Grade 10 power mechanics – Classifications of Engines Quiz

1. What is the main difference between an internal combustion engine and an external combustion engine?

Internal combustion cools the engine with air while external combustion uses water
Internal combustion always uses electricity while external combustion uses fuel
Internal combustion uses steam while external combustion uses petrol
Internal combustion burns fuel inside the engine cylinder while external combustion burns fuel outside the working cylinder
Explanation:

An internal combustion engine (like most car engines) burns the fuel–air mixture inside the cylinder where combustion produces pressure to move the piston. External combustion (like a steam engine) burns fuel outside the working cylinder to generate steam or another working fluid.

2. Which statement correctly describes a four-stroke petrol engine cycle?

It completes intake and exhaust only with two piston movements
It uses two pistons moving together to create power in one stroke
It completes induction, compression, power and exhaust strokes in four piston movements
It relies on continuous combustion like a gas turbine
Explanation:

A four-stroke engine has four distinct strokes—intake (induction), compression, power (expansion) and exhaust—over two revolutions of the crankshaft, which is the common cycle for most petrol and many diesel engines.

3. What is the main feature of a two-stroke engine compared with a four-stroke engine?

It completes the power cycle in two strokes of the piston, giving one power stroke per crankshaft revolution
It requires a cooling pump to run
It uses spark ignition for diesel fuel only
It has separate intake and exhaust valves operated by a camshaft in every stroke
Explanation:

A two-stroke engine combines the functions of intake and compression in the first stroke and power and exhaust in the second, producing a power stroke every crankshaft revolution—this is why small engines and some motorcycles use two-stroke designs.

4. What distinguishes a spark-ignition (SI) engine from a compression-ignition (CI) engine?

SI engines run on diesel while CI engines run on petrol
SI engines have no pistons while CI engines have pistons
SI engines use spark plugs to ignite the air–fuel mixture; CI engines rely on compression to ignite the fuel
SI engines are always water-cooled while CI engines are air-cooled
Explanation:

Spark-ignition engines (typically petrol) use a spark plug to ignite the fuel–air mix. Compression-ignition engines (diesel) compress air until it is hot enough to ignite injected fuel without a spark.

5. Which fuel type is most commonly used in compression-ignition engines?

Diesel fuel
Electricity
Unleaded petrol
Pure hydrogen gas
Explanation:

Compression-ignition (diesel) engines are designed to run on diesel fuel, which ignites under high compression. Petrol is used in spark-ignition engines; electricity and hydrogen are different energy sources.

6. How are engines commonly classified by cooling method?

Oil-fired and coal-fired
Battery-cooled and solar-cooled
Air-cooled and water-cooled
Spark-cooled and compression-cooled
Explanation:

Engines are often classified by cooling: air-cooled engines lose heat directly to the air (cooling fins), while water-cooled engines circulate coolant through a radiator. The other options are not standard cooling classifications.

7. What is an advantage of a water-cooled engine compared to an air-cooled engine?

Water-cooled engines never need maintenance
Water-cooled engines are lighter and have no radiator
Water-cooled engines regulate temperature more evenly, allowing better performance and lower noise
Water-cooled engines do not need any lubrication
Explanation:

Water (liquid) cooling provides more uniform temperature control across the engine, improving efficiency and reducing noise. It usually requires a radiator and maintenance, and lubrication is still necessary.

8. Which arrangement describes an inline engine?

Cylinders are arranged as opposed pairs lying flat
Cylinders are placed in a triangular cluster
Cylinders are arranged in a circular star shape around the crankshaft
Cylinders are arranged in a single straight row one after another
Explanation:

An inline engine has cylinders placed in one straight line. Radial engines are circular around the crankshaft, boxer (opposed) engines have opposing pairs, and triangular cluster is not a standard layout.

9. What is a V-engine (Vee engine) layout?

Cylinders sit in a perfect circle around the crankshaft like a wheel
Cylinders are stacked vertically on top of each other in a column
All cylinders are arranged horizontally in one plane
Cylinders are arranged in two banks set at an angle to form a V shape
Explanation:

A V-engine uses two banks of cylinders angled to each other, forming a V profile. This gives a more compact length than an inline engine and is common in many cars and trucks.

10. Which engine type uses a triangular rotor and is known as a rotary engine?

Boxer engine
Opposed-piston engine
Radial engine
Wankel engine
Explanation:

The Wankel engine is a rotary engine using a triangular rotor in an epitrochoid housing, providing smooth rotation without reciprocating pistons. Boxer is flat-opposed piston, radial has piston banks in a circle, and opposed-piston is different.

