Diesel Engine Mechanics Quiz

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Questions and Answers

What is the role of boost pressure in a mechanical blower equipped engine?

It is directly proportional to the speed of the blower. (correct)

It helps to draw in fresh air into the cylinder.

It reduces engine speed.

It decreases the temperature of the air.

What is the primary function of the crankcase ventilation system in most engines?

To promote atmospheric pressure in the crankcase.

To increase the exhaust temperature.

To enhance fuel consumption efficiency.

To prevent the buildup of combustible gases in the crankcase. (correct)

In turbo equipped engines, what factor influences the amount of boost pressure?

The fuel consumed by the engine in addition to engine speed. (correct)

The temperature of the exhaust gases only.

The speed of the blower alone.

The weight of the engine.

What is the purpose of the oil separator in the engine's ventilation system?

To trap and recover small oil droplets carried out with crankcase vapours. Signup and view all the answers

How does the eductor system function in the crankcase of a GM engine?

It draws crankcase vapours through an oil separator during engine operation. Signup and view all the answers

What type of operating cycle does the General Motors diesel engine utilize?

Two stroke operating cycle Signup and view all the answers

How many strokes of the piston are required for one power pulse in a two stroke operating cycle?

Two strokes Signup and view all the answers

Which of the following is a type of engine model mentioned in the content?

20 cylinder model Signup and view all the answers

What part of a four stroke diesel engine closes off the cylinder at the top?

Cylinder head Signup and view all the answers

What is the primary purpose of piston rings in a diesel engine?

To seal the combustion chamber Signup and view all the answers

Which of the following represents a critical internal pressure zone in a diesel engine?

Airbox Signup and view all the answers

What is a significant difference highlighted between two stroke and four stroke diesel engines?

Four stroke engines have better fuel efficiency Signup and view all the answers

What is the primary reason this engine is suited for railroad locomotives and marine installations?

Its compact nature Signup and view all the answers

Where is the main generator typically driven from on the engine?

The flywheel end Signup and view all the answers

What term is used to describe the rear of the engine where combustion air is supplied?

Turbo end Signup and view all the answers

Which component is typically located at the front end of the engine?

Governor Signup and view all the answers

What direction does the engine rotate when viewed from the rear?

Anti-clockwise Signup and view all the answers

Which of the following components is NOT mentioned as being located on the front end of the engine?

Main generator Signup and view all the answers

What role does the auxiliary generator drive serve in the engine structure?

Located at the flywheel end Signup and view all the answers

What is indicated as a major consideration in the design of this engine?

Size Signup and view all the answers

Which pumps are found at the front end of the engine?

Cooling water pumps Signup and view all the answers

What device is primarily mounted at the front end of the engine?

Governor Signup and view all the answers

What is the front end of the crankshaft used for?

Driving accessory items such as pumps Signup and view all the answers

How are the engine banks identified when viewed from the rear of the engine?

As left and right banks Signup and view all the answers

Which cylinder number is always located in the right front corner of the engine?

Cylinder number one Signup and view all the answers

In a twelve-cylinder engine, which cylinders are located on the left bank?

Seven through twelve Signup and view all the answers

What determines the size and type of pumps utilized in an engine?

The engine's size and application Signup and view all the answers

Which cylinders are numbered one through eight in a sixteen-cylinder engine?

Cylinders one through eight on the right bank Signup and view all the answers

What does the term 'accessory end' refer to?

The front of the engine Signup and view all the answers

Which description regarding engine orientation is accurate?

Engine orientation is established from the rear looking forward Signup and view all the answers

How do the cylinders on the right and left banks compare in a twelve-cylinder engine?

Right bank has one to six, left bank has seven to twelve Signup and view all the answers

Which accessory can be connected at the front end of the crankshaft?

Air compressors Signup and view all the answers

What is the primary method used by a two stroke engine to introduce fresh air into the cylinder?

Using a mechanical air pump Signup and view all the answers

What occurs simultaneously with the entry of fresh air into the cylinder of a two stroke engine?

Exhaust valves are open Signup and view all the answers

What is the effect of the angled air ports in a two stroke engine?

They cause the air to swirl in the cylinder Signup and view all the answers

What is the term used to describe the process of purging and filling the cylinder with fresh air in a two stroke engine?

Scavenging Signup and view all the answers

What happens to the piston during the scavenging process in a two stroke engine?

The piston moves upwards Signup and view all the answers

During which part of the cycle does fresh air enter the cylinder in a two stroke engine?

At the bottom of the stroke Signup and view all the answers

Why is it important for the two stroke engine to completely purge the cylinder?

To ensure maximum efficiency during combustion Signup and view all the answers

What role does the crankshaft play in the operation of a two stroke engine?

It converts linear motion into rotational motion Signup and view all the answers

How does the two stroke engine differ from a four stroke engine in terms of air introduction?

It relies on a pump for air transfer Signup and view all the answers

What is the layout design of the GM diesel engine?

A 45-degree narrow V design Signup and view all the answers

How are the cylinders of the GM diesel engine numbered?

