---
title: "Two-stroke motoring test: 2.2 kW motoring"
subject: "Power Plant Equipment"
chapter: 5
key: "semester_7/power_plant_equipment:motoring-test-2-2kw"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/motoring-test-2-2kw
site: BCT Engineering
---

# Two-stroke motoring test: 2.2 kW motoring

Power Plant Equipment · Chapter 5: Diesel Power Plant

- Asked in: 2074 Asoj, 8 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-2-2kw
- 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 2.2 kW. Then the test on the engine was carried out for one hour and the following observations were recorded: Brake torque = 150 Nm; Speed = 800 rpm; Fuel used = 2.5 kg; calorific value of fuel = 40 MJ/kg; Determine: (a) Brake power (b) Indicated power, (c) Mechanical efficiency and (d) Indicated thermal efficiency.

## Short answer

Motoring test gives FP=2.2 kW. BP=2π(800)(150)/60=12.57 kW, IP=14.77 kW, fuel heat=27.78 kW. Mechanical efficiency=85.10%; indicated thermal efficiency=53.16%.

## Answer

In the **motoring test** the engine is turned by the dynamometer without fuel; the power required equals the **friction power**, so $FP = 2.2$ kW.

**Data:** $T = 150$ N m, $N = 800$ rpm, fuel = 2.5 kg in 1 h, CV = 40 MJ/kg = 40 000 kJ/kg.

#### (a) Brake power
$$
BP = \frac{2\pi N T}{60} = \frac{2\pi \times 800 \times 150}{60} = 12\,566\ \text{W} = 12.566\ \text{kW}
$$

#### (b) Indicated power
$$
IP = BP + FP = 12.566 + 2.2 = 14.766\ \text{kW}
$$

#### (c) Mechanical efficiency
$$
\eta_m = \frac{BP}{IP} = \frac{12.566}{14.766} = 0.8510 = 85.10\%
$$

#### (d) Indicated thermal efficiency
Heat supplied:
$$
\dot Q = \frac{2.5}{3600}\times 40\,000 = 27.78\ \text{kW}
$$
$$
\eta_{ith} = \frac{IP}{\dot Q} = \frac{14.766}{27.78} = 0.5316 = 53.16\%
$$

**Answer:** BP = 12.57 kW, IP = 14.77 kW, $\eta_m$ = 85.10 %, $\eta_{ith}$ = 53.16 % (brake thermal efficiency would be 45.24 %).

## Check yourself

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

1. What is the friction power in this test?
   A. 12.566 kW
   B. 2.2 kW from the motoring reading
   C. 14.766 kW
   D. 0 kW
   Answer: B. The motoring power equals the friction power of the engine. (Key point: Friction from motoring)

2. What is BP for 150 N m at 800 rpm?
   A. 12.566 kW
   B. 120 kW
   C. 1.2 kW
   D. 125.66 kW
   Answer: A. BP = 2 pi x 800 x 150/60 = 12,566 W. (Key point: Brake power)

3. How is IP obtained?
   A. IP = BP - FP
   B. IP = BP + FP = 14.766 kW
   C. IP = BP x 2.2
   D. IP = FP/BP
   Answer: B. IP = 12.566 + 2.2. (Key point: Indicated power)

4. What is eta_m?
   A. BP/IP = 85.10%
   B. IP/BP = 117%
   C. FP/IP = 14.9%
   D. BP/Q = 45%
   Answer: A. 12.566/14.766 = 0.851. (Key point: Mechanical efficiency)

5. How is eta_ith found?
   A. IP / heat supplied (2.5/3600 x 40,000 = 27.78 kW) = 53.16%
   B. BP / heat supplied
   C. IP x heat
   D. Heat / IP
   Answer: A. 14.766/27.78 = 53.16%. (Key point: Indicated thermal efficiency)

## Close variants set in other exams

- [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: 1.5 kW motoring](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Amotoring-test-1-5kw) — 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×