11. How are engines classified by motion of the working parts?

Pneumatic engines and hydraulic engines only
Electronic engines and magnetic engines
Reciprocating engines and rotary (turbine) engines
Static engines and chemical engines
Explanation:

Engines are often grouped by motion: reciprocating engines (pistons moving back and forth) and rotary/turbine engines (continuous rotation). The other pairs are not standard engine-motion classifications.

12. What does the term 'naturally aspirated' mean when classifying engines?

The engine uses natural gas only as fuel
The engine automatically refuels itself from the environment
The engine uses water as the only coolant
The engine draws air into the cylinders without a turbocharger or supercharger
Explanation:

A naturally aspirated engine relies on atmospheric pressure to fill the cylinders, without forced induction like turbochargers or superchargers that compress intake air for more power.

13. Which of these is a common way to classify engines by intended use?

Automotive, marine, industrial (stationary) and aircraft engines
Manual and automatic engines by fuel colour
Red, blue, green and yellow engines
Indoor and outdoor only without regard to power output
Explanation:

Engines are classified by application: automotive (cars, matatus), marine (boats), industrial or stationary (generators, pumps), and aircraft engines. Colour-based or fuel-colour groupings are not standard.

14. What is the Otto cycle associated with?

Compression-ignition (diesel) engines
Spark-ignition (petrol) four-stroke engines
Steam turbines in power plants
Electric motors used in trains
Explanation:

The Otto cycle describes the ideal thermodynamic cycle for spark-ignition (petrol) engines operating on the four-stroke cycle. Diesel engines follow the Diesel cycle; steam turbines and electric motors follow different principles.

15. Why do diesel engines generally have higher compression ratios than petrol engines?

Diesel engines do not compress air at all
Diesel engines run cooler and so need higher compression to warm up
Diesel engines rely on compression to ignite fuel, so higher compression heats the air enough for ignition
Diesel engines use spark plugs that need high compression to work
Explanation:

Diesel engines compress only air to a high pressure and temperature so that injected diesel fuel ignites spontaneously. Petrol engines use a spark and therefore operate at lower compression ratios.

16. Which component is essential in a spark-ignition petrol engine but not in a diesel engine?

Fuel injector
Spark plug
Piston
Crankshaft
Explanation:

Spark plugs provide the ignition spark for petrol engines. Diesel engines ignite fuel by compression and typically do not use spark plugs (they may use glow plugs to aid cold starts). Fuel injectors, crankshaft and pistons are common to both types.

17. How are engines classified by valve train location?

Top-valve and bottom-valve without camshafts
Left-valve and right-valve only
Front-valve and rear-valve with no difference in function
OHV (overhead valve) and OHC (overhead camshaft)
Explanation:

Valvetrain location classifications include OHV (valves in the head operated by pushrods from a camshaft in the block) and OHC (camshaft(s) in the cylinder head). These are standard technical terms used in engine design.

18. What does DOHC (double overhead camshaft) allow compared to a single camshaft?

Using diesel fuel in a petrol engine without modifications
Eliminating the need for lubrication
Removal of the crankshaft entirely
Better control of more valves per cylinder, improving breathing and performance
Explanation:

DOHC uses two camshafts in the cylinder head (usually one for intake and one for exhaust), allowing more precise timing and often more valves per cylinder (e.g., four valves), which improves airflow and performance.

19. Which lubrication method is commonly used in traditional small two-stroke engines?

Lubrication by injecting water
Mixing oil with the fuel (pre-mix)
Separate oil sump without mixing
No lubrication is needed
Explanation:

Many traditional two-stroke engines use a pre-mix where oil is mixed with the fuel so the oil lubricates moving parts as the mixture passes through the engine. Larger four-stroke engines usually have a separate oil sump.

20. How is engine displacement usually expressed in road vehicle specifications in Kenya?

Cubic centimetres (cm3) or litres (L)
Square metres (m2)
Kilograms (kg)
Amperes (A)
Explanation:

Engine displacement is the total swept volume of all cylinders and is commonly shown in cm3 (e.g., 1500 cm3) or litres (e.g., 1.5 L) in vehicle specifications. Area, weight or electric current units are not used for displacement.

21. Which of the following is an advantage of a multi-cylinder engine over a single-cylinder engine?

It requires no ignition system
Smoother running and better balance at higher speeds
It always uses less fuel regardless of size
No need for any cooling system
Explanation:

Multi-cylinder engines distribute power strokes over multiple cylinders, reducing vibration and improving smoothness. They still need cooling, fuel and ignition systems; fuel use depends on design and size.

