he said.
In a sleeve valve engine (SVE) there are no proper valves. A sleeve inside the cylinder works off a cam and lever to rotate left and right around the long axis. Openings cut into the sleeve align with intake and exhaust ports in the cylinder walls allowing fuel/air in and burnt gases out. This means that there is no need for overhead poppet valves, thus reducing the diameter of a radial engine
The concept was originally developed in 1903 by American engineer Charles Knight, but the SVE reached its peak during the Second World War, when 150,000 aircraft made use of its compact dimensions to improve aerodynamics.
While employed purely as a space saving strategy, an unexpected benefit of rotating liners was that they reduced friction and decreased cylinder wear by 10 times the normal rate.
Dardalis recognised the value of incorporating the rotational feature into a diesel engine that would reduce fuel consumption. He took the aspects of SVE design that led to reduced wear and friction and applied them to his RLE in a way suited to the modern emissions oriented market.
Like the SVE, Dardalis’ design employs rotating liners: the metal cylinders in which an engine’s pistons move up and down. Typical heavy-duty diesel engines have six fixed cylinders tightly pressed into precast cavities within the engine block. A lubricated piston ring moving up and down inside each cylinder generates considerable friction. This is especially true as 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.
However, a three-dimensional model developed by the inventor shows that if the cylinders are rotated throughout the cycle; a constant, evenly distributed lubrication film between the piston and inner cylinder wall will occur. This eliminates metallic contact of piston rings and piston skirt with the liner, leading to less wear, longer life and greater efficiency.
The downside to SVEs was that they consumed a lot of oil. Also, having the sleeve lubricant close to ports contaminated the intake and exhaust gases with lubricant, leading to emissions which could not be tolerated today.
Thus, the RLE has conventional poppet valves, and the rotating liner is independent of valving but optimised for friction and wear.
A UT Austin economic analysis looked at the potential benefit for a truck driven 120,000 miles per year that averages 6.5 miles per gallon at $1.40 per gallon. It showed that Dardalis’ design could yield annual fuel savings of up to $2,000 per truck per year – a major incentive for companies with fleets of trucks.
Dardalis has set up a corporation to perfect, test and ultimately commercialise the core technology worldwide. He is now working with the John Crane Packing Company, a face seal technology producer, to perfect the prototype.
So how long will it be before the RLE starts appearing on commercial vehicles? ‘That depends on the level of funding,’ says Dardalis, ‘If funding arrives soon, we should be able to fully demonstrate the concept in 5 years or less.’