Testing of an IC engine , Actual PV diagram , Turbocharger and supercharger , IC engine , GATE & ESE

Testing of an IC engine 

Test 1 - motoring test

Part 1 - dynamo meter 

• An electrical dynamometer is used to absorb the power. During the period at which engine is tested but it is basically termed as torque measuring device. 

Part 2 - motor 

• During the motoring test the same dynamometer is used as motor and either by shorting of the spark plug in SI engine or by cutting off the fuel supply in CI engine ,the engine cylinder gets free. 
• Then the power input to the motor will be equal to the frictional power of the engine. 

Note : if motor rating is given then 

• 
  Motor efficiency = friction power / motor power
• During the both motoring test as well as dynamometer test the engine speed must remain same because friction power is the function of speed. 
• Motoring test is valid for both SI and CI and also for both two stroke and four stroke and for single cylinder as well as multi cylinder engine. 
  
  
  
  
  

Willians line method 

• It is a graph between fuel consumption rate and brake power of the engine. And its extra ploatation on the negative axis of the brake power will provide the reading for frictional power of the engine ( practically it also include the pumping loss and blow by loss) 
• It also provides the data regarding the amount of fuel consumption where engine does not developed any power. 

Question : during the testing of an IC engine following observations were made during the willian line method ,then determine the 

1. Amount of fuel consumption when engine does not develop any power 
2. Friction power of the engine 
3. Brake power of the engine when fuel consumption rate is 15 kg per hour. 
   
   
   
   

Test 3 - Morse-key test 

• Each cylinder is under free state one by one either by cutting off the fuel supply in CI engine or by shorting of the spark plug in SI engine. 
• When one cylinder is not fired then there will be decrement in the final output of the engine whereas friction is assumed to be same by making engine speed constant. 
  
  
  
  
• MKT is not valid for single cylinder engine. It requires minimum two cylinder and in order to overcome this disadvantage motoring test was developed. 
• MKT is valid for both SI and CI engine and also for two stroke and four stroke. 
  

Question : a 4 cylinder diesel engine running at the engine speed of 1200 RPM develops the brake power of 18.6 kilowatt. The average torque of the engine when one cylinder was cut out is 105 Newton metre. If the calorific value of the fuel is 42000 kilo joule per kg and the engine used 0.34 kg of the diesel per kilowatt hour. Determine the indicated thermal efficiency of the engine. 

Question : an engine working on air standard Otto cycle having ratio of clearance volume to swept volume as 1/7 and ratio of specific heat as 1.4 with specific heat at constant pressure is 1.005 kilo joule per kg Kelvin. Determine percentage decrease in efficiency if the specific heat at constant pressure is increased by 10%. 

Actual vs theoretical PV diagram 

Theoretical PV diagram 

Actual PV diagram 

Actual suction 

• In actual, suction will take only if the pressure inside the cylinder becomes less than the atmospheric pressure. 
  

Actual compression 

• In actual, compression is not an adiabatic process hence extra compression work is required to compensate the heat loss to the water jacket. 
  
  
  
  
  
  

Actual heat addition 

• In actual, combustion process is neither constant volume process nor constant pressure and it occurs in minimum piston displacement. 
  

Actual expansion 

Note : 

• Actual PV diagram is plotted by an experiment by using pressure measuring device (pressure spring of stiffness Sp in bar per centimetre )and it consists of two areas

1. Positive area or gross work 
2. Negative area or pumping loss 

Pumping loss 

• The total amount of energy or power required to overcome the resistance for the actual suction and actual exhaust stroke. 
  

Question : a four cylinder ,four stroke SI engine develops the total power output of 44 kilowatt. If the pumping work is 5% of the indicated work and the mechanical loss is the additional 7%. Then determine the total power consumed in the pumping work ? 

Question : a single cylinder 4 stroke oil engine is fitted with the rope brake mechanism ,the diameter of the brake wheel is 600 mm and the rope diameter is 26mm. The dead load on the brake is 200 Newton and the spring balance reads 30 Newton. If the engine runs at 600 RPM ,what will be the nearest magnitude of brake power of engine. 

Turbocharger and supercharger 

• Supercharger or turbocharger is basically a rotary compressor in which compression takes place from the atmospheric air conditioned to 1.7 bar and this compressed air after the the intercooler entered into the cylinder during suction stroke. 
• The turbocharger is the special arrangement of supercharging in which a turbine is used to run the compressor by utilising exhaust gas energy and it is more preferred in CI engine. 
• In supercharging rotary compressor is extracting power directly from the engine shaft to compress the air and it is more preferred in racing car and aeroplanes. 

Note : 

1. The turbocharger is more effective than the supercharger. 
2. Due to supercharging both mechanical as well as thermal stress increases. 
3. Due to supercharging the overall NOx emission of the engine increases. 
4. In case of SI engine supercharging increases the tendency of knocking and detonation. 
5. In case of CI engine the limitation of supercharging is set due to the mechanical and thermal stress loading condition. 
   
   
   
6. The overall size of the engine may increase but it's a specific size will decrease which makes the engine to be compact.