The Engine of Our Dreams Exists. It's a Clean, Powerful, Supercharged and Rotary Valved Two Stroke
How do you know an invention is genius? For me it's that moment when I see it for the first time and I immediately think "hey why didn't I think of this?" A genius invention seems very obvious and simple once you see it. And once you see it you can't unsee it ever again And you also somehow can't figure out why it was ever elusive, why didn't somebody just do it before? Today we're going to talk about just one such Invention the RevForce engine from Alpha Otto Technologies Which is an ultra powerful, clean and efficient two-stroke engine. And to understand how it works we first of course must understand what makes a conventional two-stroke engine great and also what makes it not so great. You see, a two-stroke engine is THE BEST ENGINE EVER!!! Okay, I'm going to have to stop this childish display of whatever, because yes, two strokes are fun No doubt about that. But they also have to burn oil by design and that means that they're
bad both for the environment as well as the people that breathe in this KAPOW! There's no way that something that smells this good is bad for the environment Okay, that's enough of that Two-stroke D4A is a bit crazy so don't take him too seriously. That being said he does have a point, and two-stroke engines are indeed very fun. They're very fun because they're extremely power dense and they're capable of this very impressive power density because they use both the area above and below the piston In a reciprocating piston engine one stroke equals 180° of crankshaft rotation. And a four stroke requires four strokes to complete one full combustion cycle. Going from top dead center to bottom dead center
we have our first stroke which is intake, during which air and fuel enter the cylinder The piston then goes back up and compresses the air fuel mixture which is our second stroke The air-fuel mixture is then combusted and pushes the piston back down to bottom dead center which is our third stroke. And finally the piston goes back up and pushes the exhaust gases out from the engine which is our final, fourth stroke. But a two-stroke engine does all of this: intake compression combustion exhaust in half the time of a four-stroke. And that's because it can do two things at once. As the two-stroke piston moves up it creates a vacuum below it And so the air and fuel mixture enters through the crankase and accumulates below the piston At the same time as the piston goes up it is also compressing the air and fuel mixture already above it So it's actually doing intake and compression at the same time. When the piston reaches top dead
center the air and fuel mixture gets ignited and combustion pushes the piston down As the piston moves further down it uncovers the exhaust port and exhaust gases vacate the cylinder But at the same time as the piston moves further down it pushes the air and fuel mixture already below it into the transfer port which it also uncovers as it moves even further down. The fresh air and fuel enters above the piston ready to be compressed and ignited again. In other words, everything happened within 360° of engine rotation. And every time the piston is at top dead center combustion will occur In a four stroke, combustion only occurs every other time the piston is at top dead center Twice the combustion events or power pulses within the same period of time theoretically means twice the power. On top of this a two-stroke doesn't need valves and valve springs and lifters
and rockers and cams and cam chains. It's far more simple and lightweight than a four-stroke which is why it easily beats the four- stroke in terms of power per kilogram or pound of engine mass Okay, if two strokes are more power dense then why are four strokes the dominant mainstream engine powering the world? Well, the reason is that a two-stroke engine as we just described it has three big disadvantages. Fuel inefficiency, emissions unfriendliness and poor longevity If we have air and fuel both above and below the piston, then that means that we cannot have a large quantity of engine oil lubricating the crankshaft and connecting rod and cylinder and piston skirt If we did all that oil would be pushed through the transfer port and it would end up above the piston where it would immediately kill any hopes of combustion occurring. This is why a two-stroke is lubricated using only a minimal amount of oil that is mixed with the fuel. Usually the ratio of
fuel to lubricating oil is around 50:1 in a modern two-stroke. This reduced lubrication means that engine components simply can't last as long. The fact that we have oil in the fuel means that oil will get inevitably burned together with the fuel which of course leads to poor emissions The other reason we have poor emissions is that the exhaust port of a two-stroke is always open So when the air and fuel mixture comes out of the transfer port and goes above the piston and the piston continues moving up there exists a period of time during which the air and fuel mixture is free to escape out the exhaust port. And that's exactly what happens Some fresh unburned fuel always goes right out the exhaust port before the piston moves further up and closes off this exit pathway. What we can do is make funky exhaust chambers that push some of that air and fuel mixture back into the cylinder using the power of sound, but even these are far from completely efficient, and some unburned fuel will always escape. Of course spitting unburned fuel right out the exhaust leads to poor fuel efficiency and a further worsening of the emissions So the two-stroke has a few problems. Okay but we still want that power density!
