Gas Exchange Process

Gas Exchange Process - Michigan State University Michigan...

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Unformatted text preview: Michigan State University Michigan State University College of Engineering College of Engineering Fall 2010 - ME444 Fall 2010 - ME444 Gas Exchange Processes Thomas Asmus DaimlerChrysler Corporation, Retiree Outline Outline Volumetric efficiency fundamentals Valve timing effects Tuning effects Fuel effects Anatomy of an intake event Hot (or blowdown) backflow Cylinder charging Cold (or displacement) backflow Anatomy of an exhaust event Blowdown phase Displacement Valvetrain designs Valve timing optimization 2 Goals for Gas Exchange Processes Goals for Gas Exchange Processes at Full Load at Full Load To remove burned gas as completely as possible with as little work as possible. To induct fresh charge at as high a density as is practical with as little work as possible. To provide a homogeneous mixture of air, fuel and residual gas uniformly distributed to all cylinders (this can affect knock-limited torque.) To provide in-cylinder flows to promote the desired combustion rate (this can affect the knock tendency as well as harshness.) 3 Goals for Gas Exchange Processes Goals for Gas Exchange Processes at Part Load at Part Load To provide the desired proportions of air, fuel and burned gas (residual + EGR.) To provide a homogeneous mixture of air, fuel and residual gas uniformly distributed to all cylinders (most important at part load over emissions and driveabilitysensitive modes of operation.) To provide in-cylinder flows to promote rapid combustion hence good dilute tolerance and thus the ability to control emissions and improve economy. 4 Gas Exchange Fundamentals Gas Exchange Fundamentals Volumetric Efficiency Indicated Power Output m a t m a Q Hv (F/A) n R Where n R = # of revs./pwr.stroke = 2 for 4 stroke actual vol. flow rate geometric vol. rate m a / a,0 2m a (V d N)/2 a, 0 V d N v is affected by the following : Fuel type, fuel-air ratio, fraction of fuel vaporized in the intake system, & fuel heat of vaporization Mixture temperature as influenced by heat transfer Ratio of exhaust to inlet manifold pressures Compression ratio Engine speed Intake & exhaust manifold & port design Intake & exhaust valve geometry, size, lift & timings = v = = P = 5 1 [1 + (F/A)] ( ( ) p i a,0 a p a,0 i ( v = ( ) ) ) } { r c 1 r c- 1 (r c 1) [ ] p e p i + ( -1 ) For (p e / p i ) = 1, the term in is unity. {} = C p /C v 6 Volumetric Efficiency Parametric Effects For high v v v p v i v v r c v (p e /p i ) want hi molecular wt. ( ) fuel since = a (1-F/A) + ( f (F/A) want p i p a , 0; i.e., no pressure loss across air cleaner and throttle body want i as low as possible, i.e., minimum heat transfer to inlet system want F/A no richer than necessary (assumes complete fuel evaporation prior to IVC)...
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This note was uploaded on 01/29/2012 for the course ME 444 taught by Professor Staff during the Fall '08 term at Michigan State University.

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Gas Exchange Process - Michigan State University Michigan...

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