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Motores

Motores. Es un dispositivo mecánico en el cual la energía química de la oxidación del combustible es convertida en energía calorífica, la cual a su vez es convertida en energía mecánica. La relación es normalmente desde 7:1 hasta 15:1 por peso (aire/combustible). Motores (Modulo 160401a ).

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Motores

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  1. Motores Richard Prystupa

  2. Es un dispositivo mecánico en el cual la energía química de la oxidación del combustible es convertida en energía calorífica, la cual a su vez es convertida en energía mecánica. La relación es normalmente desde 7:1 hasta 15:1 por peso (aire/combustible). Motores (Modulo 160401a)

  3. Es la fuerza aplicada en una palanca que hace rotar alguna cosa, provocando un momento torsional. Expresado en lb*pie, lb*plgs, o Newton-metros. Tq = F x distancia del radio en pie ?QUE ES TORQUE? Lectura del torque Fuerza Tornillo o tuerca conectada empieza a torcerse

  4. Es cuán rápido podemos realizar el trabajo. 1 HP = 746 Watts 1 HP = 550 lb. pie./sec. HP = T x RPM 5252 QUE ES POTENCIA? ¿Cuál es la unidad de potencia? Si

  5. CABALLOS DE FUERZA INDICADO Son los caballos de fuerza calculados teóricamente. No se encuentran previstas las perdidas por fricción o bombeo, o la energía necesaria para mover otros accesorios. RANGO DE CABALLOS DE FUERZA DE UN MOTOR(p. 8)

  6. Es la energía perdida por fricción y bombeo. (Ej. Transmisión, rodamientos, poleas, bombas) FHP = IHP – BHP (CFFr= CFI – CFF) CABALLOS DE FUERZA POR FRICCION (CFFr)

  7. Es la energía existente medida en el extremo del cigüeñal (Volante). Este es el desarrollo de los caballos de fuerza existente en el motor en operación. BHP = IHP – FHP. (CFF= CFI-CFFr) CABALLOS DE FUERZA DE FRENO

  8. Es una fuerza por unidad de área. Ej. lbs.*Plgs2 o kPa (1 lb*Plgs2 = 6.9 kPa) PRESION

  9. Es la presión por debajo de la presión atmosférica. (14.7 lbs*Plgs2 o 0 psig @ sea level). VACIO (p. 9)

  10. Es debido al peso de la atmósfera sobre la superficie de la tierra que a nivel del mar existe 14.7 lbs*Plgs2 atmosférica. PRESION ATMOSFERICA Presión ejercida sobre unidad unidades de área. 16 400 pies sobre el nivel del mar. Pr = 7.7 Lbsa*Plgs2 Atmósfera A nivel del mar Pr = 14.7 Lbsa*plgs2 Aceleración de la gravedad

  11. Øint PMS Carrera PMI RELACION CILINDRO CARRERA(p. 10) CILINDRO • El diámetro interior del cilindro • Medido a una precisión de .001” CARRERA • Es el desplazamiento del pistón desde el PMS al PMI o viceversa.

  12. PMS CILINDRO CARRERA PMI DESPLAZAMIENTO DEL MOTOR • Ej. Cilindro = 4.001” Carrera = 3.480” Motor de 8 cilindros • ¿Cual es el desplazamiento cúbico del Motor?V = ∏r² x HV = 3.14 (2) ² x 3.480” x # cil.V = 349.865 Plgs3 o 350 Plgs3.

  13. MOTOR CUADRADO (p. 10) • Cuando el diámetro interior del cilindro es igual a la carrera. 4” 4”

  14. Cuando el Øint. del cilindro es mayor que la carrera, por consiguiente, el pistón tiene menos recorrido. Son encontrados típicamente en motores automotriz y altas aceleraciones. Típicamente son de motores pequeños – 327, 350, 400 GM MOTOR SOBRECUADRADO 4” 3”

  15. Cuando el Øint. del cilindro es menor quela carrera. Grandes torques de salida a bajas rpm. Son hallados sobre grandes, pequeños motores en movimiento. Motores de bloques grandes – 396, 427, 454 son determinados por su peso y dimensiones externas, no el desplazamiento en Plgs3. MOTOR SUBCUADRADO 3” 4”

  16. VOLUMEN DE LA HOLGURA • Es el volumen remanente sobre el pistón, cuando este esta en el PMS. Holgura Pistón @ PMS Carrera

  17. Is how much air/fuel mixture is compressed by volume. It is the ratio of the total volume of the cylinder and combustion chamber clearance at BDC compared to the clearance volume at TDC. COMPRESSION RATIO What would the compression ratio bein this example?