Well, let's try to do something right here, right now. Let's try to fix the problems of the two-stroke while keeping the power density. First up, let's get rid of the transport completely. We want longevity And if we want longevity then we must have better lubrication. If we get rid of the transfer port we can have oil below the piston lubricating everything, and we won't need to mix oil into the fuel which means we are also improving emissions because we won't be burning oil anymore Now, if we remove the transfer port that also means that we must not let air and fuel come through the crankase anymore, otherwise it will again end up below the piston. So now the intake port
must also be relocated from the crankcase to the cylinder. The final problem we need to fix is fresh fuel escaping out the exhaust port and ruining our efficiency. So let's turn that into an exhaust port with an exhaust valve on top of the cylinder head, just like on a four-stroke. So let's see how this engine would work. Let's imagine combustion just occurred and the piston is going down Of course during combustion we keep the exhaust valve closed and as the piston goes down torque is generated and the air and fuel mixture burns and turns into exhaust gas. We open the exhaust valve and of course some of that pressurized exhaust gas escapes until pressure in the chamber equalizes with outside atmospheric pressure. When pressure equalizes we will still have a significant amount
of exhaust gas inside the cylinder. As the piston keeps going down it uncovers the intake port and... a major problem in our design. Remember, the exhaust gas still left in the cylinder is at atmospheric pressure The air and fuel that's supposed to come into the cylinder is also at atmospheric pressure And that means that the air and fuel is NOT coming into the cylinder. There's no vacuum
inside the cylinder nor is there anything to push the air and fuel mixture into it which means that we are stuck. There's only one way to fix this. Forced induction. We add a supercharger which pressurizes the intake air. As that air is now at a pressure higher than atmospheric it will push the remaining exhaust gas out of the cylinder and fill it with a fresh air and fuel charge. And what we have just done is create an existing engine design. Engines with an anatomy very similar to this are known as two-stroke diesels, marine two-stroke diesels. That's what's powering the tankers and
the container ships full of junk from Temu. It's not a bad design, it definitely has its purpose but for us it's a mission failed because remember at the beginning of this video we wanted to fix the problems of the two-stroke. Emissions, longevity fuel inefficiency, while retaining power density This anatomy fixes the problems but it loses the power density because now we have poppet valves poppet exhaust valves. And if we have that we have cams and valve springs and rocker arms and cam gears and cam chains and weight weight weight. Which means power density goes out the window But even even if we somehow magically retain the power density we lost something else that's very very important with this anatomy, and it is the capacity to rev higher. Marine two-stroke
diesels they run at... wait for it... 60 to 120 RPM. That makes your washing machine look like a Honda F20C They run at this very low RPM because number one they're giant engines with very heavy pistons and rods and accelerating these components to high RPM is simply impossible. But even if we had very small pistons and rods this engine could still not rev high and it could not rev high because it cannot breathe fast enough. The higher the RPM the smaller the time window to complete intake
exhaust and the other strokes. And in this two-stroke anatomy, this distance from here to here The height of the intake port, that's all the time we have in relation to the total stroke of the piston to get air in and exhaust out. Compare it to a four stroke which has the entire stroke of the piston, the entire height of the cylinder, you realize just how little time that is. And as RPM increases the time frame becomes even smaller. So the only way for this engine to rev higher would be to somehow be capable of breathing very very well, and a traditional poppet valve is simply unable to breathe that well because by its design it's an obstruction to air flow The only way to get this engine to rev higher and to breathe well enough is to use something like a rotary valve which has great airflow capacity. So why don't we do that? Why don't we replace
the poppet exhaust valve with a rotary valve? And what we have just done is created the RevForce engine Seems so obvious now right? That's what the REV in RevForce actually stands for Rotary Exhaust Valve. Now, I have talked about rotary valves on this channel before and as we know they are amazing at flowing massive amounts of air very quickly. They also have a low number of moving parts They're simple but they have problems with sealing combustion pressures. But here is where
the genius of the RevForce engine comes in. It makes these sealing inefficiencies of rotary valves irrelevant while at the same time reaping the benefits of the massive airflow capacity Now let's start from the moment when combustion occurs and the piston starts descending from top dead center. Combustion pressure builds drives the piston down and creates torque. When the piston reaches this point it uncovers the exhaust port and as you can see by that time the rotary exhaust valve has also rotated into its fully open position. The maximized opening means that a large amount of pressurized exhaust gas can freely and quickly exit the cylinder. As the exit path is now much less obstructive it allows the pressure in the cylinder to reach atmospheric faster than with a traditional poppet valve, leaving less gas in the cylinder. As the piston continues down it uncovers
the intake port where we have supercharged air which now starts entering the cylinder As you can see the rotary valve is still open and so it allows the pressurized air to quickly push out the remaining exhaust gas out of the cylinder. By the time the piston reaches bottom dead center and starts going upward the rotary valve is fully closed. This is the point when we can inject our fuel using our injector in the intake port. As the rotary valve is now fully closed it means that no fuel will be escaping out the exhaust leading to greatly improved fuel efficiency As the piston continues going up it closes off the intake port and starts compressing the air and fuel mixture during the entire remainder of the stroke. Near TDC we fire our spark plug and combustion happens again restarting the entire process. And here comes the genius part, as you can
