Engine Mechanics Quiz

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Questions and Answers

During which phase of the cycle is the exhaust valve opened?

2nd Stroke

4th Stroke (correct)

3rd Stroke

1st Stroke

What is the pressure range during the compression in the 2nd Stroke?

0.1 to 0.2 bar

10 to 16 bar (correct)

2 bar

40 to 60 bar

What must occur just before TDC in the 3rd Stroke to ensure proper combustion?

The exhaust valve closes

Ignition must be advanced (correct)

The inlet valve opens

The piston reaches BDC

How long is the interval between the spark and the flame being produced?

Approx. 1 millisecond Signup and view all the answers

What temperature can the exhaust gases reach at the end of the 4th Stroke?

800 - 1,000 °C Signup and view all the answers

What happens to the fuel-air mixture during the initial phase of the cycle?

It is sucked into the cylinder Signup and view all the answers

What is the approximate vacuum pressure created during the intake phase?

0.1 to 0.2 bar Signup and view all the answers

How far does the crankshaft rotate for a complete cycle?

720° Signup and view all the answers

What is the purpose of measuring the pressure pattern in an engine cylinder?

To analyze the combustion process and engine settings Signup and view all the answers

What is the primary purpose of the camshaft in an engine?

To time the operation of the valves Signup and view all the answers

How do the valve timings in an actual engine differ from the ideal conditions described?

Valves are timed to open earlier and close later Signup and view all the answers

What drives the intake and exhaust valves in an engine?

Camshaft and operating mechanisms Signup and view all the answers

Which component is responsible for pushing the valve off its seat?

The cam follower (tappet) Signup and view all the answers

What happens if there is a marked deviation from the normal pressure pattern during engine operation?

It indicates that engine settings may be incorrect Signup and view all the answers

How many cams are there for each cylinder in this engine system?

Two for operating both the intake and exhaust valves Signup and view all the answers

Why are the lobes positioned differently on the camshaft?

To prevent both valves from operating simultaneously Signup and view all the answers

During the four-stroke cycle, what indicates a cylinder is preparing for a new charge intake?

Valves remaining open during the crankshaft rotation Signup and view all the answers

When does the valve spring close the valve?

After the cam lobe has cleared the tappet Signup and view all the answers

Why is the exhaust expelled at very high speed from the cylinder?

To ensure a complete exhaust cycle before intake Signup and view all the answers

What is the primary function of the piezo-electric indicator in engine testing?

To produce electrical tension based on pressure Signup and view all the answers

What geometric concept is essential to understanding valve timing relative to the crankshaft?

The partitioning of a circle in degrees Signup and view all the answers

What happens to the valve spring when the cam lobe raises the cam follower?

It compresses in response to the valve being pushed off its seat Signup and view all the answers

What component contributes to closing the valves in an engine?

Spring action Signup and view all the answers

What is represented by the full revolution of the crankshaft in terms of degrees?

360° Signup and view all the answers

How many degrees are covered by two full revolutions of a camshaft?

720° Signup and view all the answers

What is the effective relationship between the turning speeds of the camshaft and crankshaft?

The camshaft turns half as fast as the crankshaft. Signup and view all the answers

At what crankshaft rotation does the intake valve begin to open relative to TDC?

5° before TDC Signup and view all the answers

What characterizes the rock position of a piston in an engine?

Minimal work is accomplished. Signup and view all the answers

How many strokes of the piston correspond to every complete revolution of the crankshaft?

Two strokes Signup and view all the answers

How much crankshaft rotation occurs after BDC when the intake valve closes?

45° Signup and view all the answers

What is the relationship between camshaft gear teeth and crankshaft gear teeth?

The camshaft gear has double the number of teeth as the crankshaft gear. Signup and view all the answers

What aspect of valve timing is emphasized for each valve opening during the piston cycle?

Each valve opens once during every four strokes of the piston. Signup and view all the answers

Why does the intake valve open slightly before TDC?

To enable the new fuel charge to start moving into the cylinder Signup and view all the answers

What role does closing the exhaust valve after TDC play during the intake stroke?

It helps to push out remaining exhaust gases Signup and view all the answers

What occurs when both the transfer port and exhaust port are covered?

A partial vacuum is developed in the crankcase Signup and view all the answers

What happens during the downward stroke of the piston in terms of the fuel charge?

The incoming fuel charge is slightly compressed and forced into the cylinder Signup and view all the answers

How does the piston moving slowly affect the mixture entering the cylinder?

More mixture enters than at high speeds Signup and view all the answers

What overall effect does the timing of the intake and exhaust valve operations have on the engine?

It enhances the engine's cooling and scavenging efficiency Signup and view all the answers

What is the consequence of keeping the intake valve open until 45° past BDC?

