What Is A Petrol Engine? Its Application, Parts and How it Works

A petrol engine is a spark-ignited internal combustion engine rather than the compression-ignited systems used in diesel vehicles.

In the spark-ignited system, the fuel is injected into the combustion chamber and combined with air. A spark from the spark plug ignites the air-fuel mixture.

In this reading, we’ll explore what a petrol engine is, its diagrams, application, parts, types, and how it works.

Let’s begin!

What Is A Petrol Engine?

A petrol engine is a type of internal combustion engine with spark ignition (spark plug), which uses petrol and similar volatile fuels to run the engine.

The design of the earlier petrol engine pre-mixes fuel and air before the carburetor compresses them. However, today’s fuel injection is electronically controlled.

A two-stroke petrol engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during only one crankshaft revolution using a petrol/air mixture.

This approach is in contrast to a four-stroke petrol engine that requires four strokes of the piston to complete a power cycle during two crankshaft revolutions.

The design of the earlier petrol engine pre-mixes fuel and air before the carburetor compresses them. Today’s fuel injection, however, operates electronically.

Well, the process differs in a small engine where the cost or complications of electronics do not suit the engine’s efficiency.

Applications

Due to their unique service, people use petrol engines extensively in a variety of fields. The applications of petrol engines include automobiles, motorcycles, aircraft, and motorboats. Also, Small engines, such as lawnmowers, chainsaws, and portable engine-generators

Today, the automobile sector and vehicles primarily use four-stroke gasoline engines. It is used in petrol cars, scooters, small motor-powered boats, motorbikes, small propeller aircraft, water spray systems, etc.

These engines have been highly applicable to the higher value of the low-punch-end capability of the engines.

The application of a two-stroke or two-cycle petrol engine is an internal combustion engine that is often found in smaller, lower-power engines such as scooters, dirt bikes, jet skis, smaller outboard motors, and lawn equipment such as lawnmowers and chainsaws.

Parts of a Petrol Engine

The various parts of a petrol engine include

1. Cylinder

These engine parts are located in the engine block, also known as the cylinder block. It contains a liner or sleeves around it. Work wears out this liner, which is easily replaceable.

The cylinders have space for the pistons to move upward and downward, making combustion take place.

Cylinders are characterized by their bore and stroke. The bore represents the inner diameter, while the stroke represents the effective length along the piston’s reciprocation, specifically the movement from the TDC to the BDC.

They are the uppermost and lowermost points of the stroke.

2. Piston

The piston is a cylindrical part that moves upward and downward in the cylinder, allowing the complete combustion cycle to take place (intake, compression, combustion, and exhaust) See how this process operates below.

The diameter of the piston is a bit less than the bore of the cylinder to avoid quick wear of the piston surface. There are three rings, known as piston rings, fitted in the circular recesses on the piston surfaces.

These aluminum rings directly contact the cylinder liner, preventing piston wear.

The two rings are compression rings; it are chamfered on the outer part, helping to prevent waste gases inside the combustion chamber from entering into the crankcase.

The third ring, known as the oil ring, prevents oil from entering the combustion chamber and ensures proper oil distribution along the cylinder walls.

3. Crankshaft

These engine parts help convert the sliding motion from the piston to rotary motion via the connecting rod. It is located below the cylinder block inside a casing called the crankcase. The crankshaft has projections bent and offset from the shaft axis.

In a multi-cylinder engine, each cylinder is provided with its crankpin, which is used to attach the piston to the connecting rod. A part of the crankshaft named the crankpin journal bearing is known as a big end, having a sliding bearing.

Counterbalance weights constitute another component of this system. Counterbalance weights are used to reduce the torsional vibrations experienced by the crankshaft due to the reciprocating imbalance of the moving piston during combustion.

The crank balance is either bolted to the crank body or forms an integral part of it.

Manufacturers either produce crankshafts in parts or as a single piece. The single-piece design is preferable because it leaves no space for vibration and offers better fiber flow and adequate stress-bearing capabilities.

4. Connecting Rod

These engine parts connect the piston to the crankshaft. Just as mentioned earlier, it converts the linear motion of the piston into the rotary motion of the crank.

One of its end parts is attached to the piston through a piston pin, also known as a gudgeon pin and a wrist pin. Another end is attached to the crankpin journal using bolts to hold down the upper and lower bearing caps, called the big end.

TThe bearing, in the form of two half-shells, is placed in the crank journal by the big end connecting rod. Both ends are not rigidly fixed to rotate at an angle. Hence, both ends are in continuous motion and under tremendous stress from the pressure of the piston.

5. Cylinder Head

These engine parts serve as a cover for the cylinder block, valve, rocker arms, and ignition element. The head gasket sits in between it and the cylinder block.

The cylinder head is made from cast iron and sometimes aluminum alloy when a lightweight part is needed, as aluminum conducts heat more quickly than cast iron.

In an overhead camshaft engine, the camshaft is placed in the head in the absence of a pushrod arrangement for the valve mechanism.

Some other parts, like the inlet, exhaust ports, and combustion chamber, also have space beneath the cylinder, making it one whole engine component.

