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The heat
is off
Wayne Ward explains how to use coatings to help improve engine
and vehicle performance – without necessarily burning more fuel
W
hen the subject of coatings was last covered in these
Formula One with exhaust heat and kinetic energy recovery. The car
pages, in 2010, most of the coatings in widespread
manufacturers involved wanted an engine formula that reflects a high-
use now were already commercially available.
tech approach to efficient motoring, and despite the performance and
What has perhaps changed most since then though
reliability of modern Formula One engines, the manufacturers have no
is the fact that coatings are now more commonly considered at the
appetite to continue along a technological dead end. MotoGP notably
design stage. Having proven their worth in the past few years through
has increased engine capacity, but mandates an ever-decreasing
experiment and in solving specific problems, more recent components
quantity of fuel for the race. Witness riders running out of fuel for
are likely to incorporate coatings from the outset.
evidence that more work is required on efficiency.
Regardless of whether you believe in global warming or that our
fossil fuel resources are close to being exhausted, it has become clear
The development of coatings for motorsport with the sole purpose of
that these issues can not be ignored; greenhouse gas emissions are the
decreasing friction has advanced the technology to the point where
subject of a great deal of legislation, and gasoline prices worldwide
production car manufacturers can justify using in a cheap engine a
keep rising. The result is a concerted drive for more fuel-efficient
coating that, ten years previously, would have been the preserve of the
vehicles. As far as the car companies are concerned, a happy customer
better-funded Formula One teams.
is a returning customer, and currently a car with low fuel consumption
The ongoing battle to increase vehicle efficiency means that not
makes a lot of customers happy, so it has become the policy of car
only is powertrain efficiency important, aerodynamics have a role to
manufacturers to supply cars that are economical.
play too. Of course, on the powertrain side, we can use coatings to
Race series have a responsibility to reflect motor manufacturer
influence efficiency, the most obvious way being to reduce friction. Yet
policy. That is not to say they are under an obligation, but if race
aerodynamics have a huge influence on the performance and efficiency
series organisers wish to be supported by motor manufacturers at
of a vehicle as well: low-drag vehicles need less power to propel them
the top levels of the sport, the series rules need to match the policies
at a given velocity. Equally, for a given power output from an engine, the
and aspirations of the motor companies. Although Audi for example
top speed will be higher where a vehicle has reduced drag.
probably doesn’t have a ready market for 800 hp V10 diesels, it
30
Coatings are an integral part of this search for increased efficiency.
All very interesting, you may say, but how are you able to play your
has made great marketing capital from its race diesel project, and
part in this aerodynamic aspect of vehicle performance? Well, the greater
continues to do so. Clean, quiet, efficient: just what customers want.
the heat rejection, the greater the cooling requirements, and with that
In addition, 2014 will bring 1.6 litre V6 turbocharged engines to
comes the need for larger coolers, which come with an aerodynamic
FOCUS : COATINGS
Fig. 1 – Shell bearings have thin metallic coatings as standard. These have had
a further dry-film lubricant coating applied (Courtesy of Swain Tech Coatings)
penalty. So we need to consider not only coatings for mitigating
have led to components becoming smaller. Despite smaller components
powertrain friction, we also need to consider heat management.
and bearing diameters, we still have high speed differences at sliding
You may be tempted to think that this aerodynamic penalty applies
contacts, and while we try our best to provide rolling-element bearings,
only to single-seater cars, where bigger coolers require bigger
journal bearings or lubrication wherever possible, friction still accounts
sidepods. In the case of single-seaters, to equate larger sidepods to
for a lot of the energy wasted in an engine.
larger coolers seems intuitive. In closed cars though, even in the
Shells for journal bearings are a prime example of a coated
case of production-based cars where the cooling ducts and coolers
component. These can have a number of coatings, but if we take the
are within the vehicle’s volume, increased air cooling requirements
example of a tri-metal bearing, the steel shell has two coated layers,
have an associated drag penalty. In NASCAR, for example, there is a
both of which are metallic. The first is a relatively thick coating of a
significant penalty associated with the need to provide a large factor of
copper alloy, usually alloyed with lead and tin. This layer is about
safety on the cooling, in case a cooling duct becomes blocked by litter
0.25 mm (0.010 in) thick and provides a support for the thin plated
carelessly discarded by a race fan. Being close to the action is great,
overlay at the bearing surface. Besides supporting the bearing surface,
but such carelessness has affected the performance of these cars, and
the copper alloy intermediate layer has a number of important roles,
therefore their design.
particularly in providing a degree of compliance at the edges of the
The previous article in Race Engine Technology on coatings (1) took
bearing and giving the bearing ‘embeddability’, the term given to the
a ‘tour’ around an engine, and pointed out the coating options for each
bearing’s capacity to cope with small particles of debris within the oil
component. Given the relatively recent focus on performance with
delivered to the journal bearing.
efficiency, this article will look at some of the important factors such as
The overlay has a very low shear strength and is also very thin.
friction, wear and heat management, and will examine how design and
Overlay materials can vary, but alloys of lead and indium are
development engineers can use coatings to help improve engine and
commonly used in racing. To maintain the shape and form of the
vehicle performance without necessarily burning more fuel.
bearing, and minimise friction, the overlay is kept very thin to prevent
excessive deformation under load and keep the contact area to a
Friction and wear
minimum. The combination of low shear strength and low contact
There are many sources of friction in an engine and transmission. With
area provide low friction during those short periods of time where full
so many moving components, it is impossible to avoid heavily loaded
hydrodynamic lubrication has yet to become established.
