Supercharging of internal combustion engines: which compressor type is most commonly used (mechanically driven) for supercharging?

Introduction / Context:
Supercharging raises the intake manifold pressure above ambient to increase engine power density. Historically and in many present applications, mechanically driven superchargers use positive-displacement machines for instantaneous boost and strong low-speed torque.

Given Data / Assumptions:

• Mechanically driven supercharger (crankshaft-driven), not exhaust-driven turbocharger.
• Automotive and stationary engine context.
• Focus on common, widely adopted hardware.

Concept / Approach:
The Roots blower is a positive-displacement rotary machine delivering nearly fixed displacement per revolution. It provides immediate boost and simple control, making it the classic choice for belt-driven superchargers. While centrifugal compressors are used in turbochargers (exhaust-driven) and in some belt-driven “centrifugal superchargers,” the most commonly referenced mechanically driven supercharger type in fundamentals is the Roots blower.

Step-by-Step Solution:
Identify mechanically driven superchargers: Roots, screw (Lysholm), and occasionally centrifugal via belt.Among these, Roots is historically prevalent and widely taught in textbooks as the standard example.Therefore, the correct answer is Roots blower.

Verification / Alternative check:
Supercharger kits and OEM applications often specify “Roots-type” or “twin-rotor” positive-displacement units for immediate response.

Why Other Options Are Wrong:

• Radial-flow compressor: more typical for exhaust-driven turbochargers.
• Axial-flow: unsuitable for small engine supercharging due to geometry and surge behavior.
• Reciprocating: impractical for high-speed continuous boost on engines.
• Scroll: uncommon for engine supercharging.

Common Pitfalls:
Confusing turbocharging (centrifugal compressor driven by turbine) with mechanically driven supercharging (Roots/screw).

Final Answer:
Roots blower (positive displacement)