Australian Cam-Drive Gasoline Engine Reaches 39.5% Efficiency in Independent Testing; Potential for Production Engine in China
|The 2.4-liter X4V2 prototype was originally designed for an aviation application. Click to enlarge.|
Australia-based Revetec is designing what it calls the Controlled Combustion Engine (CCE)—a cam-drive gasoline spark-ignited internal combustion engine that is smaller, lighter, cleaner, less expensive to manufacture and that produces higher torque due to higher mechanical transfer than equivalent conventional engines.
Revetec has prototyped 6 different versions of Revetec engine designs over the last 10 years. The latest version, the X4V2, was designed as a development engine for the aviation industry, and in early 2008 it was independently tested by Orbital Australia.
We modified the X4V2 engine to increase fuel efficiency focusing around the 2,000rpm range where most driving occurs, then sent the engine to Orbital Australia Pty Ltd for independent Certified testing...We tested the engine under the standard air/fuel ratio of 14.5:1 and also at our desired air/fuel ratio of 15.2:1 which maximizes the efficiency of the current configuration.
The Directors are pleased to announce that the X4V2 petrol engine achieved a repeatable Brake Specific Fuel Consumption (BSFC) figure of 212g/kWh (38.6% engine efficiency) with a best figure of 207g/kW-h (39.5%) at our requested target test of 2,000rpm with a BMEP load of 450kpa (approximately 75% load) and an air/fuel ratio of 15.2:1 using 98 RON petrol and a 10:1 compression ratio. We also achieved a BSFC figure under the same rev and load conditions using an air/fuel ratio of 14.5:1 of 238g/kW-h (34.4%).—Revetec
The engine. The Revetec cam-drive engine uses a pair of counter-rotating trilobate (three-lobed) scissor cams geared together, so both cams contribute to forward motion, rather than a crankshaft. Two bearings run along the profile of both cams (four bearings in all) and stay in contact with the cams at all times.
|The trilobate cams.||The X4 design.|
The bearings are mounted on the underside of the two inter-connected pistons, which maintain the desired bearing-to-trilobe clearance throughout the stroke. The two cams rotate and raise the piston with a scissor-like action to the bearings. Once at the top of the stroke the air/fuel mixture is fired. The expanded gas then forces the bearings down the ramps of the cams spreading them apart ending the stroke. The point of maximum mechanical advantage or transfer is around 20-30deg ATDC (when the piston moves approximately 10% of its travel) making the most of the high cylinder pressure.
|Piston and cam assembly. Click to enlarge.|
This compares, says Revetec, to a conventional engine that reaches maximum mechanical advantage around 60-70deg ATDC—after the piston has moved through just over 40% of its travel, losing approximately half of the cylinder pressure). The effective cranking distance is determined by the length from the point of bearing contact to the centre of the output shaft (not the stroke). A conventional engine's turning distance is half of the piston stroke.
The piston acceleration throughout the stroke is controlled by the cam “grind” which can be altered to suit a wide variety of fuels, torque requirements and/or rev ranges. The piston assembly slides rigidly through the block via an oil pressure fed guiding system eliminating piston to cylinder-bore contact, reducing wear and lubrication requirements in the cylinder, and also reducing piston side shock—making ceramic technology suitable.
One engine module can comprise two trilobate cams and either two or four pistons in an “X” configuration. The counter rotation is performed by a reverse gear set at a 1:3 ratio shaft providing two strokes of a piston to 360 degrees of output shaft rotation—the same as a conventional engine.
Revetec calculates that while a crankshaft connecting rod device in a gasoline engine is approximately 65% efficient in matching the mechanical device and cylinder pressure to an output shaft, the Revetec engine bottom end design is approximately 85% efficient.
In addition to improved efficiency, torque performance is strong. In tests using asymmetrical trilobes, Revetec says, it has achieved almost 90% of peak torque from the earliest in rpm it could start the dynamometer tests. The X4V2 aviation engine with asymmetrical Trilobes achieved 180 N·m (133 lb-ft) of torque @1,300rpm with a peak torque of 203 N·m (150 lb-ft) @3,000rpm.
Commercialization prospects. Revetec has signed agreements with a German university and a Chinese group which is funding a testing and development program. Revetec says that it is assured from the Chinese group that upon satisfactory conclusion of the test and development program two of China’s top ten car companies will jointly develop an automotive production engine. Testing was slated to recommence during late May 2009 at the university, with approximately a month of work required.
This test regimen will take pressure readings taken from within the engine’s cylinder head, as well as multiple pressure sensor readings from within the manifolds. This data will help in the modification and optimization of the engine design.