A number of coating companies also offer polymer-based coatings on
of components in contact. With the passage of time, engine speeds have
top of the bearing shell overlay coating [Fig. 1]. These are marketed as
increased, and attempts to reduce mass and mitigate frictional losses
dry-film lubricants to help when lubrication is poor, such as at engine
t
sliding contacts. From the top to the bottom of the engine, we have pairs
31
FOCUS : COATINGS
At two points in each cycle, when the point of contact
between cam and follower is close to the nose of the
cam lobe, the entrainment velocity drops to zero. If you
plot a graph of valve velocity, the two points in the cycle
occur very close to the maximum valve velocity. Where
the valve velocity is at a maximum, the point of contact
between the follower and cam has stopped moving. At
each of these points, we have a large load to support, but
there is nothing to generate any pressure in the oil film –
there is no hydrodynamic lubrication – and the oil film is
then subject to squeeze-film lubrication.
Away from these points, where the entrainment
velocity is low, the oil film is stable but has very
low thickness. Where the thickness of the oil film
approaches the height of the surface texture on the
Fig. 2 – Camshafts and cam followers are very commonly coated with
DLC or one of its derivatives (Courtesy of Diamond Hard Surfaces)
component, high points called asperities on each
surface can come into contact. At this point, we start
to experience the mixed or boundary lubrication
“A thick CrN under the
DLC will enhance the
loading capacity”
regime, whose coefficient of friction is a function of the hydrodynamic
lubrication and the dry coefficient of friction between the materials
involved in the contact.
In such situations, a low coefficient of friction is very desirable, as
are smooth surfaces. The lower the surface finish height, the shorter the
period during which mixed lubrication applies, and a low coefficient
of friction between the parts in contact ensures that when mixed or
boundary lubrication exists, the frictional losses are mitigated.
As mentioned, DLC coatings have been successfully applied to
camshafts [Fig. 2] and cam followers, but the choice of which ‘flavour’
start-up, when there are oil system problems or where the operating
of DLC to use is not straightforward, so experience is required here,
conditions of the race vehicle cause oil starvation. Cars exploiting
as this has a significant impact on the friction and wear behaviour
downforce over hills or bumps have proven susceptible to a lack of oil
of the contact under boundary lubrication conditions (2). Also, by
at the oil pump pick-up, and any car where there are significant lateral
their composition, DLC coatings can affect the interaction of the anti-
forces due to cornering can also suffer from such problems.
wear additives in the lubricant with the uncoated component in the
have been made much more reliable by using modern coatings
measurable on a full engine dyno, and will definitely be measurable
technology. The cam-to-follower contact is one that has been
on a cylinder head dyno. While the frictional gain is certainly
particularly improved by the use of low-friction coatings. Diamond-
worthwhile, hard coatings have also allowed the use of higher contact
like carbon (DLC) coatings and their derivatives have been especially
stresses between cam and follower. This means that higher forces
successful in such applications. DLC is not one coating but a large
may be used in the system, paving the way for higher levels of valve
family of coatings. They are very often not purely a carbon coating
acceleration and therefore allowing performance engineers greater
but have significant proportions of other elements in order to tailor
latitude in the development of valve-lift profiles.
their properties, and they have a range of possible structures, from
Other than the cam-to-follower contact, the use of coatings to
amorphous to crystalline. Carbon coatings within the DLC family can
mitigate frictional losses in the valvetrain is limited mainly to valve
have a mixture of graphite and diamond-type bonds; very often these
stem coatings [Fig. 3, page 34]. These are commonly one of the
coatings also contain hydrogen and, less commonly, the coatings are
thin, hard coatings, and DLC competes with other coatings such
‘doped’ with metal ions to fine-tune their properties.
as chromium nitride (CrN) and titanium nitride (TiN). On titanium
The contact stresses in the cam-to-follower contact are extremely
valves, companies responding to questions for this article said DLC on
high, and the intention is for the contact to be operating in the
titanium often requires another coating, an ‘underlayer’. One supplier
elastohydrodynamic lubrication regime. The theory and equations of
said, “A thick CrN under the DLC will enhance the loading capacity.”
elastohydrodynamic lubrication are beyond the scope of this article,
Valve coatings that can increase temperature resistance, such as
but there is some value to expanding on them a little.
The conditions for lubrication are influenced by ‘entrainment velocity’
which is the algebraic sum of the velocities involved in the contact.
