Brake thermal efficiency definition check In internal combustion engine testing, brake thermal efficiency is defined as the ratio of the heat equivalent of 1 kW·h of brake work to the heat supplied by the fuel per brake-power hour. Is this statement correct?

Introduction / Context:
Brake thermal efficiency is a cornerstone metric in engine performance. It connects the useful brake work measured at the shaft with the chemical energy delivered by the fuel. Examiners often phrase its definition in several equivalent ways, so it is important to recognize whether a statement describes the same ratio in different words.

Given Data / Assumptions:

• Brake power is the useful power at the crankshaft or output shaft.
• One kilowatt-hour corresponds to 3600 kJ of energy (heat equivalent of 1 kW·h).
• Fuel energy input per brake-power hour equals mass of fuel consumed in one hour * lower calorific value.

Concept / Approach:

Brake thermal efficiency, usually written as eta_bth, is defined by eta_bth = brake power output / fuel energy input rate. When considered over one hour at 1 kW brake output, the numerator is the heat equivalent of 1 kW·h, and the denominator is the chemical energy supplied by the fuel per brake-power hour. Thus the ratio described in the statement is indeed the brake thermal efficiency.

Step-by-Step Solution:

Verification / Alternative check:

From the continuous form, eta_bth = BP / (m_dot * CV). Multiplying numerator and denominator by 3600 converts per-second units to per-hour units and leads to the same interpretation as the statement.

Why Other Options Are Wrong:

Options limiting the definition to two-stroke engines, gaseous fuels, or stoichiometric operation add conditions that are unnecessary; the definition is general.

Common Pitfalls:

Confusing indicated thermal efficiency (uses indicated power) with brake thermal efficiency (uses brake power), or mixing up mechanical efficiency with thermal efficiency.

Final Answer:

Yes