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Four-Stroke Engine Basics and Malfunctions
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Four-Stroke Engine Basics and Malfunctions

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Questions and Answers

What is a characteristic feature of a two-stroke engine compared to a four-stroke engine?

  • It completes the power cycle in one crankshaft revolution. (correct)
  • It produces more power strokes per cycle.
  • It requires more components to operate.
  • It has a longer operational cycle.

    • During which stroke does the piston create a highly combustible environment for ignition?

  • Intake stroke
  • Power stroke
  • Exhaust stroke
  • Compression stroke (correct)

    • What occurs during the exhaust stroke of the engine cycle?

  • The piston expels burned gases from the cylinder. (correct)
  • The intake valve opens to let in new air and fuel.
  • The connecting rod connects the piston to the crankshaft.
  • The spark plug ignites the air-fuel mixture.

    • What is the primary function of the crankshaft in an engine?

    <p>To convert linear motion of the piston into rotational motion.</p> Signup and view all the answers

    What issue can arise if the step of removing burned gases from the cylinder is skipped?

    <p>Fresh air-fuel mixture may be diluted.</p> Signup and view all the answers

    In what application are two-stroke engines commonly favored over four-stroke engines?

    <p>Motorcycles and chainsaws</p> Signup and view all the answers

    What is the function of the piston during the intake stroke?

    <p>To open the intake valve and draw in the mixture.</p> Signup and view all the answers

    How many total strokes are needed in a four-stroke engine for one complete power cycle?

    <p>Four strokes</p> Signup and view all the answers

    What sequence of strokes occurs in a four-stroke engine?

    <p>Intake, compression, power, exhaust</p> Signup and view all the answers

    What happens during the exhaust stroke of a four-stroke engine?

    <p>Burned gases are expelled from the cylinder</p> Signup and view all the answers

    How does a malfunctioning intake valve affect the engine cycle?

    <p>It prevents the fuel-air mixture from entering the cylinder</p> Signup and view all the answers

    What is the role of timing in the exhaust valve operation?

    <p>To allow burnt gases to assist in expelling them</p> Signup and view all the answers

    What could result from improper execution of the exhaust stroke?

    <p>Residual exhaust gases remain in the cylinder</p> Signup and view all the answers

    Why is a four-stroke engine considered efficient?

    <p>It allows for better combustion control and cleaner emissions</p> Signup and view all the answers

    What occurs if residual exhaust gases enter a cylinder during the intake stroke?

    <p>It dilutes the incoming air-fuel mixture</p> Signup and view all the answers

    What is the function of the piston during the intake stroke?

    <p>Drawing in the fuel-air mixture</p> Signup and view all the answers

    What occurs during the Intake Stroke of the Otto Cycle?

    <p>The air and gasoline mixture is drawn into the cylinder.</p> Signup and view all the answers

    What is the function of the Exhaust Stroke?

    <p>To expel waste gases through the exhaust valve.</p> Signup and view all the answers

    How does a malfunctioning intake valve affect engine performance?

    <p>It can lead to rough idling and reduced power output.</p> Signup and view all the answers

    During the Compression Stroke, what happens to the volume and pressure in the cylinder?

    <p>Volume decreases, pressure increases.</p> Signup and view all the answers

    What distinguishes a petrol engine's ignition from a diesel engine's?

    <p>Petrol engines use a spark plug; diesel relies on high compression self-ignition.</p> Signup and view all the answers

    What is the significance of the Bottom Dead Center (BDC) in the engine cycle?

    <p>BDC is the point at which the piston is at its lowest position.</p> Signup and view all the answers

    What is the function of the spark plug in petrol engines?

    <p>To ignite the mixture at the optimal moment.</p> Signup and view all the answers

    What is meant by the compression ratio in an engine?

    <p>The ratio of minimum to maximum cylinder volume.</p> Signup and view all the answers

    What is the primary function of the spark plug in the Otto cycle?

    <p>To ignite the air and gasoline mixture</p> Signup and view all the answers

    What distinguishes diesel engines from petrol engines regarding compression ratios?

    <p>Diesel engines have higher compression ratios.</p> Signup and view all the answers

    Which of the following statements about fuel efficiency is correct?

    <p>Diesel engines are generally more fuel-efficient due to higher compression ratios.</p> Signup and view all the answers

    During which stroke does the spark plug ignite the air-fuel mixture in petrol engines?

