I'm a fully grown human of average build and
average strength. This is a tiny 125cc scooter engine that I cut in half. It is exactly 16 times
smaller than a 2 liter, 4 cylinder car engine and now I'm going to use my average strength to try and
open the valves of this engine, and although I am definitely able to do it, it takes a considerable
amount of strength and effort to open the valve It takes strength because to open the valve I
must compress the valve spring. I must overcome the resistance of the valve spring. The work and
energy I put into compressing the spring is then "stored" in the spring and once the camshaft moves away the spring decompresses and snaps the valve shut. Now I did this just a few times and
I already feel strain in my hand but the engine when running, has to do this thousands of times
every minute because we must open both the intake and the exhaust valve during every full combustion
cycle to get air in and out of the engine Which means that, to keep operating, to open the valves,
the engine must consume some of the work that it does It must consume some of the energy that
it harnesses from combustion. In other words, the valve train is reducing the power output and the
efficiency of the engine. But we don't really have a choice. Four stroke engines, which is what 99% of the engines on the road are, they need to let air in during intake. The combustion chamber must be
sealed during compression and combustion And we must let air out during exhaust. This means that we
need a system capable of sealing and unsealing the chamber thousands of times per minute while at
the same time withstanding the incredibly harsh conditions present inside the combustion chamber.
And that's exactly what poppet valves like this one actually do. They are great at sealing because
the conical shape of the valve face fits into the conical shape of the valve seat and together they
create what's known as a positive seal They're also both made out of hardened metals which
offer impressive resistance to wear and increased temperature and as combustion pressure acts
on the valve head it actually pushes it harder against the counter-sunk seat. So the greater the
pressure the better the seal Unfortunately, other than being great at sealing the poppet valve has no other inherent advantages. You can even say that from an engineering perspective this is
just a necessary evil that we worked around with decades of technological advancements. The first
thing that we had to solve is to get valve seats to even last a reasonable amount. Back in the 50s
and 60s the only way we could get valve seats to not fail very quickly was to put lead in the fuel.
One of the reasons why we leaded fuel was not just to prevent knock in the engine. It was also
to prevent valve seat failure. It protected the valve seats because the intense hammering of
the valve face against the valve seat under very high temperatures would lead to micro welds
between the face and the seat. As the valve opened again these micro welds would tear eventually
leading to valve seat recession, which is just another word for valve seat failure. The engine
would lose compression, you needed a rebuild Then we realized lead is bad for us so we phased
out leaded fuel and engineers and manufacturers were forced to develop better materials and designs and
manufacturing processes to actually get valves and seats to last a reasonable amount without lead. That was the first challenge we had to overcome The next challenge was the valve spring. It too is a big
problem because at high RPM when you try to open and close the valves many many many times in
a single second the valve spring cannot keep up It can simply not open and close that fast,
that rapidly, so instead of full opening and full closure you get something known as valve
float. The valve just floats around the seat which of course leads to a loss of performance
or even worse, in an interference engine, it leads to contact between the valve and a piston which
leads to a bent valve. Again, loss of compression you need an engine rebuild. Ducatti developed
the very complex and maintenance-heavy desmodromic system just to get rid of the valve spring. Koenigsegg
developed the extremely complex Freevalve system just to get rid of the camshaft. But neither
of these technologies ever became mainstream In the mainstream, engineers persisted with the
conventional valve and the conventional spring the conventional valvetrain. They persisted. They
pushed harder and they developed things better We got better valve spring materials, better
designs and eventually we got engines that still had conventional valve springs but they
revved to the moon. They persisted even further and we got variable valve timing and lift control
systems that can do pretty much anything that Koenigsegg's Freevalve can do. The valve remained and
