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 the operator turns the switch to the ‘on’ position, current flows through the primary winding and creates a magnetic field. Turning the switch to the ‘off’ position stops the current flow, causing the magnetic field to collapse and cut across the secondary winding. This action generates high voltage, which travels through the secondary circuit and reaches the spark plug, where it produces a spark across the electrodes
• 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 stays stationary and mounts directly on the grounded breaker plate. The other point sits at the end of an insulated movable arm (Fig. 2). The system pivots the arm at one end, allowing it to swing around this pivot. The cam lobe causes the arm to swing. When the contact closes, current flows through the primary circuit and builds up a magnetic field in the coil.

Figure 2

• Initially, when the contact breaks, the system stops the current flow and collapses the magnetic field. Subsequently, each time a lobe pushes the arm, the system repeats this process. By design, matching the number of lobes to the number of cylinders ensures that each cylinder receives high voltage to produce a spark in its spark plug. Importantly, the time during which current flows is called the dwell, and meanwhile, the distance between the separated contact points is referred to as the gap.
• The cam mounts on a shaft that the camshaft drives, and the crankshaft, in turn, drives the camshaft. Therefore, the crankshaft's position determines the point where contact and high voltage occur to produce a spark. The piston's position in the cylinder determines the crankshaft's position. As a result, the system produces a spark based on the piston's position near the end of the 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.
• Manufacturers usually use materials with excellent electrical conductivity for the central electrode, ensuring it withstands the harsh conditions inside the engine. Older spark plugs often feature a central electrode made from copper or a copper-nickel alloy. In contrast, newer high-performance spark plugs use platinum or iridium for improved durability and efficiency.
• An 'insulated electrode' means the central electrode stays electrically isolated from the metal shell or ground electrode of the spark plug. This design ensures the high voltage travels directly to the spark gap and ignites 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.
• Manufacturers compose the ground electrode using materials with high heat resistance and strong electrical conductivity, such as nickel alloy, platinum, or iridium, depending on the spark plug type.
• The spark gap separates the center electrode from the ground electrode. When the ignition system sends high voltage through the spark plug, the current bridges the gap between the electrodes and produces a spark that ignites the air-fuel mixture in the combustion chamber.
• The ground electrode also disperses the heat produced during combustion. It moves heat away from the center electrode tip to prevent excessive heat accumulation.

3.Insulation separating the two electrodes

• The insulation separates the center electrode from the ground electrode in a spark plug. It directs the electrical current through the correct path to create a spark at the spark gap. Manufacturers usually make the insulator from durable ceramic material that withstands 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 ceramic insulator manages the high temperatures produced during engine combustion and 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

To begin with, regular maintenance proves necessary for spark plugs. Moreover, worn-out spark plugs can cause engine issues. Consequently, drivers often experience increased fuel usage. Therefore, you should schedule spark-plug upkeep regularly. 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.