see the rotary valve is never in direct contact with combustion, and that means that it does not have the task of sealing off the extremely high pressures of combustion. That is done entirely and effectively of course by the piston rings. The only thing that a rotary exhaust valve seals off is air and fuel, the pressure of which is much much lower than that of combustion which means that even a loose- fitting rotary exhaust valve will be perfectly capable of preventing a measurable amount of fuel from going past it. So we have zero issues with rotary valve sealing while at the same time allowing massive airflow capacity for quick exhaust gas evacuation. Ultimately what we have here is a valved supercharged two-stroke capable of high RPM operation. It's clean because it doesn't burn oil. It's efficient because it doesn't spit unburned fuel out the exhaust
and it has good longevity because the entire rotating assembly is conventionally lubricated by engine oil as in any four-stroke engine. Something else that's interesting, is that as you can see we have an upper and a lower ring pack. The upper one controls combustion and the lower one controls the oil And as you can see the lower ring pack never goes above the intake and exhaust ports The ports never see the oil. And that means that we have the same oil consumption as in a four- stroke What's interesting is that despite this the crank case of the RevForce is still equipped with reed valves As the piston goes up it creates a vacuum under the ring pack which helps improve the sealing of the rings. And as the piston goes down it pushes a certain amount of oil out the crank case through the reeds and into the engine's semi dry sump system, which further reduces any possibility of oil getting into the combustion chamber. So the RevForce engine is clean, efficient
and capable of high RPM operation but it's also still power dense. Every stroke is still a power stroke and the engine is still lightweight and simple like a two-stroke should be. But here's the best part, It's not just a bunch of theory and CAD. It's already a living, breathing engine
Now before you type in "swap it into a Miata" let me stop you right there because no, you cannot go out and buy a RevForce engine. It is not a production engine just yet. It is at this stage what I would call a mature prototype. But as I said many times on this channel it's precisely this stage from prototype to production that requires the greatest investment of all kinds of resources But because we have a living, breathing prototype we can talk something very important: Numbers Currently the RevForce engine is an inline two-cylinder liquid-cooled two-stroke It has a displacement of 578cc and it weighs just a hair under 50 kg so you can lift it up with your own two hands, but it makes 220 horsepower. It has a peak torque output of 176.26 Nm
It has a brake mean effective pressure of 25 bar. It is very compact as you can see from the dimensions. It has a static compression ratio of 10:1 It has an expected redline of 8,000 RPM, currently tested and validated up to 7,000 RPM and it has a brake specific fuel consumption at peak power of 221 gram per kilowatt hour I believe that is everything. Did I miss something? It is oversquare by design at this stage and yeah, that's everything. So as you can see, some very very impressive numbers at this prototype stage But numbers are still not the end of the story. Not the only trick up the sleeve of this
amazing engine. Because the rotary exhaust valve is electronically controlled, so you can change the timing of this valve on the fly, and we have a supercharger, we can manipulate the pressure of that as well, and that means that we have full control of the dynamic compression ratio of this engine on the fly. And this means that the engine is multi-fuel capable. It can run on gasoline It can run on heavy fuels, it can run on CNG, it can run on hydrogen, you name it. But it cannot just run all of these different fuels, it can switch from one fuel to the other on the fly. Have a listen Okay, so it's too good to be true? Drawbacks? There's got to be some sort of fatal flaw right? Well, to be honest right now from the information that I have I cannot find a serious fault on this engine It has two ring packs so a bit more friction there but the rotary valve makes up for it because it is very low friction and it has less friction than a conventional poppet valvetrain We also have the benefit of not needing complicated exhaust shapes like conventional two-strokes because we have a rotary exhaust valve. You could say that, okay, it needs a supercharger to run but naturally aspirated engines are kind of dead, so whatever you compare it to nowadays if it's relevant and modern it probably has forced induction. Pretty much everything has
a turbo nowadays. So even if it has a supercharger, not really a, you know, some sort of major flaw So it is still much more power dense than your typical four- stroke. It is more lightweight and it's not dirty. So yeah, I've been reviewing novel engine designs on this channel for a pretty
long time and to be honest this is one of my absolute favorites so far because it sort of tries to give the two-stroke engine a future. And as you've probably noticed I'm kind of partial to two-strokes. I love them, because the first time I experienced the power delivery of a two-stroke I was hooked. It's something you really can't put into words. You got to experience it yourself to see what I'm talking about. Anyone who has knows what I'm talking about and I think the anatomy of
a two-stroke engine is genius, and I think that it deserves a future and should not be discarded And that's what the Rev Force engine does and what I like about it is that it does it in a not pipedreamy way It uses conventional components, stuff that can be easily replicated and made It doesn't need some sort of weird novel cutting-edge anatomy that would require millions upon millions upon millions just to create a, I don't know, a proof of concept, which is why I really hope that this engine does get to see production. Now the project has been currently up to this stage financed exclusively by a small research grant and out of pocket by the inventors of the engine John Krzeminski and David Dusseau. But bringing it to the final stage, to mass production is of course impossible without a further much much larger investment. So in case you're somebody who's
a bit of a petrolhead, maybe even a two stroke enthusiast and you're at the same time sitting at the helm of a, I don't know, a giant hedge fund or obscene personal wealth or something along those lines then I suggest you go down to the video description or the pinned comment you check out Alpha Otto Technologies, get in touch with them and you strike some sort of mutually beneficial deal and we all get access to this fun fun engine. Yeah I really hope that happens. I hope you enjoyed this one, that's pretty much it for today, it was a very fun one for me. Yeah, as always thanks a lot for watching and I'll be seeing you soon with more fun and useful stuff on the D4A channel
2025-06-01 10:00
