What is a Spark-ignition engine?

What is a Spark-ignition engine?

A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug.

This is in contrast to compression-ignition engines, typically diesel engines, where the heat generated from compression together with the injection of fuel is enough to initiate the combustion process, without needing any external spark.

Spark-ignition engines are commonly referred to as “gasoline engines” in North America, and “petrol engines” in Britain and the rest of the world.

Spark-ignition engines can (and increasingly are) run on fuels other than petrol/gasoline, such as Autogas (LPG), methanol, ethanol, bioethanol, compressed natural gas (CNG), hydrogen, and (in drag racing) nitromethane.

Parts Of Spark Ignition Engine

The main components of a spark-ignition engine are as follows:

  • Inlet Valve: Air-fuel mixture enters the cylinder through the inlet valve.
  • Exhaust Valve: The burnt or exhaust gases produced in the power stroke escapes out through the exhaust valve.
  • Spark Plug: It produces a spark at the end of the compression stroke, which ignites the compressed air-fuel mixture.
  • Cylinder: It is a hollow cylinder in which the piston reciprocates.
  • Piston: It is a moving part of the engine that performs reciprocating motion and transmits the power generated during power stroke to the crankshaft through the connecting rod.
  • Connecting Rod: It is that part of the engine which connects the piston to the crankshaft.
  • Crankshaft: It is used to convert the reciprocating motion of the engine into rotary motion.

How Does a Spark Ignition Engine Work?

In a spark-ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke.

The working cycle of both spark-ignition and compression-ignition engines may be either two-stroke or four-stroke.

A four-stroke spark-ignition engine is an Otto cycle engine. It consists of the following four strokes: suction or intake stroke, compression stroke, expansion or power stroke, and exhaust stroke.

In suction stroke, the air-fuel mixture enters the cylinder, and in compression stroke compression of the air-fuel mixture takes place. In power stroke combustion of fuel and power generation, and in exhaust stroke escaping of burnt gases out of the engine.

Each stroke consists of a 180-degree rotation of crankshaft rotation and hence a four-stroke cycle is completed through 720 degrees of crank rotation. Thus, for one complete cycle, there is only one power stroke while the crankshaft turns by two or more revolutions.

Application of Spark Ignition Engine

  • Two-stroke SI Engines are used in small vehicles like mopeds and scooters.
  • These engines are used for lawnmowers.
  • These are used in small electricity generating sets and pumping sets.
  • Four-stroke SI engines are largely used in automobile industries.
  • CNG engines are used in buses.
  • Radial SI engines are used in small aircraft.

Advantages Of Spark Ignition Engine

  • SI Engines are low in cost
  • SI Engine produces less pollution as compared to CI Engine
  • These engines are smaller as compared to the CI engines and hence require less space.
  • These engines are lightweight.
  • The cost of an SI engine is lower compared to CI Engine.
  • These engines require less maintenance cost.

Disadvantages Of Spark Ignition Engine

  • At high loads, these engines are less economical.
  • These engines have high fuel consumption.
  • It has less efficiency as compared to the CI engine.
  • This engine has a knocking problem.


What is meant by the spark-ignition engine?

A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug.

What cycle is a spark-ignition engine?

The spark-ignition engine exploits the Otto cycle for a four-stroke engine.

What do you mean by Otto cycle?

The Otto cycle is a description of what happens to a mass of gas as it is subjected to changes in pressure, temperature, volume, the addition of heat, and removal of heat. The mass of gas that is subjected to those changes is called the system.

Is a diesel engine a spark ignition?

Diesel combustion. The diesel engine is an intermittent-combustion piston-cylinder device. It operates on either a two-stroke or four-stroke cycle (see figure); however, unlike the spark-ignition gasoline engine, the diesel engine induces only air into the combustion chamber on its intake stroke.

What happens in spark ignition?

The term spark-ignition is used to describe the system with which the air-fuel mixture inside the combustion chamber of an internal combustion engine is ignited by a spark. The process uses an electrical field induced in a magnet or coil to build many thousands of volts that are collapsed via a timed circuit.

How is the engine spark made?

When the high voltage produced by the ignition system is applied between the center electrode and ground electrode of the spark plug, the insulation between the electrodes breaks down, current flows in the discharge phenomenon, and an electrical spark is generated.

What are the 4 stages of the Otto cycle?

The four-stroke Otto cycle is made up of the following four internally reversible processes: 1–2, isentropic compression; 2–3, constant-volume heat addition; 3–4, isentropic expansion; and 4–1, constant-volume heat rejection.

Why is the Otto cycle more efficient?

The simple answer is, In the otto, the energy available is fully used to raise the pressure in the cylinder. Higher pressure implies larger work done. But in the diesel cycle, Part of the energy is added only during the expansion, so it does not contribute to the work. Hence Otto cycle is more efficient.

How do I know if my engine is CI or SI?

Si engine is an internal combustion engine that operates on the principle of spark ignition. It uses petrol and utilizes the Otto cycle. The diesel (Ci) engine is also an internal combustion engine, which uses diesel fuel and operates on a diesel cycle.

What is the difference between two-stroke and four-stroke?

The main difference between a 2- and a 4-stroke engine is that a 4-stroke engine goes through four stages, or two complete revolutions, to complete one power stroke. A 2-stroke engine goes through 2 stages, or one complete revolution, to complete one power stroke.

Which is better Si or CI engine?

CI has more efficient than SI. CI produces more noise than SI when it works. CI produces more hydrocarbons at the exhaust stroke of the engine than SI engines.

Which engine has a carburetor?

Hence a diesel engine is also known as a Compression Ignition engine. since fuel burns with the help of hot compressed air. In a petrol engine, combustion takes place when a mixture of air and fuel gets a spark from a spark plug (spark initiates fuel burning). This mixture of air and fuel is a carburetor.

How do you increase ignition spark?

3 Ways to Get More Spark from a Car Ignition System

  • Change Your Spark Plugs. The easiest place to start is by upgrading your spark plugs to platinum or iridium.
  • Upgrade the Plug Wires.
  • Timing Changes.

Who invented the spark-ignition engine?

Oliver Lodge invented the electric spark ignition (the Lodge Igniter) for the internal combustion engine. Two of his sons developed his ideas and founded the Lodge Plug Company.