Exploring the Components of an Engine

Introduction

Every vehicle relies on engines to power their movement and ensure proper functioning. Understanding the different components of an engine is important for enthusiasts and mechanics, whether they are working on cars, motorcycles or boats. Let's delve into the intricate world of engine parts to grasp how they work together to produce power.

Components of an Engine

1.Cylinder Block

The cylinder block forms the core structure of the engine, housing the cylinders where combustion takes place. It's typically made of cast iron or aluminum and contains various passages for coolant and oil circulation.

This is the main component of the engine. It forms the middle portion of the engine.On its lower end crank case is located and on its upper end the cylinder head is located.The block has cylinders in which pistons slide up and down. The number of cylinder may vary 4, 6, 8 or sometimes even higher depending upon the size of the engine and power output needed from it.These cylinders may be in a single row (line) (Fig. 1). or may be arranged in a manner that forms two banks (Fig. 2). These banks are at a certain angle to form V.

Figure 1

The engines having all the cylinders in a row (line) are known as in line engine and in those where cylinders form a V are known as V-engines.

Figure 2

The cylinder blocks are also provided with passage for coolant. The hot gases at high pressure push the piston down in the cylinder. This causes maximum heating of cylinder block due to unutilized thermal energy. The coolant flowing through the passage takes away this heat.Most cylinder blocks are made through casting using cast iron. Sometimes iron mixed with nickel or chromium is also used. Aluminium alloy is also used to cast the cylinder block.

2.Crank Case

It forms the lower part of the engine. It accommodates crankshaft. The crankshaft is a long straight piece of metal in a vehicle that connects the engine to the wheels and helps turn the engine’s power into movement.
It is supported at its ends in the walls of crank case.The crank case has the provision to support the crankshaft. In some engines where the crankshaft is too long, it is supported in the middle portion also and crank case has provision to provide support.

Figure 3

Apart from this, the crank case acts as sump for lubricating oil.Generally the upper part of crank case is an integral part of cylinder block the lower part of crank case is bolted to it.Aluminium alloy is the most suitable material for crank case.It is light weight and has good thermal conductivity.Earlier cast iron was also used as material for crank case.

3.Cylinder Head

Cylinders are where the magic happens.They provide the space for the piston to move up and down during the combustion cycle.Engines can have different numbers of cylinders, such as four-cylinder, six-cylinder, or eight-cylinder configurations.
The cylinder head has provision for fixing the inlet and exhaust valves.This also forms the top of combustion chamber.The combustion chamber is given different shapes.Each shape produces effective combustion of fuel.
The material of cylinder head is cast iron or aluminum alloy. Machining is done so that various components can be installed smoothly.
To prevent noise and vibration reaching the body of the automobile the cylinder heads are provided with cover. The cover is made of three-layer sheet. The outer two layers are metallic and middle layer is that of plastic. This plastic layer does not allow the transmission of noise and vibration from the engine.

In wedge shape combustion chamber the turbulance of burning mixture is enhanced.The cup shaped combustion chamber prones turbulance and is particularly suitable for diesel or turbo-charged engines. In hemispheric combustion chamber combustion of fuel is relatively slow. Figure 4 represents wedge shaped and hemispherical combustion chambers.

Figure 4

4.Piston

Pistons are crucial components that move within the cylinders. They are connected to the crankshaft via connecting rods and undergo reciprocating motion. The combustion force pushes the piston down,converting thermal energy into mechanical energy.
The piston moves inside the cylinder and has reciprocatory motion. It is air tight and does not allow the leakage of charge and hot gases with the help of rings which form a part of piston ring assembly.
It also transmits the impact produced by the gases at high temperature and pressure. It accommodates the small end of the connecting rod and takes the lateral thrust due to obliquity of connecting rod.
The top portion of the piston is known as crown. Piston rings and piston pin form integral parts of piston assembly. The lower most part of piston is known as skirt. A slot is provided in the piston.
The slot accommodates the expansion of piston material when hot.This helps in reducing the clearance between skirt and cylinder bore when cold. When hot,the slot accommodates the expansion of piston material.
Aluminium alloy is the most commonly used material for piston. The alloy contains about 12% silicon which has less co-efficient of expansion as compared to aluminium and cast iron. Addition of phosphorus enhances the fatigue resistance.
Addition of cobalt and chromium further reduces the co-efficient of expansion which makes piston suitable for use when proper cooling many not be possible.Piston rings and piston pin are the components of piston sub-assembly. The outer surface of the piston ring is in close contact with the inner surface of the cylinder. The ring becomes perfect circle in the cylinder. In unassembled state, when left free, it is slightly oval.
The rings are known as compression rings when these prevent leakage of hot flue gases during expansion. In addition to compression rings, there are oil rings meant for lubrication of piston sub-assembly, particularly in big engines.

