---
title: "Engine test: fuel measured in litres"
subject: "Power Plant Equipment"
chapter: 5
key: "semester_7/power_plant_equipment:engine-test-fuel-litres"
source: https://www.bctengineer.com/q/semester_7/power_plant_equipment/engine-test-fuel-litres
site: BCT Engineering
---

# Engine test: fuel measured in litres

Power Plant Equipment · Chapter 5: Diesel Power Plant

- Asked in: 2071 Chaitra, 8 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/power_plant_equipment/engine-test-fuel-litres
- Whole chapter: https://www.bctengineer.com/md/semester_7/power_plant_equipment/chapter-5

## Question

A 4-cylinder, 4-stroke cycle engine having cylinder diameter 100 mm and stroke 120 mm was tested at 1600 rpm and the following readings were obtained. Fuel consumption = 0.27 liter/minute, Specific gravity of fuel = 0.74, B.P = 31.4 kW, Mechanical efficiency = 80%, Calorific value of fuel = 44000 kJ/kg. Determine: i) bsfc ii) imep and iii) Brake thermal efficiency

## Short answer

bsfc = 0.382 kg/kWh, imep = 7.81 bar, brake thermal efficiency = 21.43%.

## Answer

**Data:** 4 cylinders, four-stroke, $D = 0.1$ m, $L = 0.12$ m, $N = 1600$ rpm, fuel 0.27 L/min, specific gravity 0.74, $BP = 31.4$ kW, $\eta_m = 0.80$, CV = 44 000 kJ/kg.

Mass of fuel:
$$
\dot m_f = 0.27\ \text{L/min} \times 0.74\ \text{kg/L} \times 60 = 11.988\ \text{kg/h}\ (0.00333\ \text{kg/s})
$$

#### i) Brake specific fuel consumption
$$
bsfc = \frac{\dot m_f}{BP} = \frac{11.988}{31.4} = 0.3818\ \text{kg/kWh}
$$

#### ii) Indicated mean effective pressure
$$
\begin{aligned}
IP &= \frac{BP}{\eta_m} = \frac{31.4}{0.80} = 39.25\ \text{kW} \\
A &= \frac{\pi}{4}(0.1)^2 = 7.854\times10^{-3}\ \text{m}^2,\quad n = \frac{N}{2} = 800,\ k = 4 \\
p_{mi} &= \frac{60\,IP}{L A n k} = \frac{60 \times 39\,250}{0.12 \times 7.854\times10^{-3} \times 800 \times 4} \\
&= 7.809\times10^5\ \text{N/m}^2 = 7.81\ \text{bar}
\end{aligned}
$$

#### iii) Brake thermal efficiency
$$
\begin{aligned}
\dot Q &= \frac{11.988}{3600}\times 44\,000 = 146.52\ \text{kW} \\
\eta_{bth} &= \frac{31.4}{146.52} = 0.2143 = 21.43\%
\end{aligned}
$$

**Answer:** bsfc = 0.382 kg/kWh, imep = 7.81 bar, $\eta_{bth}$ = 21.43 %.

## Check yourself

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

1. How is fuel mass rate obtained from 0.27 L/min and SG 0.74?
   A. 0.27 x 0.74 x 60 = 11.99 kg/h
   B. 0.27 / 0.74 x 60
   C. 0.27 x 60 only
   D. 0.27 x 0.74 / 60
   Answer: A. Litres x SG gives kg; x60 converts per minute to per hour. (Key point: Fuel mass flow)

2. What is bsfc?
   A. Fuel per hour divided by indicated power
   B. Fuel per hour divided by brake power (kg/kWh)
   C. Brake power divided by fuel per hour
   D. Heat supplied divided by BP
   Answer: B. bsfc = 11.988/31.4 = 0.382 kg/kWh. (Key point: bsfc)

3. Which power is used in the imep formula?
   A. Brake power directly
   B. Friction power
   C. Indicated power = BP / mechanical efficiency
   D. Heat supplied
   Answer: C. IP = 31.4/0.8 = 39.25 kW is used with n = N/2 and k = 4 to get 7.81 bar. (Key point: imep)

4. Brake thermal efficiency here equals
   A. IP / (fuel rate x CV)
   B. BP / IP
   C. bsfc x CV
   D. BP / (fuel rate x CV) = 31.4/146.52
   Answer: D. Heat supplied is 11.988/3600 x 44000 = 146.52 kW, giving 21.43%. (Key point: Brake thermal efficiency)

## Close variants set in other exams

- [Engine test: 4-cylinder, B.P. 31.4 kW](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aengine-test-bp-31-4kw) — Power Plant Equipment, chapter 5, asked 2×

## Related in Power Plant Equipment

- [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×
- [Engine test: four-cylinder at 1820 rpm](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aengine-test-1820-rpm) — Power Plant Equipment, chapter 5, asked 5×
- [Engine test: four-cylinder at 1800 rpm](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aengine-test-1800-rpm) — Power Plant Equipment, chapter 5, asked 5×
- [Engine test: four-cylinder at 2000 rpm](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Aengine-test-2000-rpm) — Power Plant Equipment, chapter 5, asked 5×
- [Single cylinder engine: 60-minute trial](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asingle-cylinder-60-min-trial) — Power Plant Equipment, chapter 5, asked 2×
- [Single cylinder engine: 20-minute trial](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_plant_equipment%3Asingle-cylinder-20-min-trial) — Power Plant Equipment, chapter 5, asked 2×

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- [Air flow and fuel flow of an SI engine](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Afuel-consumption-air-flow-numerical) — Automotive Technology, chapter 2
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- [IP, BP and efficiencies of a petrol engine](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Aindicated-brake-power-efficiency-numerical) — Internal Combustion Engines, chapter 8