Four-Stroke Engine Mechanics Quiz

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Questions and Answers

What is the function of the exhaust valve in an engine?

To ignite the fuel-air mixture

To permit gases in the cylinder to escape (correct)

To admit the fuel-air mixture into the cylinder

To close the cylinder at the end of each cycle

Which component controls the timing of the valve openings and closings in an engine?

The eccenter shaft

The spark plug

The coil spring

The camshaft (correct)

What shape does the rotary piston of a Wankel engine resemble?

A triangle (epitrochoid) (correct)

A circle

A rectangle

A square

What provides the opening impulse for the engine valves?

The camshaft Signup and view all the answers

How does the Wankel engine differ from traditional piston engines in terms of vibration?

It has fewer vibrations due to reduced oscillating masses. Signup and view all the answers

What is the primary purpose of the first stroke in the four-stroke engine cycle?

Admission of the fuel-air mixture Signup and view all the answers

During the compression stroke of a four-stroke engine, what happens to the fuel-air mixture?

It is compressed into a smaller volume Signup and view all the answers

What mechanism converts the vertical motion of the piston into rotary motion in a four-stroke engine?

Connecting rod and crankshaft Signup and view all the answers

What is the role of atmospheric pressure in a four-stroke cycle engine?

To push the fuel-air mixture into the combustion chamber. Signup and view all the answers

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

The piston compresses the fuel-air mixture into a smaller volume. Signup and view all the answers

What role does the camshaft play in the operation of the four-stroke engine?

Opens and closes the inlet and exhaust valves Signup and view all the answers

In a four-stroke engine, what is created in the space above the cylinder during the intake stroke?

Partial vacuum Signup and view all the answers

How many revolutions of the crankshaft are needed to complete all four strokes of a four-stroke engine?

Two revolutions Signup and view all the answers

What occurs at the top dead center (TDC) position in the four-stroke cycle engine?

The piston changes direction. Signup and view all the answers

How does the rotary engine (Wankel) differ from the four-stroke engine in terms of cycle execution?

It completes all four strokes in a single rotation Signup and view all the answers

Why is the pressure development wasted at the bottom dead center (BDC) of the piston travel?

The piston is not moving upwards. Signup and view all the answers

What is the role of the inlet valve during the first stroke of the four-stroke cycle?

Allows the fuel-air mixture to enter the cylinder Signup and view all the answers

What occurs in the engine cycle just before the exhaust stroke starts?

Combustion of fuel occurs to expand gases Signup and view all the answers

What is the main purpose of the spark plug during the power stroke in a four-stroke engine?

To ignite the fuel-air mixture. Signup and view all the answers

What primarily happens to the fuel-air mixture as it is compressed in the compression stroke?

Its temperature increases. Signup and view all the answers

During which stroke is the exhaust valve opened to expel gases from the cylinder?

Exhaust stroke Signup and view all the answers

At what angle is diesel fuel injected into the hot, compressed air during the compression stroke?

10° - 20° before TDC Signup and view all the answers

What is the normal combustion temperature in a diesel engine?

1,700 °C Signup and view all the answers

What initiates the exhaust stroke in a diesel engine?

Opening of the exhaust valve Signup and view all the answers

How does the piston move during the power stroke?

Downward due to high-pressure force Signup and view all the answers

What mechanism allows the scavenging of exhaust gases in both diesel and gasoline engines?

Inrush of new air during the intake stroke Signup and view all the answers

Why is timing the ignition of a fuel-air mixture in a diesel engine difficult?

Ignition dependent on heat of compression Signup and view all the answers

What typically happens to the exhaust gases after TDC during the power stroke?

They are expelled immediately Signup and view all the answers

When does the fuel injection in a diesel engine cease during the power stroke?

At 16° past TDC Signup and view all the answers

What is a significant disadvantage of the radial engine?

It produces increased drag due to its design. Signup and view all the answers

Which statement about in-line engines is true?

In-line engines can have either an above or below crankshaft placement. Signup and view all the answers

What feature distinguishes an inverted in-line engine from a standard in-line engine?

Its cylinders are mounted below the crankshaft. Signup and view all the answers

What is an advantage of the in-line engine over other engine types?

It has a higher weight-to-horsepower ratio. Signup and view all the answers

Why was the radial engine widely used in military and airline aircraft?

