Conceptos basicos

5,513 views

Published on

0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
5,513
On SlideShare
0
From Embeds
0
Number of Embeds
2,451
Actions
Shares
0
Downloads
112
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Conceptos basicos

  1. 1. Motores Richard Prystupa
  2. 2. Motores (Modulo 160401a ) <ul><li>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. </li></ul><ul><li>La relación es normalmente desde 7:1 hasta 15:1 por peso (aire/combustible). </li></ul>
  3. 3. ?QUE ES TORQUE? <ul><li>Es la fuerza aplicada en una palanca que hace rotar alguna cosa, provocando un momento torsional. </li></ul><ul><li>Expresado en lb*pie, lb*plgs, o Newton-metros. </li></ul><ul><li>Tq = F x distancia del radio en pie </li></ul>Lectura del torque Fuerza Tornillo o tuerca conectada empieza a torcerse
  4. 4. QUE ES POTENCIA? <ul><li>Es cuán rápido podemos realizar el trabajo. </li></ul><ul><li>1 HP = 746 Watts </li></ul><ul><li>1 HP = 550 lb. pie./sec. </li></ul><ul><li>HP = T x RPM </li></ul><ul><li>5252 </li></ul>¿ Cu ál es la unidad de potencia? Si
  5. 5. RANGO DE CABALLOS DE FUERZA DE UN MOTOR (p. 8) <ul><li>CABALLOS DE FUERZA INDICADO </li></ul><ul><li>Son los caballos de fuerza calculados teóricamente. </li></ul><ul><li>No se encuentran previstas las perdidas por fricción o bombeo, o la energía necesaria para mover otros accesorios. </li></ul>
  6. 6. CABALLOS DE FUERZA POR FRICCION (CFFr) <ul><li>Es la energía perdida por fricción y bombeo. </li></ul><ul><li>(Ej. Transmisión, rodamientos, poleas, bombas) </li></ul><ul><li>FHP = IHP – BHP (CFFr= CFI – CFF) </li></ul>
  7. 7. CABALLOS DE FUERZA DE FRENO <ul><li>Es la energía existente medida en el extremo del cigüeñal (Volante). </li></ul><ul><li>Este es el desarrollo de los caballos de fuerza existente en el motor en operación. </li></ul><ul><li>BHP = IHP – FHP. (CFF= CFI-CFFr) </li></ul>
  8. 8. PRESION <ul><li>Es una fuerza por unidad de área. </li></ul><ul><li>Ej . lbs.*Plgs 2 o kPa (1 lb*Plgs 2 = 6.9 kPa) </li></ul>
  9. 9. VACIO (p. 9) <ul><li>Es la presión por debajo de la presión atmosférica. (14.7 lbs*Plgs 2 o 0 psig @ sea level). </li></ul>
  10. 10. PRESION ATMOSFERICA <ul><li>Es debido al peso de la atmósfera sobre la superficie de la tierra que a nivel del mar existe 14.7 lbs*Plgs 2 atmosférica. </li></ul>Atmósfera Aceleración de la gravedad 16 400 pies sobre el nivel del mar. Pr = 7.7 Lbs a *Plgs 2 A nivel del mar Pr = 14.7 Lbsa*plgs 2 Presión ejercida sobre unidad unidades de área.
  11. 11. RELACION CILINDRO CARRERA (p. 10) <ul><li>CILINDRO </li></ul><ul><li>El diámetro interior del cilindro </li></ul><ul><li>Medido a una precisión de .001” </li></ul><ul><li>CARRERA </li></ul><ul><li>Es el desplazamiento del pistón desde el PMS al PMI o viceversa. </li></ul>Ø int Carrera PMI PMS
  12. 12. DESPLAZAMIENTO DEL MOTOR <ul><li>Ej. Cilindro = 4.001” </li></ul><ul><li>Carrera = 3.480” </li></ul><ul><li>Motor de 8 cilindros </li></ul><ul><li>¿ Cual es el desplazamiento cúbico del Motor ? V = ∏r² x H V = 3.14 (2) ² x 3.480” x # cil. V = 349.865 Plgs 3 o 350 Plgs 3 . </li></ul>PMS CARRERA PMI CILINDRO
  13. 13. MOTOR CUADRADO (p. 10) <ul><li>Cuando el diámetro interior del cilindro es igual a la carrera. </li></ul>4” 4”
  14. 14. MOTOR SOBRECUADRADO <ul><li>Cuando el Ø int. del cilindro es mayor que la carrera, por consiguiente, el pistón tiene menos recorrido . </li></ul><ul><li>Son encontrados típicamente en motores automotriz y altas aceleraciones. </li></ul><ul><li>Típicamente son de motores pequeños – 327, 350, 400 GM </li></ul>4” 3”