    <p>Power stroke</p> Signup and view all the answers

    What is one advantage of diesel engines over petrol engines?

    <p>Higher energy content of the fuel</p> Signup and view all the answers

    How do diesel engines achieve self-ignition?

    <p>Through the higher compression ratios and thermal efficiency</p> Signup and view all the answers

    What happens to the pressure within the cylinder during combustion?

    <p>It increases rapidly</p> Signup and view all the answers

    Which of the following characteristics is more prominent in petrol engines compared to diesel engines?

    <p>Spark ignition</p> Signup and view all the answers

    What method do diesel engines use to ignite the air-fuel mixture?

    <p>Higher compression ratios</p> Signup and view all the answers

    What is the compression ratio of the 2015 VW Golf TDI?

    <p>16.2:1</p> Signup and view all the answers

    Which component primarily increases fuel supply in diesel engines?

    <p>Fuel injectors</p> Signup and view all the answers

    How do diesel engines compare to petrol engines in terms of fuel efficiency?

    <p>Diesel engines produce approximately 33.7 mega joules per liter.</p> Signup and view all the answers

    Which is a characteristic of the power stroke in diesel engines?

    <p>Combustion ignites and forces the piston down.</p> Signup and view all the answers

    What distinguishes the way petrol engines manage air intake compared to diesel engines?

    <p>Diesel engines lack a throttle body.</p> Signup and view all the answers

    At what RPM do diesel engines typically produce more torque?

    <p>Low RPMs</p> Signup and view all the answers

    What happens during the compression stroke of a diesel engine?

    <p>The piston moves up, compressing the air.</p> Signup and view all the answers

    Study Notes

    Four-Stroke Engine Basics

    • Four Strokes: Intake, Compression, Power, Exhaust
    • Intake Stroke: Piston moves down; intake valve opens; air-fuel mixture enters
    • Compression Stroke: Piston moves up; air-fuel mixture is compressed; creates a combustible environment
    • Power Stroke: Spark plug ignites the mixture; combustion drives the piston down; generates power
    • Exhaust Stroke: Piston moves up; opens exhaust valve; pushes burnt gases out

    Intake Valve Malfunctions

    • Malfunction Prevents Air-Fuel Mixture Entry: Disrupts suction and causes the engine to stall
    • Incomplete Combustion: Can result in engine misfiring or decreased power
    • Exhaust Valve Opens: May expel unburnt fuel, making the engine more inefficient

    Exhaust Stroke Importance

    • Residual Exhaust: Can dilute fresh air-fuel mixture reducing engine efficiency
    • Designed Valve Timing: Opens before BDC, allowing pressure to assist in expulsion

    Two-Stroke vs Four-Stroke Engines

    • Two-Stroke: Single revolution, two strokes, completes cycle quickly; lighter and more compact
    • Four-Stroke: Two revolutions, four strokes, more complex operation, efficient and low emissions
    • Four-Stroke Examples: cars, motorcycles
    • Two-Stroke Examples: motorcycles, chainsaws

    Key Components of a Four-Stroke Engine

    • Piston: Moves up and down in cylinder
    • Connecting Rod: Links piston to crankshaft
    • Crankshaft: Converts linear motion of piston to rotational motion

    Petrol vs Diesel Engines

    • Operation: Both use four-stroke cycle, but ignition methods differ
    • Spark Plug Ignition: Petrol engines ignite the air-fuel mixture with a spark plug
    • Self-Ignition: Diesel engines use high compression to ignite the air-fuel mixture
    • Compression Ratio: Diesel engines have higher compression ratios, typically 16.2:1 compared to petrol 9.6:1
    • Energy Content: Diesel has 15% more energy per volume than petrol
    • Efficiency: Diesel engines are more efficient due to high compression ratio; higher thermal efficiency due to the way combustion happens

    Diesel Engine Components

    • Throttle Mechanism: Diesel engines lack a throttle body; pressing the accelerator increases fuel supply
    • Fuel injectors: Introduce atomized diesel fuel into the high-pressure, high-temperature air

    Diesel Cycle

    • Intake Stroke: Intake valve opens; piston descends and draws in air
    • Compression Stroke: Intake valve closes; piston ascends; compresses air; temperature rises
    • Power Stroke: Fuel injected into highly compressed air; combustion forces piston down; produces power
    • Exhaust Stroke: Piston ascends; expels burnt gases through exhaust valve

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    Description

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