Exhaust system
An exhaust system is usually tubing used to guide waste exhaust gases
away from a controlled combustion inside an engine or stove. The entire
system conveys burnt gases from the engine and includes auto parts more
than one exhaust pipes. Depending on the overall system design, the
exhaust gas may flow through one or more of:
1) Cylinder head and exhaust manifold
2) A turbocharger to increase engine power.
3) A catalytic converter to reduce air pollution.
4) A muffler (North America) / silencer (Europe), to reduce noise.
Design criteria
An exhaust pipe must be carefully designed in
auto parts 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 carbon
monoxide or other harmful exhaust gases if they are not properly
vented to the outdoors. Also, the gases from most types of machine are
very hot; the pipe must be heat-resistant, and it must not pass through
or near anything which can burn or can be damaged by heat. A chimney
serves as an exhaust pipe in a stationary structure.
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 heat up 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, as in the image in the "Terminology".
Two-stroke engines
In a 2-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.
Motorcycles
In most motorcycles all or most of the exhaust system is visible and may
be chrome plated as a display feature.
On a two-cylinder motorcycle, "siamese exhaust pipes" are where
two of the
cylinders blow into the same exhaust pipe or run parallel and connect
with a crossover. This usage is derived from "Siamese twin".
Ship's or large boat's onboard engine
With a ship's or large boat's onboard below-decks diesel engine:-
1) Lagging the exhaust pipe stops it from overheating the engine room
where people must work to service the engine.
2) Feeding water into the exhaust pipe cools the exhaust gas and thus
lessens the back-pressure at the engine's cylinders' exhaust ports and
thus helps the cylinders to empty quicker.
Outboard motors
Outboard motors the exhaust system is usually a vertical passage through
the engine structure and to decrease out-of-water noise blows out
underwater, sometimes through the middle of the propeller.
Terminology
Large truck's diesel exhaust pipe
Manifold or header
A header 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 particular engine
revolutions per minute range.
In every manufacture 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. 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.
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
Header-back is to 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 mainly produced as aftermarket performance
systems for cars without turbochargers.
Waste collection vehicle's diesel exhaust pipe
Turbo-back
Turbo-back is to 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.Few turbo-back (and header-back) systems replace stock
catalytic converters with others having less flow restriction.
With or without catalytic converter
Some systems eliminate the catalytic converter, which may or may not be
legal depending on place and whether the car will be driven on public
roads.
Cat-back
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 are a very popular aftermarket performance
enhancement. They generally use larger diameter pipe than the stock
system. Good systems will have mandrel-bent turns that allow the exhaust
gas to exit with as little back pressure as possible. The mufflers
included in these kits are often glasspacks, again to reduce back
pressure. If the system is engineered more for show than functionality.
Tailpipe and tip
With trucks, sometimes the silencer is crossways under the front of
the cab and its tailpipe blows sideways to the offside. 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
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 petrol filler flap is normally on the opposite
side to the exhaust tailpipe for reasons of packaging but also to
position it closest to the curb.
The end of the final length of exhaust pipe where it vents to open air,
generally the only visible part, often ends with just a straight or
angled cut, but may include a fancy tip. The tip is usually chromed, and
is often of larger pipe than the rest of the exhaust system. This
produces a final reduction in pressure, as well as prevents rusting of
the tips, and can be used to enhance the appearance of the car. These
are the least expensive parts of the system.
Two outlets symbolized V-8 power, and only the most expensive cars 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,
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 avoids
anyone working by the truck when stationary from getting a directed
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
Also known as side pipes, lake pipes are exhaust pipes, normally
brightly chromed, which exit the front wheelarch of a car and then pass
down the sill/rocker panel, finally opening sideways in front of the
rear wheel. They are sometimes seen on custom cars and hot rods.
Dangers
There are many known dangers linking an automobile ventilation
system to the breathable air inside a car. The most common and
undetectable is when air-conditioning exhaust fumes slowly seep into the
ventilation system of a car. While this might cause a prevalent odor,
there is no evidence linking the inhalation of this smell to any medical
or health risk.
