CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@zaveri • 14 May, 2012 • 4 likes
The morse test is a test conducted to determine the power developed in each cylinder in a multicylinder ic engine.

first the the power developed by all the cylinders together is determined experimentally.

Then the power of the individual cylinders are determined by cutting off the power supply to the spark plug of the cylinder under test.

then the power developed by the engine with the remaining cylinders is determined experimentally and this value is subtracted from the first value, and this gives you the power developed in the cylinder, whose spark plug was cut off.

similarly this test is carried out on all the cylinders of the engine individually.

Now what i wanted to know is that when there is no production of the electric spark in a cylinder, then what happens to the fuel in that cylinder ?
@engg.ashish • 18 May, 2012 nothing its comes out with exhaust gases as the fuel that comes in engine is not in liquid form it is in vapor form so it can leave engine without burning but
here new question arises in diesel engine there is no spark plug it burns by compression thn the fuel is burnt by compression and the temp. of engine like wise in ic engine, fuel in that cylinder can be semi burnt by some compression and temperature or somewhat
@zaveri • 19 May, 2012 engg.ashish

I am not so sure about it, but i think the morse test is only for petrol engines (spark-ignition engines).
@engg.ashish • 19 May, 2012 zaveri Em talking about petrol engines but giving examples of diesel engine to demonstrate the compression ratio which will be generated in petrol engine for partly burning of petrol air mixture in morse test
@LIRIL • 08 Feb, 2015 • 3 likes In Diesel engine the fuel supply in particular cylinder is cut off. Whereas in Petrol engine the spark plug in shut off.
@zaveri • 11 Feb, 2015
In Diesel engine the fuel supply in particular cylinder is cut off. Whereas in Petrol engine the spark plug in shut off.
As if i din't know that.
@Shashank Moghe • 11 Feb, 2015 • 1 like @LIRIL is spot on correct there. If there is no spark in a SI engine, the fuel that comes in goes out of the exhaust, unburned. Similarly, in CI engines, we must cut off the fuel injector signal to inject fuel so that there is no combustion and the power from that individual cylinder can be determined.

In (SI + DI) engines, we have the option of cutting the fuel injector AND the spark signal, and this might be more logical an option since it will save fuel.

P.S: The Morse test is for both petrol and diesel engines.
@Saddam Nalband • 18 Feb, 2015 As spark is responsible of burning the fuel in the cylinder, when there is no production of spark in the cylinder the fuel remains as it is.
@n1kh1l • 22 Feb, 2015 • 1 like I dont know about morse test but in marine engines we take peak pressure and indicator diagram of individual cylinders to calculate power.
When fuel is cutoff to a particular cylinder than we get compression pressure instead of peak pressure.
@kiran ramesh • 09 Apr, 2015 Why should we maintain constant friction power in morse test?
@Shashank Moghe • 09 Apr, 2015 Bmep = Imep- Fmep. Can you explain your question further? Which cylinder's Friction power are you talking about?
@Gurvinder1993singh • 10 Sep, 2015 Gwg
@amankishu4 • 28 Oct, 2015 @engg.ashish
In SI engines, no partial combustion takes places because octane rating of fuel is high and compression ratio is less. So fuel mixture won't auto ignite. And if partial combustion (fast rate of oxidation) happens then it will auto ignites complete mixture then knocking occurs which means there is some other problem with engine. Pressure developed without spark is called motoring pressure which may be of order 5-10bar and, with spark cylinder pressure can go upto 100bar or beyond depending on cylinder displacement.
During cylinder motoring, unburned fuel can vaporise or go under slow oxidation which doesn't account for significant pressure increase. So fuel comes out of exhuast valve in vapor form thus increasing hydrocarbon emission any slightly CO gas too.
@Mohit Patil • 02 Mar, 2020 • 1 like

The purpose of the Morse test is to figure out the Indicated Power of SI and CI engines. The test suggests making each of the cylinders inoperative one by one. For example, if you are working with a Diesel engine, you will have to halt the diesel from entering the cylinder.

If you are working with a petrol engine, you could control or short the spark plug, which is responsible for the blasts inside the cylinder.

When the cylinder is not operating (all of a sudden), the speed of the engine goes down. Before the readings are noted, the speed of the engine needs to be restored - which can be done by adjusting the load. 

Following would be the calculation for 4-cylinder engine -

B = bp of the engine with all cylinders operative

B1 = bp of engine with cylinder 1 inoperative

B2 = bp of engine with cylinder 2 inoperative

B3 = bp of engine with cylinder 3 inoperative

B4 = bp of engine with cylinder 4 inoperative

l1,l2,l3 and l4 = ip of engine 1,2,3,4 respectively

F1,F2,F3,F4 = fp of cylinders 1,2,3,4 respectively


B = (I1-F1) + (I2-F2) + (I3-F3) + (I4-F4) = (I1+I2+I3+I4) - (F1+F2+F3+F4).

Now for B1, you'll have to take out "I1" will be eliminated from the equation. 

Hence B1 = (I3+I3+I4) - (F1+F2+F3+F4).. 

Some of the power is lost because of the friction of the piston. 

Total IP of engine = I1+I2+I3+I4 = I

Mechanical efficiency = B/I. 


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