Air–fuel preparation for spark-ignition engines: which device mixes air and petrol in the required proportion and supplies it during the suction stroke?

Introduction / Context:
Traditional spark-ignition (petrol) engines used carburettors to meter and mix fuel with incoming air based on pressure drops at a venturi. Although modern engines use electronic fuel injection, the conceptual role of a carburettor remains fundamental in engine basics and legacy systems.

Given Data / Assumptions:

• Petrol (SI) engine with intake depression during the suction stroke.
• Need to create a combustible mixture over a range of operating conditions.
• Mechanical metering without high-pressure fuel injection.

Concept / Approach:
A carburettor uses the venturi effect: as air speeds up through a constriction, static pressure drops, drawing fuel through a calibrated jet into the airstream. Auxiliary circuits handle idle, transition, and enrichment. By contrast, diesel engines employ direct injection of fuel into hot compressed air, not a carburettor.

Step-by-Step Solution:

Verification / Alternative check:
Historic automotive designs and small engines (mowers, generators) widely used carburettors; the description aligns directly with their operation.

Why Other Options Are Wrong:

• Fuel pump: Moves fuel from tank to carburettor; does not mix air and fuel.
• Injector: Used in EFI systems or diesel CI, not the classic device described.
• None of these: Carburettor clearly fits.

Common Pitfalls:
Assuming all modern engines have carburettors; most modern SI engines use injection, but the question explicitly references suction-stroke mixing typical of carburettors.

Final Answer:
carburettor