Development of Design Knowledge for GDI Internal Combustion Engines

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Presentation transcript:

Development of Design Knowledge for GDI Internal Combustion Engines P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Models to Predict New & Better Anatomy of Artificial Horse …..

How to develop Design Knowledge???

Thermodynamic Modeling : Development of Pseudo GDI Engine Modeling of IC engine process can be carried out in many ways. Multidimensional, Transient Flow and heat transfer Model. Thermodynamic Transient Model USUF. Fuel-air Thermodynamic Model. Air standard Thermodynamic Model

Intake System of Modern Engines

Engine Intake Process : USUF Model Any instant during intake, the equation of state for incylinder ideal gas is expressed as: Rate of change of incylinder gas properties:

Geometrical Shape of A Puppet valve Passage For lower valve lift the minimum area is the valve curtain area. For larger lifts the minimum area is the valve seat area. For Low Lift:

Air Flow Through Intake Valves : No MPFI The air flow rate is related to the intake manifold stagnation pressure p0,in and stagnation temperature T0,in, Static pressure just down stream of the valve and a reference area AR. AR is a characteristic of the valve design. The real gas flow effects are included by means of an experimentally determined discharge coefficient CD.

Air Flow Through Intake Valves : with Fuel Injection GDI Engine: MPFI Engine:

Variation of In-cylinder temperature during Intake First law for USUF : GDI Engine: MPFI Engine:

Operating modes of the GDI engine Superior output mode : SOM Injection in late intake stroke Wider spray with high penetration for charge homogenization A/F – Stoichiometric Homogeneous A-F Mixture Complete Vaporization of Fuel Ultra Lean combustion mode : ULCM Very lean stratified mixture : A/F ~ 30 Injection during compression Compact spray, deflected from the piston top to the spark plug Distinct Stratification At spark , ignitable mixture conditions It is two engines in one place

Feel the In-Cylinder Processes in GDI Engine:SOM Start of injection End of injection

Sizing of Nozzle Instantaneous fuel Flow rate: Mass of Gasoline per cycle:

Simplified Engineering Droplet Path Tracking & fuel Evaporation model In a simplified engineering model a representative diameter for the entire group is defined to compute evaporation rate. Equivalent diameter of same number of uniformly sized droplets having same total surface area.

Simplified Engineering Droplet Path Tracking & fuel Evaporation model In a simplified engineering model a representative diameter for the entire group is defined to compute evaporation rate. Equivalent diameter of same number of uniformly sized droplets having same total surface area.

Prediction of Droplet Paths After the spray break up there is a drag force exerted on the droplets from the surrounding gases. This drag tends to decrease the relative velocity between the drop and the gas flow. From the Newton's Second Law, the equation is: Where dsmd is the droplet diameter, ug and usmd are the velocities of the gas flow and the liquid fuel droplet, respectively. And the drag coefficient CD is given as:

Details of Heat and Mass Transfer across Droplet

The mass transfer number BM is equal to: Droplet evaporation The droplet evaporation rate is given by where d is the droplet diameter, DAB the gas diffusivity, Sh* the non-dimensional Sherwood number, and Bm the mass transfer number. The mass transfer number BM is equal to:

Tracking of Post Injection Events inside Cylinder

New Knowledge Required to Develop GDI Engines Effect of Geometrical and Spray Parameters Injector location, Spray orientation, Injection timing, Droplet diameter, Spray cone angle, Type of spray, Fuel temperature

Required Features of CFD Package Capability to model flow in complex geometry Capability to model turbulent flow Capability of handling moving boundaries Generalized multi-block capability Spray model Robust Algorithm

Deforming Mesh

Initialize all variables Source terms of Gas Phase Equation = 0 Solve for Gas Phase Equations Solve for Droplet Equations Cal. Gas Phase Source Terms Converged ? ya Next Time Step No Droplet Tracking Algorithm