Measuring Engine Brake Horsepower

The question asks about the equipment used to measure the brake horsepower of an engine. Brake horsepower (BHP) is the power output of an engine measured at the crankshaft or output shaft, after accounting for frictional losses within the engine itself but before power is transmitted to the wheels (in a vehicle context). It represents the usable power produced by the engine.

Understanding the Options

Let's look at the given options and what they typically measure:

• Dynamometer: A dynamometer is a device used for measuring force, torque, or power. Engine dynamometers are specifically designed to measure the torque and rotational speed of an engine, which allows for the calculation of engine power, including brake horsepower.
• Multimeter: A multimeter is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can measure voltage, current, and resistance in electrical circuits. It is not used to measure mechanical power like engine horsepower.
• Voltmeter: A voltmeter is an instrument used for measuring the electric potential difference (voltage) between two points in an electric circuit. It is exclusively for electrical measurements and has no application in measuring engine mechanical power.
• Ammeter: An ammeter is an instrument used for measuring the electric current in a circuit. It is also exclusively for electrical measurements and is not used for measuring engine mechanical power.

Identifying the Correct Equipment for Brake Horsepower

Based on the function of each instrument, the equipment specifically designed to measure the power output of an engine, such as brake horsepower, is a dynamometer.

A dynamometer applies a load to the engine and measures the resisting torque and the engine's rotational speed. Engine power is then calculated using the formula:

\(\text{Power} = \frac{2 \pi \times \text{Speed (N)} \times \text{Torque (T)}}{ \text{Constant}}\)

The constant depends on the units used for speed (e.g., RPM) and torque (e.g., Nm or lb-ft) and the desired power units (e.g., Watts or Horsepower).

Why Other Options Are Incorrect

The other options are electrical measuring instruments:

• A multimeter measures electrical properties like voltage, current, and resistance.
• A voltmeter measures only voltage.
• An ammeter measures only current.

These tools are essential for working with electrical systems but are not used to measure the mechanical power output of an engine.

Summary of Instrument Uses

Therefore, the correct equipment for measuring the brake horsepower of an engine is a dynamometer.

Revision Table: Engine Measurement Tools

Additional Information: Types of Engine Power

Besides brake horsepower (BHP), other terms are used to describe engine power:

• Indicated Horsepower (IHP): This is the theoretical power developed inside the engine cylinders, calculated from the pressure-volume diagram. It represents the total power produced before any losses due to friction within the engine.
• Frictional Horsepower (FHP): This is the power lost due to friction between moving parts within the engine (like pistons, crankshaft bearings, etc.) and the power consumed by engine accessories (like water pump, oil pump).

The relationship between these is:

\(\text{IHP} = \text{BHP} + \text{FHP}\)

Mechanical efficiency is defined as the ratio of brake horsepower to indicated horsepower:

\(\text{Mechanical Efficiency} = \frac{\text{BHP}}{\text{IHP}}\)

While IHP is measured indirectly or calculated, BHP is measured directly using a dynamometer, making it a practical measure of an engine's useful output power.