Engine Construction L2

How many degrees of crankshaft rotation occur in one complete four-stroke cycle?

• 180°

• 360°

• 540°

• 720°

Answer explanation

In a four-stroke engine, one complete cycle consists of intake, compression, power, and exhaust strokes, requiring two revolutions of the crankshaft. Therefore, 360° x 2 = 720° of crankshaft rotation occurs in one complete cycle.

The four strokes in the correct order are:

• Compression, Power, Exhaust, Induction

• Induction, Compression, Power, Exhaust

• Power, Induction, Exhaust, Compression

• Exhaust, Power, Induction, Compression

Answer explanation

The correct order of the four strokes in a four-stroke engine is Induction (intake of air-fuel mixture), Compression (compression of the mixture), Power (combustion and power stroke), and Exhaust (expulsion of exhaust gases).

The basic function of an engine is to convert:

• Electrical energy to heat

• Chemical energy to mechanical energy

• Heat energy to chemical energy

• Mechanical energy to electrical energy

Answer explanation

The correct answer is 'Chemical energy to mechanical energy' because engines primarily convert the chemical energy stored in fuels into mechanical energy to perform work.

The compression ratio of a petrol (spark-ignition) engine is typically:

• 4 : 1

• 10 : 1

• 16 : 1

• 22 : 1

Answer explanation

The typical compression ratio for petrol (spark-ignition) engines is around 10:1. This ratio allows for efficient combustion and power output, making 10:1 the correct choice among the options provided.

A diesel (compression-ignition) engine usually has a compression ratio of about:

• 8 : 1

• 10 : 1

• 12 : 1

• 18 : 1

Answer explanation

A diesel engine typically operates with a higher compression ratio than a petrol engine to ignite fuel through compression. The common range for diesel engines is around 14:1 to 22:1, making 18:1 a good choice.

“Top Dead Centre” (TDC) means the piston is:

• At its uppermost point in the cylinder

• At its lowest point

• Halfway down the bore

• At maximum speed

Answer explanation

"Top Dead Centre" (TDC) refers to the position of the piston at its uppermost point in the cylinder, where it is closest to the cylinder head. This is the correct answer, as the other options describe different piston positions.

“BDC” stands for:

• Basic Drive Cycle

• Bottom Dead Centre

• Base Data Compression

• Brake Drive Control

Answer explanation

"BDC" stands for "Bottom Dead Centre," which is a term used in engineering, particularly in relation to the position of a piston in an engine. The other options do not accurately represent this acronym.

The stroke of an engine is:

• The bore diameter

• The distance the piston travels from TDC to BDC

• The pressure in the cylinder

• The firing order sequence

Answer explanation

The stroke of an engine refers to the distance the piston travels from the top dead center (TDC) to the bottom dead center (BDC).

Torque is a measure of:

• Turning force

• Linear distance

• Engine temperature

• Oil pressure

Answer explanation

Torque is defined as a measure of turning force, which indicates how effectively a force can cause an object to rotate around an axis. Therefore, the correct answer is 'Turning force'.

The SI unit of torque is:

• Kilogram-metre

• Newton metre

• Joule

• Watt

Answer explanation

The SI unit of torque is the Newton metre (Nm), which measures the rotational force. Kilogram-metre is not a standard unit for torque, while Joule and Watt are units of energy and power, respectively.