Today's video has been
brought to you by Squarespace. What is up Engineheads? Today we're doing a detailed comparison of the
benefits and drawbacks of air-cooled, oil-cooled and water-cooled engines. So first let's answer the question,
why do engines even need cooling. Well there's a very simple
way to answer that question. Get your hands. And rub them together. Feeling the heat? Well, that heat is a consequence of friction. And there's plenty of friction
happening inside the engine. But by far the largest source of friction
inside the engine, up to about 40% of the total friction, is the sliding of the
piston rings against the cylinder bore. Now, the faster you rub your palms together,
the more friction and heat you generate. And the same thing happens to the engine. The higher the RPM, the faster the piston
rings travel against the cylinder bore. And the more passes they
complete in a single minute. And the more they do this,
the more heat they generate. Now, if this heat is left uncontrolled, it's of
course going to heat to the engine overheating. which is eventually going to cause it to
melt, which is obviously going to distort the parts of the engine, leading
to catastrophic engine failure. So how do we control all this heat? Well the earliest and simplest
answer is to use the air, that's already available
everywhere outside the engine This means that air-cooled engines don't need
any additional cooling equipment like liquids, or awkward containers, or hoses, or whatever. Air-cooled engines cool themselves simply
by being in contact with the surrounding air, and transferring their heat onto this air. You can easily recognize air-cooled
engines by the increased number of fins on their cylinder heads, and sometimes
even on other parts of the engine as well. These fins serve the purpose of increasing
the outer surface area of the engine, over which air can pass and
heat exchange can occur. In other words, by increasing the outer surface area, we increase the space
over which heat can be distributed and dissipate. And that's the basics of air cooling. Obviously, this makes air-cooled engines dead simple. And this has the potential to make them pretty light weight, and their maintenance very easy, and their production costs low. But there's a price to be paid for the simplicity. And the first item
on that price list is uneven cooling If we imagine an air-cooled
engine in the stream of air, we can see that the front part of
the engine does indeed get cooled. But the back part of the engine
which isn't in direct contact with the oncoming air, doesn't get cooled so well Another major issue is that cooling will be
greatly reduced when the engine is stationary. This means that air-cooled engines are susceptible to overheating if they get
stuck in slow moving traffic. Now, this issue can be to an extent
addressed by the installation of fans. But these do of course increase the complexity and production cost, and they also
create a parasitic load on the engine. But the main issue with air-cooled engines is that they're inherently limited in their cooling capacity. Because obviously we're limited in
the extent to which we can increase the outer surface area of the engine with fins And this limited cooling capacity
is one of the main reasons why air engines typically need to
run richer than the liquid cooled ones. Now, running rich refers to the
air-fuel ratio inside the engine. At 14.7 units of air mass to 1 unit of fuel mass, the engine is said to be running
at a stoichiometric air-fuel ratio. In theory, at least at this air-fuel ratio all the
air and fuel inside the cylinder, are consumed or burned during the combustion process leaving no
excess air on or fuel left inside the cylinder. Now, if we add more fuel and transform
the air-fuel ratio to let's say 13:1, we're set to be running
rich 12:1, 11:1, even 10:1. All these air-fuel ratios are possible
inside the engine depending on the engine, but all of these are rich air-fuel ratios. And in theory, we're going to have excess
fuel in the cylinder at these air-fuel ratios. At air-fuel ratios higher than 14.7:1. For example, 15:1, 16:1, 17:1, even 20:1. We're set to be running lean. In theory, there's going to be excess air
inside the cylinder at these air-fuel ratios. Now, the more fuel we introduce into the
cylinder, the cooler the engine is going to run. This occurs because when fuel
is introduced into the cylinder, it transforms from fuel into fuel vapor. But for this to occur, energy is needed. And that energy is heat. So, as fuel vaporizes, it absorbs a relatively
large amount of heat from its surroundings. And this then reduces temperatures. This is known as evaporative cooling
And it's the same basic principle behind sweating. When we're hot, our bodies sweat, and this cools you down, because heat energy is
required to evaporate the sweat off of our skin. And that heat energy is the excess
heat already present inside our bodies. So as you sweat, body heat is expelled in order
to evaporate the sweat, and this cools you down. Now, air-cooled engines rely on running richer
than liquid-cooled engines, to ensure that engine doesn't overheat even when outside temperatures
are high and the vehicle is stationary. But running richer than required
not only reduces power potential, it also can dramatically
increase hydrocarbon emissions, which is one of the reasons why air-cooled
engines are no longer present in cars. Another fact which contributes
to increased emissions, is that air-cooled engines typically require more
time to reach optimal operating temperature. This is because their cooling system is always on. The fence are always there, and
the air is always around engine. You cannot turn off any of these things. And this is why air-cooled engines typically run cold longer after startup, which
also increases hydrocarbon emissions. So air cooling obviously has its limits. But engineers soon realise
that they could overcome these limits by leveraging a liquid that's
already present inside the engine. But more about that after
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purchase of a website or domain. Now, the line between air-cooled and
oil-cooled engines can be boring. And this is because all oil-cooled
engines are also air-cooled. And on almost all oil-cooled engines you
will find the same air cooling fins that you can find on engines that are only air-cooled. The other reason is that many air-cooled engines, like the Volkswagen Porsche Flat-fours and
