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Development of Thermodynamic Models for Engine Design

This study focuses on the development of thermodynamic models for designing engines, including air and residual gas properties, compression processes, combustion, heat transfer, and combustion rate. Various equations and parameters are used to model these processes accurately.

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Development of Thermodynamic Models for Engine Design

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  1. Development of Thermodynamic Models for Engine Design P M V Subbarao Professor Mechanical Engineering Department Methods to Design for Performance….

  2. Air+residual gas Fuel+Air+residual gas First Law Analysis: Transient Compression of gaseous Control Mass Compression Process SI Engine CI Engine

  3. Transient Thermodynamic Model for Compression Process Expressing the gradient of the specific heat as:

  4. Variable Property Model

  5. Properties of Gases

  6. Specific Heat of flue gas:

  7. Properties of Fuels

  8. g cp cv

  9. Frictionless Compression Equation

  10. In above Eq., the rate of the heat loss dQloss/dθ is expressed as: The convective heat transfer coefficient is given by the Woschni model as

  11. Instantaneous Mean Velocity of Cylinder Gas Mixture The velocity of the mixture is given as: The value of C1is given as: for compression process: C1=0 and for combustion and expansion processes: C1=0.00324.

  12. Pressure Profile During Compression

  13. Surface Area for heat loss/gain

  14. Measurement of Engine Wall Temperature Crank Angle,q

  15. Explicit Numerical Integration For a crank rotation of dq

  16. The Onset of Compression Process

  17. Inlet Valve : Operation Schedule pcyl Patm

  18. Work Consumed by compression Process

  19. Modeling of Combustion Process In above Eq., the rate of the heat loss dQloss/dθ is expressed as: The convective heat transfer coefficient is given by the Woschni model as For combustion and expansion processes: C1=0.00324.

  20. Finite Rate of Heat Release : Single Phase Combustion A typical heat release curve consists of an initial spark ignition phase, followed by a rapid burning phase and ends with burning completion phase .99 The curve asymptotically approaches 1 so the end of combustion is defined by an arbitrary limit, such as 90% or 99% complete combustion where xb = 0.90 or 0.99 corresponding values for efficiency factor a are 2.3 and 4.6 The rate of heat release as a function of crank angle is:

  21. Real MFB Curve in an Engine

  22. The rate of the heat input dQgen/dθ (heat release)can be modeled using a dual Weibe function Dual Phase Combustion • Where p and d refer to premixed and diffusion phases of combustion. • The parameters θp and θd represent the duration of the premixed and diffusion combustion phases. • Qp and Qd represent the integrated energy release for premixed and diffusion phases respectively. • The constants a, mp and md are selected to match experimental data. • It is assumed that the total heat input to the cylinder by combustion for one cycle is:

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