32
contact (3). The gain from running new DLC-coated followers might be
TiAlCrN, will probably become more important as the temperature of
combustion products continues to rise. While the loads in the valveto-guide contact are low, the intermittent nature of the valve action
t
There are a number of highly stressed contacts in the engine that
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High-performance coatings and a wealth
of experience in the surface engineering
sector makes a huge difference to:
Minimize friction losses, decrease
wear and improve performance.
Extensive knowledge of surface engineering, interactions and failure-mechanisms
allow us to provide solutions to the most demanding applications.
RET_ADTEMP.indd 1
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FOCUS : COATINGS
means lubrication of the contact is rather less than ideal;
the low friction coefficient minimises adhesive wear of
the guide. In race series that allow pneumatic valve return
Fig. 3 – These valves are DLC coated; this reduces
friction between stem and guide, and seat wear can also
be greatly reduced (Courtesy of Industrial Hard Carbon)
systems (PVRS, or air springs as they are sometimes called),
the bore in which the pneumatic systems operate is often
coated to reduce friction and mitigate seal wear. Formula
One and MotoGP, which both have high engine speeds, use
PVRS systems.
The use of coatings on pistons and rings has been common
for a long time. Piston rings for racing have progressed from
hard metal-sprayed coatings such as molybdenum to the hard,
thin coatings such as DLC and TiN. The motion of the piston
is reciprocating and there are two points at which the piston
and its rings come to a halt – top dead centre (TDC) and
bottom dead centre (BDC). Again, we have a contact where
the conditions for full hydrodynamic lubrication are not met
throughout the operating cycle.
As far as rings are concerned, the change to thin, lowfriction coatings has a number of benefits compared to the
older sprayed metal coatings. Their most attractive property as a ring
low friction and so is used in much the same way as the resin-bonded
coating is reduced friction, which is of direct interest to the design
polymer coatings. There is one piston company that is noted for its
engineer and development engineer alike. The lower coefficient
use of resin-bonded graphite coatings on piston skirts, and it has
of friction allows some latitude in how the advantage is best used.
gone further by introducing a ‘tread pattern’ into the coating for some
Frictional losses can be reduced compared to a sprayed ring if the
applications, which it says enhances dynamic oil control.
is DLC. There have been several barriers to the use of DLC for piston
old sprayed coatings were a labour-intensive process that required
skirts until relatively recently. Initially, the processing temperatures
machining after coating, but the modern engineering coatings are
required precluded its use for aluminium and a number of steels that
very thin and repeatable, so no post-coating machining is required.
temper at low temperature. In solving this problem for materials such
Coatings such as TiN and DLC are also less susceptible to wear.
as carburising steels, the use of DLC on aluminium has become more
As regards piston skirts, there are a wide range of coatings with the
realistic. However, the simple application of DLC to an existing piston
aim of, or that have the effect of, reducing frictional losses and wear.
is likely to create serious problems, and it has taken piston makers
There are four main types of coating used here – hard engineering
some time to develop piston machining to the stage where the piston
coatings, polymer/resin coatings, graphite-based coatings and
does not simply become a reciprocating file.
phosphating.
Phosphate-based coatings are aimed essentially at improving the
If we were to take an optimised DLC-coated piston and examine
it alongside a similar but conventional uncoated piston, the
running-in of the piston in the bore when the engine is initially run.
difference would be striking. One such optimised piston was shown
They are not especially low friction in themselves, but owing to the oil
in a previous article (5), and the machining can easily be seen
retained in their porous structure, they are a popular choice to provide
to be much smoother than would be found on a conventionally
increased lubricity. They are very thin and provide neither compliance
machined piston skirt and ring lands. DLC-coated pistons need to
nor a surface that can wear into shape.
have a very well optimised skirt profile so that no wear-in of the
Polymer/resin coatings have been applied to racing pistons for
skirt is necessary. The DLC coating is not prone to wear, and areas
decades. They are aimed at both friction reduction and improved
that are too heavily loaded are likely to see the coating damaged,
running-in behaviour. The coating consists of a low-friction polymer
with hard debris possibly produced as a result. Owing to the low
such as PTFE in a resin binder. They are applied and cured at low
strength, low stiffness and high ductility of the aluminium substrate,
temperatures, making them suitable for use on aluminium pistons.
the low-ductility coating simply cracks under high local loads as
They make a useful contribution to friction reduction and have a
the substrate deforms. The adhesion of DLC to aluminium can be
thickness that allows them to wear into a shape that suits the use of
affected by the specific treatment used, the composition and any
the engine. This is not a new concept: thick resin composite coatings
pre-treatments – for example, micro-peening with silicon carbide has
have been used in the past (4) for piston skirt profile development; the
been proved to increase adhesion and maintain low friction for DLC
coating wears into a shape that is then ‘reverse engineered’ to make
on aluminium alloys (6).
the production piston.
