Engine Piston Assembly Quiz

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Questions and Answers

What is the primary function of a piston skirt?

To enhance combustion efficiency

To anchor the piston rings

To reduce friction as the piston moves (correct)

To support the piston within the cylinder (correct)

What is a garter spring primarily used for in a piston assembly?

To control the expansion of the piston rings

To dampen vibrations during engine operation

To provide sealing by pressing the piston rings against the cylinder wall (correct)

To hold the piston securely in the cylinder

Which type of piston ring is specifically designed to control engine oil consumption?

Compression ring

Oil control ring (correct)

Expansion ring

Scraper ring

Which characteristic best describes a dry cylinder liner?

Has a long service life Signup and view all the answers

What is the main purpose of honing a cylinder liner?

To improve the surface finish for better sealing Signup and view all the answers

Why are inlet and exhaust valves typically equipped with two springs?

To ensure proper closure and prevent valve bounce Signup and view all the answers

How does a valve rotator function in an engine, and what type of fuel is it primarily used with?

By rotating the valve to ensure even wear; used with high-viscosity fuels Signup and view all the answers

What is critical vibration in an engine, and why is it important to manage?

It occurs at specific frequencies that can cause structural damage Signup and view all the answers

What is the key difference between indicated power and brake power in an engine?

Indicated power is calculated without losses, while brake power includes frictional losses. Signup and view all the answers

What characterizes a dual fuel engine?

It can operate simultaneously on two different fuels. Signup and view all the answers

In a 4-stroke engine cycle, which stroke is responsible for power generation?

Power Stroke Signup and view all the answers

What is scavenging in a 2-stroke engine?

The method by which exhaust gases are expelled from the cylinder. Signup and view all the answers

What is a stoichiometric mixture in combustion engines?

A balanced mixture of fuel and air that maximizes combustion efficiency. Signup and view all the answers

What are the typical strokes and bores for low-speed engines compared to high-speed engines?

Low-speed engines have longer strokes and larger bores. Signup and view all the answers

What is the purpose of valve overlap in an engine?

To enhance the timing of intake and exhaust events for performance. Signup and view all the answers

Which types of bearings are most commonly used in engines?

Plain bearings for supporting rotating shafts. Signup and view all the answers

Study Notes

Dual Fuel Engine

A dual fuel engine operates on two different types of fuel, typically a combination of gas and diesel.

Engine Speeds

Low-speed engines: Typically operate at speeds less than 300 RPM.
Medium-speed engines: Operate in the range of 300 to 1200 RPM.
High-speed engines: Operate at speeds greater than 1200 RPM.

Strokes and Bores

Low-speed engines: Often have longer strokes (up to 300 mm) and larger bores.
Medium-speed engines: Shorter strokes compared to low-speed, with bores around 200-400 mm.
High-speed engines: Short strokes and smaller bores (usually less than 200 mm).

Engine Numbering

An engine is numbered based on its type, model, and configuration, often including parameters like displacement and cylinder arrangement.

Heat Engine

A heat engine converts thermal energy to mechanical work. An example is a steam engine.

Air Standard Cycle in Diesel Engines

The air standard cycle for diesel engines usually follows the Diesel cycle, involving adiabatic compression, constant pressure heat addition, adiabatic expansion, and constant volume heat rejection.

Indicated-Power vs. Brake-Power

Indicated power measures the total power produced within the cylinder, whereas brake power measures the output power available at the crankshaft after losses due to friction.

Parasitic Load

Parasitic load refers to energy consumed by components when the engine is not producing useful work. Examples include alternators and water pumps.

Stoichiometric Mixture

A stoichiometric mixture achieves optimal combustion efficiency. Gasoline typically has a ratio of 14.7:1 (air to fuel), while diesel ranges from 14:1 to 18:1.

Combustion Engine Description

A combustion engine can be described by its cycle (e.g., Otto, Diesel) and configuration (e.g., inline, V-type).

Petrol in CI Engines

Petrol cannot be used in a Compression Ignition (CI) engine due to its lower ignition temperature and octane rating leading to pre-ignition.

4-Stroke Engine Cycle

The 4-stroke cycle consists of intake, compression, power, and exhaust strokes, with each stroke completing during two revolutions of the crankshaft.

Power Stroke in 4-Stroke Engine

The power stroke occurs during the combustion process when the mixture ignites and forces the piston down.

Revolutions per Power Stroke in 4-Stroke Engine

One power stroke occurs every two revolutions of the crankshaft; the camshaft rotates at half the crankshaft speed.

Revolutions per Power Stroke in 2-Stroke Engine

In a 2-stroke engine, one power stroke occurs every revolution of the crankshaft; camshafts are generally not used.

2-Stroke Engine Cycle

The 2-stroke cycle involves a single crankshaft revolution for both intake and power strokes, using scavenging techniques for gas exchange.

Scavenging

Scavenging is the process of clearing exhaust gases from the cylinder after combustion to make room for fresh air-fuel mixture.

Scavenging Methods

Loops Scavenging: Efficient for high-speed engines; drawbacks include loss of fresh fuel.
Cross Scavenging: Better mixing of air and fuel; can lead to increased exhaust pollution.

Engine Emissions Pollutants

Major pollutants include carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM).

Hazards of Emissions

CO can cause suffocation, HC contributes to smog and health issues, NOx is linked to respiratory problems, and PM can lead to heart disease.

Engine Valve Overlap

Valve overlap occurs when both the intake and exhaust valves are open at the same time, improving scavenging and cylinder filling.