From front to rear starting with the right front cylinder Signup and view all the answers

Where are the exhaust systems of the GM diesel engine mounted?

On the top between the cylinder banks Signup and view all the answers

What is the timing interval between opposing cylinders in the GM diesel engine?

45 degrees apart Signup and view all the answers

Which components are located at the front end of the GM diesel engine?

Governor, water pumps, and lube oil pumps Signup and view all the answers

What occurs to the pressure in the cylinder during the intake stroke of a four stroke engine?

The pressure decreases below atmospheric pressure. Signup and view all the answers

Which component is responsible for converting the piston’s up and down motion into rotary motion?

Crankshaft Signup and view all the answers

What is the initial motion of the piston during the intake stroke in a four stroke engine?

Moving downwards to increase volume. Signup and view all the answers

Which of the following statements accurately describes the role of the intake valve during the intake stroke?

It opens and closes at high speeds. Signup and view all the answers

What effect does the movement of the piston have on the volume of the cylinder during the intake stroke?

The volume of the cylinder increases. Signup and view all the answers

During which part of the four stroke cycle does the intake valve function primarily?

Intake stroke Signup and view all the answers

How does the crankshaft movement relate to the piston movement in a four stroke engine?

The crankshaft rotates while the piston moves linearly. Signup and view all the answers

What degree of crankshaft rotation is required for the eight-cylinder engine to generate a power pulse?

45° Signup and view all the answers

What is the power pulse generation interval for a sixteen-cylinder engine?

22.5° Signup and view all the answers

Which engine model would require a power pulse every 30° for balance?

Twelve-cylinder Signup and view all the answers

Why is balancing the twelve and twenty-cylinder models challenging?

Because of the need for a power pulse every 30° Signup and view all the answers

What ensures a balanced firing order in an engine?

Even distribution of power pulses Signup and view all the answers

Where is the Injector Timing tag located on the engine?

At the rear corner of the engine Signup and view all the answers

What happens to the exhaust in engines equipped with turbochargers?

It is collected in the manifold and sent through the turbine Signup and view all the answers

What degree of separation exists between paired cylinders, like number one and seven, on the twelve-cylinder model?

45° Signup and view all the answers

Which characteristic defines an 'Unbalanced' firing order in engines?

Pulses are generated every 45° between opposing cylinders Signup and view all the answers

Which engines are mentioned as having a balanced firing order?

Eight-cylinder and sixteen-cylinder Signup and view all the answers

What is the primary function of the air pump in a two stroke engine?

To pump fresh air into the combustion chamber Signup and view all the answers

Which component differentiates a two stroke engine's intake process from that of a four stroke engine?

A row of ports in the cylinder wall Signup and view all the answers

What is a characteristic function of the fuel injector in a two stroke engine?

To spray fuel for optimal combustion Signup and view all the answers

What is the significance of having ports located in the lower portion of the cylinder wall in a two stroke engine?

They enable simultaneous intake and exhaust functions Signup and view all the answers

Which design feature of a two stroke engine contributes to its unique airflow dynamics?

The presence of an airbox surrounding the ports Signup and view all the answers

Why is the design of the two stroke engine beneficial for specific applications like locomotives and marine installations?

It provides a higher power-to-weight ratio Signup and view all the answers

What role does the chamber known as the airbox play in a two stroke engine?

It helps to pump fresh air into the cylinder Signup and view all the answers

Which statement accurately reflects the construction of a two stroke engine?

The cylinder head is sealed both at the top and bottom Signup and view all the answers

What is the effect of the angled air ports in a two stroke engine during operation?

They facilitate a more efficient air/fuel mixture during intake Signup and view all the answers

How many revolutions of the crankshaft are needed for a four stroke engine to produce one power impulse?

Two complete revolutions Signup and view all the answers

What design feature helps minimize the overall width of the two stroke General Motors diesel engine?

Close distance between opposing cylinders Signup and view all the answers

What is the function of air ports in a two stroke engine?

To admit fresh air into the cylinder Signup and view all the answers

In terms of power impulse production, how does a two stroke engine compare to a four stroke engine?

It requires fewer strokes per power impulse Signup and view all the answers

Which configurations can the General Motors diesel engine be available in?

8, 12, 16, and 20 cylinder models Signup and view all the answers

What type of crankshaft arrangement do opposing cylinders in the General Motors diesel engine share?

A common crankshaft eccentric Signup and view all the answers

What is the primary fuel and combustion air source for a two stroke engine?

Fresh air supplied by an air pump Signup and view all the answers

What is a critical feature of the crankshaft in a two stroke diesel engine during operation?

It facilitates one power impulse per revolution Signup and view all the answers

How are the cylinder banks arranged in the two stroke General Motors diesel engine?

