The INNengine promises to revolutionize ICE technology with rotary, opposed pistons.
The perfection of the internal combustion engine has been sought for almost 150 years. In the process, some innovative and downright odd designs have emerged. Granada, Spain-based INNengine has developed an innovative opposed piston design that does away with crankshafts, replacing them with rotary cam tracks, the pistons functioning in a way similar to roller lifters in pushrod overhead valve engines. Mechanical simplicity and light weight are major advantages, as is a unique advantage offered by the cam system: variable compression ratio. The company has prototypes running now, and is developing engines for both automotive and aviation use.
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Episode Transcript:
In the internal combustion engine world, there have only ever been two successful operating principles: four-stroke, and two-stroke.
Now, we all understand the operating principles behind piston engine technology, and many of us are familiar with variants like the Miller or Atkinson cycles—but in essence, internal combustion engine technology has not changed in over a century.
Granada, Spain-based INNengine, however, has developed a novel engine technology that the company boldly states will revolutionize the internal combustion engine: a one-stroke, valveless and crank-less opposed piston design.
Mechanically, the engine uses four cylinders arranged radially around a central shaft that carries cam tracks on which the pistons ramp up and down on in the manner of a roller lifter in a conventional ICE valvetrain. Compression is created by the combustion chamber formed by the two opposing pistons, much like successful diesel applications like the Junkers Jumo and the Napier Deltic. And like those diesels, the INNengine uses cylinder wall ports for breathing, closing the exhaust ports before the intake ports to create uniflow scavenging.
Gasoline direct injection is used, and the charge spark ignited. The system is effectively a two-stroke design, with an innovative mechanical coupling to the output shaft. The clever cam track system not only eliminates the crankshaft, but by phasing the cam tracks relative to the output shaft in the manner of current variable valve timing technology, the system can create a variable compression ratio, which opens interesting possibilities for engine load management, control of spark knock and emission controls.
The company has built working engines, including prototypes for aviation use, and is talking about alternate fuels, including hydrogen.
From an engineering perspective, there are questions about this engine’s viability for production automotive use: without the mechanical advantage of a connecting rod and crankshaft, low RPM torque would appear to be limited, suggesting higher RPM operation with short gear ratios. Lubrication of the entire system, especially the cam tracks, is an unknown quantity, as is the ability of the system to meet very strict modern emission controls with gasoline fuels.
Scavenging the cylinders will require careful tuning, possibly by ram effect, and more probably for production engines, by blower scavenging, as seen in the venerable GM 71-Series diesels.
But the concept is intriguing, especially as a small, auxiliary engine as a range extender for electric vehicles. Could the INNengine keep the internal combustion process alive in the age of electric vehicles? Here at engineering.com, we’ll be following this interesting technology, and we’ll report on developments going forward.