the conventional valvetrain remained and with a lot of effort we made it better and better. But
there's something that no amount of technological development can resolve with the valve because
it's an inherent problem in its shape and that's that the valve, which is supposed to let air in
and out of the engine is actually an obstacle to air flow. It impedes and slows down the flow of
gases in and out of the engine. Imagine you have a container A and a container B. Now imagine that you want to get the maximum amount of gases at the maximum speed from container A to container
B. What kind of shape would you use? Well, both physics and common Ssense tell us that the best
shape is a simple, straight, open-ended tube But unfortunately with valves, we can kiss a straight
tube goodbye. The shape of the valve means that instead of a straight tube we have something
like this. The gas must flow around the valve It cannot go straight out through the tube. The aerodynamic shape of the valve does help to smooht out the air flow but still, the gas must go
around the valve. It must circumvent it to get in and out of the chamber. There is no denying the
fact that gases would have a much easier time if the poppet valve simply wasn't there. But we got
around this too. We created clever intake manifolds with variable lengths and clever resonances to ram
the air past the valve. We created forced induction in the form of super and turbocharges to stuff
more air into the chamber. We created long and complicated exhaust manifolds to help suck the
exhaust gas out of the chamber. When you think about it a lot of the development of the internal
combustion engine has actually been an effort to work around the valve. When You observe a typical
engine you will see that a cylinder head together with the intake and exhaust manifolds takes up
more space than the heart of the engine which is the engine block where the crankshaft rods and
pistons are. We need more space for the breathing equipment because valves make breathing hard. But
what if there was a better way? What if we simply got rid of the valve instead of trying to
constantly work around it? Of course many engineers asked this very question over the years and they
did indeed come up with a bunch of alternatives One of the more promising and more elegant ones
is called a rotary valve. Instead of a poppet valve, valve seat, spring, retainer, rocker arm, lifter and
camshaft, all we have is a rotating barrel with cavities As the barrel rotates the cavities line
up with other cavities in the cylinder head to let air in and out of the engine. So what we actually
have now is a straight open-ended obstruction-less tube which means dramatically improved airflow
compared to a poppet valve, which means better performance and less need for complicated intake
and exhaust manifolds. We also don't have valve springs which means we're not wasting energy on
compressing them which means again more power more efficiency Also because there's no valve springs
there's no possibility for valve float at any RPM which means that achieving ridiculous RPM is much
easier now. Also this system, the rotary valve barrel system is much more simple than a conventional
valvetrain. It has a greatly reduced number of parts which means less complexity, less chance
of failure and also reduced engine size and weight So the rotary valve is better than a conventional
valvetrain in every way? Okay. So where is it then? If it's better in every way, why have we been using the poppet valve for the past 100 years and not the rotary valve barrel? Well that's
because the rotary valve is better than the poppet in everything except one thing, and that one
thing is sealing. It is difficult to achieve a good seal with a rotary valve arrangement like
this one but it's not impossible. It is difficult because to seal, the rotary valve barrel must
either rotate inside a round seal or rotate together with some sort of o-ring and then the
o-ring will seal against some sort of casing We have plenty of o-rings and round seals in every
engine. For example the crankshaft and the camshaft ends they rotate in round seals. But
there's an issue. None of the parts that have round or rubber o-rings and round seals on them,
none of them are exposed directly to combustion heat But a rotary valve barrel is. Because it's
exposed directly to combustion heat it expands a lot more Now the problem with expansion is that
a round seal, an Oring, a rubber round seal needs very tight tolerances to operate. When the part
expands maintaining these tolerances becomes very hard and then the seals either fail or wear
much faster than we want to. But as I said it's not impossible to do it and, in fact, it has been
done. A man by the name of Ralph Watson has built and operated an engine with a system
very similar to the one I'm showing you here succesfully and raced it successfully since 1989.
