This is a rotary Wankel engine. It features
a triangular rotor spinning inside an epitrochoidal housing This is a Liquid Piston Engine and it features an epitrochoidal rotor spinning inside a triangular housing and apparently that makes it better in every way and gives it the power to change everything So today we're going to take
an in-depth look at this engine, we'll analyze it we'll see its benefits, its drawbacks and
we'll compare it with traditional piston and traditional Wankel engines to see its potential
to change everything change [Music] everything Obviously to analyze the engine we must first
understand it, and the best way to understand it is to compare it with a conventional Wankel
engine. So the rotor rotates and as it does that it creates an empty space AKA vacuum. The vacuum
pulls in air and fuel through the intake ports on the engine covers. The rotor rotates some more
and it compresses the air and fuel mixture into the two tiny spaces on the side. The spark plug
ignites the mixture, combustion pressure builds, it pushes the rotor and torque is generated. As the
rotor continues spinning it pushes the exhaust gases out through the side of the housing. Each
rotation of the rotor yields three combustion events And now the Liquid Piston engine. Which doesn't feature any pistons nor are they liquid It's called a Liquid Piston because the original
idea of the inventors of this engine was to use an actual liquid as a piston. Now that didn't work out
but the name Liquid Piston stayed so now we have a pistonless engine with metal rotors from a company
called Liquid Piston. Now the engine itself is not called a Liquid Piston. The engine is called
the "X - engine" and according to Liquid Piston "The X-engine is not", that's a capital NOT
"a Wankel engine, it has a fundamentally different thermodynamic cycle, architecture and operation"
Let's observe. So the air comes into the engine through the crankshaft. The crankshaft has air
holes in it. The air goes through the rotor and then fills a volume inside the housing. As the
rotor continues rotating the intake port on the rotor ends up being past this seal here
here, so the air and fuel end up being trapped right here Now the rotor compresses the air-fuel
mixture which eventually ends up all squeezed into this tiny space where it gets ignited by a
spark plug. Combustion occurs, pressure builds, it acts on the rotor and torque is generated. As
the rotor continues to rotate it exposes the combusted mixture to the exhaust cavity of the
rotor. The pressurized mixture rushes into this cavity which overlaps with an exhaust port
in the cover and so exhaust gases escape from the engine Now if we observe both engines in operation
we can conclude that the non-Wankel X-engine which has a "fundamentally different thermodynamic cycle
architecture and operation" does three combustion events per single rotation of the rotor just
like a Wankel, also just like a Wankel it does intake, compression, combustion and exhaust. So
how is it then fundamentally different? Is this statement nonsense? It's actually not. It is
an exaggeration but it's not complete nonsense And that's because the inverted geometry of the
Liquid Piston X-engine enables it to overcome an inherent limitation of the traditional Wankel.
Now Mr. Kenichi Yamamoto who is the father of Mazda's Wankel engine and he was at the forefront of
Mazda's development and inspirational efforts to make the Wankel engine viable for mass production,
he wrote a book in 1981 which is surprisingly called "The Rotary Engine" In that book he
discusses at length the benefits, the drawbacks of the rotary engine, he does many calculations
and he also talks about the compression ratio And it turns out that the Wankel engine
has a compression ratio, a practical sensible compression ratio limit which is around 12:1.
Due to its geometry the Wankel engine cannot go higher than a compression ratio of 12:1 and
this means two things. Number one, it limits the efficiency of the Wankel engine, because usually
the higher the compression ratio the greater the engine's efficiency. Number two, it makes a diesel
or a compression ignition version of a traditional Wankel engine impossible, unfeasible. Many big names
have tried, nobody has succeeded. Also it turns out that Mr Yamamoto's conclusions stand correct
more than 40 years later because Mazda's newest and only currently mass-produced Wankel engine, which
is used as a range extender in the Mazda MX-30 R-EV has a compression ratio of 11.9:1. But the
different geometry of the Liquid Piston engine means that it does not have a compression ratio
limit which means that a compression ignition engine like a diesel engine is definitely possible.
And that is exactly what Liquid Piston has done with their compression ignition version of their
design which can run on diesel or any other heavy fuel But the different geometry of the X-engine enables another very important benefit and that is the pistonless implementation
of the Atkinson cycle. Liquid piston calls this the "High Efficiency Hybrid Cycle" but in
reality it is a pistonless Atkinson cycle Now the whole premise of the Atkinson cycle is to have
a combustion or expansion stroke that is longer than the compression stroke. Now the compression
stroke wastes, it consumes, it saps energy whereas the combustion stroke generates energy. So if
we make the combustion stroke longer, larger than the um compression stroke then we give the
energy the opportunity to extract as much energy from the combustion stroke as possible, which means
reduced energy losses and improved efficiency Now traditional piston engines they can also run the
Atkinson cycle by manipulating intake valve timing However, when they achieve Atkinson they do so by
reducing the compression stroke so the expansion stroke ends up being greater than the compression
stroke, but this is not ideal because reducing the compression stroke also reduces performance. What
we want to do is increase the expansion or the combustion stroke without reducing the compression
stroke. Traditional piston engines cannot do this without a system of complex intermediary rods and
this was James Atkinson's original idea However, this greatly increases friction, size, weight, cost,
complexity and it also greatly reduces the RPM limit of the engine which is why this design never
saw widespread use. Now if we observe the unique geometry of the X-engine in operation and we overlay
its expansion... there's no stroke, expansion volume over its compression volume we will see that the
shape of the rotor as well as the size and the positioning of the intake and exhaust ports and
cavities results in the combustion volume being noticeably larger than the compression
volume. The traditional piston engine and the traditional Wankel engine they cannot achieve
this because the static sizes of their compression and combustion volumes are always the same. The
fact that the X-engine achieves this without any auxiliary systems or a great number of additional
parts is most certainly noteworthy and impressive And because we have a greater expansion volume
it also means that we have less wasted energy and therefore less energy, in other words less pressure
and less heat in the exhaust gas coming out of the engine. This helps the engine have reduced
noise and it also helps it run cooler The fact that the engine also doesn't have cams or valves
further reduces noise and the fact that we don't have a reciprocating piston reduces vibration.