Figure 5

Piston pin, also known as gudgeon pin is third component of piston sub-assemble. It is supported at its both ends in the circular wall of piston. Its middle portion holds the small end of the connecting rod. It is a simple cylindrical component with provision of lubrication inside the small end of connecting rod.

5.Connecting Rod

As the name indicates it connects the piston with crankshaft. Its one end holds the piston pin and is known as small end. Other end, known as big end, holds the crank pin.It may have circular, rectangular, I, T or even H section. It is a steel forging and is highly polished for enhanced endurance strength. It is provided with a passage for transferring lubricating oil from the big end bearing (crank pin) to small end bearing (piston pin).

6.Crankshaft

The crankshaft requires detailed study as it is important component of the engine used in an automobile. Multicylinder engines are used in automobiles. The crankshaft of a multicylinder engine due to its shape and loading requires special attention of designers.
Basically a crankshaft converts the reciprocating motion of the piston(s) to rotating one.It applies the principle of simple machine known as wheel and axle. The crankshaft is made from steel forging or casting and is machined to provide suitable journals for connecting rod and main bearings.
The parts of the crankshaft from main bearing journal to the connecting rod bearing journals are called crank arms or cheeks. The length of the crank arm determines the stroke of the engine. From the centre of the main bearing journal to the centre of the connecting rod bearing journal is half the engine stroke.
The part of the crank shaft inside the connecting rod bearings is called the crank pin and those inside the main bearings are called the main journals (Fig. 6).

Figure 6

The number of main bearings varies with the design of the engine and number of cylinders. There must be atleast two i.e., one at the front and another at the rear of the crankshaft. More main bearings mean, less possibility of vibration and distortion of crankshaft of given size. To minimise the vibration in the engine crankshaft and flywheel are balanced separately and then often tested for balance when mounted together.
The crankshaft transforms the linear motion of the pistons into rotational motion. It's connected to the pistons through connecting rods and is supported by bearings. The rotational energy generated by the crankshaft drives the vehicle's wheels.

7.Camshaft

It is a long straight piece of metal with a cam on it joining parts of machinery,especially in a vehicle. It is responsible for opening/closing of valve. It carries one cam for each valve to be operated and valve lift is determined by the distance that the toe of the cam projects above the rounded base of the cam.
The camshaft controls the opening and closing of the engine's valves. It's synchronized with the crankshaft through timing belts or chains and has lobes that push against the valves to actuate them at the right time during the engine's cycle.
The camshaft is driven by the crankshaft either by a pair of meshing gears or by means of a pair of timing sprockets connected by a chain. The camshaft rotates at 1/2 the speed of crankshaft as the valves open only once in complete cycle that require two crankshaft rotations in 4-stroke engine.
The overhead camshaft (OHC) is a lately introduced modification in engine design.Earlier valves were operated with the help of camshaft located in the lower portion of engine. The push due to cam lobe was transferred to valve through push rods and rocker arms. The push rods and rocker arms resist the changing speed and direction due to their inertia.
Sufficient force is needed to move them. Due to this, the push rod bends or flexes slightly. Bending and flexing also occurs in rocker arm but as the push rods are thin and long it is significant in them. At lower speed of engine the flexing of push rod has little affect but at high engined speed it causes a lag in valve action. This causes a limit to the engine speed while designing an engine.

Figure 7

With the camshaft located in cylinder head, cam lobe directly pushes bucket tappet or rocker arm and necessity of push rod is eliminated (Fig. 7).
There may be one over head camshaft known as single overhead camshaft (SOHC) or two overhead camshaft (Double overhead camshaft, DOHC). In double over head camshaft engines, one camshaft operates intake valves and other operates exhaust valves.
To drive the camshaft either timing gears (Fig. 8) or sprockets and timing chain are used (Fig. 9). The use of sprocket and chain is preferred as these provide silent operation.Here the camshaft and crankshaft rotate in the same direction where as with gears the direction of movement is opposite.

Figure 8

Figure 9

Double overhead camshafts (DOHC) are driven by a variety of methods. Figure 10.shows a DOHC V-6 engine using a single timing belt to drive all the four camshafts, two for intake values and two for exhaust valves. In most of the V-type engines the intake camshafts are towards the inner side and exhaust camshafts are towards the outer side of the engine.

Figure 10

Conclusion

Understanding the components of an engine provides insight into how these complex devices operate. Vehicle performance and efficiency depend on every component, from the basic cylinder block design to complex systems like cooling and fuel injection. The next time you lift your car's hood, take a moment to take in the advanced engineering that drives your journey.