EMISSIONS #1 - COMBUSTION CHEMISTRY

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Questions and Answers

What percentage of the energy released by combustion is used to propel the vehicle?

20%

What is the primary component of gasoline?

Hydrocarbons

What is the result of a more efficient engine?

Lower exhaust emissions

Why are advanced closed loop engine control systems used in modern vehicles?

To decrease exhaust emissions Signup and view all the answers

What is the purpose of understanding the combustion process?

To diagnose and repair the emissions control system Signup and view all the answers

What are hydrocarbons composed of?

Hydrogen and carbon atoms Signup and view all the answers

What can cause hydrocarbons to increase only slightly?

A slight lean misfire due to a false air entering the engine Signup and view all the answers

What has led to the increased emphasis on maintenance in modern vehicles?

Advances in technology to achieve emissions targets Signup and view all the answers

What is the trend in exhaust emission standards?

They are continually tightening Signup and view all the answers

What is the result of oxygen starved combustion environment?

Formation of carbon monoxide (CO) Signup and view all the answers

What is the normal operating condition for higher concentrations of carbon monoxide?

During cold operation, warm-up, and power enrichment Signup and view all the answers

What is the reason for excessive carbon monoxide emissions?

Leaky injectors, high fuel pressure, improper closed loop control Signup and view all the answers

What is the normal operating condition for very little carbon monoxide production?

During warm idle or cruise Signup and view all the answers

What is the result of high cylinder temperature and pressure during combustion?

Formation of oxides of nitrogen (NOx) Signup and view all the answers

What is the principal by-product of efficient combustion?

Carbon dioxide (CO2) Signup and view all the answers

What can cause poor mixing of fuel and air?

Excessively low intake air temperatures Signup and view all the answers

What is the primary reason for the emission of hydrocarbons in an automobile engine?

Wall quenching during combustion Signup and view all the answers

What happens to the hydrocarbon in the pores of combustion chamber deposits during combustion?

It remains unaffected Signup and view all the answers

What is the most common cause of excessive hydrocarbon emissions?

Misfire Signup and view all the answers

What occurs when the combustion flame front reaches the cool walls of the combustion chamber?

The flame is extinguished Signup and view all the answers

What happens to the air/fuel mixture during compression in the presence of combustion chamber deposits?

Hydrocarbon is forced into the pores Signup and view all the answers

What is the result of a total misfire due to a shorted spark plug wire?

A dramatic increase in hydrocarbons Signup and view all the answers

Why do combustion chamber deposits contribute to excessive hydrocarbon emissions?

Because they are porous and trap hydrocarbons Signup and view all the answers

What is a common cause of misfire that can lead to excessive hydrocarbon emissions?

All of the above Signup and view all the answers

Study Notes

Harmful Exhaust Emissions

Even modern automobile engines produce some level of harmful emission output due to imperfect combustion.
Hydrocarbon (HC) emissions occur when combustion does not take place, such as during a misfire, resulting in large amounts of hydrocarbons being emitted.
Wall quenching, a normal process, also creates a small amount of hydrocarbon due to the cooling of the combustion chamber walls, extinguishing the flame before all fuel is fully burned.
Combustion chamber deposits can also force hydrocarbons into pores, which are then released during the exhaust stroke.

Combustion Chemistry

A gasoline-powered internal combustion engine releases chemical energy stored in fuel through combustion, with only 20% being used to propel the vehicle, and 80% being lost to friction, aerodynamic drag, and heat.
Modern engines are more efficient than those of the late '60s and early '70s, but exhaust emission standards continue to tighten.

Combustion Process

The combustion process involves the burning of gasoline, which is primarily made up of hydrocarbons (HC), chemical compounds of hydrogen and carbon atoms.
Understanding combustion chemistry is essential for diagnosing and repairing emission control systems.

Carbon Monoxide (CO) Emission

Carbon monoxide (CO) is a byproduct of incomplete combustion, occurring when there is insufficient oxygen present during combustion.
CO forms when carbon atoms bond with only one oxygen atom due to an oxygen-starved environment.
Rich air/fuel ratios, leaky injectors, high fuel pressure, and improper closed loop control can cause excessive carbon monoxide emissions.

Oxides of Nitrogen (NOx) Emission

High cylinder temperature and pressure during combustion can cause nitrogen to react with oxygen to form Oxides of Nitrogen (NOx).

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