Another benefit of the relatively simple design, the relatively low number of moving parts
together with the three combustion events per rotor revolution creates is high power density. The current spark ignition version prototype of the X engine it's called X-Mini. It's 70cc,
3.6 horsepower, 4.5 lb but according to Liquid Piston the mature design will be
5 horsepower and only 4 lb this gives us a power density of 1.2 horsepower per pound which is very
impressive and we can see just how impressive it is if we compare it to a conventional piston based
scooter engine which is also 70 cc, 6 horsepower but it's 8.8 lb and it's much bigger and it has
a power density of 0.68 horsepower per pound So it manages only a bit over half of what the X-Mini can do. So we can conclude that this is a very lightweight, extremely compact, high power
density engine which offers reduced noise and vibrations compared to most conventional piston
based engines. These are the key benefits the engine brings to the table and based on this
Liquid Piston believes that the engine can be potentially very attractive for things like
generators and auxiliary power units, UAVs, range extenders, handheld power equipment, mopeds and
other small vehicles, lawn and garden equipment, robotics and the company also plans to enter the
urban mobility and automotive markets. Now this is without a doubt a very interesting design and
I believe it deserves the attention that it's getting due to its innovative and creative nature.
However, I also personally believe that outside of niche specific UAV and generator applications
this engine has a very low chance of market entry and mass production and application. Liquid
piston engines have resolved the compression ratio imitation of the Wankel but they have not resolved
the apex seals. This engine still has apex seals They have simply changed location. Instead of being
in the rotor they are now in the housing According, to Liquid Piston this is a significant benefit because the seals no longer have to withstand centrifugal forces According to a technical paper they wrote
their current models exhibit a 35% reduction in by-blow compared to a conventional Wankel and
they believe that ultimately 65% reduction may be possible. This is simply not enough for a mass application in many different markets because decent piston engines they have a quarter or a
fifth of the blowby of a Wankel. Just like the Wankel the X-engine has a complex multi-seal Arrangement
which does not lend itself well to mass production or longevity. If you observe Mazda's video on their
assembly of their latest range extender Wankel you will see that the engine is mostly assembled
by hand in a process that requires skill and finesse So even a company that is has been working
with rotary engines for decades did not manage to simplify and automate the process. And if you
observe the assembly process of a modern piston engine you will see that it's very different
to the rotary. But one of the greatest issues that the Liquid Piston design has is lubrication. Now
any engine with apex seals struggles to lubricate the apex seals because the apex seals cannot
benefit from a constantly reapplied oil film on the cylinder like piston rings can do. So what
conventional rotary engines did to lubricate the apex seals is to inject small quantities of
oil into the intake into the air fuel mixture and this would then lubricate the apex seals
which are in the combustion space of the engine This meant that the engine burns oil by design
and this is one of the main reasons why rotary engines have poor emissions and why they're not on
the market anymore and why they don't last as much and why they last a lot more if you mix two-stroke oil into the fuel for rotary engines Now Liquid Piston has the benefit of stationary apex
seals so they can lubricate them directly through access points in the housing of the engine and
liquid piston claims this would allow them to lubricate the apex seals much better and have
oil consumption of the engine comparable to a four stroke piston engine. I personally believe this
is a bit overly optimistic and in any case having to burn oil to lubricate an integral part of the
engine negatively impacts either engine longevity or emissions or possibly both but that's
the minor issue in terms of lubrication of the Liquid Piston engine. The major issue is the crankshaft.