A similar coating is resin-bonded graphite. Graphite is noted for its
34
The most recent anti-friction coating to be developed for pistons
to improve ring sealing, with no increase in frictional loss. The
One company has developed a coating based on anodising, and is
treating pistons. The porosity in the aluminium oxide structure of the
t
same ring tension is maintained, or ring tension can be increased
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RET_ADTEMP.indd 1
22/06/2012 16:56
FOCUS : COATINGS
anodising is impregnated with ceramics to provide improved wear
Fig. 5 – Coated gears aimed at low friction can also offer short-term
protection against lubrication failure (Courtesy of Oerlikon Balzers)
resistance [Fig. 4].
The rest of the cranktrain has also been subject to much investment
in terms of coatings, which are often applied to piston pins and con
rods, although these applications are aimed mainly at wear prevention
rather than frictional losses. The application of coatings to crankshafts
is so rare that there is no good data available to judge the success
of hard coatings in reducing friction. However, when writing a
crankshafts article in 2010, two crankshaft suppliers admitted to me
they were offering DLC-coated crankshafts commercially (7).
Low-friction, hard coatings can offer an advantage for gears where
lubrication is marginal, and may offer some protection against failure
due to loss of lubrication where the oil is being lost from a gearbox
or cam drive casing. Coated gears have proved more durable than
uncoated gears in tests conducted by NASA (8). The applications of
coated gears for motorsport are mainly in transmissions [Fig 5].
the heat produced and how we manage unwanted heat can all affect
the performance of the car or bike over the course of a race. Coatings
Managing heat for car performance
can play a significant part in improving this performance. We can use
Heat is something that internal combustion engines produce in great
them to improve volumetric and combustion efficiency, improve the
quantities. Very roughly, 30% of the energy contained in the fuel
efficiency of the turbocharger assembly and decrease the amount of
burned in a typical passenger car engine is turned into useful work
heat rejected to the oil and water systems on the car.
at wide-open throttle. Throttling in gasoline engines reduces this
In terms of combustion, we can improve the efficiency of fuel
efficiency. The remaining 70% has to go somewhere, and as you will
conversion by rejecting less heat from the combustion chamber. This
be aware either from experience or a knowledge of physics, it is turned
can be achieved by increasing the thermal resistance of the combustion
into heat. This heat exits the engine in small quantities by radiation,
chamber walls. In practical terms, we do this by using materials with
but very largely through the exhaust port or into the oil and water
lower thermal conductivity. However, low-conductivity walls mean
systems. We have to reject all of this heat to the atmosphere.
high wall temperatures, and high wall temperatures do not help cylinder
Heat is a by-product of combustion that is largely wasted.
filling. Low-conductivity walls also mean that we probably need to look
Production cars use a little of it for cabin heating but, beyond this, only
to materials other than aluminium alloys, which are known and loved for
turbocharged engines benefit from lots of heat being produced. Ideally,
their high thermal conductivity and low density.
we would like the chemical energy stored in the fuel to be converted
An engine that keeps heat in the combustion chamber would be
into work with no heat generated. How successful we are as engineers
a heavy engine. Coatings can help in this regard, by making our
in optimising the conversion of chemical energy into heat, how we use
lightweight aluminium engine components behave as if they were
made from something less thermally conductive. A thin layer of
Fig. 4 – This piston has been anodised and then the
porous structure thus created has been impregnated
with ceramics to provide a very hard-wearing
surface (Courtesy of Tech Line Coatings)
an insulating coating is very effective as a thermal insulator, and a
number of companies we spoke to for this article are involved in the
subcontract coating of race engine components for this purpose.
The coatings need to be highly insulating, very thin and preferably
have low density. Many of them are based on metal oxides and, if
they are working properly, will get very hot. If they are too thick, and
have too high a mass, they will heat the incoming charge, causing it
to expand, and this can lead to serious losses of volumetric efficiency.
What we want to happen is for the mass of the hot coating material to
be so small that the incoming charge cools it with little heat transfer.
A further disadvantage of the charge temperature increasing is the
likelihood of knock occurring. Knock is uncontrolled combustion,
and can lead to serious damage and even catastrophic failures
of the engine. In the interests of reliability, knock is best avoided,
although some engines are known to give their best performance
at the onset of knock, or even during ongoing knock. Highcompression gasoline engines are known to be prone to knock, as
compression. Although real race engines don’t conform to the ideal
36
t
pre-combustion temperatures are higher than in engines of lower
IBC Coatings Technologies, INC offers a
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and surface treatments:
• Low friction Vanadium carbide – TDC+™
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• Ion Plasma Nitriding – DHIN+™ (crankshafts, springs…)
• More than 10 different types of Diamond like coatings DLC+™
(gears, pins, valves, stems, camshafts, spindles, bearings)
• Thermal Diffusion ceramic coating CERATOUGH™ for
Aluminum, Titanium, Magnesium, Steel, Nickel alloys…
(Pistons, Housings, Cylinders)
• Abrasion, erosion and corrosion resistant Boriding –
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Surface engineering developments are available per customer demand.
