Stages of Combustion in C.I Engines
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Questions and Answers

What is the ignition delay period in a CI engine also known as?

  • Preparatory phase (correct)
  • Controlled combustion phase
  • Rapid combustion phase
  • Point of combustion

    • Which curve does the pressure-time curve separate from during the start of combustion in a CI engine?

  • Afterburning curve
  • Ignition delay curve
  • Controlled combustion curve
  • Motoring curve (correct)

    • Why is the ignition delay period in a CI engine extremely important?

  • Due to its effect on knocking
  • Due to its impact on engine starting ability (correct)
  • Due to its influence on afterburning
  • Due to its relation to rapid combustion

    • What happens to fuel immediately upon injection into the combustion chamber of a CI engine?

    <p>It has an ignition delay period</p> Signup and view all the answers

    What is the specific period of inactivity called between the time when fuel hits the hot air in the combustion chamber and the time it starts burning?

    <p>Ignition delay period</p> Signup and view all the answers

    Where is the delay period shown on a pressure crank angle diagram in a CI engine?

    <p>Between points a and b</p> Signup and view all the answers

    What causes diesel knock in a compression-ignition (CI) engine?

    <p>Improper fuel injection timing</p> Signup and view all the answers

    How does an increase in engine speed affect the delay period in milliseconds?

    <p>Decreases the delay period</p> Signup and view all the answers

    Which factor contributes to diesel knock related to injector nozzles?

    <p>Injector clogging</p> Signup and view all the answers

    Why is controlling diesel knock essential for engine efficiency?

    <p>To optimize fuel injection systems</p> Signup and view all the answers

    How does an increase in engine output affect the air-fuel ratio and delay period?

    <p>Decreases air-fuel ratio and increases delay period</p> Signup and view all the answers

    What does a higher compression ratio in a CI engine lead to?

    <p>Increased diesel knock</p> Signup and view all the answers

    What is the primary characteristic of diesel knock in a CI engine?

    <p>&quot;Sharp metallic sound&quot;</p> Signup and view all the answers

    How does an increase in the minimum auto ignition temperature impact the delay period?

    <p>Decreases the delay period</p> Signup and view all the answers

    Why might a CI engine with excessive carbon deposits experience knocking?

    <p>&quot;Combustion knock&quot;</p> Signup and view all the answers

    What aspect does the Cetane number evaluate in diesel fuel used in CI engines?

    <p>Fuel's combustion characteristics.</p> Signup and view all the answers

    What is the primary role of a higher Cetane number in diesel fuels?

    <p>Improve ignition characteristics</p> Signup and view all the answers

    How does a higher Cetane number affect the ignition delay in diesel engines?

    <p>Shortens the ignition delay</p> Signup and view all the answers

    What potential issue might arise from extremely high Cetane numbers in diesel fuels?

    <p>Increased engine knock</p> Signup and view all the answers

    Why is efficient mixing of air and fuel essential in the combustion chamber of a CI engine?

    <p>To achieve optimal power generation</p> Signup and view all the answers

    What is the purpose of a high compression ratio in Compression Ignition (CI) engines?

    <p>Promote better combustion efficiency</p> Signup and view all the answers

    Why must the combustion chamber be robustly constructed in a CI engine?

    <p>To withstand high pressures and temperatures</p> Signup and view all the answers

    How do the shape and geometry of the combustion chamber influence combustion in CI engines?

    <p>Impact turbulence and squish patterns</p> Signup and view all the answers

    Why should the combustion chamber design be compatible with the engine's ignition system?

    <p>To ensure proper functioning of the engine's ignition system</p> Signup and view all the answers

    What is the difference between the physical delay and the chemical delay?

    <p>Physical delay is the time between injection and ignition, while chemical delay is the time between ignition and rapid combustion.</p> Signup and view all the answers

    In a compression-ignition engine, what role does the delay period play in the combustion process?

    <p>It allows for sufficient time for fuel atomization and mixing with air.</p> Signup and view all the answers

    What factor influences the physical delay in the ignition process of an engine?

    <p>Compression ratio</p> Signup and view all the answers

    Why is the physical delay shorter for light fuels compared to heavy viscous fuels?

    <p>Light fuels evaporate faster than heavy fuels.</p> Signup and view all the answers

    Which phase is characterized by rapid pressure rise during combustion?

    <p>Uncontrolled Combustion Phase</p> Signup and view all the answers

    How does the chemical delay differ from the physical delay in terms of impact on engine performance?

    <p>Chemical delay impacts heat release rate, while physical delay depends on fuel type.</p> Signup and view all the answers

    What determines the duration of the period of rapid combustion in an engine?

    <p>Compression ratio</p> Signup and view all the answers

    What distinguishes the ignition lag in spark ignition engines from that in compression-ignition engines?

    <p>In compression-ignition engines, ignition lag is essentially equal to chemical delay.</p> Signup and view all the answers

    How do higher combustion chamber temperatures impact the physical delay?

    <p>Higher temperatures shorten physical delay by facilitating jet breakup and improving evaporation.</p> Signup and view all the answers

    What role does high turbulence play in reducing the physical delay?

    <p>High turbulence reduces physical delay by improving fuel atomization and mixing with air.</p> Signup and view all the answers

    Which component is crucial in preventing excessive temperatures within the combustion chamber?

    <p>Cooling passages</p> Signup and view all the answers

    What technology is employed to control nitrogen oxide (NOx) emissions in modern CI engines?

    <p>Selective catalytic reduction (SCR)</p> Signup and view all the answers

    What is the primary function of swirl in a combustion chamber?

    <p>Facilitate better mixing</p> Signup and view all the answers

    Which method involves introducing fuel directly into the combustion chamber using high-pressure injectors?

    <p>Jet and Direct Injection</p> Signup and view all the answers

    What type of motion does tumble refer to in the context of a combustion chamber?

    <p>Vertical swirling</p> Signup and view all the answers

    Which design feature is responsible for enhancing turbulence by forcing the air-fuel mixture into the combustion zone?

    <p>Squish method</p> Signup and view all the answers

    What role does the pre-chamber design play in enhancing turbulence within the combustion chamber?

    <p>Generating a high-velocity jet that enters the main chamber</p> Signup and view all the answers

    How does the intake system contribute to turbulence within the combustion chamber?

    <p>By shaping the combustion chamber geometry</p> Signup and view all the answers

    Which method is most effective in promoting efficient and rapid mixing of air and fuel in the combustion chamber?

    <p>Direct Injection</p> Signup and view all the answers

    Which technology uses high-velocity jets to induce turbulence and initiate combustion in a controlled manner?

    <p>Turbulent Jet Ignition (TJI)</p> Signup and view all the answers

    What is the purpose of introducing exhaust gas into the intake air using EGR (Exhaust Gas Recirculation)?

    <p>To reduce NOx emissions</p> Signup and view all the answers

    In the context of combustion chambers for CI engines, which type features a shallow depth cavity in the piston?

    <p>Shallow Depth Chamber</p> Signup and view all the answers

    What is the main advantage of open combustion chambers in CI engines?

    <p>Minimum heat loss during compression</p> Signup and view all the answers

    What technology allows for the adjustment of valve timing, duration, and lift to influence air intake and exhaust processes?

    <p>Variable Valve Timing (VVT)</p> Signup and view all the answers

    Which chamber type is defined as having a divided combustion space with pressure differences between compartments during combustion?

    <p>Indirect-Injection Chambers</p> Signup and view all the answers

    What type of intake design can be tailored to induce turbulence in the incoming air-fuel mixture?

    <p>Intake Port Design</p> Signup and view all the answers

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