It permits a longer time for the new charge to flow into the cylinder Signup and view all the answers

What effect does atmospheric pressure have on the incoming mixture during the intake stroke?

It creates a momentum that aids the mixture into the cylinder Signup and view all the answers

What is a significant disadvantage of the radial engine?

It has greater drag due to working parts. Signup and view all the answers

What is one of the key strengths of the radial engine?

It is the most widely used due to its dependability. Signup and view all the answers

How is an in-line engine typically constructed?

It usually has a single crankshaft positioned above or below the cylinders. Signup and view all the answers

What advantage does an 'inverted' in-line engine provide?

Shorter landing gear and improved pilot visibility. Signup and view all the answers

Why might larger air-cooled in-line engines face issues?

They have difficulty with proper cooling. Signup and view all the answers

What feature contributes to the better streamlining of an in-line engine?

Its small frontal area. Signup and view all the answers

What was the primary application of radial engines historically?

Designed for high power applications in military and airline aircraft. Signup and view all the answers

Which of the following is NOT a characteristic of in-line engines?

They always have multiple crankshafts. 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.
These engines are categorized by power source (gas, oil, or steam), combustion location (internal or external), and movement of working parts (reciprocating, rotary, or turbine).
Internal combustion engines burn fuel inside the cylinders.
External combustion engines burn fuel outside the cylinders, such as steam engines.
Reciprocating internal combustion engines (commonly used in aviation) use pistons that move back and forth inside the cylinders.

Four-Stroke and Two-Stroke Cycle Engines

Four-stroke cycle engines complete a cycle of events (intake, compression, ignition, and exhaust) in four piston strokes.
Two-stroke cycle engines complete the same cycle in two piston strokes.
Four-stroke cycle engines generally offer better fuel efficiency.
Two-stroke cycle engines offer greater power output per engine size.
Four-stroke cycle operations include intake, compression, combustion, and exhaust.

Fundamental Engine Working Parts

Cylinder: The main combustion and gas expansion chamber.
Cylinder Head: Closes one end of the cylinder.
Piston: Moves up and down inside the cylinder, with rings for a gastight seal.
Connecting Rod: Connects the piston to the crankshaft.
Crankshaft: Converts the reciprocating motion of the piston into rotary motion.
Valve(s): Control the flow of air-fuel mixture into and out of the cylinder.
Camshaft: Controls the opening and closing of the valves.
Push Rods and Rocker Arms: Transmit camshaft motion to the valves.

Rotary Internal Combustion Engines (Wankel Engine)

Rotary engine uses a rotary piston instead of reciprocating ones.
The piston shape is trochoid.
The energy from combustion is directly transferred to the shaft.
The structure is more stable than traditional piston engines, with fewer vibrations.

Fundamentals of Engine Parameters

Volumetric Efficiency (VE): Measures the amount of fuel/air mixture in the cylinder compared to the maximum possible volume.
Thermal Efficiency: Measures the proportion of fuel energy converted to useful power.
Mechanical Efficiency (ME): Measures the proportion of useful power output to the power produced internally by the engine.
Piston Displacement (PD): The total volume of air/fuel mixture swept by the pistons.
Compression Ratio: The ratio of the maximum and minimum cylinder volumes.

Operating Principle

The operating principle of reciprocating engines involves taking in fuel/air, compressing, burning the mixture to create expansion of gases, then removing the exhaust gases.
These actions take place in a cycle within either two or four strokes of the piston and each piston stroke translates into movement of the entire crankshaft from one end of its trajectory to the other.

Valve Operation

Valves control the flow of mixture or gases into and out of the cylinder.
Valve timing helps improve engine efficiency and fuel economy.
Camshaft actions control valve opening and closing times.
The timing is important to have optimum fuel/air mixture for proper combustion.

Principles of Diesel Engine Operation

Diesel engines ignite fuel by heat from compression rather than a spark.
Compression raises the temperature of the intake air.
Fuel is injected into the highly compressed air, and combustion occurs.

Speed and Power Control

Diesel engines use timing of compression and fuel injection to control speed and power.
Air is pre-compressed in diesel engines, followed by the fuel injection.

Classification of Reciprocating Engines

Engines are classified by cylinder arrangement (in-line, V-type, opposed, and radial).
Their design affects engine performance, weight, cooling, and other characteristics.

Radial Engines

Radial engines have cylinders arranged in a circle around a central crankshaft.
They were once popular in aircraft.
Rotary and static-radial types exist.

Designation of Reciprocating Engines

Manufacturer codes are used to identify engine models.

Firing Order and Ignition Interval

Firing order is the sequence by which cylinders ignite.
Timing is precise to ensure smooth functioning.

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Description

Test your knowledge on engine operation cycles with this quiz. You will answer questions about valve timings, combustion processes, and the roles of various engine components. Perfect for automotive engineering students or enthusiasts.