  15. 15. MOTOR SUBCUADRADO <ul><li>Cuando el Ø int. del cilindro es menor quela carrera. </li></ul><ul><li>Grandes torques de salida a bajas rpm. </li></ul><ul><li>Son hallados sobre grandes, pequeños motores en movimiento. </li></ul><ul><li>Motores de bloques grandes – 396, 427, 454 son determinados por su peso y dimensiones externas, no el desplazamiento en Plgs 3 . </li></ul>3” 4”
  16. 16. VOLUMEN DE LA HOLGURA <ul><li>Es el volumen remanente sobre el pistón, cuando este esta en el PMS. </li></ul>Pistón @ PMS Holgura Carrera
  17. 17. COMPRESSION RATIO <ul><li>Is how much air/fuel mixture is compressed by volume. </li></ul><ul><li>It is the ratio of the total volume of the cylinder and combustion chamber clearance at BDC compared to the clearance volume at TDC. </li></ul>What would the compression ratio be in this example?
  18. 18. COMPRESSION RATIO What would the compression ratio be in this example? 15:1
  19. 19. VOLUMETRIC EFFICIENCY (p. 11) <ul><li>The ratio expressed as a percentage of the volume of atmospheric air drawn into the cylinder on the intake stroke ( 4 stroke natural aspiration ) compared to the displacement. </li></ul><ul><li>VE = Actual Output x 100 </li></ul><ul><li>Theoretical Output </li></ul>
  20. 20. SCAVENGE EFFICIENCY <ul><li>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. </li></ul><ul><li>Associated with two-stroke engines. </li></ul>
  21. 21. THERMAL EFFICIENCY <ul><li>States how well the engine changes fuel energy into mechanical energy. </li></ul><ul><li>Most engines are about 25 to 35% efficient. (Most goes out the exhaust). </li></ul>
  22. 22. BASIC ENGINE OPERATION (p. 12) <ul><li>INTERNAL COMBUSTION ENGINES </li></ul><ul><li>Fuel is burnt inside the engine in the cylinders. </li></ul>
  23. 23. INTERNAL COMBUSTION ENGINES <ul><li>The 3 main requirements to allow fuel to burn in an engine are: Fuel, Air and Ignition. </li></ul>
  24. 24. INTERNAL COMBUSTION ENGINES <ul><li>The compression process generates heat, in some cases it is enough to ignite the mixture without a spark. (Diesel engine). </li></ul>
  25. 25. INTERNAL COMBUSTION ENGINES <ul><li>Upon the power stroke, the piston transfers the energy to the connecting rod which then is transferred to the crankshaft into rotary motion. </li></ul>
  26. 26. Four Stroke (Cycle) Engines (p. 13 – Fig. 8) <ul><li>On a 4 cycle engine, it takes 720 degrees of the crank to rotate to complete 1 cycle. </li></ul>
  27. 27. Four Stroke (Cycle) Engines <ul><li>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. </li></ul>
  28. 28. Four Stroke (Cycle) Engines <ul><li>Slightly past BDC, the intake valve closes and the piston moves upward compressing the air/fuel mixture. </li></ul>
  29. 29. Four Stroke (Cycle) Engines <ul><li>The air/fuel mixture is ignited at TDC (both valves are still closed – compression stroke ). </li></ul>
  30. 30. Four Stroke (Cycle) Engines <ul><li>The piston moves past TDC as complete burning of the air/fuel mixture begins to take place. </li></ul><ul><li>The expanding gases push the piston downward in the cylinder producing power ( power stroke ). </li></ul>
  31. 31. Four Stroke (Cycle) Engines <ul><li>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 ). </li></ul>
  32. 32. Four Stroke (Cycle) Engines <ul><li>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. </li></ul>
  33. 33. Four Stroke (Cycle) Engines
  34. 34. Four Stroke (Cycle) Engines
