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INTERNAL COMBUSTION ENGINES AND GAS TURBINES Performance Parameters

ASSIGNMENT 4

Question 1. A gasoline engine works on Otto cycle. It consumes 8 litres of gasoline per hour and

develops power at the rate of 25 kW. The specific gravity of gasoline is 0.8 and its calorific value is 44000

kJ/kg.

engine.

Ans: 31.96%

Find

the

indicated

thermal

efficiency

of

the

Question 2. Find the air-fuel ratio of a 4-stroke, 1 cylinder, air cooled engine with fuel consumption time for 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 the density of air as 1.175 kg/m3 and specific gravity of fuel to be 0.7. The lower heating value of fuel is 44 MJ/kg and the dynamometer constant is 5000. Hints: Power output (P) = WN / Dynamometer Constant Ans: bsfc: 131.25 g/kWh; η = 62.3377

Question 3. 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 4100

rpm, the fuel consumption is 19.8 kg/hr and the torque developed is 160 Nm. Calculate:

 (i) Brake power: 68.66 (ii) The brake mean effective pressure: 6.66 105 Pa (iii) Brake thermal efficiency if the calorific value of the fuel is 44000 kJ/kg: 29.03% (iv) The relative efficiency on a brake power basis assuming the engine works on the constant volume

cycle r = 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 a stroke of 100 mm. On test it develops a torque of 75 Nm when running at 3000 rpm. If the clearance volume in each cylinder is 60 cc the relative efficiency with respect to brake thermal efficiency is 0.5 and the calorific value of the fuel is 42 MJ/kg; Determine

 (i) Fuel consumption in kg/hr: 6.8264 kg/hr (ii) Brake mean effective pressure: 4.6875 bar

Question 5. A six-cylinder, four-stroke engine gasoline engine having a bore of 90 mm and stroke of 100

mm has a compression ratio 8. The relative efficiency is 60%. When the indicated specific fuel

consumption is 3009 g/kWh. Estimate

 (i) The calorific value of the fuel: 35417.035 kJ/kg (ii) Corresponding fuel consumption given that imep is 8.5 bar and speed is 2500 rpm: 20.28

kg/h.

Question 6. A 4-cylinder, 4-stroke cycle engine having cylinder diameter 100 mm and stroke 120 mm was tested at 1600 rpm and the following readings 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 = 44000 kJ/kg. Determine :

(i) bsfc: 0.38174 kJ/kW.hr

(ii) imep : 780.85 kN/m²

Question 7. A six-cylinder 4-stroke petrol engine having a bore of 90 mm and stroke of 100 mm has a compression ratio of 7. The relative efficiency with reference to indicated thermal efficiency is 55% when indicated mean specific fuel consumption is 0.3 kg/kWh. Estimate the calorific value of the fuel and fuel consumption in kg/hr. Given that indicated mean effective pressure is 8.5 bar and speed is 2500 r.p.m.

Ans: Cv = 51150.6 kJ/kg.

Question 8. A two stroke diesel engine was motored when the meter reading was 1.5 kW. Then the test on the engine was carried out for one hour and the following observations were recorded: Brake torque = 120 Nm; Speed = 600 rpm; Fuel used = 2.5 kg; calorific value of fuel = 40.3 MJ/kg; Cooling water used = 818 kg; Rise in temperature of cooling water = 10°C. Exhaust gas temperature = 345°C. Room temperature = 25°C; A/F = 32:1. Determine:

 (i) bp : 7.54 kW (ii) ip : 9.04 kW (iii) Mechanical efficiency: 83.4% (iv) Indicated thermal efficiency: 32.3% (v) Draw heat balance sheet on minute basis and also in percentage.

Heat supplied = 1679 kJ/min. = 100%

 (a) Heat in B P 20.94% (b) Heat in cooling water = 33.97% (c) Heat in exhaust gases = 27.51% (d) Heat unaccounted = 11.78%

Question 9. The following observations were recorded during a trial on a 4-stroke diesel engine :

Power absorbed by non-firing engine when Driven by an electric motor = 10 kW Speed of the engine = 1750 rpm Brake torque = 327.4 Nm Fuel used = 15 kg/hr. Calorific value of fuel = 42000 kJ/kg Air supplied = 4.75 kg/min. Cooling water circulated = 16 kg/min. Outlet temperature of cooling water = 65.8°C Temperature of exhaust gas = 400°C Room temperature = 20.8°C Specific heat of water = 4.19 kJ/kg·K Specific heat of exhaust gas = 1.25 kJ/kg·K Determine:

 (i) bp : 60.01 kW (ii) Mechanical efficiency: 85.71% (iii) bsfc: 0.25 kg/kW.hr (iv) Draw up heat balance sheet on kW basis Question 10. A single cylinder engine running at 180 rpm develops a torque of 8 Nm. The indicated power of the engine 1.8 kW. Find the loss due to friction power as the percentage of brake power.

Ans: 19.37% of brake power.

Question 11. A 3 liter spark – ignition V6 engine operates on a four-stroke cycle at 3000 rpm. The compression ratio is 9, the length of the connecting rod is 17.2 cm and the engine is square. The combustion ends at 20° after TDC.

Determine:

 a. The cylinder bore and stroke length; B= 8.6 cm, L = 8.6 cm b. The average piston speed; 8.6 m/s c. The clearance volume of the cylinder; 62.5 cm³ d. The distance piston travels from TDC at the end of combustion : 21.18 cm e. The volume in the combustion chamber at the end of combustion: 81.1 cm³
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