Typical brake specific fuel consumption (BSFC) for diesel engines For a compression-ignition (diesel) engine operating at or near rated load, the approximate specific fuel consumption per brake power hour is closest to which value?

Introduction / Context:Brake specific fuel consumption (BSFC) measures how much fuel mass is required to produce one unit of brake power for one hour. It is a key indicator of engine efficiency, commonly expressed as kg per brake power hour or g/kWh. The question seeks the characteristic value for diesel engines.

Given Data / Assumptions:

• Engine type: compression-ignition diesel.
• Operating region: near rated load and speed where BSFC is typically minimized.
• Units: kg per brake power hour.

Concept / Approach:Diesel engines generally demonstrate superior thermal efficiency compared with spark-ignition engines due to higher compression ratios and unthrottled operation. Typical BSFC values for well-tuned medium-speed diesels cluster around 0.2 kg per bp·h (approximately 200 g per bhp·h). Petrol engines usually show higher values, around 0.3 kg per bp·h at comparable conditions.

Step-by-Step Solution:Identify typical diesel BSFC band: roughly 0.18–0.25 kg per bp·h depending on size and tuning.Select the nominal textbook value representing efficient diesel operation: 0.2 kg per bp·h.Compare with alternatives: 0.3–0.35 kg per bp·h is characteristic of petrol engines or poorly loaded diesels.

Verification / Alternative check:Engine maps from manufacturers show minima near 190–220 g per kWh for many modern diesels, in agreement with the 0.2 kg per bp·h magnitude.

Why Other Options Are Wrong:

• 0.25 kg and 0.3–0.35 kg: higher than the typical optimum diesel value; plausible for smaller or poorly tuned units but not the standard figure.
• 0.15 kg: unrealistically low for conventional diesels at rated conditions.

Common Pitfalls:Confusing indicated specific fuel consumption (ISFC) with brake values; mechanical losses make BSFC higher than ISFC.

Final Answer:0.2 kg