When it comes to unusual engines, the INNengine e-Rex stands out. Based in Granada, Spain, this company has created unique engines: the e-Rex and the Rex-B. The e-Rex has four cylinders and eight pistons. That’s right—these pistons push towards each other to create compression, then pull away to allow intake and exhaust. It shares some traits with a two-stroke engine, which isn’t surprising considering the innovation.
Both engines feature a design where the pistons sit on a spinning disk, sometimes called a thrust plate. Engineer Csaba Csere refers to it as this, while others might call it “axial cams.” The e-Rex uses two plates, while the Rex-B has one plate with four pistons.
Now, the term “1Stroke” can be misleading. Even though INNengine markets it as a one-stroke engine, it actually performs two main tasks: combustion and exhaust, and intake and compression. They prefer this label to move away from the negative views associated with traditional two-stroke engines that often burn oil. Their engines focus on being cleaner and more efficient.
One exciting feature of the e-Rex is its opposing pistons, aimed at achieving balance. INNengine even tested this by placing a coin atop the engine while it ran. The coin hardly moved! In contrast, a typical car engine vibrated significantly. The ability of its thrust plates to adjust piston position also allows for variable compression ratios, adding efficiency without unnecessary complexity.
Despite its small size—500cc and weighing just 85 pounds—the e-Rex boasts a remarkable strength of 120 horsepower at atmospheric pressure. During testing, the e-Rex was fitted into a Mazda Miata, generating buzz online. However, some commenters suggested that a supercharger boosts the power output, which might be true but focuses more on improving airflow than compressing air for extra power.
The crucial point here is the scavenging process: the supercharger effectively helps the engine pull in fresh air while pushing out exhaust gases, keeping cycles efficient.
Furthermore, INNengine simplifies design by removing the complicated valve systems found in traditional four-stroke engines. With no valves, there’s no risk of deposits building up, making the engine cleaner and easier to maintain. The company envisions using engines like the e-Rex as range extenders in electric vehicles, pairing power density with reduced emissions similar to classic four-stroke engines.
Interestingly, calling it a “1Stroke” engine is a marketing choice. True one-stroke engines would produce power more frequently—every 180 degrees of crankshaft rotation. But this innovative approach fits nicely within the trend of finding more efficient engine designs, much like how Mazda’s rotary engines are sometimes referred to with inflated cubic measurements.
As the automotive world evolves, voices in the industry are excited about advancements like those from INNengine. With the demand for cleaner, more efficient engines growing, innovations like the e-Rex may pave the way for the future of transportation.
