What is spark plug? Defination,Maintenance and parts of it

Introduction

Defination of sparkplug

Spark plug is a device used to produce electric spark to ignite the compressed air fuel mixture inside the cylinder. The spark plug is screwed in the top of the cylinder so that it electrode project in the combustion chamber.

• Basically,sparkplug has two electrodes which are made of metal conductor.One electrode is centre electrode and other is grounded electrode. There is a suitable gap between the electrodes. The spark jumps the gap and ignites the fuel-air mixture. There is outer metallic shell with ceramic insulator. Inside the ceramic insulator, electrode is located.
• The ignition coil supplies high voltage current to this electrode. The ground electrode is given a specific shape to provide suitable gap as shown in Fig 1. The gap varies from 0.9 mm to 2 mm. The bigger the gap higher is the voltage required. The spark plug is provided with a resistance built into center electrode that does not allow television or radio interference.
• This interference is due to ignition. The mounting of the spark plug is done with help of screwed end. A gasket between the plug and seat makes it leak proof. Tapered screwed ends provide leak proof seat without gasket.
• The material used to make electrodes is nickel and chrome alloy. This alloy is corrosion resistant. Sometimes copper core or platinum tip on electrodes is provided for longer life.

Figure 1

• There is a primary circuit and a secondary circuit in the ignition system. The primary circuit handles low voltage while the secondary circuit handles high voltage. The circuits have windings. Primary winding consists of less number of turns, say in hundreds, while secondary winding has large number of turns, in thousands.
• When switch is in ‘on’ position,current flows through primary winding and produces magnetic field. When switch is in ‘off ’ position, current flow stops and magnetic field crumples and cuts the secondary winding.This produces high voltage that is supplied to spark plug through the secondary circuit and spark is produced across the electrodes of spark plug.
• The contact points are located on the breaker plate of the distributor. There is a cam provided. The number of lobes in the cam is equal to number of cylinders. With movement of cam, the points close and open and act as mechanical switch to make and break the primary circuit.
• One point of the switch is stationary and is mounted on grounded breaker plate. The other point is located at the end of insulated movable arm (Fig 2). The arm is pivoted at one end and swings about this pivot. The cam lobe causes the swinging action of the arm.When contact is created the current flows, in the primary circuit and magnetic field is built up in the coil.

Figure 2

• When contact is lost the current flow stops and magnetic field crumples. The process is repeated each time lobe pushes the arm. The number of lobes being equal to number of cylinders ensures that each cylinder gets high voltage to produce spark in the spark plug. The duration for which current flows is known as ‘dwell’. The distance when points are separated is ‘gap’.
• The cam is mounted on shaft driven by camshaft which in turn is driven by crankshaft. Therefore, the point, where contact and high voltage occurs (thus producing spark) is determined by the position of crankshaft. The crankshaft position is determined by the position of piston in the cylinder. Hence spark is produced according to position of piston in the cylinder towards the end of compression stroke.

A spark plug consist of mainly three parts

1. Center electrode or insulated electrode
2. Ground electrode or outer electrode
3. Insulation separating the two electrodes

Now we discuss about all this three parts in detail.

1.Center electrode or insulated electrode

• The insulated electrode, also called the center electrode, is an essential part of a spark plug. It is a metal rod extending from top to bottom, reaching into the engine's combustion chamber. Its main role is to transmit high-voltage electricity from the ignition coil to the spark plug's tip electrode, generating the spark that lights the air-fuel mixture.
• The central electrode is usually composed of materials with good electrical conductivity and able to endure the tough conditions inside the engine. Older spark plugs frequently feature a central electrode crafted from copper or a copper-nickel mix. Nevertheless, newer, top-performing spark plugs often utilize platinum or iridium for the central electrode.
• An "insulated electrode" means the central electrode is electrically isolated from the metal shell or ground electrode of the spark plug. This isolation ensures the high voltage goes directly to the spark gap for igniting the air-fuel mixture.

2.Ground electrode or outer electrode

• The outer electrode, also known as the ground electrode, is a crucial part of a spark plug located near the tip but separate from the central electrode. It collaborates with the central electrode to generate a spark across the gap, sparking the air-fuel mixture in the engine's chamber.
• The ground electrode is located near the central electrode and typically runs from the base of the spark plug shell to the central electrode.
• The ground electrode is composed of materials with high heat resistance and good electrical conductivity, such as nickel alloy, platinum, or iridium, depending on the spark plug type.
• The gap between the center electrode and ground electrode is known as the spark gap. When high voltage passes through the spark plug from the ignition system, it bridges the gap between the electrodes, resulting in a spark that ignites the air-fuel mixture in the combustion chamber.
• The ground electrode is also involved in dispersing heat produced during combustion. It assists in moving heat from the center electrode tip to avoid excessive heat accumulation.

3.Insulation separating the two electrodes

• The material that separates the center electrode from the ground electrode in a spark plug is called insulation. It is essential for directing the electrical current through the correct path to create a spark at the spark gap. Usually, the insulator is made of durable ceramic material that can withstand high temperatures.
• The main function of the insulator is to block the direct flow of electrical current between the center electrode and the ground electrode, allowing a spark to occur only across the spark gap to ignite the air-fuel mixture.
• The high temperatures produced during combustion in the engine are managed by the ceramic insulator, which protects the electrical parts from overheating, ensuring the spark plug retains its structure.
• The ceramic material resists fouling, reducing the buildup of deposits from combustion, thus ensuring a constant spark gap throughout the spark plug's lifespan.

Maintenance of sparkplug

Regular maintenance is needed for spark plugs, as they can cause engine issues and increased fuel usage if worn out. Replacing them as recommended helps maintain engine performance.Here some tips which should you consider for sparkplug maintenance.

In the vast world of automotive technology, the simple spark plug is essential, providing the spark that starts our travels. Recognizing the importance of spark plugs and maintaining them properly leads to a smoother ride and supports environmentally friendly driving. Let's acknowledge the innovation in the humble spark plug as we drive towards the future.