6. Camshaft

This component of the internal combustion petrol engine is a shaft containing a cam fitted on it. Its function is to control the valves directly by sitting over them or through the rocker arm and pushrod mechanism.

The valve timing is determined by the size of the camshaft. That is, the opening and closing of valves are governed by the camshaft, which is mounted on the crankshaft either directly through a reduction gear or indirectly through a pulley and a timing belt.

A pushrod and tappet mechanism, along with the rocker arms, was necessary for the camshaft’s gear-driven coupling to the crank. Chilled iron castings and billet steel, used to make high-quality ones, commonly form the camshaft.

The purpose of the chilled iron is to offer greater wear resistance and surface hardness.

7. Valves

IC engines use valves, also referred to as poppet valves. It is made of a long, thin circular rod called a valve stem and a flat circular disk called a valve head, which is tapered along the thin rod.

The function of the valve is to enable a fresh intake of fuel and air and the release of waste gases (exhaust.) The sliding motion of the camshaft and its associated linkages is what causes the valve to open and close.

Steel alloys filled with sodium increase the heat transfer capacity of engine valves. Finally, the valves are of two sections: the intake/inlet valve, which allows fresh charge to enter the chamber when open, and the exhaust/outlet valve, which allows the escape of the exhaust gases.

8. Rocker Arm

This internal combustion engine part plays an important role as it transmits the rotary motion of the cam or crankshaft through a tappet/latch and converts it into a linear motion of the valve stem, helping to depressing the valve head

The rocker head is made from steel stampings for light- and medium-duty engines, whereas the heavy-duty diesel engine rocker head is made of cast iron and forged carbon steel, as it offers greater strength and stiffness.

The rocker’s arms oscillate about a fixed pivot rod in the cylinder head.

9. Crankcase

These internal combustion engine components are located below the cylinder block containing the bearings that rotate the crank. This main bearing is a sliding bearing with an adequate oil supply in it.

Four-cylinder inline petrol engines contain three bearings in the crankcase, one at each end and one in the middle, while diesel engines have five main bearings, one at each end and one between each cylinder.

Cast iron and aluminum, the same materials used to make the cylinder block, form the crankcase. A crankcase serves many purposes for the engine, as it helps to protect its inner mechanism from dust, dirt, and some other materials.

It also serves as housing that encloses the crankshaft and the connecting rod, keeping the oil and air.

10. Oil Pump and Sump

The function of the oil pump is to pump the oil to various parts of the engine for proper lubrication, cleaning, and cooling. The crankshaft gear in the engine is what drives the oil pump.

Various engine components receive pressurized oil, which aids in lubricating and cooling the system.

The oil sump serves as storage, containing a chamber that keeps the oil. To prevent dirt and debris from entering the engine, the oil pump lifts the oil from the sump through a wire mesh strainer.

The oil filter and oil cooler allow the oil to pass through before distributing it to the engine parts. The oil returns to the oil sump after doing its job.

Diagram of a Petrol Engine

Types of Petrol Engine

Petrol engines are classified by configuration, cycle, and ignition method. Here are the main types of petrol engines based on the stroke cycle:

Two-Stroke Petrol Engine

In two-stroke types of petrol engines, the compression and power strokes of the four-stroke cycle are carried out within the inlet and exhaust strokes. This arrangement makes it require just one revolution of the crankshaft to complete the cycle.

The reduced number of parts in a 2-stroke petrol engine, the simple design, and the lack of an oil sump mean these types of engines are more reliable in cold temperatures. This feature also makes them suited for use in machines like snowmobiles and snowblowers.

Four Stroke Petrol Engine

The four-stroke petrol engine requires four strokes of the piston to complete a power cycle during two crankshaft revolutions. They are used in petrol cars, scooters, small motor-powered boats, motorbikes, small propeller aircraft, water spray systems, etc.

How Petrol Engine Works

Due to lower compression ratios and the fact that gasoline burns more quickly than diesel, gasoline engines rotate at higher rotation speeds than diesel engines.

Because pistons in gasoline engines tend to have much shorter strokes than pistons in diesel engines, it typically takes less time for a piston in a petrol engine to complete its stroke than a piston in a diesel engine.

However, the lower compression ratios of gasoline engines give them lower efficiency than diesel engines. The average thermal efficiency of gasoline engines is around 20%, which is almost half that of diesel engines.

However, reports indicate that some newer engines have significantly higher thermal efficiency (up to 38%) compared to previous spark-ignition engines.

The process differs from a diesel engine in the method of mixing the fuel and air and in using spark plugs to initiate the combustion process.

Advantages

The following are the advantages of petrol engines:

Petrol engines are generally more powerful, by way of horsepower, than diesel.
Petrol engines naturally benefit from being easier to tune.
It has a better ratio of price to power and burns fuel more eco-friendly than diesel does.
Petrol is usually cheaper than diesel fuel.

Disadvantages

The following are the drawbacks of a petrol engine:

Generally, the petrol engine’s lifespan is almost always shorter than that of the diesel.
Diesel engines usually have a higher residual (resale) value.
Petrol engines get fewer miles per gallon (sometimes significantly) than their diesel counterparts.

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What Is A Petrol Engine, Its Application, Parts and How it Works?