Controlled combustion engines...way of the future?
It’ll only be a matter of time, guaranteed. The boys and girls at Australia’s Revetec are well underway testing what will hopefully become the world’s first production Controlled Combustion Engine (CCE). They are very advanced in their development and are reportedly in talks with several manufacturers across Asia. Based in Gold Coast, Queensland, Australia, Revetec Holdings Limited has been working on this revolutionary idea since 1995 and believes it is nearing production readiness.
I’m not sure why it’s called a "controlled" combustion engine, because every combustion engine worth it’s salt, as they say, can be controlled. Otherwise it would be a runaway forest fire, wouldn’t it? But I digress. What I can however do is explain how it works. Firstly, this engine has no crankshaft. At least, not in the traditional sense. By nature, the CCE must have opposing pistons (I hope Subaru is paying attention).
Each opposing piston is connected to each other by a shaft and move back and forth together as a single unit. When one cylinder is under compression, the other is experiencing its exhaust stroke, and so on. The underside of each piston has rollers that make contact with a pair of tri-lobed cams that are in turn fixed to the output shaft. As the piston moves down during the power stroke, the rollers, being in contact with the lobes, force them apart in a scissor-like manner. This sets up a turning force in both. The cams turn in opposite direction, but this is not a problem.
The outer cam drives the output shaft directly, but the inside cam is mated to a planetary gear-set on its inner side that reverses the direction of the drive thus aiding the outside cam in turning the output shaft. I’m thinking wildly here. Theoretically, inside cam could drive another output shaft via a hollow shaft arrangement, possibly driving auxiliary devices, or be used to drive the engine in the opposite direction (anticlockwise, as opposed to clockwise). Could this perhaps be a way of simplifying reverse gear requirements in a CVT transmission? Oh the possibilities.
The advantages of this type of engine are reportedly many, some outside the scope of this article, but some of the most notable are reduced weight (less moving and installed parts), reduced piston wear, and increased fuel economy. It is reported to use less fuel as it can idle at far slower speeds (currently it idles at 300rpm but it is believed to be able to idle at about half that with variable valve timing) and can be run at leaner mixtures than conventional engines because of the combustion characteristics. Because the lobes of the cams can be shaped in different ways the piston can be made to stay at compression or exhaust stroke longer (or shorter) than would currently be possible with a crankshaft arrangement.
This can be done pretty much in the same was as adjusting the shape of camshaft lobes to get different valve event characteristics in conventional engines. This has an effect on the combustion process and can make for cleaner and more complete burning of fuel. Hmmm...Do I detect a Honda engineer reading this article? Perhaps there could be a way to vary the characteristics of the drive camshaft the same way VTEC does for the valve camshaft...Oh the possibilities!
The CCE engine is so dynamic that it can be adapted to use diesel, LPG, or any other fuel that a conventional crankshaft engine can use, or even be fitted to operate as a 2-stroke. And those aren’t the only variants possible. While the actual design must have opposing pistons, it is not confined to a flat configuration. In development at present is an X4 (you know, like you have V4, I4, and H4? Well this is almost like a radial engine shaped like an X) which is intended for use in the aircraft industry.
The most recent I4 design achieved an impressive 140Nm@3700rpm from a 1.35L 16v normally aspirated unit. The larger X4, measuring 2.4L and utilising pushrod 8-valve technology and no gizmos such as variable valve timing or turbocharging, gave an output of 92hp and 202Nm in a November 2007 bench test. The torque figure compares well with other 2.4L on the market. Though the power rating seems a bit low, this particular engine is intended for use in light aircraft use so the characteristics are somewhat different than would be required in a car. Impressive nonetheless, considering the archaic vavletrain and induction systems. Twin cams, variable valve timing, direct injection, variable intake runners, turbocharging, and even nitrous oxide can be added to either of these engines to make the product even sweeter. Oh the possibilities!