The initial checks and preparation are as follows:
- Ensure the weather is fine, RPM steady and constant
- The exhust temperatures are normal and steady
- The indicator instrument should be opened and the cylinder cleaned internally with the brush provided for the Before assembling the piston of the instrument the cylinder wall is to be lubricated with afew drops of oil specially provided for the same.
- Before connecting the indicator instrument to the indicator cock , blow through the indicator cock to clear the passage through the dock
- Adjust the length of the connecting cord so no slack occurs in the drum This ensures true drum motion. Place the indicator paper on the drum and fix it tight within the paper clips. Draw the atmospheric line by touching the stylus on the paper and turning the drum with the cord.
Operations (3) to (5) should be repeated for each unit.
Procedure for taking power card:- The indicator with paper properly mounted is connected to the cock outlet, and cord connected to the actuating lever driven by engine. Open the indicator cock and touch the stylus tip on the paper mounted on drum ,for a short while till one full diagram is drawn. Ensure the stylus is withdrawn immediately when a full diagram is recorded. This will ensure overwriting on the diagram already recorded. Blow through the indicator cock before taking the indicator card. This should be repeated for each unit.
Procedure for taking Draw card.:- Mentally count the firing sounds and in the same timing pull the drum cord with stylus touching the paper. The Draw card is drawn. This comes by practice.
The additional information to be recorded is as follows:-
(1) Exhaust temperatures of all units.
(2) Cooling water outlet temperatures from each cylinder head.
(3) Lub-oil pressure , inlet and outlet temperatures.
(4) Scavenge air pressure and temperature.
(5) T/C temperature across turbine.
(6) Air pressure drop across air cooler.
(7) Air pressure drop across air filter.
(8) Turbine RPM.
(9) Fuel oil consumed during the period of the experiment, taken from fuel flow meter during the period of experiment.
(10) RPM calculated as a mean from counter readings taken at commencement of experiment and end of experiment
(11) engine load control position
The total indicated power is calculated as follows.
The area of each power diagram is found by a planimeter or by use of Simpsons rules.This area is given in mm2 . the area divided by length of the diagram in mm is the mean height of the diagram given in mm. The main spring of the instrument has a spring constant given by 1 mm= x KN/M2 . Hence the mean effective pressure of each cylinder unit can be calculated and the mean effective pressure is given by P in the formula for power. The power produced by each cylinder unit is given by P*L*A*N *2* π /60 kw., where :
- P is the mean effective pressure given in KN/M2
- L is the length of stroke given in
- A is the area of bore of each cylinder given in M2.
- N IS the RPM measured from counter readings .
This gives the product in KNM/ sec , which is KW
The total power is sum of all individual powers produced in each unit
The specific fuel oil consumption (SFOC) is calculated as follows :
From the fuel oil clock readings we get the fuel consumed by the engine in litres.
If it is v litres consumed in the time duration of the experiment given in hours, say t hours . Then the mass of fuel oil consumed is given by v* ρ, where ρ is the density of the fuel oil at the corresponding temperature. Given in grams . The SFOC is now given by , say for a six cylinder engine as ( P1 + P2+P3 +P4 + P5 +P6 ) / V* ρ grams per KW hour, where ( P1 +P2 + P3 + P4 +P5 +P6 ) is the total power produced by the engine.
Quality analysis:- Apart from estimation of I power and SFOC , the Draw card is used to check if peak pressures and compression pressures of all units are the same. If they are not suitable corrective action should be taken as follows :
- For uniform peak pressure the individual fuel pump rack settings may be adjustted.
- If individual compression pressure are low, first confirm by compression card and then the unit may have to be opened to renew broken or worn out piston rings
- It is also essential that the power produced in each unit is uniform
By doing this adjustment exercise the engine works vibration free and efficiently
(note:- Additional information is given to enable the candidate to answer any cross questions)
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