Anatomy Of Engine

The Combustion Chamber

The heart and lungs of the engine, where air is sucked in and combined with fuel before being tumbled, swirled, compressed, burnt and then released to exhaust. It’s known as the four-stroke Otto cycle.

In petrol engines, the spark plug initiates combustion giving a smooth burn that develops pressure, forcing the piston down. However, under high pressure and temperature some petrol fuels can show a tendency to combust spontaneously. This can result in a ‘knocking’ or ‘pinking’ sound as small erratic bursts of combustion occur. As a result, an engine may suffer from depleted performance and in the most severe cases permanent damage can occur. Petrol’s octane rating is a measure of how well the fuel can resist this knocking.

“Timing the combustion is critical to effective energy transfer from the burning fuel to the engine. A higher octane quality allows for an earlier spark, which means the piston can be pushed down more effectively and for longer”

Fuel Injectors

It is the job of the fuel injector to ensure that the fuel is dispersed and mixed into the air in the exact pattern and volume required. In a diesel engine, they have to inject high-pressure fuel through holes no thicker than a human hair.

Some fuels can lead to fouling of the injector holes, which can disrupt the spray pattern, resulting in poor combustion and power loss. “Diesels can be particularly vulnerable to injector deposits and that can really affect the spray pattern”

Inlet Valves

These perform the job of opening and closing several hundred times a minute to, depending on engine design, allow the air, or the air/fuel mix, into the combustion chamber. In a conventional port fuel injected petrol engine, inlet valves can be prone to deposit formation, which can have potentially disruptive effects.

“If petrol inlet valves have been prone to deposit formation, you can end up with an engine that runs lean under acceleration, so you have less available power and a poorer response”

Piston Rings

The piston rings are designed to form a seal between the piston and the cylinder wall and slide up and down the cylinder bores several thousand times a minute.

“Inside an engine is a tough place to be, especially at the top and the bottom of the stroke where the piston speed is effectively zero. It is difficult to maintain lubrication and friction can occur between the piston rings and cylinder walls”

The interface between these components is difficult to lubricate.  The rings must form a tight seal to prevent lubrication oil from getting into the combustion space, which could lead to increased engine emissions, and to prevent combustion gases from entering the crankcase.

Source: Shell.com