Listas de Motores Térmicos

b In what way may these graphs be used in putting forward an argument in favor of the compressionignition engine 5 A sixcylinder fourstroke petrol engine having a cylinder bore diameter of 82 mm and a stroke of 80 mm develops maximum power at a speed of 4800 revmin The imep at this speed was found to be 1100 kPa the engine being coupled to a hydraulic dynamometer having a value of K 16 The load on the dynamometer was 290 N Calculate the indicated power brake power and mechanical efficiency of the engine 1116 kW 87kW 78 6 A singlecylinder engine has a bore of 70 mm and a stroke of 76 mm The average pressure during each working stroke is 620 kPa Calculate a the average force on the piston 6 the work done on the piston during one working stroke c the power developed in the cylinder if the piston makes 2000 working strokes per minute d the power available at the flywheel if the engine has a mechanical efficiency of 85 per cent 7 The average pressure acting on each piston crown of a fourcylinder fourstroke engine on test was 850 kPa the piston diameter being 60 mm and piston stroke 75 mm a Calculate the power developed by the engine the crankshaft speed being 4200 revmin b If the mechanical efficiency of the engine is 80 per cent calculate the torque developed at the output shaft of the engine 8 A singlecylinder two stroke diesel engine develops 7 kW at 2800 revmin Calculate the work done on the piston in joules in one stroke If the piston is 100 mm diameter and the stroke is 150 mm calculate the average pressure on the piston in kPa 9 The following results were obtained from an engine tested with a dynamometer having a bp formula WN20 000 kilowatts Speed N revmin 1000 1500 2000 2500 3000 3500 4000 4500 Load W N 104 108 110 110 105 96 865 772 On a base of revmin plot the engine load and bp curves Make comments on these curves and indicate the speed at which maximum torque occurs 10 A fourcylinder fourstroke engine produces an indicated power of 61 kW when rotating at 50 revs The compression ratio is 85 to 1 when using a clearance volume of 664 cm3 Calculate a the swept volume of the cylinder 6 the indicated mean effective pressure at 50 revs 17 a Describe an experiment to find the approximate indicated power of a fourcylinder internal combustion engine using the Morse testb Show a typical formula used to find i brake power ii indicated power and iii mechanical efficiency c Indicate on a base of engine speed the types of graph which may be plotted as a result of this experiment 18 Describe how an engine is tested under laboratory conditions for power and fuel consumption State the equipment and calculations required to obtain the final conclusions Show a typical fuel consumption and power curve 19 State how the brake thermal efficiency of the engine can be determined from the results obtained in the experiment of Question 18above EXERCISE 2 Problems 1 An engine is tested against a dynamometer at 3300 revmin and exerts a force of 200 N at the end of a torque arm of length 035 m Calculate a the torque transmitted by the engine 70 Nm b the brake power developed by the engine at this speed 242 kW 2 Calculate the torque of an engine which develops 22 kW at a speed of 21 revs 1667 Nm 3 Using the values given in the table below plot the graph for engine torque against speed Engine torque Nm 450 492 500 490 453 410 360 Speed revmin 1200 1500 1800 2100 2400 2700 3000 a From the graph obtain the maximum torque and the speed at which it occurs 500 Nm 1800 revmin b Calculate the power at that speed 9425 kW 4 a Plot torque and brake power curves for both spark and compressionignition engines from the following data Petrol engine Speed revmin 600 1200 1800 2400 3000 3600 4200 4800 Torque Nm 90 110 104 90 74 59 44 26 Brake power kW 14 22 29 355 41 45 46 38 Compressionignition engine Speed revmin 600 1200 1800 2400 3000 3600 Torque Nm 95 98 97 95 90 83 Brake power kW 10 22 32 41 47 46