Post on 18-Dec-2015
Design of Intake Systems for better in-cylinder Turbulent Flow
P M V SubbaraoProfessor
Mechanical Engineering Department
Introduce and Control Organized Turbulence …..
A Task unlikely to be completed in the near future ?!?!
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
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.
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.
Generation of Swirl during Induction
Deflector Wall Port
Directed port
Shallow-Ramp Helical Port
Steep-Ramp Helical Port
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).
• 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:
NC ss
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