Motores

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Motores
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Motores (Modulo 160401a)

• 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 71 hasta 151
  por peso (aire/combustible).

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?QUE ES TORQUE?

• Es la fuerza aplicada en una palanca que hace
  rotar alguna cosa, provocando un momento
  torsional.
• Expresado en lbpie, lbplgs, o Newton-metros.
• Tq F x distancia del radio en pie

Lectura del torque
Fuerza
Tornillo o tuerca conectada empieza a torcerse
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QUE ES POTENCIA?

• Es cuán rápido podemos realizar el trabajo.
• 1 HP 746 Watts
• 1 HP 550 lb. pie./sec.
• HP T x RPM
• 5252

Cuál es la unidad de potencia?
Si
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RANGO DE CABALLOS DE FUERZA DE UN MOTOR (p. 8)

• 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.

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CABALLOS DE FUERZA POR FRICCION (CFFr)

• Es la energía perdida por fricción y bombeo.
• (Ej. Transmisión, rodamientos, poleas, bombas)
• FHP IHP BHP (CFFr CFI CFF)

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CABALLOS DE FUERZA DE FRENO

• 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)

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PRESION

• Es una fuerza por unidad de área.
• Ej. lbs.Plgs2 o kPa (1 lbPlgs2 6.9 kPa)

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VACIO (p. 9)

• Es la presión por debajo de la presión
  atmosférica. (14.7 lbsPlgs2 o 0 psig _at_ sea
  level).

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PRESION ATMOSFERICA

• Es debido al peso de la atmósfera sobre la
  superficie de la tierra que a nivel del mar
  existe 14.7 lbsPlgs2 atmosférica.

Presión ejercida sobre unidad unidades de área.
16 400 pies sobre el nivel del mar. Pr 7.7
LbsaPlgs2
Atmósfera
A nivel del mar Pr 14.7 Lbsaplgs2
Aceleración de la gravedad
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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.

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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.

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MOTOR CUADRADO (p. 10)

• Cuando el diámetro interior del cilindro es igual
  a la carrera.

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4
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MOTOR SOBRECUADRADO

• 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

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3
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MOTOR SUBCUADRADO

• 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.

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4
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VOLUMEN DE LA HOLGURA

• Es el volumen remanente sobre el pistón, cuando
  este esta en el PMS.

Holgura
Pistón _at_ PMS
Carrera
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COMPRESSION RATIO

• 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.

What would the compression ratio be in this
example?
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COMPRESSION RATIO
What would the compression ratio be in this
example?
151
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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 stroke natural aspiration)
  compared to the displacement.
• VE Actual Output x 100
• Theoretical Output

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SCAVENGE EFFICIENCY

• 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.

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THERMAL EFFICIENCY

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

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BASIC ENGINE OPERATION (p. 12)

• INTERNAL COMBUSTION ENGINES
• Fuel is burnt inside the engine in the cylinders.

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INTERNAL COMBUSTION ENGINES

• The 3 main requirements to allow fuel to burn in
  an engine are Fuel, Air and Ignition.

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INTERNAL COMBUSTION ENGINES

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

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INTERNAL COMBUSTION ENGINES

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

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Four Stroke (Cycle) Engines (p. 13 Fig. 8)

• On a 4 cycle engine, it takes 720 degrees of the
  crank to rotate to complete 1 cycle.

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Four Stroke (Cycle) Engines

• 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.

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Four Stroke (Cycle) Engines

• Slightly past BDC, the intake valve closes and
  the piston moves upward compressing the air/fuel
  mixture.

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Four Stroke (Cycle) Engines

• The air/fuel mixture is ignited at TDC (both
  valves are still closed compression stroke).

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Four Stroke (Cycle) Engines

• 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).

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Four Stroke (Cycle) Engines

• 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).

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Four Stroke (Cycle) Engines

• 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.

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Four Stroke (Cycle) Engines
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Four Stroke (Cycle) Engines
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TWO STROKE (CYCLE) ENGINES (p.15-fig. 9)

• Two stroke engines complete one cycle in 360
  degrees.
• 2 stroke engines may use valves or ports.

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TWO STROKE (CYCLE) ENGINES

• When the piston is moving downward, spent gases
  begin leaving the piston cylinder.

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TWO STROKE (CYCLE) ENGINES

• The air/fuel mixture begins entering the cylinder
  close to the bottom of the stroke.

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TWO STROKE (CYCLE) ENGINES

• 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.

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TWO STROKE (CYCLE) ENGINES

• Near TDC, the mixture is ignited and the
  expanding gases begin to push the piston
  downwards.

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TWO STROKE (CYCLE) ENGINES

• 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.

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TWO STROKE (CYCLE) ENGINES

• The intake valve (or port) opens while the piston
  is still moving downward and the cycle begins
  again.

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TWO STROKE (CYCLE) ENGINES
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TWO STROKE vs. FOUR STROKE

• 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

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CRANKSHAFT ROTATION

• 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).

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NUMBERING OF CYLINDERS
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FIRING ORDER (p. 17)
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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.

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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.

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RUNNING MATES (Crankshaft Throws)
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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.