  18. COMPRESSION RATIO What would the compression ratio bein this example? 15:1

  19. VOLUMETRIC EFFICIENCY (p. 11) • The ratio expressed as a percentage of the volume of atmospheric air drawn into the cylinder on the intake stroke (4 strokenatural aspiration) compared to the displacement. • VE = Actual Output x 100 Theoretical Output

  20. It is the ratio expressed as a percentage of the fresh air contained in the cylinder to the total volume of air and exhaust gases in the cylinder at the time the port closes. Associated with two-stroke engines. SCAVENGE EFFICIENCY

  21. States how well the engine changes fuel energy into mechanical energy. Most engines are about 25 to 35% efficient. (Most goes out the exhaust). THERMAL EFFICIENCY

  22. INTERNAL COMBUSTION ENGINES Fuel is burnt inside the engine in the cylinders. BASIC ENGINE OPERATION (p. 12)

  23. The 3 main requirements to allow fuel to burn in an engine are: Fuel, Air and Ignition. INTERNAL COMBUSTION ENGINES

  24. The compression process generates heat, in some cases it is enough to ignite the mixture without a spark. (Diesel engine). INTERNAL COMBUSTION ENGINES

  25. Upon the power stroke, the piston transfers the energy to the connecting rod which then is transferred to the crankshaft into rotary motion. INTERNAL COMBUSTION ENGINES

  26. On a 4 cycle engine, it takes 720 degrees of the crank to rotate to complete 1 cycle. Four Stroke (Cycle) Engines (p. 13 – Fig. 8)

  27. On the intake stroke, the intake valve opens before the piston reaches TDC (valve overlap) and begins to move downwards pulling air/fuel mixture into the cylinder. Four Stroke (Cycle) Engines

  28. Slightly past BDC, the intake valve closes and the piston moves upward compressing the air/fuel mixture. Four Stroke (Cycle) Engines

  29. The air/fuel mixture is ignited at TDC (both valves are still closed – compression stroke). Four Stroke (Cycle) Engines

  30. The piston moves past TDC as complete burning of the air/fuel mixture begins to take place. The expanding gases push the piston downward in the cylinder producing power (power stroke). Four Stroke (Cycle) Engines

  31. Slightly before the piston reaches BDC, the exhaust valve opens and the piston pushes the burned gases out of the cylinder as it moves up (exhaust stroke). Four Stroke (Cycle) Engines

  32. As the piston nears TDC, the exhaust valve starts closing and the intake valve starts opening and the cycle begins again. This is known as valve overlap and occurs at the end of the exhaust stroke. Four Stroke (Cycle) Engines

  33. Four Stroke (Cycle) Engines

  34. Four Stroke (Cycle) Engines

  35. Two stroke engines complete one cycle in 360 degrees. 2 stroke engines may use valves or ports. TWO STROKE (CYCLE) ENGINES(p.15-fig. 9)

  36. TWO STROKE (CYCLE) ENGINES • When the piston is moving downward, spent gases begin leaving the piston cylinder.

  37. TWO STROKE (CYCLE) ENGINES • The air/fuel mixture begins entering the cylinder close to the bottom of the stroke.

  38. As the piston starts moving upward, air/fuel is still entering the piston chamber but is stopped early in the stroke. The remainder of the stroke is used to compress the air/fuel mixture in the piston chamber. TWO STROKE (CYCLE) ENGINES

  39. Near TDC, the mixture is ignited and the expanding gases begin to push the piston downwards. TWO STROKE (CYCLE) ENGINES

  40. Near the end of the cycle, the exhaust valve (or port) opens and the spent gases begin exhausting. 2 stroke engines need to be artificially aspirated to force out the exhaust gases and to push in the fresh air/fuel mix. TWO STROKE (CYCLE) ENGINES

  41. The intake valve (or port) opens while the piston is still moving downward and the cycle begins again. TWO STROKE (CYCLE) ENGINES

  42. TWO STROKE (CYCLE) ENGINES

  43. simpler and lighter do not have valves fire once every revolution, (~75% more hp than 4 stroke) can work in any orientation not as efficient as 4 stroke fire once every two revolutions More efficient than 2 stroke Better fuel consumption No mixing oil/fuel TWO STROKE vs. FOUR STROKE

  44. Is determined as if viewing the engine from the main power takeoff or flywheel end. (Rear) If the engine turns to the right its rotation clockwise (CW). If engine rotates to the left its rotation is counterclockwise (CCW). CRANKSHAFT ROTATION

  45. NUMBERING OF CYLINDERS

  46. FIRING ORDER (p. 17)

  47. FIRING ORDER • The position of the crankshaft throws and the lobes on the camshaft determine the firing order of an engine. • The order is designed to give an even number of pulses throughout the complete rotation of the crankshaft. • This is the sequence of order for the cylinders to receive ignition.

  48. RUNNING MATES (Fig. 11) • This applies to four stroke engines only because every cylinder fires in one complete revolution (360 degrees) on 2 stroke engines. • Running mates refer to pistons which reach TDC simultaneously, but only one fires. (720˚ cycle) • Assists in balancing of the crank and pistons. Running mate arrangements: • 4 cyl. Inline engine: 1-4, 2-3. • 8 cyl. Inline engine: 1-8, 2-7, 3-6, 4-5. • V 6 engine: 1-6, 2-5, 3-4.

  49. RUNNING MATES (Crankshaft Throws)

  50. ENGINE CLASSIFICATION (p. 18) Engines are classified by: • cylinder and crankshaft arrangements. • valve arrangement. • position of camshaft. • cooling methods. • induction methods. • engine speeds. • operating (stroke) cycle. • ignition methods and type of fuel consumed.

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