---
title: "Two-stroke motoring test: 1.5 kW motoring"
subject: "Power Plant Equipment"
chapter: 5
key: "semester_7/power_plant_equipment:motoring-test-1-5kw"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/motoring-test-1-5kw
site: BCT Engineering
---

# Two-stroke motoring test: 1.5 kW motoring

Power Plant Equipment · Chapter 5: Diesel Power Plant

- Asked in: 2070 Chaitra, 10 marks
- Video: [MOTORING TEST & WILLIAM'S LINE METHOD FOR MEASURING FRICTION POWER](https://www.youtube.com/watch?v=AaGAOH6N7UU) — Professor kartik
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/motoring-test-1-5kw
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-5

## Question

A two stroke diesel engine was motored when the meter reading was 1.5 kW. Then the test on the engine was carried out for one hour and the following observations were recorded: Brake torque = 120 Nm; Speed = 600 rpm; Fuel used = 2.5 kg; calorific value of fuel = 40.3 MJ/kg; Determine: (a) Brake power, (b) Indicated power, (c) Mechanical efficiency and (d) Indicated thermal efficiency.

## Short answer

BP = 7.54 kW, IP = 9.04 kW, mechanical efficiency = 83.41%, indicated thermal efficiency = 32.30%.

## Answer

In a **motoring test** the engine is turned by the dynamometer without fuel; the power absorbed equals the **friction power**: $FP = 1.5$ kW.

**Data:** $T = 120$ N m, $N = 600$ rpm, fuel = 2.5 kg in 1 h, CV = 40.3 MJ/kg = 40 300 kJ/kg.

#### (a) Brake power
$$
BP = \frac{2\pi N T}{60} = \frac{2\pi \times 600 \times 120}{60} = 7540\ \text{W} = 7.540\ \text{kW}
$$

#### (b) Indicated power
$$
IP = BP + FP = 7.540 + 1.5 = 9.040\ \text{kW}
$$

#### (c) Mechanical efficiency
$$
\eta_m = \frac{BP}{IP} = \frac{7.540}{9.040} = 0.8341 = 83.41\%
$$

#### (d) Indicated thermal efficiency
$$
\begin{aligned}
\dot Q &= \frac{2.5}{3600}\times 40\,300 = 27.99\ \text{kW} \\
\eta_{ith} &= \frac{IP}{\dot Q} = \frac{9.040}{27.99} = 0.3230 = 32.30\%
\end{aligned}
$$

**Answer:** BP = 7.54 kW, IP = 9.04 kW, $\eta_m$ = 83.41 %, $\eta_{ith}$ = 32.30 % (brake thermal efficiency = 26.94 %).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The friction power in this problem is
   A. 7.54 kW
   B. 9.04 kW
   C. 0 kW
   D. 1.5 kW, the motoring reading
   Answer: D. The engine is driven without fuel, so power absorbed is friction power. (Key point: Friction power from motoring)

2. BP = 2*pi*600*120/60 equals
   A. 7.54 kW
   B. 75.4 kW
   C. 0.754 kW
   D. 4.52 kW
   Answer: A. 2*pi*600*120/60 = 7540 W. (Key point: Brake power)

3. Mechanical efficiency is
   A. 9.04/7.54
   B. 7.54/9.04 = 83.41%
   C. 1.5/9.04
   D. 7.54/27.99
   Answer: B. IP = BP + FP = 9.04 kW; eta_m = BP/IP. (Key point: Indicated power and mechanical efficiency)

4. eta_ith is
   A. BP / heat supplied = 26.94%
   B. IP / BP
   C. IP / heat supplied = 9.04/27.99 = 32.3%
   D. FP / heat supplied
   Answer: C. Indicated thermal efficiency uses indicated power. (Key point: Indicated thermal efficiency)

## Close variants set in other exams

- [Two-stroke motoring test: 2.2 kW motoring](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-2-2kw) — Power Plant Equipment, chapter 5, asked 6×
- [Two-stroke motoring test: 2 kW motoring](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-2kw) — Power Plant Equipment, chapter 5, asked 6×
- [Two-stroke motoring test: 4.5 kW motoring](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-4-5kw) — Power Plant Equipment, chapter 5, asked 6×
- [Two-stroke motoring test with specific fuel consumption](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-sfc) — Power Plant Equipment, chapter 5, asked 6×
- [Two-stroke motoring test: 5 kW motoring](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-5kw) — Power Plant Equipment, chapter 5, asked 6×

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