An exhaust
system is usually piping used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt
gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust
gas may flow through one or more of:
DESIGN CRITERIA
An exhaust
pipe must be carefully designed to carry toxic and/or noxious gases away from
the users of the machine. Indoor generators and furnaces can quickly fill an enclosed space with poisonous
exhaust gases such as hydrocarbons, carbon monoxide and nitrogen oxides, if they are not properly vented to the outdoors.
Also, the gases from most types of machines are very hot; the pipe must be
heat-resistant, and it must not pass through or near anything that can burn or
can be damaged by heat. A chimney serves as an exhaust pipe in a stationary structure.
For the internal combustion engine it is important to have the
exhaust system "tuned" (refer to tuned exhaust) for optimal efficiency. Also this should meet the
regulation norms maintained in each country. In China, China 5; In European
countries, EURO 5; In India, BS-4, etc.
MOTORCYCLES
In
most motorcycles all or most of the exhaust
system is visible and may be chrome plated as a display feature. Aftermarket exhausts may be made
from steel, aluminium, titanium, or carbon fiber.
Motorcycle
exhausts come in many varieties depending on the type of engine and its intended
use. A twin cylinder may flow its exhaust into separate exhaust sections, such
as seen in the Kawasaki EX250 (also known as the Ninja 250 in the US, or the GPX 250). Or, they may flow into a
single exhaust section known as a two-into-one (2-1). Larger engines that come
with 4 cylinders, such as Japanese super-sport or super-bikes (such the
Kawasaki ZX series, Honda's CBR series, Yamaha's YZF series, also known as R6 and
R1, and Suzuki's GSX-R series) often come with a twin exhaust system. A
"full system" may be bought as an aftermarket accessory, also called
a 4-2-1 or 4-1, depending on its layout. In the past, these bikes would come
standard with a single exhaust, as seen on the Kawasaki ZX-6R 2000 and 2001
models. However, EU noise and pollution regulations have generally stopped this
practice, forcing companies to use other methods to increase performance of the
motorcycle.
A 2-stroke exhaust can be made to be
quieter than 70dBa at 6000 rpm without sacrificing any power gains. The latest
generations of 4-stroke street motorcycle engines that can come close to a 2T
in redline RPM but still having the extra weight and inertia of cams and valves
make the differences in being "cleaner burning" negligible, with the
decreased engine service life to be expected, while also having the sound of a
4T exhaust carrying for miles in many cases. Additionally, "the nature of
the beast" is that a 4T exhaust note above 6000 rpm is unduly harsh to the
human ear.
TRUCKS
In many trucks / lorries all or most of the exhaust system is visible. Often in
such trucks the silencer is surrounded by a perforated metal sheath to avoid
people getting burnt touching the hot silencer. This sheath may be chrome plated as a display feature. Part of the pipe between the
engine and the silencer is often flexible metal industrial ducting; this helps
to avoid vibration from the engine being transferred into the exhaust system.
Sometimes a large diesel exhaust pipe is vertical, to blow the hot noxious gas
well away from people; in such cases the end of the exhaust pipe often has a
hinged metal flap to stop debris, birds and rainwater from falling inside.
TWO-STROKE ENGINE
In a two-stroke engine, such as that used on dirt bikes, a bulge in the exhaust pipe known as an expansion chamber uses the pressure of the exhaust to create a pump that squeezes more air and
fuel into the cylinder during the intake stroke. This provides greater power
and fuel efficiency. See Kadenacy effect.
MARINE ENGINES
With an onboard diesel or petrol
(gasoline) engine below-decks on marine vessels:-
·
Lagging the exhaust pipe stops it from
overheating the engine room where people must work to service the engine.
·
Feeding
water into the exhaust pipe cools the exhaust gas and thus lessens the
back-pressure at the engine's cylinders. Often in marine service the exhaust
manifold is integral with a heat exchanger which allows sea water to cool a
closed system of fresh water circulating within the engine.
OUTBOARD MOTORS
In outboard motors the exhaust system is usually a vertical passage
through the engine structure and to reduce out-of-water noise blows out
underwater, sometimes through the middle of the propeller.
TERMINOLOGY
Aftermarket exhaust manifold
In
most production engines, the manifold is an assembly designed to
collect the exhaust gas from two or more cylinders into one pipe. Manifolds are
often made of cast iron in stock production cars, and
may have material-saving design features such as to use the least metal, to
occupy the least space necessary, or have the lowest production cost. These
design restrictions often result in a design that is cost effective but that
does not do the most efficient job of venting the gases from the engine.