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IBC Coatings Technologies, INC, 902 Hendricks Drive Lebanon , IN 46052
Phone: 765-482-9802, Fax: 765-482-9805
E-mail: [email protected], www.ibccoatings.com
RET_ADTEMP.indd 1
22/06/2012 17:12
FOCUS : COATINGS
properties and resistance to thermal shocks
Fig. 6 – Coating the surfaces of the combustion chamber, including the piston
crown and valve faces, reduces heat rejection. Note also the coated ports at the
back of the exhaust valve head (Courtesy of Swain Tech Coatings)
that ceramics have, and they aren’t subjected
to rapidly fluctuating pressures. Both polymer
coatings and ceramic coatings can be used to
good effect in inlet systems.
Exhaust systems, and the management of heat
transfer within and from them, is one area where
coatings can make a huge difference. The return
of the turbocharger to top-level racing makes the
management of exhaust heat more important.
There are two reasons for the significance of
effective thermal insulation and prevention of
radiated heat with turbocharged engines. First,
the turbine becomes more efficient if the turbine
inlet temperature is higher. Second, owing to
the fact that more charge is burned within a
turbocharged engine of given capacity compared
air cycle, they do show the same trend in terms of cycle efficiency
to a naturally aspirated engine running at the same speed, the exhaust
versus compression ratio – that is, a higher compression ratio gives
gas temperatures and flow rates are very much higher. Consequently, the
increased efficiency – so there is a tendency to use engines with high
heat transferred from the hot exhaust system to its surroundings needs to
compression ratios. Turbocharged and supercharged engines are
be more carefully managed in a turbocharged car.
particularly prone to knocking combustion, especially where ambient
Keeping heat within the exhaust gas not only gives benefit to a
temperatures are high and where post-compressor charge cooling is
turbocharged engine, although turbocharged engines do benefit
poor. Metallic coating of piston tops has been proved over many years
most from effective thermal insulation. The first place where the
to protect piston crowns from the damage associated with knock (9).
engineer can look to minimise heat transfer is within the engine itself,
If we add a thermal barrier coating to the top surface of the piston,
and reduce heat transfer via that route, other surfaces that are not
specifically the exhaust port.
We will assume that as much heat as possible has been retained
treated in the same way will be subject to increased heat transfer,
within the combustion chamber. There are a number of design features
as the temperature in the combustion chamber will be increased.
that can be incorporated into an exhaust port to minimise heat transfer
We might expect to find that people are coating other combustion
to the water jacket, but coating with a thermally insulating material
chamber surfaces, and indeed a number of coating companies offer a
is an effective method. For naturally aspirated engines, reduced heat
service to coat the combustion chamber surfaces in the head and the
transfer to the coolant is the only real benefit of an insulated exhaust
flat faces of the valves which see combustion [Fig. 6].
port as it allows the use of a smaller cooler, with the attendant benefits
A lot of work was done on adiabatic and ‘low heat rejection’ engines
of reduced aerodynamic drag. By keeping the heat in the exhaust
between the late 1970s and early 2000s as car companies sought to
gases, we can expect the exhaust system to run hotter. This transfers
develop more efficient engines. Engines that were not required to have
heat to its surroundings by radiation, convection and conduction. We
any cooling circuit were believed to be highly desirable, especially for
can minimise conduction between the exhaust system and the cylinder
military applications, where cooling ducts and grilles are weak points
head by using thermal barrier coatings on the mating face of the
on such vehicles. Much of the work centred on developing thermal
exhaust or cylinder head if there is direct contact.
barrier coatings for use in combustion chambers. Similar materials and
Coating the exhaust system itself is a process offered by a number of
processes developed then (10) are still used these days for
thermal barrier applications. There is a lot of good data, such
as the paper by Civiniz et al (11), on the positive effects of
thermal barrier coatings on combustion chamber surfaces,
which has been generated through the work carried out on
engines with low heat rejection.
There are a number of low thermal conductivity coatings
that can be used in the inlet system of a race engine to
insulate the system’s components from heat generated
in the combustion chamber. A cooler inlet means higher
charge density, and this is good for cylinder filling. Unlike
combustion chamber coatings, those used on inlet system
components do not need to have the high-temperature
38
Fig. 7 – Coating the exhaust headers and turbine
housing can improve the turbocharger’s transient
response (Courtesy of Swain Tech Coatings)
companies I contacted when researching this article. Again, insulating
‘thermal barrier’ coatings are used here, based on ceramics [Fig. 7].
For turbocharged engines these have the dual benefits of retaining heat
within the exhaust system in order to improve turbine response, and
mitigating the effects of radiated heat on the surrounding components.
So popular is ceramic coating of exhausts that such coatings are
offered in a range of colours!
While ceramic exhaust coatings are effective in reducing exhaust
heat radiation, they cannot by any means be said to prevent it. There
are a number of reasons for minimising the radiation of heat from the
exhaust to adjacent components, but two that will be of real interest to
engineers are performance and reliability.
