Design of Intake Systems for better in-cylinder Turbulent Flow

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Design of Intake Systems for better in-cylinder
Turbulent Flow

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Introduce and Control Organized Turbulence .. A
Task unlikely to be completed in the near future
?!?!
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A Segment of Reconstructed Turbulent Flame
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Influence of turbulent scale Intensity on
minimum ignitionenergy
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Intelligence in Engine Turbulence
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Large Scales Parents Vortices
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Quick Combustion with Fuel Economy

• To promote quick combustion, sufficient
  large-scale turbulence is needed at the end of
  the compression stroke.
• Large scales of turbulence will result in a
  better mixing process of air and fuel and it will
  also enhance flame development.
• Too much turbulence leads to excessive heat
  transfer from the gases to the cylinder walls,
  and may create problems of flame propagation .
• The key to efficient combustion is to have enough
  turbulence in the combustion chamber prior to
  ignition.
• This turbulence can be created by the design of
  the intake port

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Schematic diagram of the experimental setup
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Types of Intake Flows

• There are two types of structural turbulence that
  are recognizable in an engine tumbling and
  swirl.
• Both are created during the intake stroke.
• Tumble is defined as the in-cylinder flow that is
  rotating around an axis perpendicular with the
  cylinder axis.

Swirl is defined as the charge that rotates
concentrically about the axis of the cylinder.
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Tumble Motion

• For most of the modern stratified charge and
  direct injection SI engines, tumble flows are
  more crucial than the swirl flows.
• Tumble flow generates proper mixing of air and
  fuel, and for high flame propagation rate.
• Also a well defined (single vortex) tumbling
  flow structure is more stable.
• TR is defined as the ratio of the mean angular
  velocity of the vortices on the target plane to
  the average angular velocity of the crank.
• The negative or positive magnitudes of TR
  indicate the direction of the overall in-cylinder
  tumble flow in a given plane as CW or CCW
  respectively.

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The ensemble average velocity vectors during
intake stroke Flat Piston
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Variation of tumble ratio with crank angle
positions at various engine speeds
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Pentroof Pistons
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Variation of tumble ratio with crank angle
positions
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Valve Geometry Vs Turbulence
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Control of Turbulence Level
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Turbulence Level versus engine speed
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Control of Integral Scale
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Integral Scale Vs Speed
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Variation of turbulent intensity with volumetric
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Tumble based Injection systems
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Generation of Swirl during Induction
Deflector Wall Port
Shallow-Ramp Helical Port
Directed port
Steep-Ramp Helical Port
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Measures of Swirl

• Two different values are calculated to assess the
  swirl intensity.
• Swirl number or swirl coefficient and swirl
  component or swirl number.
• The first, the swirl number, is the ratio of
  angular momentum to the axial momentum

This angular momentum is calculated in the centre
of the swirl (not on the cylinder axis).
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Selection of Valve Lift Valve Geometry
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• The other is herein called the swirl component
  and is the swirl parameter relevant for
  experimental tests with a paddle wheel placed in
  the axis of the cylinder

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Swirl Generation through Valve Seat
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Pistons for Swirl based systems