Assessment of Engine Breathing Capacity P M V Subbarao Professor Mechanical Engineering Department Measure of Filling & Emptying Effectiveness….
Stream Tube formed by Flow Through Valves Equivalent Converging-Diverging Nozzle Configurations: Mild Separation. Severe Separation
Capacity of A Valve Passage Mass flow rate through any cross section of area A
Invariant non-Uniform Area Flow Paths
Conservation of mass Conservation of Momentum Conservation of Energy Isentropic Flow Through Variable Area
Bell The Cat : A Story for Kids
Engineering Understanding of Accoustics The fact that the engineer knows about the chocking is great but it is not enough for today's sophisticated industry. A cat is pursuing a mouse and the mouse escape and hide in the hole. Suddenly, the mouse hear a barking dog and a cat yelling. The mouse go out to investigate, and cat is catching the mouse. The mouse ask the cat I thought I hear a dog. The cat reply, yes you right. My teacher was right, one language is not enough today.
Speed of Travel of A Disturbance The people had recognized for several hundred years that sound is a variation of pressure. The ears sense the variations by frequency and magnitude which are transferred to the brain which translates to voice. Thus, it raises the question: what is the speed of the small disturbance travel in a quiet medium. This velocity is referred to as the speed of sound. Let us generate and analyze a disturbance.
Valve Opening : A Disturbance for Cylinder Expansion Stroke Exhaust Stroke
c High pressure and High temperature fluid in a closed Cylinder closed. Role of Sonic Velocity in Engineering Stagnation Conditions. p manifold
w c+u c-u u Role of Sonic Velocity in Engineering c Velocity of sound at any give flow velocity u. p manifold
Role of Sonic Velocity in Engineering Velocity of sound when flow velocity w=c. w c+c c-c u=c c p manifold
Exhaust Gas Flow Through VALVES
Choking of Nozzle Extent of Valve Opening
Mach Number Mach number of a flight For an ideal and calorically perfect gas:
Actual Geometry of Valve Stream Tube Minimum Area
Specific Mass flow Rate through Valve Passage Mass flow rate per unit area of cross section:
Conditions for Choked Flow
Isentropic Compressible Flow Through Inlet Valve When the flow is chocked: A R Instantaneous Reference inlet valve flow area Resource : The total pressure in the inlet manifold – Cylinder pressure
Isentropic Compressible Flow Through Exhaust Valve When the flow is chocked: A R Instantaneous Reference exhaust valve flow area Resource : The total pressure in the cylinder – Static Pressure in Exhaust manifold
Early Choking of Valve Passage Extent of Valve Opening
Frictional Subsonic Flow Sonic Efects Effect of Sonic Conditions and Irreversibilities Isentropic Subsonic Flow Mass of Fresh air :Intake Process
Typical Intake Poppet Valve Geometry
Typical Exhaust Poppet Valve Geometry
Effect of Frictional Losses: Intake System
Effect of Frictional Losses: Exhaust System
Frictional Compressible Flow Through Inlet Valve The real gas flow effects are included by means of an experimentally determined discharge coefficient C D. The air flow rate is related to the upstream stagnation pressure p 0 and stagnation temperature T 0, Static pressure just down stream of the valve and a reference area A R. A R is a characteristic of the valve design. When the flow is chocked:
Discharge Coefficient: The value of C D and the choice of reference area A R are linked together. The product C D. A R is the effective flow area of the valve assembly, A E. In general valve head area or port area or curtain area are used as reference areas.
Friction & Turbulent Gas Flow through INLET VALVES a b c
EXHAUST VALVES