It is turbocharged engines that benefit from the retention of heat
within the exhaust, as we have discussed, and it can be argued that
there is a performance disadvantage with retaining heat within the
exhaust of a naturally aspirated engine. The time taken for a wave to
travel to the end of the exhaust system (or a pipe junction within the
exhaust) is a function of the speed of sound within the gas in which
the wave is propagated. Within a gas of fixed composition, the speed
of sound increases with the square root of absolute temperature.
Therefore, for a highly optimised exhaust system, any pipes making up
the system would need to be slightly longer to provide the same tuning
response as the non-insulated exhaust.
However, the difference in length would be extremely small, and
it is unlikely that anyone driving a car equipped with an exhaust
system with a thermal barrier coating would notice any difference.
For a 10 C exhaust gas temperature difference for an 800 C exhaust
gas temperature, the length of a 1000 mm exhaust system would
need to increase by less than 0.5% in order to maintain the same time
interval between a pressure wave leaving the exhaust valve and the
corresponding reflected wave arriving back.
The effect of retaining heat within the exhaust can have a noticeable
effect on performance of the vehicle for other reasons. A hot exhaust
can transfer heat by radiation and convection to the inlet system,
engine casings and transmission. The rate of heat transfer to the inlet
system can increase inlet charge temperature, and this has a negative
effect on the trapped charge mass within the cylinder, and hence on
performance. Where heat is transferred to the engine and transmission
cases, it will naturally have to be removed through increased
cooling. As already mentioned, increased cooling requirements affect
aerodynamic drag on the vehicle.
The effect of reducing heat transfer on reliability is a real effect
but one that is not easy to quantify, although it is one that many will
understand the logic of. High temperatures affect the mechanical
properties of materials. In some cases, modest increases in temperature
above ambient will improve tensile strength. However, many of the
external components of a typical race engine will be made from
materials such as aluminium, which definitely do not benefit from
being run at high temperatures. Also, with the widespread use of
electronics comes the use of soldered connections, and sensors,
actuators and various other boxes of electronics can be seen to fail at
Aerodynamics play a large part in determining the packaging of
30-42 COATINGS (v.GR).indd 39
t
low mileage without sufficient protection from heat.
22/06/2012 15:50
FOCUS : COATINGS
the components within the engine bay. As a result of this, hot parts
definitely more suited to your particular application than others. You
are forced into close proximity with those that need to be protected
should take time to avail yourself of the facts, and seek the advice
from heat. Thermal barrier coatings on exhausts are one part of the
of the coating companies and their in-house expertise. Make sure
solution here, but the use of heat shielding is also important to provide
you know your facts, to prevent being seen as ‘the salesman’s dream
a physical barrier to radiated heat. Coatings are applied extensively to
customer’. Many of the reputable suppliers will give good advice,
heat shields, either as thermal insulation or as a reflective layer.
and will even point you to solutions to your problems from other
Heat transfer by radiation is a function of the fourth power of the
companies if their particular product doesn’t suit your application. As
temperature difference between the emitting and absorbing bodies,
one company we spoke to put it, “Where we offer a helpful coating
and is directly proportional to a property of the absorbing body known
solution we offer it, but if there is more appropriate technology
as emissivity (also sometimes called absorbance or absorptivity). We
available from others we make prospects aware of those options.”
would like our heat shields to provide a combination of reflectivity to
prevent thermal radiation directly reaching the components that might
References
suffer reliability problems without themselves reaching a high enough
1. Ward, W., Focus article on coatings, Race Engine Technology, issue
temperature to become an efficient emitter of thermal radiation. In
47, June/July 2010
cases where no steps are taken to isolate the engine from the effect
2. Erdemir, A., “Friction and wear of diamond and diamond-like carbon
of exhaust heat, and where oil/water/air cooling cannot be increased,
films”, Proc. ImechE, Part J, Journal of Engineering Tribology, 2002
we have to accept that coolant temperatures – and, as a consequence,
3. Renondeau, H., Taylor, R.I., Smith, G.C., and Torrance, A.A.,
internal component temperatures – will be increased.
“Friction and wear performance of diamond-like carbon and Cr-doped
Some coatings are marketed with the stated aim of increasing heat
diamond-like carbon coatings in contact with steel surfaces”, Proc.
dissipation. Unfortunately, there is very little good quality, comparative
ImechE, Part J, Journal of Engineering Tribology, 2008
data concerning these coatings for automotive applications, although
4. Yagi, T., and Yamagata, I., “Experimental Method of Determining Piston
there are some bold claims made regarding improved performance of
Profile by Use of Composite Materials”, SAE Technical Paper 820769
coolers treated with such ‘thermal dispersion’ coatings.