  35. 35. TWO STROKE (CYCLE) ENGINES (p.15-fig. 9) <ul><li>Two stroke engines complete one cycle in 360 degrees. </li></ul><ul><li>2 stroke engines may use valves or ports. </li></ul>
  36. 36. TWO STROKE (CYCLE) ENGINES <ul><li>When the piston is moving downward, spent gases begin leaving the piston cylinder. </li></ul>
  37. 37. TWO STROKE (CYCLE) ENGINES <ul><li>The air/fuel mixture begins entering the cylinder close to the bottom of the stroke . </li></ul>
  38. 38. TWO STROKE (CYCLE) ENGINES <ul><li>As the piston starts moving upward, air/fuel is still entering the piston chamber but is stopped early in the stroke. </li></ul><ul><li>The remainder of the stroke is used to compress the air/fuel mixture in the piston chamber. </li></ul>
  39. 39. TWO STROKE (CYCLE) ENGINES <ul><li>Near TDC, the mixture is ignited and the expanding gases begin to push the piston downwards. </li></ul>
  40. 40. TWO STROKE (CYCLE) ENGINES <ul><li>Near the end of the cycle, the exhaust valve (or port) opens and the spent gases begin exhausting. </li></ul><ul><li>2 stroke engines need to be artificially aspirated to force out the exhaust gases and to push in the fresh air/fuel mix. </li></ul>
  41. 41. TWO STROKE (CYCLE) ENGINES <ul><li>The intake valve (or port) opens while the piston is still moving downward and the cycle begins again. </li></ul>
  42. 42. TWO STROKE (CYCLE) ENGINES
  43. 43. TWO STROKE vs. FOUR STROKE <ul><li>simpler and lighter </li></ul><ul><li>do not have valves </li></ul><ul><li>fire once every revolution, (~75% more hp than 4 stroke) </li></ul><ul><li>can work in any orientation </li></ul><ul><li>not as efficient as 4 stroke </li></ul><ul><li>fire once every two revolutions </li></ul><ul><li>More efficient than 2 stroke </li></ul><ul><li>Better fuel consumption </li></ul><ul><li>No mixing oil/fuel </li></ul>
  44. 44. CRANKSHAFT ROTATION <ul><li>Is determined as if viewing the engine from the main power takeoff or flywheel end. (Rear) </li></ul><ul><li>If the engine turns to the right its rotation clockwise (CW). </li></ul><ul><li>If engine rotates to the left its rotation is counterclockwise (CCW). </li></ul>
  45. 45. NUMBERING OF CYLINDERS
  46. 46. FIRING ORDER (p. 17)
  47. 47. FIRING ORDER <ul><li>The position of the crankshaft throws and the lobes on the camshaft determine the firing order of an engine. </li></ul><ul><li>The order is designed to give an even number of pulses throughout the complete rotation of the crankshaft. </li></ul><ul><li>This is the sequence of order for the cylinders to receive ignition. </li></ul>
  48. 48. RUNNING MATES (Fig. 11) <ul><li>This applies to four stroke engines only because every cylinder fires in one complete revolution (360 degrees) on 2 stroke engines. </li></ul><ul><li>Running mates refer to pistons which reach TDC simultaneously, but only one fires. (720 ˚ cycle) </li></ul><ul><li>Assists in balancing of the crank and pistons. </li></ul><ul><li>Running mate arrangements: </li></ul><ul><li>4 cyl. Inline engine: 1-4, 2-3. </li></ul><ul><li>8 cyl. Inline engine: 1-8, 2-7, 3-6, 4-5. </li></ul><ul><li>V 6 engine: 1-6, 2-5, 3-4. </li></ul>
  49. 49. RUNNING MATES (Crankshaft Throws)
  50. 50. ENGINE CLASSIFICATION (p. 18) <ul><li>Engines are classified by: </li></ul><ul><li>cylinder and crankshaft arrangements. </li></ul><ul><li>valve arrangement. </li></ul><ul><li>position of camshaft. </li></ul><ul><li>cooling methods. </li></ul><ul><li>induction methods. </li></ul><ul><li>engine speeds. </li></ul><ul><li>operating (stroke) cycle. </li></ul><ul><li>ignition methods and type of fuel consumed. </li></ul>

×