Grade 10 power mechanics – Introduction to Engines Quiz

An engine converts the chemical energy in fuel into mechanical energy (motion) so the vehicle can move. It does not primarily store electricity or only transmit power.

In internal combustion engines (like petrol and diesel engines) combustion occurs inside the cylinders. In external combustion engines (like steam engines) fuel burns outside and the working fluid (steam) does the work.

A four-stroke cycle goes: intake (air-fuel enters), compression (mixture compressed), power (ignition pushes piston), and exhaust (burnt gases expelled).

A two-stroke engine completes its cycle in two piston movements (one upward and one downward), combining functions of intake/compression and power/exhaust into fewer strokes.

Petrol engines use spark plugs to ignite the compressed air-fuel mixture. Diesel engines rely on compression ignition and do not use spark plugs for normal running.

The crankshaft receives the piston's reciprocating motion via the connecting rod and turns it into rotary motion that drives the vehicle's wheels.

Piston rings seal the combustion chamber, control oil consumption, and help transfer heat from the piston to the cylinder wall.

A spark plug provides the electrical spark that ignites the compressed air-fuel mixture in petrol engines, causing the power stroke.

Torque is a measure of rotational force produced by the engine; it's what helps a vehicle accelerate or climb slopes.

Engine power is commonly measured in horsepower or kilowatts. Litres measure volume, newtons force, and degrees measure temperature.

Engines are cooled either by air passing over them (air-cooled) or by circulating coolant (liquid/water cooling). Proper cooling prevents overheating.

A carburettor meters and mixes air with petrol to create the combustible mixture for the engine; modern cars now often use fuel injection instead.

Diesel engines use high compression to raise air temperature; when diesel fuel is injected, it ignites due to the heat (no spark plug required for normal running).

Four-stroke engines are generally more fuel-efficient and produce fewer pollutants than two-stroke engines because they separate intake/compression and power/exhaust more cleanly.

Engine displacement is the combined swept volume of all cylinders and is often used to indicate engine size (e.g., 1.6 L = 1600 cc).

Fuel injection precisely meters fuel electronically and is more efficient and cleaner than carburettors, so it is now common in modern vehicles.

Compression ratio compares the cylinder's largest and smallest volumes; higher ratios generally increase efficiency but require higher octane fuel.

The flywheel evens out the pulses from each power stroke, helping the engine run smoothly and assisting in starting and clutch operation.

Proper valve timing ensures valves open and close at the correct points in the cycle for efficient intake and exhaust; incorrect timing reduces performance.

Lubricating oil forms a film between moving parts, reducing wear and helping carry away heat and contaminants, which preserves engine life.

Most family cars in Kenya run on petrol (gasoline). Diesel is common for minibuses and heavy vehicles, while kerosene and biogas are not typical for modern passenger cars.

Idle describes the engine running slowly without driving the vehicle, such as when stopped at traffic lights.

The camshaft has lobes that push valves open in timing with the pistons; proper camshaft action is essential for correct engine breathing.

Over time oil collects particles and loses its protective properties; regular changes keep parts lubricated and extend engine life.

Octane rating shows how well petrol resists knocking under compression; higher-octane fuels are used in high-compression engines to prevent damaging knock.