5. Ward, W., Focus article on pistons, Race Engine Technology, issue
There are two mechanisms by which coatings can increase the
43, December/January 2010
ability of a surface to transfer heat to the atmosphere. The first is to
6. Amano, Y., Nanbu, H., Kameyama, Y., and Komotori, J., “Tribological
increase the surface area of the cooler; in this case the coating turns
Properties of Aluminum Alloy treated by Fine Particle Peening/DLC
the surface into a very thin heat sink. While there are a number of
Hybrid Surface Modification”, Proc. 14th International Conference on
paints and powder coatings that are ‘wrinkle-finish’ it would be
Experimental Mechanics, 2010
very easy to take a step backwards here if the coating itself has a
7. Ward, W., Focus article on crankshafts, Race Engine Technology,
higher thermal resistance than the bare metallic cooler. The second
issue 49, September/October 2010
mechanism is to process a cooler with a coating that combines high
8. Krantz, T.L., Cooper, C.V., Townsend, D.P., and Hansen, B.D.,
heat capacity and high thermal conductivity. Such coatings have been
“Increased Surface Fatigue Lives of Spur Gears by Application of a
specifically developed for the cooling of electronics, as described in
Coating”, NASA/TM-2003-212463
the paper by Stappers et al (12). These coatings are engineered to take
9. Towers, J. M., and Hoekstra, R. L., “Engine Knock, A Renewed
large amounts of heat into the surface of the coating and then allow
Concern In Motorsports – A Literature Review”, SAE Paper 983026
rapid conduction to cooler parts of the surface.
10. Bose, P. K., Beg, R.A., Saha, S.K., Ghosh, B.B., Das, S.K., and
The coatings as described by Stappers et al are very specialised and
Majumdar, A., “Glass Ceramic Coating – an Alternative to Plasma Spray
are developed to use the transition between solid and liquid states
for Internal Combustion Engine Components”, SAE Paper 2000-01-2918
of particles trapped within the coating. They are therefore aimed at
11. Ciniviz, M., Hasimoglu, C., Sahin, F., and Salman, M.S., “Impact of
removing heat at very specific temperatures. Coatings with improved
thermal barrier coating application on the performance and emissions
surface conduction could be made by using metallic coatings with
of a turbocharged diesel engine”, Proc. IMechE, Journal of Automobile
similar combinations of properties. Silver is a possible candidate here,
Engineering, 2008
as it is highly thermally conductive and has a high heat capacity.
12. Stappers, L., Yuan, Y., and Fransaer, J., “Novel Composite Coatings
Summary
152, 2005
Where we are looking to maximise engine output by reducing friction
and managing heat more effectively, looking to make the engine
CREDITS
installation more reliable by shielding vital components from excess
The author would like thank the following for their assistance: Linda
Stappers of Katholieke Universiteit Leuven, Domenico Magnacca of
Sulzer Metco Europe, Richard Tucker of Swain Tech Coatings, Franck
Derangere of Ionbond PVD France, Toby Middlemiss of Oerlikon
Balzers, Carrie Bordeaux of Industrial Hard Carbon, Chris Osborne of
Tecvac, Chris Walker of Diamond Hard Surfaces, Leonard Warren of
Tech Line Coatings and Hitoshi Kawai of Miyaki USA/Kashima Coat.
heat, attempting to improve turbocharger response by retaining heat
energy within the exhaust flow, or trying to minimise heat rejection to
water and oil in an attempt to reduce cooling requirements, coatings
can help.
There is a wide array of coatings on the market, and some are
40
t
for Heat Sink Applications”, Journal of The Electrochemical Society, vol
Run cool,
look even cooler.
Our high performance ceramic
exhaust and engine coatings will
help you do just that.
We’re not called
PERFORMANCE COATINGS
for nothing!
For more information please call us on
+1 253 735 1919
or visit
www.performancecoatings.com
PERFORMANCE COATINGS
60 - 37th Street NE, Auburn, WA 98002, USA
HARD CARBON COATINGS AND
ENGINEERING SOLUTIONS FOR
MOTORSPORT APPLICATIONS
BY
1-866-5-RAPTOR
www.CarbonRaptor.com
www.IndustrialHardCarbon.com
RET_ADTEMP.indd 1
22/06/2012 16:58
FOCUS : COATINGS
SOME EXAMPLES OF COATING SUPPLIERS
AustriA
Zzuhl Ltd. ZN
+43 125 33033 1694
FrANCE
HEF Group
+33 47 75 55 222