Flat-sixes also feature an oil cooler on them. So some people refer to them as being
oil-cooled, rather than air-cooled. But a clear distinction can be made An engine is classified as oil-cooled
not by the presence of an oil cooler. But by the fact that a part of
the oil is specifically circulated through dedicated channels, with the clear intent
of cooling rather than lubricating the engine. A telltale sign of an oil-cooled
engine will be increased oil capacity. Now, one of the most widely known
examples of oil-cooled engines has been manufactured by Suzuki for many years. And these are engines featuring their
SACS, or Suzuki Advanced Cooling System. This system was present on GSX-R, as well as
GSF, Bandit, DR and other Suzuki motorcycles. The increased oil capacity which
reveals their oil-cooled nature is very obvious on these machines. For example, a GSXR 750 from the late 80s
needs, 4.7 liters of oil for an oil change. In comparison to this, an air-cooled
only or a water-cooled 750CC motorcycle carries noticeable less oil. Now, the oil pump of the SACS system
has a dual-chamber, dual rotor design. One side of the oil pump
circulates oil at a high pressure, to ensure the lubrication of engine internals
and the prevention of metal to metal contact. But the other side of the oil pump
circulates oil at the low pressure, but at high volumes, to ensure optimal cooling. Now, the cooling side has dedicated channels, which fall in the vicinity
of the combustion chamber. The main source of engine heat. And they cool it by circulating large volumes
of oil, quickly all around the chamber. Now, the cooling channels also feature small
ridges which act as boundary layer breakers. They prevent a zero velocity boundary layer
from forming directly on the surface of the cooling channel, and reducing the
efficiency of the heat exchange. After this, the oil circulates through an
oil cooler which is essentially a radiator. And a radiator is another device
that relies on increased surface area, to maximize heat exchange with
the air passing through and over it. Now, the oil is distributed to multiple
thin tubes that go through the radiator. And these tubes have an extremely large
number of very small fins attached to them. Now the oil transfers its heat away to the
tubes and the tubes transfer it to the fins, and then the fins are cooled by the air. In this respect, you can say that all
engines are ultimately air-cooled. And that the liquid is only used to store the heat and transport it away from
the source to the radiator. And then the radiator can be
ideally suited in the stream of air. And the radiator also isn't limited in
the surface area increasing via fins, in the sense that the engine itself is. Leading to even cooling across the
entire surface of the radiator. So oil cooling has the advantage of being able
to circulate all around the combustion chamber, take heat away right from the source,
and evenly cool all parts of the engine. The downside is the presence of an oil cooler,
which increases complexity and production cost. But most air-cooled only
engines also have an oil cooler, so the only real disadvantage is increased
servicing costs due to increased oil capacity. But there's another drawback to oil cooling. And it has to do with the
heat capacity of engine oil. Now, unused engine oil has an average heat
capacity of around 2 kilojoules/Kelvin. This means that it can absorb 2
kilojoules of energy in the form of heat, before its temperature increases by 1 Kelvin. Water on the other hand has a heat
capacity of 4.18 kilojoules per Kelvin, which means that water can absorb twice the amount
of heat before its temperature starts increasing. Making water the ideal
solution for cooling engines, if you plan to make your
engines generate a lot of heat. And that's exactly what modern engines are doing. Modern engines tend to run closer to
the stoichiometric air-fuel ratio in many conditions, in order to increase
efficiency and reduce fuel consumption. But the closer we are to the stoichiometric ratio,
the higher the heat generated by combustion. Also, force induction in the form of turbocharging
or supercharging, is present on many modern engines. And that too increases heat. Modern engines especially those high-performance
ones on motorcycles, tend to rev very very high. And that's another source of increased heat. And all of this together with
ever-increasing demands for power, efficiency, and reduced emissions,
tends to make modern engines run very hot And in most cases, oil simply isn't adequate to
absorb all this heat generated by the engine. And this is where water cooling steps in Oil now has only a secondary
minor role in cooling the engine, and the main task of cooling belongs to water. Water circulates through dedicated channels all
around the engine block in the cylinder head. Meaning that it absorbs heat quickly and
efficiently from all around the engine, and cools the engine evenly. Now, water alone doesn't
circulate through the engine. It's actually a mixture of water and anti-freeze. As the name suggests, anti-freeze
prevents the water from freezing. When water turns into ice, it expands. So if water were to freeze inside an engine
block, it would likely crack the engine block. Anti-freeze also serves as a rust
inhibitor, and prevents corrosion which would occur inside the engine if
water alone was used in the cooling system. To ensure proper situation, a
water pump is also necessary. And it's usually driven by the engine via a belt. Altough in more recent vehicles, the
water pump can also be electronic which reduces the parasitic hold on the engine. As in the case of oil cooled,
water is passed through a radiator. And radiator dissipates the heat absorbed
from the engine into the surrounding air. Another key component of water
cooling is the thermostat. And it ensures that water doesn't
circulate through the radiator, until the engine reaches
optimal operating temperature. This reduces emissions and engine wear, by dramatically reducing the time it takes
the engine to reach operating temperature. So water cooling is by far the most
efficient and capable engine cooling system. And this is why modern engines have it. But the price to be paid for it
is increased production costs, increased maintenance, and increased number of
parts required for water cooling to operate. And there you have it, the advantages and
drawbacks of different engine cooling systems. As always, thanks a lot for watching. And I'll be seeing you soon,
with more fun and useful stuff. On the D4A channel.
