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How do you know when an invention is genius? For me, it’s that moment when I see the invention for the first time and I immediately think….why didn’t I think of this? Once you see it is seems so simple that you can’t figure out why it was ever elusive and why nobody made it before?
And today we are going to talk about just one such invention. The RevForce engine from Alpha Otto technologies and to understand the RevForce engine we first must understand what makes a two-stroke engine great and also what makes it not so great.
In a reciprocating piston engine, 1 stroke equals 180 degrees of crankshaft rotation. And a 4 stroke requires 4 strokes to complete 1 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 combusted and pushes the piston back down to bottoms 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.
The two stroke does all of this, intake compression combustion and exhaust in half the time, because, unlike a 4 stroke it uses both the area above AND below the piston which means that it can do two things at the same time. Ok, if two strokes are more power dense why are four strokes the dominant mainstream engine powering the world? The reason is that a two two stroke engine, as we just described it has three disadvantages when compared to a four stroke and they are poor longevity, emissions unfriendliness and fuel inefficiency.
So, the two stroke has problems…..but we still want that impressive power density don’t we? Ok, let’s see if we can fix the problems of the two stroke.
First up let’s get rid of the transfer port. We want longevity and if we want longevity we want better lubrication. If we get rid of the transfer port we can have oil below the piston and we won’t need to mix oil into the fuel which means we will improve efficiency and emissions. If we remove the transfer port that also means that we must not let air and fuel come through the crankcase, otherwise it will end below the piston again. So the intake port must also be relocated from the crankcase to an area above the cylinder.
The final problem we need to fix is fresh fuel escaping out the exhaust port. So let’s turn that into an exhaust port with an exhaust valve, just like on a four stroke engine.
There is 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 the cylinder and fill it with a fresh air and fuel charge.
And….. what we have just created is in fact very similar to existing marine two stroke diesels. Engines with an anatomy very similar to this are what’s powering the world’s tankers and container ships. The other problem is that this design is not suitable for high rpm operation.
Valved two strokes simply can't breathe fast enough for high rpm because the height of their intake port in relation to the total cylinder height or piston stroke is all the time they have to clear the exhaust gas and fill the chamber with air and fuel. Remember, a four stroke has the entire stroke, the entire height of the cylinder to evacuate all the exhaust and even then we can struggle at very high rpm and that’s because traditional poppet valves are an obstruction to airflow, they simply don’t allow massive quantities of gas to be moved past them rapidly.
So what if we got rid of the poppet valve and made an exhaust port with a rotary valve instead? And voila…..we have just created the RevForce engine. That’s what the REV stands for: Rotary Exhaust Valve. Now I have already talked about rotary valves on my channel and while they have potential for massive air flow they tend to have issues with sealing. But the genius of the revforce lies in the fact that it makes the downsides of a rotary valve largely irrelevant while still reaping the benefits. Lets observe the operating principle of the revforce to understand why this is the case.
A special thank you to my patrons:
Daniel
Zwoa Meda Beda
valqk
Toma Marini
Cole Philips
Allan Mackay
RePeteAndMe
Sam Lutfi
Cakeskull
#d4a #twostroke #supercharged
00:00 Two Stroke Recap
04:25 Fixing the Problems of the Two Stroke with Valves
09:01 Why Poppet Valved Two Stoked Can't Breathe Fast Enough
11:26 Enter RevForce
16:26 Not just a bunch of CAD
16:38 Numbers and multi-fuel