Timing Diagrams

Timing diagrams visually represent valve operation phases in both 4-stroke and 2-stroke engines.

Differences Between 2 and 4-Stroke Engines

2-stroke engines produce power every crankshaft revolution, while 4-stroke engines do this every two revolutions. 4-stroke engines have more components, leading to complexity.

Engine Securing to Ship

Engines are secured to ships using bedplate and chocks to minimize vibration and stabilize during operation.

Bedplate Purpose

Acts as a foundation for the engine and distributes engine loads; typically made of cast iron or steel.

Chock Materials

Common materials for chocks include rubber (good vibration dampening, but wear over time) and metal (durability, but less vibration dampening).

Earthing the Bedplate

Earthing prevents electrical hazards by connecting the bedplate to the ship's hull, dissipating electrical currents.

Dry vs. Wet Sump

Dry Sump: Oil is stored in an external reservoir; advantages include lower engine height.
Wet Sump: Oil is stored in the oil pan; simpler but may lead to oil starvation during heavy maneuvers.

Engine Bearings

Types include plain (for low friction), roller (for higher load), and ball bearings; each offers different performance characteristics depending on application.

Plain Bearings Materials

Common materials are bronze and aluminum-based alloys, often constructed to ensure durability and resistance to wear.

Split Plain Bearings

Splitting allows for easier installation and removal without needing to disassemble the entire engine.

Conrod Plain Bearins

Larger bottom half for load distribution and to accommodate the crankshaft design, reducing stress.

Marine Palm

A configuration that connects the conrod to the piston, allowing for multi-directional flexibility during operation.

Oblique Conrods

Used for compact engine designs and reducing overall engine height, improving weight distribution.

Piston Skirt Purpose

Provides stability and aligns the piston in the cylinder; absence can lead to excessive piston wear and noise.

Garter Spring Function

A garter spring helps hold the piston rings in place and is typically located at the top of the piston.

Piston Rings Types and Functions

Types include compression rings (seal combustion gases), oil control rings (regulate oil), and scraper rings (remove excess oil).

Cylinder Liners Types

Two types:
- Cast iron liners (durability, low cost)
- Composite liners (lighter, enhanced thermal expansion properties).

Purpose of Honing

Honing provides a smooth surface finish on liners to improve sealing and lubrication, typically achieved through abrasive processes.

Medium-Speed Engine Cylinder Head Ports

Four ports facilitate efficient gas exchange, allowing separate paths for intake and exhaust gases.

Timing Marks on Camshaft Drive

Timing marks ensure correct alignment between the crankshaft and camshaft, crucial for synchronized valve operation.

Valve Bridge/Yoke Arrangement

This arrangement ensures even distribution of force across the valve springs, leading to consistent valve operation.

Valve Operation Arrangements

Spring-loaded, pneumatic systems, or hydraulic actuation are some ways valves can be opened and closed.

Double Springs for Valves

Inlet/exhaust valves use two springs to provide redundancy, enhancing reliability and ensuring proper closure under various conditions.

Valve Rotator Function

Valve rotators promote even wear and reduce seat deposits; commonly used with fuels that create high deposits, like diesel.

Differences in Low-Speed and Medium-Speed Engines

Low-speed engines typically feature larger components and a simpler design facilitating lower operational speeds.

Crosshead Function

The crosshead connects the piston to the crankshaft, allowing for vertical piston movement and reducing side loading on the piston.

Piston Rod Connection in Low-Speed Engines

Piston rods are typically attached using a bolted or pinned connection, ensuring robust linkage to the crosshead.

Stuffing Box Function

Ensures a seal around the moving parts (like shafts), preventing leaks of fluids or gases and maintaining pressure.

Crankshaft Construction Methods

Methods include:
- Forged crankshafts (high strength).
- Cast crankshafts (resistance to fatigue).
- Built-up crankshafts (combined sections for flexibility).

Crankshaft Witness Marks

Witness marks indicate the original alignment and help in assessing wear or misalignment during maintenance checks.

Oil Control Rings in Low-Speed 2-Stroke Engines

Generally, low-speed 2-stroke engines do not require oil control rings due to their design often using oil mist for lubrication.

Piston Ring Ends Sketching

Piston ring ends can be shaped as butt, angled, or tapered to facilitate proper sealing and oil control.

Piston Ring Shape Purpose

Specific shapes help optimize combustion sealing and accommodate thermal expansion while reducing blow-by gases.

Low-Speed Engine Exhaust Valve Function

The exhaust valve allows spent combustion gases to exit the cylinder after power is produced, preventing back pressure.

Fuel Injector Location in Low-Speed Engines

Fuel injectors are typically located around the cylinder head, directing fuel into the combustion chamber.

Golden Rule of Vibration

The rule states that vibrations should be minimized to avoid engine damage and improve operation efficiency.

Leaf Spring Damper Function

Leaf spring dampers limit torsional vibrations, enhancing stability and performance of rotating systems.

Viscous Damper Function

Viscous dampers limit vibrations by utilizing fluid damping principles, effectively absorbing energy from oscillations.

Moment Compensator Function

A moment compensator balances forces during engine operation, reducing excessive shaking and wear.

First vs. Second-Order Moments

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Description

Test your knowledge on the components and functions of engine piston assemblies. This quiz covers the roles of the piston skirt, garter springs, oil control rings, and more. Challenge yourself to see how well you understand these crucial elements of engine mechanics.