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Assignments Of 4 Stroke Petrol Engine


Classification of Petrol Engines

•         Two Stroke cycle Petrol Engines

•         Four Stroke cycle petrol Engines


Construction :

•         A piston reciprocates inside the cylinder

•         The piston is connected to the crank shaftby means of a connecting rod and crank.

•           The inlet and exhaust valves are Mounted on the cylinder head.

•         A spark is provided on the cylinderHead.

•           The fuel used is petrol

Four Stroke Petrol Engine- Working

(a)Suction Stroke (First Stroke of the Engine)

•         Piston moves down from TDC to BDC

•         Inlet valve is opened and the exhaust valve is closed.

•         Pressure inside the cylinder is reduced below the atmospheric pressure.

•         The mixture of air fuel is sucked into the cylinder through the inlet valve.

(b)   Compression Stroke : (Second Stroke of the piston)

•         Piston moves up from BDC to TDC

•         Both inlet and exhaust valves are closed.

•         The air fuel mixture in the cylinder is compressed.

(c)Working or Power or Expansion Stroke: (Third Stroke of the Engine)

•         The burning gases expand rapidly. They exert an impulse (thrust or force) on the piston. The piston is pushed from TDC to BDC

•         This movement of the piston is converted into rotary motion of the crankshaft through connecting rod.

•         Both inlet and exhaust valves are closed.

(d)Exhaust Stroke (Fourth stroke of the piston)

•         Piston moves upward from BDC

•         Exhaust valve is opened and the inlet valve is closed.

•         The burnt gases are forced out to the atmosphere through the exhaust valve (Some of the burnt gases stay in the clearance volume of the cylinder)

•         The exhaust valve closes shortly after TDC

•         The inlet valve opens slightly before TDC and the cylinder is ready to receive fresh charge to start a new cycle.

Summary :

•         Compression ratio varies from 5 to 8

•         The pressure at the end of compression is about 6 to 12 bar.

•         The temperature at the end of the compression reaches 250o C to 350o C



ASSIGNMENT 4Question 1.

 A gasoline engine works on Otto cycle. It consumes 8 litresof gasoline per hour anddevelops power at the rate of 25 kW. The specific gravity of gasoline is 0.8 and its calorific value is 44000kJ/kg. Find the indicated thermal efficiency of the engine.


: 31.96%

Question 2

.Find the air-fuel ratio of a 4-stroke, 1 cylinder, air cooled engine with fuel consumption timefor 10 cc as 20.0 sec. and air consumption time for 0.1 m³ as 16.3 sec. The load is 16 kg at speed of 3000 rpm. Also find brake specific fuel consumption in g/kWh and thermal brake efficiency. Assume thedensity of air as 1.175 kg/m3 and specific gravity of fuel to be 0.7. The lower heating value of fuel is 44MJ/kg and the dynamometer constant is 5000.Hints: Power output (

) =

WN / 

Dynamometer Constant


: bsfc: 131.25 g/kWh; η = 62.3377


. A six-cylinder, gasoline engine operates on the four-stroke cycle. The bore of each cylinder is 80 mm and the stroke is 100 mm. The clearance volume per cylinder is 70 cc. At the speed of 4100rpm, the fuel consumption is 19.8 kg/hr and the torque developed is 160 Nm.Calculate:(i) Brake power:


(ii) Thebrake mean effective pressure:







(iii) Brake thermal efficiency if thecalorific value of the fuel is 44000 kJ/kg:


(iv) The relative efficiency on a brake power basis assuming the engine works on the constant volumecycle

= 1.4 for air.

Question 4.

 A gasoline engine is specified to be 4-stroke and four-cylinder. It has a bore of 80 mm and astroke of 100 mm. On test it develops a torque of 75 Nm when running at 3000 rpm. If the clearancevolume in each cylinder is 60 cc the relative efficiency withrespect to brake thermal efficiency is 0.5 andthe calorific value of the fuel is 42 MJ/kg;Determine


Fuel consumption in kg/hr:

6.8264 kg/hr


Brake mean effectivepressure:

4.6875 bar


.A six-cylinder, four-stroke engine gasoline engine having a bore of 90 mm and stroke of 100mm has a compression ratio 8. The relative efficiency is 60%. When the indicated specific fuelconsumption is 3009 g/kWh. Estimate


The calorific value of the fuel:

35417.035 kJ/kg


Corresponding fuel consumption given that


is 8.5 bar and speed is 2500 rpm:



.A 4-cylinder, 4-stroke cycle engine having cylinder diameter 100 mm and stroke120 mmwas tested at 1600 rpm and the followingreadings were obtained.Fuel consumption = 0.27 litres/minute,Specific gravity fuel = 0.74,B.P. = 31.4 kW, Mechanical efficiency = 80%, Calorific value of fuel= 44000kJ/kg.Determine :(i)



0.38174 kJ/kW.hr




780.85 kN/m


(iii) Brake thermal efficiency:


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