Typical brake specific fuel consumption (BSFC) for a petrol engine: The approximate specific fuel consumption per brake power hour for a conventional petrol (SI) engine is

Introduction / Context:
Brake specific fuel consumption (BSFC) expresses how many kilograms of fuel are required to produce one brake power hour. Recognizing typical BSFC values is useful for quick performance and economy estimates.

Given Data / Assumptions:

• Conventional naturally aspirated petrol engine at or near best-efficiency operating point.
• Representative, rounded values rather than exact manufacturer data.
• Fuel quality and engine technology typical of textbook examples.

Concept / Approach:
Petrol SI engines typically show BSFC in the neighborhood of 0.25 kg per brake power hour at best efficiency, with values rising at idle or far from optimal load/speed. Diesel engines, by contrast, often achieve lower BSFC (around 0.2 kg/BP·h or less) due to higher compression ratio and lean operation.

Step-by-Step Solution:

Verification / Alternative check:
Dynamometer maps show minima in the 230–300 g/kWh range. Converting 0.25 kg/BP·h using 1 BP = 0.746 kW gives a similar magnitude in g/kWh, reinforcing the selection.

Why Other Options Are Wrong:

• 0.2 kg: More representative of diesel engines at good operating points.
• 0.3 kg and 0.35 kg: Possible at non-optimal loads/speeds but not the typical “about” best value taught in fundamentals.

Common Pitfalls:
Confusing metric (g/kWh) with imperial (lb/bhp·h) units; always check the basis.

Final Answer:
0.25 kg