--- title: "Morse test for friction power" subject: "Internal Combustion Engines" chapter: 8 key: "semester_6/internal_combustion_engines:morse-test-four-cylinder-numerical" source: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/morse-test-four-cylinder-numerical site: BCT Engineering --- # Morse test for friction power Internal Combustion Engines · Chapter 8: Engine performance and testing of engines - Asked in: year not given, 6 marks - Video: [Morse test to find Indicated power or Frictional power of each cylinder of multi-cylinder I.C.engine](https://www.youtube.com/watch?v=XqnLc6ssvkU) — MechTech KnowHow - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/morse-test-four-cylinder-numerical - Whole chapter: https://www.bctengineer.com/md/semester_6/internal_combustion_engines/chapter-8 ## Question Explain the Morse test for finding the indicated power of a multi-cylinder engine. In a Morse test on a four-cylinder, four-stroke petrol engine running at constant speed of 2000 rpm, the brake power with all cylinders working was 62.5 kW. When cylinders 1, 2, 3 and 4 were cut out in turn, the brake powers were 45.1 kW, 44.5 kW, 45.6 kW and 44.8 kW respectively. Find the indicated power of each cylinder, the total indicated power, friction power and mechanical efficiency. ## Short answer Morse test: each cylinder cut out, IP of cut cylinder = BP_all - BP_cut. Here cylinder IPs are 17.4, 18.0, 16.9, 17.7 kW; total IP =70.0 kW, FP =7.5 kW, ηm =89.3%. ## Answer #### Morse test It is used for multi-cylinder engines. The engine is run at a fixed speed and load, and the brake power $B$ is measured with all cylinders firing. Then one cylinder is cut out (by shorting the spark plug in an SI engine, or cutting the fuel in a CI engine) and the load is reduced so that the speed returns to the original value. The new brake power $B_1$ is measured. The other cylinders keep running, and the friction and pumping power of the dead cylinder is still the same, so $$ IP_1 = B - B_1 $$ is the indicated power of the cut-out cylinder. The process is repeated for each cylinder and $IP = \sum IP_i$. Then $FP = IP - B$ and $\eta_m = B/IP$. It gives a result without any indicator, but it assumes that friction does not change when a cylinder is cut out. #### Calculation | Cylinder cut out | $B_i$ (kW) | $IP_i = 62.5 - B_i$ (kW) | |---|---|---| | 1 | 45.1 | 17.4 | | 2 | 44.5 | 18.0 | | 3 | 45.6 | 16.9 | | 4 | 44.8 | 17.7 | | Total | | 70.0 | $$ \begin{aligned} IP &= 17.4 + 18.0 + 16.9 + 17.7 = 70.0\ \text{kW} \\ FP &= 70.0 - 62.5 = 7.5\ \text{kW} \\ \eta_m &= \frac{62.5}{70.0} = 0.893 \end{aligned} $$ **Answer:** cylinder indicated powers 17.4, 18.0, 16.9 and 17.7 kW; IP = 70.0 kW; FP = 7.5 kW; $\eta_m$ = 89.3%. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the Morse test, what is done after cutting out a cylinder? A. The load is increased B. The load is reduced so that speed returns to the original value, then BP is measured C. The engine is stopped D. The fuel is doubled Answer: B. Speed is restored to its original value by reducing the load, and the new brake power is measured. (Key point: Morse test procedure) 2. How is the indicated power of the cut-out cylinder found? A. IP_1 = B + B_1 B. IP_1 = B - B_1 C. IP_1 = B_1 / B D. IP_1 = B x B_1 Answer: B. The drop in brake power equals the indicated power of the dead cylinder, since friction is assumed unchanged. (Key point: Cylinder indicated power) 3. For this data, what are total IP and FP? A. 70.0 kW and 7.5 kW B. 62.5 kW and 0 C. 70.0 kW and 62.5 kW D. 17.4 kW and 7.5 kW Answer: A. IP = 17.4 + 18.0 + 16.9 + 17.7 = 70.0 kW, and FP = 70.0 - 62.5 = 7.5 kW. (Key point: Total IP and friction) 4. What is the mechanical efficiency? A. 112% B. 89.3% C. 10.7% D. 72% Answer: B. eta_m = BP/IP = 62.5/70.0 = 0.893. 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