Business Constructs Potent 500cc ‘One-Stroke’ Motor, Swiftly Embeds It in a Miata

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By Car Brand Experts


My fascination lies with unconventional engines—bring on a rotary, a turbine, or perhaps even a flat-eight, and I will be content. That’s why my excitement peaked upon learning that INNengine of Granada, Spain had crafted an opposed-piston engine that delivers a remarkably robust performance in an exceptionally compact form.
This motor forgoes the traditional cylinder head, as well as the crankshaft, camshaft, and valves. It comes as no surprise that this engine weighs merely 85 pounds. Yet, it is capable of producing 120 horsepower with a mere half-liter displacement, thanks to what the company describes as a single-stroke combustion cycle. An ideal fit for a Miata, as it turns out.

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Despite featuring four cylinder banks, the INNengine (in varying configurations) sports eight pistons. The design stems from its opposed-piston layout, where each piston’s compression stroke opposes a second piston within the same cylinder bank, rather than against a static cylinder head. However, it retains only four combustion chambers, which gives it a sound reminiscent of a four-cylinder engine.

No conventional connecting rods are visible in this engine (at least not in the traditional sense). Instead, the pistons rest on rollers that move along a lobed circular plate, offering the flexibility to adjust the engine’s timing and compression ratio. As the lobe reaches its apex, the piston swiftly moves towards top-dead-center, where fuel is directly injected into the cylinder and ignited by a spark plug within the compressed air-fuel mixture.

<em>INN Engine</em>
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INN Engine

This mechanical arrangement also enhances engine balance, minimizing the typical downsides of an internal combustion engine—referred to as noise, vibration, and harshness.

Upon ignition, the piston pushes back against the plate, causing it to rotate. This synchronized motion between each part of the engine via a common shaft eliminates the need for additional timing components. The movements of both pistons in the same cylinder bank closely mirror each other’s actions virtually.

As the pistons reach the lowest point of their strokes, corresponding intake and exhaust ports are uncovered. One piston is timed to reach bottom-dead-center slightly ahead of the other, allowing the exhaust gases to exit through the exhaust port, creating a vacuum within the cylinder—a method known as scavenging. Meanwhile, fresh air is drawn in through the intake port, while the combustion byproduct is expelled. This setup assigns the pistons a dual role, executing tasks typically carried out by valves in a standard combustion engine—eliminating the common issue of carbon deposits on direct injection valves.

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Strength is also generated at both extremities of the engine, allowing the connection of a gearbox to either (or both) side of the engine to transfer the energy to a vehicle’s wheels.

Presently, the motor functions as a two-stroke cycle, featuring both a compression stroke and an exhaust stroke. INNengine has recognized this and labeled the engine as such due to the common expectation that a two-stroke engine would require an oil and fuel mixture. Most two-stroke engines do necessitate this. The organization mentions that the name “one-stroke” was proposed by an “external ICE institution,” and they found it to be “appealing,” hence why INNengine opted to retain it.

<em>INN Engine</em>INN Engine

Is it probable that INNengine’s combustion technology will propel a car? Probably not, at least not directly linked to a gearbox. The Mazda model showcased in INNengine’s demo video was a remarkable concept, but the company appears to be focusing on the electric vehicle market as a supplementary power source, especially considering the industry’s imminent direction.

If this technology had been introduced several decades ago or earlier, there might have been a chance for adoption in the primary market (think of Felix Wankel’s renowned rotary engine). However, interfering with perfection in today’s era, particularly as combustion technology could be on the decline, seems unlikely to succeed. Hence, a supplementary power source seems to be the most rational advancement for this technology, particularly if the aim is to produce more lightweight, economical electric vehicles.

More Bizarre Engine Tales From The Drive

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BMW once crafted a quad-turbo six-cylinder diesel engine, and the world is richer for it.

Have insights to share or queries for the writer? Reach out to them directly: rob@thedrive.com

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