In a narrow 'V' type design with a 45° angle Signup and view all the answers

Study Notes

Introduction

Diesel engines come in four-stroke and two-stroke operating cycles
General Motors diesel engines use a two-stroke operating cycle, requiring two piston strokes for one power pulse.
The document will cover general engine arrangement, model types (8, 12, 16, and 20 cylinders), and internal pressure zones (crankcase, airbox, and top deck)
Individual components will be detailed in a future chapter

Engine Operating Cycles

General Motors diesel engines use a two-stroke operating cycle, meaning one power pulse requires two piston strokes (one up and one down).
Compared to four-stroke cycles, it's simpler to describe the two-stroke cycle

Four Stroke Engine - Construction

Most four-stroke diesel engines share similar construction.
Cylinders are sealed top and bottom by the cylinder head and piston rings.
Intake and exhaust valves in the cylinder head control gas flow.
A crankshaft and connecting rod convert piston motion to rotary motion

Four Stroke Engine - Intake Stroke

Crankshaft rotation moves the piston down, increasing cylinder volume.
Pressure decreases below atmospheric, drawing fresh air into the cylinder through the intake valve.
The new air charge is ready for combustion.
The intake valve closes when the piston reaches the bottom (BDC).

Four Stroke Engine - Compression Stroke

The piston moves up, reducing the cylinder volume and increasing the pressure and temperature.
Usually, diesel engines have a compression ratio between 16:1 and 20:1, this ratio is the volume with the piston at BDC divided by the volume at TDC
This high temperature makes the fuel ignite when injected because of the heated air increasing temperature due to compression.

Four Stroke Engine - Power Stroke

Fuel is injected into the cylinder near top dead center (TDC).
The hot air and fuel combustion increase cylinder pressure.
This high pressure forces the piston down, creating a rotary motion on the crankshaft.

Four Stroke Engine - Exhaust Stroke

The piston moves upwards, reducing volume and increasing pressure.
This increased pressure pushes exhaust gases out of the cylinder through the exhaust valve while fresh air is being pulled in.
The cylinder prepares for the next intake stroke

Four Stroke Engine - Conclusion

Four distinct piston movements are needed to produce one power stroke on a four-stroke engine: (intake, compression, power, and exhaust).
Two complete revolutions are needed for one power stroke output by the crankshaft.

Two Stroke Engine - Construction

Two-stroke engines differ from four-stroke in design, especially in the air intake and exhaust
Fresh air is pumped into the airbox.
Fresh air enters the cylinder through ports which are surrounded by a chamber known commonly as the airbox. These ports are angled slightly off-center to create swirl as air enters.

Two Stroke Engine - Scavenging (Start)

A crankshaft rotation forces fresh air into the airbox.
Fresh air enters the cylinder through ports as the exhaust valves are open.

Two Stroke Engine - Scavenging (Finish)

Piston moves up, blocking fresh air, and pushing remaining exhaust gases out the cylinder through exhaust valves.
Exhaust valves close allowing compression.

Two Stroke Engine - Compression

Piston moves upwards compressing the air in the cylinder.
Pressure and temperature increase as the air is compressed.
The initial cylinder pressure in two-stroke engines is slightly higher due to air pump volume, and reduced effective stroke.

Two Stroke Engine - Injection

Fuel is injected into the cylinder as the piston approaches top dead center (TDC)
The fuel mixes with the compressed, heated air and quickly ignites.

Two Stroke Engine - Power

Combustion increases cylinder pressure and forces the piston down creating a rotary motion on the crankshaft

Two Stroke Engine - Exhaust

Exhaust gases are pushed out of the cylinder through the exhaust valves.
Fresh air is pumped into the airbox in preparation for the next cycle.

Two Stroke Engine- Conclusion

Two-stroke engines use one complete crankshaft rotation to produce one power pulse

Review

Four-stroke engines need two revolutions.
Two-stroke engines require one revolution
Two-stroke engines use air ports to admit fresh air
Fresh air is crucial as it's pulled in by a crankcase
Air is pumped into a chamber (airbox) before entering the cylinder.
Exhaust gasses are expelled.

General Engine Arrangement

General Motors diesel engines are "narrow V" design with two banks of cylinders at a 45-degree angle
Cylinder numbering starts from the right front corner of the engine.
The layout is designed for compactness, which makes it suitable for railroad locomotives.
Components like the governor, water pumps, and oil pumps are located at the front, while the exhaust system is on the top.

Internal Pressure Divisions

Engines have positive and negative pressure zones: positive in the airbox & negative in the crankcase.
Positive pressure is needed to force fresh air into the cylinders.
Negative pressure prevents back-flow of exhaust gases.
The amount of boost pressure is directly proportional to the engine speed.
The top deck of the engine is common to the crankcase, and the entire assembly is kept near negative pressure from crankcase pressure

Serial Numbers

Used for part identification, and track production history
The model, or production date, place of manufacture, and production sequence number are crucial information found on serial numbers
Usually found on a plate on the engine banks

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Description

Test your knowledge on diesel engine mechanics, including functions of the crankcase ventilation system, boost pressure in turbo engines, and the operating cycles of different engine models. This quiz covers essential components and their roles to deepen your understanding of diesel technology.