A spark plug is a crucial engine component that generates a spark to ignite the air-fuel mixture in internal combustion engines. This small component plays an indispensable role in igniting the air-fuel mixture and powering vehicles and machinery. The spark plug's ability to endure extreme heat and pressure while consistently producing a precisely timed spark is vital for engine efficiency, performance, and environmental impact.

This blog will throw light on different aspects of a Spark Plug, its diagram, parts, working, and functions. This topic in mechanical engineering is important for your upcoming examinations like SSC JE ME and RRB JE Mechanical Engineering.

Spark Plug

Spark plugs are crucial components in internal combustion engines that ignite the air-fuel mixture within the combustion chamber, initiating the combustion process. They consist of an insulated center electrode and a grounded side electrode, separated by a gap. When high voltage is applied across this gap, a spark is generated, igniting the compressed air-fuel mixture. 

What are Spark Plugs?

A spark plug serves as a vital ignition device in internal combustion engines, typically employed in petrol or natural gas-powered engines. It plays a pivotal role in initiating the combustion process, producing precisely timed sparks that enhance the efficiency of the air-fuel mixture combustion and consequently improve vehicle performance.

A spark plug comprises an insulated center electrode, a grounded side electrode, and a gap between them. This essential engine component initiates combustion by generating a spark to ignite the air-fuel mixture.

Fig 1: Construction of Spark Plug

1. Plug Terminal: Connects to the high-tension cable from the distributor cap, conducting high voltage to the central electrode.
2. Ceramic Insulator: Composed of aluminium oxide ceramic, it insulates and separates the central electrode from the ground, handling voltages of up to 40,000 Volts. It can have profiles to prevent flashover.
3. Metal Body: A precision-rolled steel shell with threaded precision for secure installation and removal. It grounds the cylinder head and aids in heat dissipation.
4. Central Electrode: Typically made of nickel-based alloys with a copper core, it can be platinum or iridium. High voltage is applied from the secondary winding through the distributor.
5. Ground Electrode: Welded to the metal body, it forms a spark path with the central electrode. It's constructed from nickel-based alloys, iridium, or may have titanium reinforcement.
6. Sealing Washer/Gasket: Provides a seal with the cylinder head and contributes to heat dissipation.
7. Insulator Tip: Extends into the combustion chamber and significantly influences the spark plug's thermal rating.
8. Electrode Gap: The gap between the central electrode and the ground electrode is critical for spark generation. An appropriate gap ensures sufficient spark for fuel ignition and prevents misfires.

Working of a Spark Plug

A spark plug functions by creating a controlled spark across the gap between its center and side electrodes. This spark ignites the compressed air-fuel mixture in the engine's combustion chamber, facilitating combustion.

Fig 2: Spark plug

• A high-voltage current from the distributor is directed to the spark plug.
• The central and ground electrodes are subjected to a high voltage, often reaching up to 40,000 V.
• The significant voltage difference between the central and ground electrodes ionises the air within the electrode gap.
• Ionised gas transforms into a conductor, enabling the flow of electric current from the central electrode to the ground electrode, generating a spark.
• The produced spark ignites the air-fuel mixture within the engine cylinder.

Functions of Spark Plug

The various functions of Spark plug are:

• Ignition: Generates a spark to ignite the air-fuel mixture in the engine cylinder.
• Heat Dissipation: Helps dissipate heat from the combustion process.
• Electrical Insulation: Provides insulation to prevent unwanted electrical arcing.
• Combustion Control: Influences combustion efficiency and timing.
• Performance: Contributes to engine performance and power output.
• Emission Control: Affects the reduction of harmful emissions.

Requirements of a Good Spark Plug

The characteristics of an Ideal Spark Plug are:

• High Voltage Reliability: Capable of withstanding voltages up to 40,000 V without failing.
• Effective Insulation: Exhibits excellent insulation properties, even at temperatures as high as 1000°C, to prevent arcing and flashover.
• Resistance to Thermal Shock: Can endure abrupt temperature changes, such as exposure to hot exhaust gases and cold intake mixtures.
• Secure Sealing: Forms a tight and gas-tight seal with the combustion chamber.
• Pressure Resilience: Can withstand oscillating pressure of approximately 100 bar.
• Mechanical Strength: Possesses high mechanical strength to ensure reliable installation.
• Efficient Thermal Conduction: Facilitates effective heat transfer through the insulator tip and electrodes.
• Spark Erosion Resistance: Resists wear and tear from spark erosion, combustion gases, and residues.
• Deposits Prevention: Prevents the accumulation of deposits on the insulator.