22. What classifies an engine as an 'opposed' or 'boxer' engine?

Cylinders are stacked vertically on top of each other like a tower
Cylinders are arranged in a circle like spokes
Cylinders are connected with belts instead of a crankshaft
Cylinders are arranged in two banks opposite each other so pistons move horizontally in opposite directions
Explanation:

Boxer (opposed) engines have opposing cylinder banks so pistons move in and out opposite each other, giving good balance. The other descriptions do not match the boxer layout.

23. Which engine classification applies to a gas turbine used to generate electricity?

Wankel piston engine
Two-stroke reciprocating engine
Rotary (turbine) engine
Boxer piston engine
Explanation:

Gas turbines are rotary engines where continuous combustion drives a rotor. They are not reciprocating piston engines (two-stroke or boxer) or Wankel, which are different types of internal combustion engines.

24. What is the purpose of a turbocharger when classifying an engine as turbocharged?

It cools the engine by circulating additional water
It uses exhaust gases to drive a turbine that compresses intake air, increasing engine power
It is a decorative part with no functional effect
It replaces the gearbox to increase speed
Explanation:

A turbocharger harnesses exhaust gas energy to spin a compressor that forces more air into the engine, allowing more fuel to burn and increasing power. It does not cool the engine directly or replace transmission components.

25. Which classification fits an engine that runs on liquefied petroleum gas (LPG) or compressed natural gas (CNG)?

Gas-fuelled internal combustion engine
External combustion steam engine
Hydraulic power unit
Pure electric motor
Explanation:

Engines designed to run on LPG or CNG are gas-fuelled internal combustion engines. They combust gas inside the cylinders. They are not steam engines, electric motors, or hydraulic units.

26. What classification describes engines by the number of strokes per cycle?

Fast-stroke and slow-stroke engines
Direct-stroke and indirect-stroke engines
Two-stroke and four-stroke engines
Single-revolution and triple-revolution engines
Explanation:

Engines are commonly classified by strokes per cycle into two-stroke and four-stroke types. The other terms are not standard classifications in engine theory.

27. Which type of engine burns fuel inside the engine's cylinders?

Steam turbine
Electric motor
Internal combustion engine
External combustion engine
Explanation:

An internal combustion engine (ICE) produces power by burning fuel inside its cylinders so the expanding gases act directly on pistons or rotors.

28. Which ignition method is used by diesel engines?

Electric ignition
Compression ignition
Spark ignition
Flame ignition
Explanation:

Diesel engines compress air to high pressure and temperature so the injected diesel fuel ignites by compression, not by a spark.

29. Which are the four strokes of a four-stroke petrol engine?

Suck, Squeeze, Burn, Blow
Start, Run, Stop, Cool
Fill, Heat, Push, Release
Intake, Compression, Power, Exhaust
Explanation:

The official names for the four-stroke cycle are intake (suction), compression, power (combustion/expansion) and exhaust.

30. In a two-stroke engine, how often does a power stroke occur relative to crankshaft revolutions?

Once every two crankshaft revolutions
Once every four crankshaft revolutions
Once every crankshaft revolution
Twice every crankshaft revolution
Explanation:

A two-stroke engine produces one power stroke per crankshaft revolution, while a four-stroke produces one power stroke every two revolutions.

31. How is an air-cooled engine cooled?

By passing air over fins on the cylinder
By circulating water through a radiator
By using a refrigerant like a fridge
By circulating oil only with no air movement
Explanation:

Air-cooled engines use cooling fins and airflow to remove heat directly from the cylinder surfaces rather than using water in a radiator.

32. Which engine uses pistons that move back and forth in cylinders?

Electric motor
Rotary (Wankel) engine
Gas turbine
Reciprocating engine
Explanation:

Reciprocating engines use pistons moving in a straight line (back and forth) inside cylinders to convert pressure into mechanical motion.

33. Which cylinder arrangement has cylinders set in two banks forming a 'V' shape?

Inline engine
V engine
Boxer engine
Radial engine
Explanation:

A V engine arranges cylinders in two angled banks that form a 'V' when viewed from the front, common in many cars and trucks.

34. Which engine type has cylinders opposite each other on a horizontal plane?

V engine
Boxer (opposed) engine
Inline engine
Radial engine
Explanation:

A boxer or horizontally opposed engine places cylinders in two banks directly opposite each other, giving low center of gravity and good balance.

35. Which engine has cylinders arranged in a circle around the crankshaft?

V engine
Radial engine
Inline engine
Boxer engine
Explanation:

Radial engines mount cylinders in a ring around a central crankshaft; they were common in older aircraft designs.