Inefficiencies generally occur due to the nature of the combustion engine and
its cylinders. Since cylinders fire at different times, exhaust leaves them at
different times, and pressure waves from gas emerging from one cylinder might
not be completely vacated through the exhaust system when another comes. This
creates a back pressure and restriction in the engine's exhaust system that can
restrict the engine's true performance possibilities. In Australia, the pipe of
the exhaust system which attaches to the exhaust manifold is called the 'engine
pipe' and the pipe emitting gases to ambient air called the 'tail pipe'.
Regardless of the negative
attributes focused upon by potential sellers of steel tube exhaust outlet
configurations, engineers who design engine components choose conventional cast
iron exhaust manifolds can similarly list positive attributes, such as an array
of heat management properties and superior longevity than any other type of
exhaust outlet design. For the average consumer, having trouble with an exhaust
outlet system may qualify as 'poorer performance'.
A header (sometimes called set of extractors in Australia) is a manifold specifically designed for
performance. During design, engineers create a manifold without regard to
weight or cost but instead for optimal flow of the exhaust gases. This design
results in a header that is more efficient at scavenging the exhaust from the cylinders. Headers are
generally circular steel tubing with bends and folds calculated to make the
paths from each cylinder's exhaust port to the common outlet all equal length,
and joined at narrow angles to encourage pressure waves to flow through the
outlet, and not back towards other cylinders. In a set of tuned headers the pipe lengths
are carefully calculated to enhance exhaust flow in a particular engine revolutions per
minute range.
Headers
are generally made by aftermarket automotive companies, but
sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car performance enthusiasts buy
aftermarket headers made by companies solely focused on producing reliable,
cost-effective well-designed headers specifically for their car. Headers can
also be custom designed by a custom shop. Due to the advanced materials that
some aftermarket headers are made of, this can be expensive. Luckily, an
exhaust system can be custom built for any car, and generally is not specific
to the car's motor or design except for needing to properly connect solidly to
the engine. This is usually accomplished by correct sizing in the design stage,
and selecting a proper gasket type and size for the engine.
HEADER-BACK
The Header-back (or header back) is the part of the
exhaust system from the outlet of the header to the final vent to open air everything
from the header back. Header-back systems are generally produced as aftermarket performance systems for cars
without turbochargers.
TURBO-BACK
The Turbo-back (or turbo back) is the part of the exhaust
system from the outlet of a turbocharger to the final vent to open air.
Turbo-back systems are generally produced as aftermarket performance systems for cars
with turbochargers. Some turbo-back (and header-back) systems replace stock
catalytic converters with others having less flow restriction.
WITH OR WITHOUT
CATALYTIC CONVERTER
Some systems
(including in former time all systems) (sometimes nowadays called catless or de-cat) eliminate the catalytic
converter. It is illegal and is against Federal Law in the United States and
other countries to not have a catalytic converter. Converters may not be
removed from a vehicle that is used only for "off-road" driving in
the United States. The main purpose of a catalytic converter on an automobile
is to reduce harmful emissions of hydrocarbons, carbon monoxide and nitrogen
oxides into the atmosphere. They work by transforming the polluted exhaust
components into water and carbon dioxide.
CAT-BACK
Cat-back (also cat back and cat back) refers to the portion of the
exhaust system from the outlet of the catalytic converter to the final vent to open air.
This generally includes the pipe from the converter to the muffler, the
muffler, and the final length of pipe to open air.
Cat-back
exhaust systems generally use larger diameter pipe than the stock system. The
mufflers included in these kits are often glass packs, to reduce back pressure. If the system is engineered more
for show than functionality, it may be tuned to enhance the lower sounds that
are lacking from high-RPM low-displacement engines.
Tailpipe and exhaust
With trucks,
sometimes the silencer is crossways under the front of the cab and its tailpipe
blows sideways to the offside (right side if driving on the left, left side if driving on the right). The side of a passenger car on
which the exhaust exits beneath the rear bumper usually indicates the market
for which the vehicle was designed, i.e. Japanese (and some older British)
vehicles have exhausts on the right so they are furthest from the curb in
countries which drive on the left, while European vehicles have exhausts on the
left.
The end of
the final length of exhaust pipe where it vents to open air, generally the only
visible part of the exhaust system part on a vehicle, often ends with just a
straight or angled cut, but may include a fancy tip. The tip is sometimes chromed. It is often of larger pipe than the rest of the exhaust
system. This produces a final reduction in pressure, and sometimes used to
enhance the appearance of the car.
