Introduction to Combustion Chemistry
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Questions and Answers

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

  • 50%
  • 20% (correct)
  • 10%
  • 80%
  • Which component is primarily responsible for the combustion process in an internal combustion engine?

  • Oxygen
  • Hydrocarbons (correct)
  • Nitrogen
  • Water vapor
  • As the efficiency of an engine increases, what happens to exhaust emissions from the tailpipe?

  • They decrease. (correct)
  • They remain unchanged.
  • They increase significantly.
  • They fluctuate unpredictably.
  • What has led to the development of advanced closed loop engine control systems in vehicles?

    <p>Increased focus on fuel economy and emissions control.</p> Signup and view all the answers

    What is the primary chemical reaction that occurs during the combustion process in an engine?

    <p>Hydrocarbons react with oxygen to form CO2 and H2O.</p> Signup and view all the answers

    Which gases primarily compose air entering an internal combustion engine?

    <p>Oxygen and nitrogen</p> Signup and view all the answers

    What is a consequence of failing emission control systems in internal combustion engines?

    <p>Increased tailpipe emissions</p> Signup and view all the answers

    What type of chemical compounds are hydrocarbons considered to be?

    <p>Compounds made of hydrogen and carbon atoms</p> Signup and view all the answers

    What is the ideal air/fuel ratio referred to as?

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

    What is a consequence of operating at air/fuel ratios richer than stoichiometry?

    <p>Compromised fuel economy</p> Signup and view all the answers

    What is produced during a perfectly operating engine under ideal combustion conditions?

    <p>Water vapor and carbon dioxide</p> Signup and view all the answers

    During which stroke does the air and fuel move into the cylinder?

    <p>Intake Stroke</p> Signup and view all the answers

    What role does the octane rating of fuel play during the Compression Stroke?

    <p>Prevents spontaneous ignition</p> Signup and view all the answers

    What occurs when the spark plug ignites the air/fuel mixture?

    <p>A flame-front spreads through the mixture</p> Signup and view all the answers

    Which chemical compound is NOT produced during combustion in an ideal engine?

    <p>Carbon monoxide</p> Signup and view all the answers

    What happens during the Compression Stroke just before the piston reaches Top Dead Center?

    <p>Pressure increases and the mixture superheats</p> Signup and view all the answers

    At what position of the piston is the maximum pressure ideally created?

    <p>8 to 12 degrees past top dead center</p> Signup and view all the answers

    What are the main combustion by-products if the mixture and spark timing are precise?

    <p>Water vapor and carbon dioxide</p> Signup and view all the answers

    What initiates the Exhaust Stroke in the engine cycle?

    <p>The exhaust valve opening</p> Signup and view all the answers

    What is primarily emitted when combustion does not occur at all?

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

    What is a notable cause of excessive hydrocarbon emissions in gasoline engines?

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

    Which of the following is NOT a cause of excessive hydrocarbon emissions?

    <p>Excessive oil pressure</p> Signup and view all the answers

    What happens during the combustion process when there are carbon deposits in the combustion chamber?

    <p>Hydrocarbons are forced into the deposits and are released during the exhaust stroke</p> Signup and view all the answers

    What condition indicates a misfire in an engine?

    <p>Large amounts of hydrocarbons emitted</p> Signup and view all the answers

    What causes an increase in hydrocarbon emissions during a complete misfire?

    <p>Shorted spark plug wire</p> Signup and view all the answers

    Which scenario typically results in lower emissions of carbon monoxide (CO)?

    <p>Engine at warm idle</p> Signup and view all the answers

    What is the primary cause of carbon monoxide being produced in an engine?

    <p>Incomplete combustion due to insufficient oxygen</p> Signup and view all the answers

    What primarily composes the Oxides of Nitrogen (NOx) produced by an engine?

    <p>Nitric oxide (NO)</p> Signup and view all the answers

    What operating condition is likely to produce higher concentrations of carbon monoxide?

    <p>Warm-up phase</p> Signup and view all the answers

    How does intake air temperature affect hydrocarbon emissions?

    <p>Lower temperatures can cause poor mixing</p> Signup and view all the answers

    What is the stoichiometric air/fuel ratio ideal for complete combustion?

    <p>14.7 to 1</p> Signup and view all the answers

    Which of the following could NOT be a cause of excessive carbon monoxide emissions?

    <p>Proper closed loop control</p> Signup and view all the answers

    Study Notes

    Introduction to Combustion Chemistry

    • The combustion process in gasoline engines releases energy stored in the fuel, with only 20% used for propulsion and 80% lost as heat.
    • Modern engines are more efficient than older ones, leading to lower exhaust emissions.
    • Despite improvements, emission standards continue to tighten, prompting advanced engine control systems.

    Understanding the Combustion Process

    • Gasoline is primarily composed of hydrocarbons (HC), which are chemical compounds of hydrogen and carbon atoms.
    • Combustion requires a mixture of hydrocarbons and air, which is composed of 21% oxygen, 78% nitrogen, and other inert gases.
    • The ideal air/fuel ratio for optimal combustion is 14.7:1 (stoichiometry).
    • Richer air/fuel ratios negatively impact fuel economy and emissions.
    • Leaner air/fuel ratios negatively impact power, driveability, and emissions.

    Ideal Combustion Conditions

    • In ideal conditions, hydrocarbons react with oxygen to produce water vapor (H2O) and carbon dioxide (CO2).
    • Nitrogen (N2) passes through the engine unaffected by the combustion process.

    The Four-Stroke Combustion Cycle

    • During the Intake Stroke, air and fuel are drawn into the cylinder, with precise fuel delivery for the ideal air/fuel ratio.
    • The Compression Stroke increases pressure and heat, requiring high-octane fuel to prevent premature ignition.
    • The Power Stroke begins with spark plug ignition, initiating a flame front that spreads through the air/fuel mixture.
    • Combustion produces heat and pressure, with peak pressure occurring around 8-12 degrees past top dead center.
    • The Exhaust Stroke expels combustion byproducts (water vapor, carbon dioxide, nitrogen, and pollutants) through the exhaust system.

    Harmful Exhaust Emissions

    • Incomplete combustion leads to harmful emissions.
    • Hydrocarbon (HC) emissions are caused by unburned fuel, often due to misfires or wall quenching.
    • Carbon monoxide (CO) emissions occur due to incomplete combustion, resulting from oxygen-starved environments.
    • Oxides of Nitrogen (NOx) emissions are formed when high temperatures and pressures cause nitrogen to react with oxygen.

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    Description

    Explore the fundamentals of combustion chemistry, focusing on gasoline engines' processes and efficiency. Learn about the composition of gasoline, the importance of the air/fuel ratio, and the implications for emissions and engine control systems. This quiz covers key concepts essential for understanding combustion.

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