Exhaust System: Description and Operation
Exhaust System Description
Note:
Use of Non-OEM parts may cause driveability concerns.
The exhaust system carries exhaust gases, treated by the catalytic converter, through a resonator, if applicable and into the exhaust muffler where exhaust noise is lessened.
In order to secure the exhaust pipe to the exhaust manifold, a flange and seal-joint coupling is utilized.
Exhaust hangers and rubber insulators help to support the weight of the exhaust pipe along with insulating any exhaust system vibration, rattle, or noise.
Exhaust hangers also space the exhaust system away from the underbody of the vehicle and allows the exhaust system to expand as the exhaust system warms up.
Exhaust heat shields are used to protect the body and other components from damage due to the heat from the exhaust system.
The exhaust system may be comprised of the following components:
* Exhaust manifold
* Exhaust pipes
* Catalytic converters
* Exhaust muffler
* Exhaust resonator, if equipped
* Exhaust hangers
* Exhaust heat shields
Catalytic Converter
Through developments in various emissions reduction system, significant reductions in emissions have been achieved. The developments have been primarily concerned with refinements in engine calibration and the optimization of exhaust system catalytic converter configurations.
The catalytic converter is similar to a muffler in appearance however, within the outer stainless steel shell (4), there is a ceramic monolith (1) which is honeycombed in the direction of the exhaust, as shown. The ceramic monolith is surrounded by a mat (2), which has the primary function of holding the monolith firmly in place to prevent any contact with the inner shell (3). A mesh (5 and 6) at each end of the converter prevents exhaust gases from fouling and eroding the mat.
Surfaces of the ceramic monolith that are exposed to exhaust gases are coated with a catalytic material. This material contains rhodium and platinum, which act to facilitate the chemical reactions necessary to oxidize carbon monoxide and hydrocarbons into harmless carbon dioxide.
The catalytic converter is a substance that accelerates a chemical reaction without itself being changed. Engine exhaust gases contain carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx). When the exhaust gases flow through the monolith, reactions with the catalytic converter occur. CO and HC are converted by oxidation with oxygen (O2) in the exhaust gases to produce carbon dioxide (CO2) and water vapor (H2O). NOx is converted by reduction with CO to produce nitrogen (N2). The catalytic converter is called a three-way type because it simultaneously converts three components of exhaust gas (CO, HC and NOx) to harmless natural gases.
Service Notes
* Vehicles fitted with a catalytic converter should not be operated with leaded gasoline. Lead will contaminate the catalytic converter.
* Do not drop the catalytic converter as it will damage the ceramic monolith.
* Do not allow water, oil or fuel to enter the converter as the ceramic monolith will be contaminated.
* Do not drive the vehicle with the engine misfiring or with any of the spark plug leads disconnected.
Note:
Catalytic converter can be damaged or rendered infective, if:
* Operated outside the limits of the closed loop mixture control system.
* The engine burns excessive amount of oil.
* The exhaust temperature at the converter is too high (exceeds 840°C).
Resonator
Some exhaust systems are equipped with a resonator. The resonator, located either before or after the muffler, allows the use of mufflers with less back pressure. Resonators are used when vehicle characteristics require specific exhaust tuning.
Muffler
The exhaust muffler reduces the noise levels of the engine exhaust by the use of tuning tubes. The tuning tubes create channels inside the exhaust muffler that lower the sound levels created by the combustion of the engine.
The rear muffler on vehicles fitted with the LFW engine option contains a variable exhaust valve. The purpose of the valve is to reduce exhaust noise for minimal impact on performance and back pressure. The valve consists of a spring loaded flap which is closed at lower gas flow (lower engine speed/load) forcing the exhaust gasses through a more restrictive path therefore providing improved noise performance. As gas flow increases with higher engine load/speed, the valve opens providing a less restrictive path for the exhaust gases and therefore providing good wide open throttle performance.