36. What describes a turbocharged engine?

An engine with a turbine-driven compressor to force more air into the cylinders
An engine that uses a bigger carburettor but no compressor
An engine that is cooled by a turbine
An engine that only runs on turbo fuel
Explanation:

A turbocharger uses exhaust-driven turbine to drive a compressor that increases intake air pressure and density, boosting engine power.

37. Which fuel is typically used in spark-ignition engines?

Petrol (gasoline)
Kerosene
Heavy fuel oil
Diesel
Explanation:

Spark-ignition engines (like most car petrol engines) use petrol which is ignited by a spark from the spark plug.

38. Which fuel is typical for compression-ignition engines?

Gasoline blended with oil
Ethanol
Diesel
Petrol
Explanation:

Compression-ignition engines are designed to run on diesel fuel, which ignites under high compression without a spark.

39. What is an advantage of multi-cylinder engines compared to single-cylinder engines?

Always cheaper to manufacture
Smoother running with less vibration
Use less oil by design
Require no maintenance
Explanation:

Multiple cylinders allow power strokes to overlap and balance forces, producing smoother operation and reduced vibration.

40. Where is the camshaft located in an overhead cam (OHC) engine?

Outside the engine, in the cooling system
Above the cylinders in the cylinder head
Inside the fuel tank
Deep in the oil sump below the crankshaft
Explanation:

In an overhead camshaft design the cam(s) sit in the cylinder head above the valves, reducing valve-train complexity and inertia.

41. Which device produces the spark in a petrol engine cylinder?

Glow plug
Fuel injector
Spark plug
Oil pump
Explanation:

The spark plug creates the electrical spark inside the combustion chamber that ignites the petrol-air mixture.

42. Compared to petrol engines, diesel engines generally have:

Lower torque output for the same size
Requirement for spark plugs to ignite fuel
Lighter weight for the same power
Higher thermal efficiency and better fuel economy
Explanation:

Diesel engines typically operate at higher compression ratios and are more fuel-efficient, producing better thermal efficiency and often more torque.

43. What is a characteristic advantage of the rotary (Wankel) engine?

Needs many cylinders to work
High power-to-weight ratio and smooth rotation
Extremely good fuel economy compared to diesel
Uses pistons for very large displacement
Explanation:

Wankel rotary engines are compact and produce smooth rotary motion with a high power-to-weight ratio, though they have other trade-offs.

44. Which orientation describes a vertical engine?

Crankshaft axis is horizontal
All cylinders point downward only
Crankshaft axis is vertical
Engine is always mounted sideways
Explanation:

A vertical engine has its crankshaft axis oriented up-and-down; this classification describes the engine's geometric orientation.

45. How are engines classified as stationary or mobile?

Based only on the number of valves
Based on the sound they make
Based on the type of spark plug used
Based on where they are used: fixed installation or in vehicles/moving equipment
Explanation:

Stationary engines are used in fixed installations (generators, pumps) while mobile engines are used in vehicles and movable machinery.

46. What is a double-acting engine?

An engine where the working fluid acts on both sides of the piston producing power on both movements
An engine that acts twice as slow as normal engines
An engine that uses two different fuels at the same time
An engine that has two cylinders only
Explanation:

Double-acting engines (common in some steam engines) apply pressure alternately to both sides of the piston so power is produced on both strokes.

47. How is lubrication typically done in a two-stroke engine?

Oil mixed with the fuel to lubricate moving parts
A separate oil sump like in most four-stroke car engines
No lubrication is used at all
Only by spraying water
Explanation:

Many two-stroke engines rely on oil mixed into the fuel to lubricate the piston and crankcase, unlike four-strokes with separate sump lubrication.

48. Small motorcycle engines commonly used in Kenya often have how many cylinders?

Single-cylinder
Inline six-cylinder
V8
Radial with five cylinders
Explanation:

Most small motorcycles and boda-bodas use single-cylinder engines because they are simpler, lighter and cheaper to maintain.

49. Which engine component helps diesel engines start better in cold weather by pre-heating the combustion chamber?

Spark plug
Carburettor
Air filter
Glow plug
Explanation:

Glow plugs heat the combustion chamber in diesel engines during cold starts to help vaporise fuel and reach ignition temperature.

50. Which valve type uses a sliding cylindrical sleeve to open and close ports instead of poppet valves?

Sleeve valve
Ball valve
Reed valve
Poppet valve
Explanation:

Sleeve valves use a movable sleeve that slides to align ports for gas flow; poppet valves are the usual mushroom-shaped valves in many modern engines.

51. Which classification describes engines that run on combustible gas such as CNG or biogas?

Diesel engines
Gas engines
Electric motors
Steam engines
Explanation:

Gas engines are spark-ignited engines adapted to burn gaseous fuels like compressed natural gas (CNG) or biogas.

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