sulzer Metco
+33 55 53 70 490
www.zzuhl.com
www.hef.fr
www.sulzer.com
GErMANY
Axyntec
+49 8217 4999140
www.axyntec.de
EsK Ceramics
+49 8315 6180
www.esk.com
Kexel Motortechnik
+49 2663 6823
www.kexel.de
systec sVs Vacuum Coatings GmbH
+49 9353 79030
www.systec-vacuum.com
itALY
Breda Coatings
+39 0261 543911
Lafer spA
+39 0523 517940
sulzer Metco
+39 0290 39241
www.rtmbreda.it
www.lafer.eu
www.sulzer.com
NEtHErLANDs
Hauzer techno Coatings
+31 77 355 9777
www.hauzer.nl
sWitZErLAND
ionBond
+41 62 287 8686
sulzer Metco
+41 56 618 8181
www.ionbond.com
www.sulzer.com
n
uK
Anochrome Group
+44 (0)1902 567567
www.anotec.co.uk
Camcoat Performance Coatings
+44 (0)1925 445688
www.camcoat.com
Diamond Hard surfaces
+44 (0)1327 354330
www.diamondhardsurfaces.com
Dynamic Ceramic
+44 (0)1270 501000
www.dynacer.com
E/M Coating services
+44 (0)1252 523000
www.eltro.co.uk
Hardide
+44 (0)1869 353830
www.hardide.com
Materials & surface Engineering Ltd
+44 (0)7958 077234
www.mat-surf-eng.com
Motrac racing
+44 (0)151 357 1062
www.motrac-racing.com
Oerlikon Balzers
+44 (0)1908 377277
www.oerlikon.com
surface technology
+44 (0)1294 211988
www.surfacetechnology.co.uk
tecvac
+44 (0)1954 233700
www.tecvac.com
teer Coatings
+44 (0)8702 203910
www.teercoatings.co.uk
Ws2 Coatings
+44 (0)1430 861222
www.ws2.co.uk
Zircotec
+44 (0)1235 434320
www.zircotec.org.uk
Zzuhl Ltd
+44 (0)1422 230203
www.zzuhl.com
usA
AirBorn Coatings
+1 704 483 5000
www.airborn.cc
Armoloy of Western PA
+1 610 751 5111
www.armoloy-wpa.com
Calico Coatings
+1 888 236 6079
www.calicocoatings.com
Caps Brite Hot Coatings
+1 559 233 1461
www.capsbhc.com
Central Connecticut Coatings
+1 860 528 8281
www.centralctcoatings.com
Embee Performance
+1 714 546 6907
www.embeeperformance.com
Finishline Coatings
+1 503 659 4278
www.finishlinecoatings.com
Hekimian racing Engines
+1 617 926 0608
www.hekimianracing.com
HM Elliott
+1 704 663 8226
www.hmelliottcoatings.com
iBC Coating technologies inc
+1 765 482 9802
www.ibccoatings.com
industrial Hard Carbon (Carbon raptor)
+1 704 489 14889
www.industrialhardcarbon.com
ionBond
+1 973 586 4700
www.ionbond.com
Jet Hot Coatings
+1 336 447 2028
www.jet-hot.com
Keco Coatings
+1 800 336 5326
www.kecocoatings.com
Lincoln Performance Coatings
+1 402 475 3671
www.lincolnindustries.com
Micro surface Corporation
+1 800 248 4221
www.microsurfacecorp.com
Miyaki Co., Ltd us Office
+1 310 755 5160
www.kashima-coat.com
Morgan Advanced Ceramics
+1 610 366 7100
www.diamonex.com
NiC industries
+1 541 826 1922
www.nicindustries.com
Nitroplate
+1 615 826 4914
www.nitroplate.com
Northeast Coating technologies
+1 207 985 3232
www.northeastcoating.com
Panacea Powder Coating
+1 260 728 4222
www.panaceapowder.com
Performance Coatings
+1 253 735 1919
www.performancecoatings.com
PolyDyn Performance Coatings
+1 888 765 9396
www.polydyn.com
Praxair surface technologies
+1 713 849 9474
www.praxair.com
robbjack (Crystallume)
+1 866 783 9700
www.robbjack.com
ruktech
+1 801 783 2325
www.ruktech.com
swain tech Coatings
+1 585 889 2786
www.swaintech.com
tech Line Coatings
+1 865 365 1435
www.techlinecoatings.com
toefco Powershield Coatings
+1 269 683 0188
www.toefco.com
uCt Coatings
+1 772 872 7110
www.uctcoatings.com
us Chrome Corp
+1 203 378 9622
www.uschrome.com
42
ï WS2Í TUNGSTEN DISULPHIDE
High Performance Dry Lubricant
COEFFICIENCY OF FRICTION 0.03 DYNAMIC
Ws2 dry lubricant is being successfully used
by F1, F3 and World Superbike teams to
prevent seizing and galling on Titanium race parts.
Applied to military spec DOD-85645 at
0.5microns thick its low coeffiency of friction
is used extensively to reduce wear on gears,
shafts, threads and suspension parts.
For more information please contact us at either:
EUROPEAN ENQUIRIES
NORTH AMERICAN ENQUIRIES
WS2 COATINGS Limited
Micro Surface Corporation
Unit 17b, HOSM Ind. Estate,
Holme on Spalding Moor, York, YO43 4BB
Call Dave Clark / Alan Davies on
Tel. +44 (0)1430 - 861222
Fax. +44 (0)1430 - 861110
Email: [email protected] Website: www.ws2.co.uk
PO Box 788
465 E. Briscoe Drive, Morris, IL 60450, USA
Call Ed Fabiszak on
Tel. +1-800-248-4221
Email: [email protected]
Website: www.microsurfacecorp.com
RET_ADTEMP.indd 1
22/06/2012 17:14
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