Remember, the crankshaft has air holes in it to get air into the engine and because air comes through
the crankshaft it means that we cannot subject the crankshaft to an oil bath or even pressurized oil
and so the Liquid Piston engine as we can see from their "How It's Made" video uses sealed bearings instead of Journal bearings or ball bearings which are submerged in oil,
which are constantly exposed to oil Sealed bearings are simply an inferior solution in terms
of longevity compared to what conventional piston and rotary engines use and this together with
apex seals is likely the reason why both the spark ignition and the compression ignition version
of the X-engine are expected to last only 1,000 hours between rebuilds. Modern gasoline engines in
cars and bikes, good bikes, they usually manage 3500 - 4000 hours, small frame diesel
generators also 4000 - 5000 hours. Large diesels, industrial diesels, 5, 6, 7, 8, 9, 10,000 hours and many
users push many of these engines well beyond that uh uh in certain applications and the engines can
last a lot longer and we can see that the X-engine simply is inferior in this regard. And even
the conventional rotary engine benefits from an oil sump and proper lubrication of its internals
because everything before the face seals of the rotary is lubricated by pressurized oil and this
include includes the gears of the rotor as well as the eccentric shaft. The final problem that
the X engine shares with the Wankel is large spaces in the combustion area. These negatively
impact efficiency because the larger the space in the combustion area the more effective it is at
absorbing energy from the combustion in the form of heat In other words, these large spaces they
rob the rotor of the energy of the combustion The other thing that's bad for efficiency is that,
just like the Wankel, the X-engine has large face seals on both sides of the rotor. These two things
then ultimately lead to relatively unimpressive thermal efficiency figures for the X-engines.
We have 25% for the spark ignition version and 45% for the compression ignition version. Now 25%
for a small 70cc engine is not that bad but this is also what very inexpensive mass production
ready piston engines achieve easily. To replace them the X-Mini needs to do better. Now 45% for a
diesel is pretty decent and although we do have diesels that can do 50% and above, small frame
generators, they're usually somewhere between 35 - 40% So this engine definitely offers, the
diesel version of the X-engine, definitely offers an improvement here. Unfortunately the X-engine
achieves its peak output of 36 KW at 7,000 RPM whereas conventional diesel generators do the
same at around 2500 RPM which means that the X-engine has no hope of lasting nearly as long
as a conventional diesel generator and this is of course further augmented by the apex seal as well as the poor lubrication we discussed earlier. The other issue which may
prevent a vehicle-based diesel application is lack of torque which is yet another feature that the X-engine shares with a conventional Wankel Because both designs are devoid of the conventional crank
and rod leverage they have inherently pretty low torque. If we use the horsepower and RPM figures to calculate torque for both of the X engines get 2.5 NM of torque
for the X-Mini and we get 50 NM of torque for the compression ignition. If we compare this with
equivalent piston based engines we get that even the absolutely archaic Honda Super Cub 70 cc from
the late 60s does noticeably better in terms of torque Whereas a conventional diesel generator can
do more than three times as much torque However, it must be noted that the conventional diesel
engine also weighs more than 10 times as much and is 2.5 times larger. Another potential
problem that the X-engine shares with the Wankel is that this engine is pretty much unsuitable
for variable valve timing because we do not have a cam and valves the only variable valve
arrangement that can be used used is one similar to the power valve that we can see on two stroke
engines, and although some rotary Mazda engines in the past they had something like this and it
does help it's simply not as effective and not as flexible as a modern variable valve lift and
timing system that can be seen on most modern piston based engines. So let's try to sum things
up. We have a very lightweight, very compact, very power-dense engine which is also potentially
very quiet and doesn't vibrate too much But we also have poor emissions, poor torque, poor
longevity and potentially a difficulty to be adapted to inexpensive rapid mass production. So
the poor torque, poor emissions and poor longevity make it unsuitable for road legal vehicle
applications. The same reasons also make it problematic for a range extender. The difficulty
for rapid inexpensive mass production is likely going to be a barrier for handheld power, lawn and
garden applications. So what is this engine good for? Well fortunately there is somebody out there
who isn't too concerned with engine longevity or emissions and has a lot of money, that somebody
is the army of the United States of America and these engines, the compression ignition versions are great
for them as power generators because Number one, they're very lightweight so they can be easily
carried around, they're very small so they can pack a lot of them into an airplane. Who cares if
they don't last too long? Because they last long enough and they can always ship more of them
in the airplane. The emissions? Really nobody's concerned with that in the Army because the Army
is concerned with annihilating enemies so air quality really isn't on the list of priorities.
And this probably explains why the Army has given a multi-million dollar grant to Liquid
Piston to further develop these engines The spark ignition version is probably going to be great
for UAVs as well, because power dense, lightweight, quiet - what more could you ask for? It's also small.
I also think that likely in the future UAVs are going to be a field where we might see some very
interesting internal combustion engine designs that are going to be very small, very lightweight
and UAVs aren't constrained with emissions and stuff like that, nor do the engines need to last
very long, so we might see some very interesting stuff there in the future, because battery
technology simply isn't there yet and it's too heavy and whatever So overall,
this is definitely a very interesting engine design I really like the reverse Wankel idea
it is no doubt uh creative and it's innovative and I am sympathetic of the fact that
emerging new engine designs they need to claim very widespread potential application to attract
investors, but outside of these few niche specific applications where this engine will likely excel
and offer genuine benefits I don't see a lot of potential for a more widespread application. So
there you have it, the non - Wankel, reverse - Wankel Liquid Piston X - engine, which does not have pistons
nor are they liquid. As always, thanks a lot for watching and I'll be seeing you soon with more stuff...
uh fun and useful stuff on the d4a channel this is the first time I ever got the outro wrong and I'm
going to keep it in the video. Thanks for watching
