Exhaust and Emissions
Exhaust and emission systems on newer vehicles have become more complex than in the past. The emission system is used to monitor air-fuel ratios and has many benefits to the operator and the environment. For many years, automotive manufacturers were just concerned about getting the hot exhaust gases out to the side or rear of the vehicle. Today exhaust and emission systems are complex mechanisms that provide safety, efficiency, and concern for our fragile environment. Periodically, exhaust and emission system components need replacing. This section focuses on identifying the components and purposes of the exhaust and emission system.

Purpose of the Exhaust and Emission System
Exhaust and emission systems are designed to deal with the inefficient by-products of the internal combustion process. The exhaust system is designed to dampen the sound of the engine. The emission system is designed to lower the pollution of the vehicle.

Exhaust Components
The exhaust system consists of the following components:

• Exhaust Manifolds
  
• Exhaust Pipes
  
• Muffler
  
• Hangers and Clamps
  

Exhaust Manifolds
The exhaust manifolds, usually made out of cast iron, connect directly to the engine. The exhaust manifolds are designed to harness the exhaust gases from the numerous cylinders into one pipe. Inline engines have one exhaust manifold, while V-engines have two (one for each bank of cylinders).

Exhaust Pipes
Exhaust pipes are tubes of steel that connect other components such as the exhaust manifolds to the catalytic converter. An exhaust pipe also connects the catalytic converter to the muffler. This pipe is called the intermediate pipe. Another pipe, a tail pipe, expels the exhaust from the muffler.

Muffler
The muffler, usually oval or cylindrical in shape, is used to deaden the sound from the engine. It is basically a silencer to aid in the reduction of noise pollution and is located after the catalytic converter, but before the tail pipe.

Hangers and Clamps
Exhaust hangers suspend the whole exhaust system. The hanger must allow some flexibility. The exhaust is connected to the engine and to the body. As the engine runs, it vibrates. If the exhaust system was connected solidly to the body, stress cracks would develop. The hangers have tough rubber components to allow for flexing and vibrating. The exhaust clamps connect the exhaust pipes to the muffler and catalytic converter. Exhaust clamps are usually a type of U-bolt. On new exhaust systems, welds instead of clamps hold the exhaust pipes to the muffler and the catalytic converter.

Emission Components
The environment has become a big concern for many people, and rightfully so. Vehicles produce a large amount of by-products that are harmful to our ecosystem. Consumers can minimize pollution by driving more efficient vehicles and by driving less. Planning trips will save petroleum, money, and harmful environmental effects. Emission system components presented are:

• Catalytic Converter
  
• Positive Crankcase Ventilation (PCV)
  
• Exhaust Gas Recirculation (EGR)
  
• Charcoal Canister
  
• Oxygen Sensors
  

Catalytic Converter
The catalytic converter is placed under the automobile in the exhaust system between the exhaust manifold(s) and muffler. It contains a catalyst that promotes the chemical change of carbon monoxide, hydrocarbons, and nitrogen oxides into water vapor, carbon dioxide, nitrogen, and oxygen. Carbon monoxide is a poisonous chemical. Nitrogen oxide is the principle component that causes smog.

PCV
The positive crankcase ventilation (PCV) system is designed to remove the effects of blow-by. As the engine runs, some unburned fuel and water vapor get past the cylinders and into the crankcase. Water can turn oil into sludge, while unburned fuel can dilute the oil. If not taken care of, water and unburned fuel can cause corrosion and increase engine wear. The PCV system recirculates the water vapor and unburned fuel back into the intake. This process will eventually burn the components in the combustion process. In the PCV system is a PCV valve that needs servicing at regular intervals. The PCV valve is commonly found between the cylinder head valve cover and the air cleaner. It is usually in a tube or connected directly into the valve cover.

EGR
The exhaust gas recirculation system reduces nitrogen oxide emissions by diluting the air-fuel mixture with the exhaust gases. Most EGR systems have an EGR valve that is operated by a vacuum from the engine. The EGR valve regulates the amount of exhaust gases that are directed to the intake system. The EGR valve is typically mounted on the intake manifold on top of the engine.

Charcoal Canister
A charcoal canister is put into the emission system to lower the release of hydrocarbons into the air. On many vehicles it looks like a coffee can and is located under the hood. On newer vehicles, it is located under the vehicle near the fuel tank.

Oxygen Sensors
Oxygen sensors are usually placed before and/or after the catalytic converter. The oxygen sensor monitors the oxygen content in the vehicle’s exhaust. It sends signals to the computer to maintain a 14.7 to 1 (the best) air to fuel ratio. This ratio of air to fuel makes the engine run smooth, efficient, and in the end, pollute less.

Summary
As technology advances, the internal combustion engine will become more efficient and pollute less. Over time, components have been added to vehicles to lower noise and reduce chemical pollution. The exhaust system reduces noise, while the emission control system converts harmful gases into more environmentally friendly by-products.

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