In the late
1950s in the United States manufacturers had a fashion in car styling to form
the rear bumper with a hole at each end through which the exhaust would pass.
Two outlets symbolized V-8 power, and only the most expensive cars (Cadillac,
Lincoln, Imperial, Packard) were fitted with this design. One justification for
this was that luxury cars in those days had such a long rear overhang that the
exhaust pipe scraped the ground when the car traversed ramps. The fashion
disappeared after customers noted that the rear end of the car, being a
low-pressure area, collected soot from the exhaust and its acidic content ate
into the chrome-plated rear bumper.
When a bus, truck or tractor or excavator has a vertical exhaust pipe (called stacks or pipes
behind the cab), sometimes the end is curved, or
has a hinged cover flap which the gas flow blows out of the way, to try to
prevent foreign objects (including droppings from a bird perching on the exhaust pipe when the
vehicle is not being used) getting inside the exhaust pipe.
In some
trucks, when the silencer is front-to-back under the chassis, the end of the
tailpipe turns 90° and blows downwards. That protects anyone near a stationary
truck from getting a direct blast of the exhaust gas, but often raises dust
when the truck is driving on a dry dusty unmade surface such as on a building site.
LAKE PIPES
A consequence
of the problematic nature in adaptation of large diameter exhaust tubing to the
undercarriage of ladder-frame or body-on-frame chassis architecture vehicles with altered geometry
suspensions, lake pipes evolved to become a front-engined vehicle exhaust
archetype crafted by specialty motor sport engine specialists of the 1930s, 40s
and 50s, whose preoccupation was optimization of the acoustic effect associated with high output
internal combustion engines. The name is derived from their use on the vast,
empty dry lake beds northeast of Los
Angeles County,
where engine specialists of yore custom crafted, interchanged and evaluated
one-piece header manifolds of various mil thicknesses, a function of
temperature, humidity, elevation and climate they anticipated.
No intrinsic
performance gain to be derived, per se, lake pipes evolved a function of
practicality. Common instances, their manifolds routed straight out the front
wheel-whels posing an asphyxiation axiom to the race driver, "lake
pipes" were fashioned, extending from the header flange along the rocker
panels, bottom-side of the vehicle, beneath the doors, thus allowing (1)
suspension tuners a lower ride height sufficient for land speed record
attempts, and (2) engine tuners ease and flexibility of interchanging different
exhaust manifolds without hoisting the vehicle, thus precluding having to
wrench undercarriage of the vehicle.
Body-on-frame
chassis architecture ceding to superleggera, unit-body and monocoque archetypes, in tandem with smog abatement legislation
rendered lake pipes, as a bona fide performance prerequisite, obsolete. No
meaningful performance gain to be had for contemporary vehicles, lake pipes
persist into the 21st century as a superfluous, retrograde aesthetic, usually
chrome plated with various options, allowing the driver to control whether
exhaust gas is routed the standard exhaust system, or through lake pipes, which
are commonly fashioned by laker
caps which,
affixed by fasteners at the terminal end of exhaust tips, serve to (1)
"cap" the exhaust system when not in use, and/or (2) signal
authorities that the presence of lake pipes is merely cosmetic.
EXHAUST SYSTEM TUNING
Aftermarket exhaust system including headers and a white
plasma-sprayed ceramic coating
Many
automotive companies offer aftermarket exhaust system upgrades as a subcategory
of engine tuning. This is often fairly expensive as
it usually includes replacing the entire exhaust manifold or other large components. These upgrades however can
significantly improve engine performance and do this through means of two main
principles:
·
By
reducing the amount of heat from the exhaust being lost into the underbonnet
area. This reduces the underbonnet temperature and consequently lowers the
intake manifold temperature, increasing power. This also has positive side
effect of preventing heat-sensitive components from being damaged. Furthermore,
keeping the heat in the exhaust gases speeds these up, therefore reducing back
pressure as well.
Back pressure is most commonly reduced by replacing exhaust
manifolds with headers, which have smoother bends and normally wider pipe
diameters.
Exhaust Heat
Management is
the term that describes reducing the amount of exhaust heat radiated out from
the exhaust pipe and components. One dominant solution to aftermarket upgraders
is the use of a ceramic
coating applied
via thermal spraying. This not only reduces heat loss
and lessens back pressure, but also provides an effective way to protect the
exhaust system from wear and tear, thermal degradation and corrosion.
WORKING