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Turbulent Flames in SI Engine: Understanding Combustion for High-Speed Achievements

Explore the essential phenomena of combustion through turbulent flames in SI engines, crucial for high-speed engine development with acceptable fuel consumption. Learn about mixture burn time, laminar flame velocity, and the transition from laminar to turbulent flames. Discover the impact of turbulence on engine design decisions, heat transfer rates, ignition delay times, and more. Gain insights into turbulent flow structures, flame dynamics, and the role of vortices in engine cylinders. Dive into quantitative and qualitative analyses of turbulence, including velocity distributions, vortex structures, and energy-containing eddies. Uncover lessons from nature, like hurricanes, to better understand turbulent flows and optimize engine performance.

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Turbulent Flames in SI Engine: Understanding Combustion for High-Speed Achievements

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  1. Combustion through Turbulent Flames in SI Engine P M V Subbarao Professor Mechanical Engineering Department An essential phenomena for development of high speed Engine with Acceptable fuel consumption …..

  2. Mixture Burn Time B Sl : Laminar Flame velocity How does the flame burn all the mixture in the cylinder in the time available, especially at high engine speeds? It is impossible to build an engine which runs more than 10 rpm with laminar flames !!!!

  3. Knowledge of Turbulence: A single solution to many Problems! • A major input into the engine design is a statement on the turbulence structure in the engine cylinder. • In fact, details of the turbulence structure in the engine are needed for determining; • Heat transfer rates, • Ignition delay times, • Minimum ignition energy and • The rate mixing and burnup of quench layers,

  4. Induction of Global Vortex Motion in Engine Cylinder

  5. Shape of Flame & Single Global Vortex Motion

  6. Transition of Laminar Kernel to Turbulent Flame • Every turbulent flow will be locally laminar. • The largest packet of gas that can be laminar is crucial for early transition of laminar kernel into turbulent flame. • When the flame kernel becomes larger than the smallest packet of gas that can be turbulent, the flame front will become wrinkled. • As the kernel grows its flame front will become gradually more wrinkled as it experiences a growing spectrum of turbulent gas packets. • It is important to describe and establish quantitative and qualitative turbulence in an engine cylinder to achieve higher speeds with better fuel economy.

  7. Transition of Laminar Kernel to Turbulent Flame

  8. Description of Turbulent Flow in Engine Cylinder

  9. Ensemble Mean Velocity in Engine Cylinder During a Cycle

  10. Structure of Turbulence in Engine Cylinder

  11. Quantitative Description of Turbulence • The instantaneous velocity U(q) in the cylinder at any crank angle q during a cycle i is expressed as: Where • Where n is the number of strokes in an engine cycle, • U(q) the phase averaged velocity. • u(q,i) the fluctuating velocity. • Similarly the turbulence intensity u' can be determined by

  12. Identification of Structures in Turbulent Cylinder Flow

  13. Evidence of Organized Structure in an Engine1200 rpm motored engine 90 Cycle Mean Velocity Distribution In Mid- Plane Instantaneous Velocity Distribution In Mid Plane During Cycle 20 Instantaneous Velocity Distribution In Mid Plane During Cycle 1

  14. Qualitative Description of Turbulent Flow : Lessons from Nature A Hurricane : THE VORTEX

  15. Description of in Turbulent Flows The size of energy-containing (largest) eddies may be Estimated as: The Structure of Vortex where, ω = ∇×u is the vorticity. The vortical structures visualized by iso-surfaces of vorticity and Laplacian of pressure.

  16. Distribution of Vortices in a Turbulent Field |ω| Iso-surface representations of vortical structures

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