USCG Exam PracticeDiesel engine principles (motor propulsion)
Brake horsepower and indicated horsepower are both performance terms applied to a diesel engine. Which statement correctly distinguishes them and identifies what their ratio represents?
- A. Brake horsepower is developed in the cylinders; indicated horsepower is measured at the output shaft; their ratio is thermal efficiency
- ✓ Indicated horsepower is developed in the cylinders; brake horsepower is delivered at the output shaft; their ratio is mechanical efficiencyCorrect
- C. Brake horsepower equals indicated horsepower minus the power consumed by the turbocharger blower; their ratio is volumetric efficiency
- D. Indicated horsepower is measured by a dynamometer on the output shaft; brake horsepower is calculated from cylinder pressure diagrams; their ratio is specific fuel consumption
Why B is correct
Indicated horsepower is the power developed inside the cylinders; brake horsepower is the power actually delivered at the output shaft. The difference between them is friction (mechanical) loss, and their ratio — BHP divided by IHP — is mechanical efficiency. (DOE-HDBK-1018 Vol.1 §1-8)
Cited:DOE-HDBK-1018 Vol.1 §1-8