It efficiently combines high power output with dependability. Signup and view all the answers

Radial engines were typically manufactured with how many cylinders?

Between 3 and 28 cylinders. Signup and view all the answers

What challenge is presented by the air-cooled in-line engine as the engine size increases?

Issues with adequate cooling. Signup and view all the answers

What design aspect of the in-line engine aids in streamlining?

Its small frontal area. Signup and view all the answers

What is the standard configuration for virtually all production of reciprocating engine-powered aircraft?

Opposed air-cooled engines Signup and view all the answers

How is engine displacement indicated in the engine's designation?

With a three-digit number rounded to the nearest 10 in³ Signup and view all the answers

What does the first suffix letter in an engine's designation signify?

Type of power section Signup and view all the answers

What information does the number following the first suffix letter provide in an engine's designation?

Design type of the nose section Signup and view all the answers

What does a mode number like '4', '5', or '6' indicate in an engine's designation?

Crankshaft vibration mode Signup and view all the answers

What character in the designation suffix may indicate the type of magneto utilized with the engine?

Last character in the suffix Signup and view all the answers

Which specific designation suffix indicates a dual magneto in an engine?

Letter 'D' Signup and view all the answers

Why have double-V (fan-type) engines fallen out of use in aircraft manufacturing?

Higher weight compared to opposed engines Signup and view all the answers

Study Notes

Piston Engine Fundamentals

Piston engines are machines that convert heat energy from burning fuel into mechanical energy.
Internal combustion engines burn fuel within the cylinders.
External combustion engines burn fuel outside the cylinders (like steam engines).
Engines are classified by the source of power (gas, oil, or steam), the location of combustion (internal or external), and the movement of the working parts (reciprocating, rotary, or turbine).
Reciprocating engines are the most common in general aviation.
Fundamental accessories in a reciprocating engine include the carburettor/fuel injection system, ignition coil, distributor, battery, spark plugs, starter, and generator.

Four-Stroke and Two-Stroke Cycle Engines

Four-stroke engines complete one power cycle in four piston strokes (intake, compression, power, and exhaust).
Two-stroke engines achieve a power cycle in two strokes.
Two-stroke engines are simpler, but often less efficient and produce more pollution.
A four-stroke engine has a crankshaft that makes two revolutions to complete a four-stroke cycle.
Key components include pistons, connecting rods, crankshafts, cylinders, and valves.

Fundamentals of Engine Parameters

Volumetric Efficiency (VE): Describes the amount of fuel/air in the cylinder relative to the theoretical maximum. (80-100% for normally aspirated engines)
Thermal Efficiency: The percentage of the fuel's energy that's converted to usable power. (typically less then 33% of the total)
Mechanical efficiency: Takes away any power losses from the workings of the parts of the engine.
Piston Displacement: the total volume of air/fuel mixture an engine can draw in during one complete engine cycle in liters or cubic inches, calculated using area of the piston and length of stroke.
Compression Ratio: The ratio between the volume of a combustion chamber and cylinder, calculated using volume of the combustion chamber as well as the area of the piston and length of the stroke.

Operating Principle

Reciprocating engines rely on the process of compressing and burning fuel/air mixtures in a closed space.
This results in an expansion of gas that produces power to turn the crankshaft.
Four basic events are involved: admission of fuel/air mixture, compression of mixture, combustion, and exhaustion of gases.

Valve Operation

Valves open and close at specific points of the piston's movement (usually regulated by the camshaft and timed using precise mechanisms).
The timing of valve openings and closings is critical for efficient engine operation.

Classification of Reciprocating Engines

Engines are classified by their cylinder arrangements relative to the crankshaft, such as in-line, V-type, opposed, and radial.
The arrangement can affect factors like frontal area, cooling, and weight.

Designation of Reciprocating Engines

Manufacturers use codes to indicate engine type.
Codes include letters relating to the type of engine and numbers signifying displacement.

Firing Order and Ignition Interval

Firing order specifies the sequence in which cylinders ignite fuel.
Precise timing and order are crucial for smooth operation, minimizing vibrations and maximizing power in multi-cylinder engines.

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Description

Test your knowledge on the workings of a four-stroke engine with this quiz. It covers topics such as exhaust valves, camshaft functions, and the differences between rotary and traditional engines. Perfect for automotive enthusiasts and engineering students alike!