Assignment:
Q1 A petrol engine working on the Otto cycle has a compression ratio of 9:1, and at the beginning of compression the temperature is 32° C. After heat energy supply at constant volume, the temperature is 1700° C. The index of compression and expansion is 1.4. Calculate:
(a) temperature at the end of compression;
(b) temperature at the end of expansion;
(c) air standard efficiency of the cycle.
Q2 In a diesel cycle the pressure and temperature of the air at the start of compression are 1 bar and 57° C respectively. The volume compression ratio is 16 and the energy added at constant pressure is 1250 kJ/kg. Calculate:
(a) theoretical cycle efficiency;
(b) mean effective pressure.
Q3 An indictor diagram taken from one cylinder of a 6 cylinder 2- stroke engine has an area of 2850 mm2 and the length 75 mm when running at 2 rev/s . The indictor spring rate is 1 mm = 0.2 bar. Given that the cylinder bore is 550 mm and the stroke is 850 mm, calculate the indicated power of the engine, assuming each cylinder develops the same power.
Q4 A 6-cylinder, 4-stroke diesel engine has a bore of 150 mm and a stroke of 120 mm. The indicted mean effective pressure is 9 bar, the engine runs at 300 rpm, and the mechanical efficiency is 0.85. Calculate the indicated and the brake power.
Q5 A single 4-stroke engine is attached to a dynamometer which provides a braking load of 362 N. The radius at which the brake acts is 800 mm. If at this load the engine has a speed of 318 rpm, find the brake power.
Q6 A single 4-stroke oil engine has a cylinder diameter of 180 mm and a stroke 300 mm. During a test the following results were recorded, Area of indicator = 500 mm2 Length of indicator card = 70 mm Card scale (spring rate) 1 mm = 0.8 bar Brake load = 354 N Calculate:
(a) the indicted power;
(b) the brake power;
(c) the brake thermal efficiency.
Q7 A 3-cylinder, 4-stroke engine has a bore of 76 mm and a stroke of 125 mm. It develops 12 kW at the shaft when running at 1500 rpm. If the mechanical efficiency is 85% and it bums 3.2 kg of oil per hour of calorific value 42000 kJ/kg, find the indicted mean effective pressure, assuming all cylinders produce the same power, and the brake thermal efficiency.
Q8 A 4-cylinder, 4-stroke engine of 78 mm bore and 105 mm stroke develops an indicated power of 47.5 kW at 4400 rpm. The air/fuel ratio is 21 kg air/kg fuel, the fuel consumption is 13.6 kg/h and the calorific value of the fuel is 41.8 MJ/kg. Calculate for the engine:
(a) the indicated mean effective pressure;
(b) the indicated thermal efficiency;
(c) the volumetric efficiency referred to inlet conditions of 1 bar, 15° C.
Q9 A 6-cylinder, 4-stoke diesel engine has a bore of 210 mm and a stoke of 315 mm. At 750 rpm, the brake mean effective pressure is 4.89 bar and the specific brake fuel consumption is 0.195 kg/kWh. The air to fuel mass flow ratio is 28 to 1 and the atmospheric conditions are 0.95 bar, 17° C. Calculate the volumetric efficiency.