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Today I’d like to introduce you to a very special engine. It claims to be a 1 stroke engine. It has no crankshaft and no cylinder head and it squeezes out 120hp naturally aspirated from only 500cc of displacement and weighs only 35 kilograms. It’s called INNengine and it comes from the beautiful city of Granada in Spain. The engine has already been manufactured and it was even installed and tested in a Mazda mx-5. Today we will take an in-depth look at this engine, we will explain how it works and we will discuss its potential, its benefits and drawbacks and we will see what makes sense and what doesn’t.

First up, let’s see how this thing works and what makes it a 1 stroke engine. To understand that we must learn about the anatomy of this little thing. As you can see we have a total of 8 pistons in an opposed piston arrangement. Instead of a crankshaft we have this complex shaped wavy thing and the pistons ride on rollers along the wavy surface. As the combustion force pushes down the piston the piston pushes down on the wavy thing, as the piston goes down the slope it also forces the wavy thing to rotate. There are two wavy things connected to each other via a common shaft. All 8 pistons act on the wavy things and the forces generated by all 8 pistons are transferred through the shaft resulting in a single torque output at both ends of the shaft. So in theory you could connect a drivetrain at both ends. For example one of these at the center with an axle at both ends could create a simple, well balanced and very lightweight four-wheel drive vehicle.

We can connect a drive-train on both ends of this engine because this engine does not have a cylinder head and it doesn’t have camshafts or valves. So it does not need to use one end of the engine to drive the cams via an easily accessible and serviceable cam chain or cam belt. How does it work without cams or valves then? Well instead of valves we have intake and exhaust ports which are opened and closed by the piston, just like in a typical 2 stroke engine. At the middle between the two pistons we have an injector and a spark plug which ignites the air fuel mixture.

As the combustion pressure builds it pushes on the piston sending them outward. As the pistons move they uncover the intake and exhaust ports. 4 pistons on one side of the engine deal with intake and 4 pistons on the other side of the engine deal with exhaust. So how do we prevent exhaust gasses from escaping out through the intake and messing everything up? Well, we do that just like we do it in a traditional engine, by relying on scavenging which occurs when both the intake and exhaust valves are open at the same time.

The exhaust port of the INNengine likely gets uncovered first which allows the pressurized gasses to start escaping out from the combustion area. Since they are pressurized they escape rapidly and leave a void or vacuum behind them. This vacuum is at a lower pressure than the intake charge outside the chamber which is at atmospheric pressure, which means that the intake charge rushes into the combustion area and fills it with fresh air. The upward sloped part of the wavy thing then pushes the pistons back up and so they close the intake and exhaust ports and now start compressing the air. The injectors add fuel and we now have a compressed air fuel mixture in the combustion area and the process starts once again. The spark plug fires, combustion occurs, pressure builds, the pistons are forced down, they rotate the wavy thing and torque is generated.

So what we have here is a very simple engine without cams or valves but with direct injection, but also without all the deposits that accumulate on the intake valves, because we have no valves. So we have the benefits of direct injection without the drawbacks.

Bur this is clearly not a 1 stroke engine. Here we have the combustion stroke which overlaps with the exhaust stroke, followed by the intake stroke which then overlaps with the compression stroke. This is a 2 stroke engine, a direct injection two stroke without the emissions problems because the oil is under the piston and never burned, which I personally find more impressive than the 1 stroke gimmick. The other thing is the opposed piston design and this is an advantage because opposed pistons designs are more efficient than a non-opposed design. In a non-opposed design some of the energy of combustion is simply wasted on heating up the combustion chamber above the piston. The combustion chamber doesn’t go anywhere and it just absorbs the energy as heat. But in an opposed design we have a piston instead of a combustion chamber which means that more combustion energy gets to be transferred and converted into useful torque leading to improved efficiency.

A special thank you to my patrons:
Daniel
Pepe
Brian Alvarez
Peter Della Flora
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
Cole Philips

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