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?

  • 40%
  • 10%
  • 30%
  • 20% (correct)
  • What is the primary component of gasoline?

  • Oxygen
  • Hydrocarbons (correct)
  • Nitrogen
  • Carbon dioxide
  • What is the result of a more efficient engine?

  • Lower exhaust emissions (correct)
  • No change in exhaust emissions
  • Higher exhaust emissions
  • Unpredictable exhaust emissions
  • Why are advanced closed loop engine control systems used in modern vehicles?

    <p>To decrease exhaust emissions</p> Signup and view all the answers

    What is the purpose of understanding the combustion process?

    <p>To diagnose and repair the emissions control system</p> Signup and view all the answers

    What are hydrocarbons composed of?

    <p>Hydrogen and carbon atoms</p> Signup and view all the answers

    What can cause hydrocarbons to increase only slightly?

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

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

    <p>Advances in technology to achieve emissions targets</p> Signup and view all the answers

    What is the trend in exhaust emission standards?

    <p>They are continually tightening</p> Signup and view all the answers

    What is the result of oxygen starved combustion environment?

    <p>Formation of carbon monoxide (CO)</p> Signup and view all the answers

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

    <p>During cold operation, warm-up, and power enrichment</p> Signup and view all the answers

    What is the reason for excessive carbon monoxide emissions?

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

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

    <p>During warm idle or cruise</p> Signup and view all the answers

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

    <p>Formation of oxides of nitrogen (NOx)</p> Signup and view all the answers

    What is the principal by-product of efficient combustion?

    <p>Carbon dioxide (CO2)</p> Signup and view all the answers

    What can cause poor mixing of fuel and air?

    <p>Excessively low intake air temperatures</p> Signup and view all the answers

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

    <p>Wall quenching during combustion</p> Signup and view all the answers

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

    <p>It remains unaffected</p> Signup and view all the answers

    What is the most common cause of excessive hydrocarbon emissions?

    <p>Misfire</p> Signup and view all the answers

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

    <p>The flame is extinguished</p> Signup and view all the answers

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

    <p>Hydrocarbon is forced into the pores</p> Signup and view all the answers

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

    <p>A dramatic increase in hydrocarbons</p> Signup and view all the answers

    Why do combustion chamber deposits contribute to excessive hydrocarbon emissions?

    <p>Because they are porous and trap hydrocarbons</p> Signup and view all the answers

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

    <p>All of the above</p> 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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    Description

    Learn about the harmful exhaust emissions produced by automobile engines, including hydrocarbons, carbon monoxide, and nitrogen oxides, and their causes in the combustion chamber.

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