Spanish company, INNengine, has developed an opposed-piston engine that is compact yet powerful. Weighing just 85 pounds, this unique engine produces 120 horsepower with only half a liter of displacement. What sets this engine apart is its single-stroke combustion cycle, which eliminates the need for a cylinder head, crankshaft, camshaft, and valves.
The INNengine features eight pistons, despite having four cylinder banks. This is because it is an opposed-piston motor, where each piston’s compression stroke is performed against a second piston in the same cylinder bank. However, it still has four combustion chambers and sounds like a four-cylinder engine.
One interesting aspect is that there are no traditional connecting rods. Instead, the pistons sit on rollers that ride against a lobed circular plate, which can be adjusted to affect timing and compression ratio. Fuel is directly injected into the cylinder at top-dead-center, where a spark plug ignites the compressed air-fuel mixture.
This engine configuration offers better balance, reducing the typical noise, vibration, and harshness associated with internal combustion engines. The synchronized motion between the pistons and the plate allows for minimalized drawbacks.
Scavenging, a technique where exhaust gases escape and create a vacuum in the cylinder, is made possible by the timing of the pistons. Fresh air is then pulled in through the intake port, removing the need for valves and eliminating carbon-laced valves found in direct injection engines.
Furthermore, power can be output from both ends of the engine, making it suitable for connecting to a gearbox to propel a vehicle’s wheels.
The INNengine is technically a two-stroke cycle engine, despite being marketed as a one-stroke engine. This is because it has a compression stroke and an exhaust stroke. INNengine states that they called it a one-stroke engine due to the assumption that a two-stroke engine requires fuel mixed with oil, which is not the case for their engine.
While it is unlikely that INNengine’s combustion technology will directly power cars’ wheels, the company sees potential in the electric vehicle (EV) market as a range extender. As EVs become more popular, the lightweight and cost-effective nature of this engine makes it a logical choice for extending EVs’ range.
Although it may not have immediate mass-market application, the INNengine proves to be an innovative and promising development in combustion technology. As the industry moves towards electric power, this Spanish engine may find its place as a range-extending solution for future EVs.