Types of Spark Plugs - Detailed Comparison

There are various types of spark plugs available in the industry. The device is used in the head of the cylinder combustion engine. A spark plug is used to ignite the air fuel mixture by producing the spark. It is essential to select the spark plug based on the material, size and performance requirement. 

Spark Plug Types - Detailed Explanation 

There are mainly 7 types of spark plugs used in industries. The plugs are selected mainly based on the type of material and functionality. It is crucial to choose the right spark plug to ensure better engine efficiency, longevity, and smoother ignition performance. For more details, candidates can refer to the information provided below. 

Copper Spark Plug

A copper core with a nickel alloy coating is used in the copper spark plug. It has a shorter lifespan. This type of spark plug provides excellent conductivity. They are used in older vehicles or low-performance engines. 

Platinum Spark Plug

A platinum disc on the centre electrode is used for the core material. They have a longer lifespan than copper and have better performance. Platinum spark plugs are expensive. It is used in modern cars with electronic ignition systems.

Double Platinum Spark Plug

They have extended the life and are better for waste spark ignition systems. It is made of Platinum on both centre and ground electrodes. Double platinum spark plugs are more expensive than single platinum spark plugs. They are used in Distributor-less ignition systems (DIS).

Iridium Spark Plug

They are made up of an Iridium centre electrode. Iridium Spark Plug has the Longest lifespan, best performance and high durability. It is more expensive. They are used in high-performance or modern engines requiring less frequent maintenance. 

Silver Spark Plug

This kind of spark plug is used for the best electrical and thermal conductivity. They are made of a silver centre electrode. They are commonly used in motorcycles and performance vehicles. They wear out faster, raw and are not commonly used. 

Resistor Spark Plug

They have slightly less performance than non-resistor types. Resistor Spark Plug contains a resistor to reduce electromagnetic interference. It is used in modern vehicles with sensitive electronic systems.

Non-Resistor Spark Plug

They have no resistor inside. They have slightly better performance and are used in racing or older vehicles with fewer electronics. 

Cold Spark Plugs vs Hot Spark Plugs

The table below draws a comparison between cold spark plugs and hot spark plugs.

Advantages of Spark Plug

• Ignition Source: Spark plugs provide a reliable ignition source, initiating combustion in the engine by creating a controlled spark between electrodes.
• Efficient Combustion: They contribute to efficient combustion of the air-fuel mixture, optimizing engine performance and fuel efficiency.
• Improved Engine Power: Spark plugs play a crucial role in maintaining and enhancing engine power by ensuring timely and precise ignition.
• Emissions Control: Properly functioning spark plugs help in reducing emissions by ensuring complete combustion, contributing to environmental sustainability.
• Smooth Engine Operation: By facilitating smooth and consistent ignition, spark plugs contribute to stable engine operation and performance.
• Enhanced Fuel Economy: Efficient combustion promoted by spark plugs leads to better fuel economy, benefiting both drivers and the environment.

Disadvantages of Spark Plug

While spark plugs are essential for internal combustion engines, they do have some disadvantages:

• Dependence on Maintenance: Spark plugs require regular inspection and replacement, and neglecting this maintenance can lead to decreased engine performance.
• Carbon Deposits: Over time, carbon deposits can accumulate on the spark plug electrodes, affecting performance and requiring cleaning or replacement.
• Fouling: Spark plugs can foul due to oil or fuel contaminants, leading to misfires, reduced efficiency, and the need for cleaning or replacement.
• Corrosion: Exposure to harsh conditions can cause corrosion on spark plugs, affecting their conductivity and overall effectiveness.
• Limited Lifespan: Despite advancements in materials, spark plugs have a finite lifespan and eventually need replacement, contributing to maintenance costs.

Applications of Spark Plug

Spark plugs are fundamental components in internal combustion engines, widely used in various applications to initiate combustion. Some key applications include:

• Automotive Engines: Spark plugs are integral to gasoline-powered vehicles, facilitating the ignition of the air-fuel mixture in the combustion chambers of internal combustion engines.
• Motorcycles: Spark plugs are essential in motorcycle engines, ensuring efficient combustion and reliable ignition for optimal performance.
• Small Engines: From lawnmowers to chainsaws and generators, small engines in various equipment rely on spark plugs for ignition.
• Aircraft Engines: Spark plugs are used in some aircraft engines, playing a crucial role in initiating combustion and powering aviation propulsion systems.
• Marine Engines: Spark plugs are employed in outboard motors and other marine engines to facilitate combustion and ensure reliable performance on watercraft.

This article enumerated about Spark Plug. We recommend our readers that they should appear in the SSC JE Mechanical mock tests and SSC JE ME Previous Years Papers. Also, get enrolled in the AE/JE Mechanical coaching to get a firm grip on the subject.

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