Now what Mr Watson did is that he made a custom rotary valve system for a British BSA 90 degree V twin
engine. His system employs conventional material o-rings together with wavy rings, additional bronze
seals and springloaded levers to ensure that the o-rings perform as they should during engine
operation and that the valve remains sealed The rotary barrel sits on oiled bearings and has overall
proven itself as an effective and reliable system As I said this engine has been used and raced
extensively for several decades In fact the project is so good that it outlived Ralph Watson
himself. The car, the BSA special now has a new owner Although this is not some sort of mass
produced daily driven application it is still very valuable because it's an obvious proof of
concept that rotary valve technology can work and can be employed in practice. But what
we also have now is an ambition to take rotary valve technology into the mainstream, into mass
production, and this ambition comes in the form of a company called Vaztec from North Carolina
in the United States. In fact, the animation I've been showing you is from Vaztec's website. The
company's composed largely of ex GM engine developers who want to take this technology
into mass production and their design is a rotary valve barrel with cavities similar to Ralph
Watson's. There are differences in sealing but the big difference is that Vaztec's cylinder head no
longer has any oil in it, Their design does not need oil in the cylinder head, in fact all the oil
now stays in the engine block. They have patented a rotary valve sealing system that consists of
Upper and Lower valve seals together with gland gaskets thrust washers and support bearings and
they have presented their concept on a conference of the Japanese Society of Automotive Engineers
in 2022 where they won an award for their paper Here you can see the comparison of the required parts
between the Vaztec system and an equivalent 50cc power equipment engine. As you can see, the Vaztec
cylinder head requires less than half the parts At this time they have goals to introduce
the technology to small handheld engines and power equipment but aim to expand to the vehicular
applications in the future. So, overall sounds very promising right? Rotary valves. Many
benefits. So are we going to see it in the next decade maybe two? Is it going to happen? Well, maybe.
It is promising, the benefits are undeniable but the timing is not ideal. We have two obstacles
for rotary valves becoming mainstream in the near future The first obstacle is that many industries
are now going through a, let's say a love affair with electrification. Whether that love affair
actually turns into a marriage, only time will tell But the love affair does to an extent impede
large scale investments into combustion technology The other issue is that many major important
combustion technology manufacturers and developers have spent insane amounts of research
and development into the conventional poppet valvetrain so they want to see a return on their
investment, which means that they preferably want to keep selling the conventional valvetrain for as long as possible. So the timing is not ideal despite the benefits. Speaking of the
benefits, are there any drawbacks, other than the sealing? Well there are two minor ones that I can
notice from a superficial examination of Internet material because I never had anything in my hands. The first drawback, little one, is that the size of the rotary valve barrel and its proximity to
the combustion chamber means that it might be difficult to locate a spark plug right in the
center of the chamber. As you can see on Vaztec's little CAD drawing, the spark plug is on the
side. It also might be difficult to find space for a direct injector because the barrel takes up a
lot of space. Whether this will be true for larger engines with larger combustion chambers
I don't really know, just something to keep in mind The other small drawback that I noticed, and this
is from the BSA special, Ralph Watson''s car We can see traces of combustion around, on the underside
of the valve, and this is because the rotary valve cavity is not sealed against the combustion
chamber. We are only sealing the sides of the barrel So some of the combustion gas, some of the
combustion energy escapes out the chamber and goes into the little tiny space which is around the
valve. This is a very small volume but it's still a little loss of energy and thus a little loss
of efficiency. It's probably a very small loss which is far outweighed by the elimination of
valve springs and camshafts and whatnot but again something to keep in mind. There's also
a little benefit when you think about camshafts and rotary valves. The rotary valve barrel is
just rotating, just like a camshaft and it's also driven by a timing belt or timing chain
just like a camshaft, which means that we can take a variable valve timing gear and attach it
to the rotary valve barrel and get variable valve timing using existing technology very easily. So, a
nice convenient little benefit. I guess that's pretty much it. Definitely a promising technology
with its little challenges in terms of sealing and the timing for it isn't ideal but it's still,
regardless of whether it happens in the next decade or two or not, it is still worth knowing about
because it serves as a very nice demonstration of the shortcomings of the ubiquitous poppet
valve. So that's pretty much it, as always thanks a lot for watching I'll be seeing you soon with
more fun and useful stuff on the D4A channel
