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Mechanical Design of Engine Parts

Mechanical Design of Engine Parts. P M V Subbarao Professor Mechanical Engineering Department. Design for Survival …. MOST EXOTIC NEED OF HUMANS :Mobile Power : Animal Driven Vehicles. An Exclusive Thermodynamic Characteristic of Humans. Life on Earth.

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Mechanical Design of Engine Parts

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  1. Mechanical Design of Engine Parts P M V Subbarao Professor Mechanical Engineering Department Design for Survival …

  2. MOST EXOTIC NEED OF HUMANS :Mobile Power : Animal Driven Vehicles

  3. An Exclusive Thermodynamic Characteristic of Humans Life on Earth The humans are extra-somatic heterotrophs. Motive Power is An important Extra-somatic Need Autotrophs Heterotrophs

  4. Human Evolution due to Mobility

  5. Evolution of Intelligent Species : Artificial Horse World's first inexpensive car : In Benz Velo, 1893 0.7 hp & 20 km/hr. 14 liters per 100 kilometers.  World’s most fuel efficient car : Volkswagen's diesel-hybrid XL1, 2013, 75 hp & 306 km/hr. 1.0 liter per 100 kilometers

  6. Busy Roads in 21st century

  7. A Faraday Future FF 91 electric car FF91 is displayed on stage during an unveiling event at CES in Las Vegas, Nevada January 3, 2017. REUTERS/Steve Marcus

  8. Prius : Toyoto Hybrid vehicle

  9. The Type of Prime Mover for Light Vehicle Sales in Two Decades

  10. Future Targets for Fuel Economy of LCVs

  11. Major Components of A Multi Cylinder Engine Connecting rod

  12. Characteristics of Real Engine at Maximum Fuel Consumption Control System of A Conventional I.C. Engine

  13. The Ultimate Characteristic of Sustainable Creation

  14. Engine Geometric Ratios Engine Compression Ratio Cylinder Bore-to-Stroke Ratio Kinematic Rod Ratio

  15. Heat Loss Vs RBS

  16. Frictional Loss Vs Geometry & Speed of Engine

  17. Trending of Current Engines: Bore/Stroke Ratio Bore – to –Stroke Ratio

  18. Extreme Limits of RBS • The extremes to this relationship is the inertial forces origination from the piston motion. • To achieve high power density, the engine must operate at a high engine speed (up to 18,000 rpm for the Formula 1 engine), which leads to high inertial forces that must be limited by using a large bore-to-stroke ratio. • For applications that demand high efficiency, a small bore-to-stroke ratio is necessary and, again because of the inertial forces of the piston, requires a slower engine speed and lower power density. • For the marine application that has a 2.5 m stroke, the engine speed is limited to 102 rpm.

  19. Kinematic Rod Ratio

  20. Effect of Rod Ratio on ISFC : PI Engine

  21. Effect of Rod Ratio on Heat Balance : PI Engine

  22. Effect of Rod Ratio on Heat Balance

  23. Indicative Specific Fuel Consumption

  24. Piston Displacement & Speed Instantaneous Piston Displacement:

  25. Piston Speed during High Load Conditions • For a four stroke engine: • For 1800 < q <3600 -Piston moves upward. • For 3600 < q <5400 - Piston moves downward. • The speed of the piston

  26. Rod Ratio Vs Piston Speed • Short Rod is slower at BDC range and faster at TDC range. • Long Rod is faster at BDC range and slower at TDC range.

  27. Role of Thermofluids on Engine Geometry • Thermodynamic performance decides the compression ratio. • Heat transfer and combustion mechanism decide the bore-to-stroke ratio. • Fuel economy and safety decide rod ratio. • These geometric ratios are to be taken as input to Mechanical Design of Engine parts. • What is next major information required for design?

  28. The Ultimate Goal of Thermodynamic Modelling

  29. Cold Period of Operation Hot Period of Operation

  30. Combustion Generated Pressure-Crank Angle Diagram

  31. In-cylinder Processes in a Diesel Engine

  32. In-cylinder Processes in Next generation HCCI-DI Engine

  33. Engine Cylinder – Piston system /injector

  34. Cylinder & Cylinder Liner • Function: To retain the working fluid & guide the Piston.

  35. Stress in Cylinder • Design of cylinder involves determination of wall thickness. • The forces: Force due to Gas Pressures & Side thrust. • Types of stresses generated: Longitudinal Stress, Circumferential Stress & Bending Stress due to side thrust. Net Longitudinal Stress Net Circumferential Stress

  36. Design of Cylinder • The thickness (t) of cylinder wall is determined by thin cylinder formula. • Industry practice: The thickness (t) of cylinder wall is determined by an empirical formula.

  37. Empirical Relations of Liner design • Liners are designed using empirical relations. Thickness of water jacket wall Thickness of water space : 10mm for a bores below 75mm. For bores greater than 75mm.

  38. The Piston

  39. Design Considerations • In designing a piston for I.C. engine, the following points should be taken into consideration : • Strength to withstand the high gas pressure and inertia forces. • Minimum mass to minimise the inertia forces. • Form an effective gas and oil sealing of the cylinder. • Provide sufficient bearing area to prevent undue wear. • disperse the heat of combustion quickly to the cylinder walls. • High speed reciprocation without noise. • Rigid construction to withstand thermal and mechanical distortion. • support for the piston pin.

  40. Design of Piston Head • The piston head or crown is designed keeping in view the following two main considerations, i.e. • Adequate strength to withstand the straining action due to pressure of explosion inside the engine cylinder. • Dissipate the heat of combustion to the cylinder walls as quickly as possible. • Simplification of Geometry & Loading • The top of the piston may be considered as a flat, fixed on the cylindrical portion of the piston crown. • subjected to uniformly distributed load of maximum intensity of gas pressure. • The thickness of the piston top (head) based on the straining action due to fluid pressure is given by

  41. Geometry of Connecting Rod

  42. Beam Cross-Section for connecting rod H-Beam I-Beam

  43. Load Modeling Equations • Connecting rod load modeling considers • the static force applied by the piston which results from the combustion pressure, and • the dynamic load due to the linear oscillation of the piston mass. • Oscillating inertial force of the conrod is neglected in first approximation.

  44. Loading equation: Compressive Force The compressive force aligned to conrod axis:

  45. Loading equation: Tensile Force The tensile force aligned to conrod axis

  46. Loading equation: Bending Force • Force due to inertia of the connecting rod or inertia bending forces. • Consider a connecting rod PC and a crank OC rotating with uniform angular velocity ω rad / s. • Draw the Klien’s acceleration diagram to find the acceleration of various points on the connecting rod. The inertia force acting on each point will be as follows: Inertia force at C = m × ω2 × CO Intertia force at D = m × ω2 × dO Intertia force at E = m × ω2 × eO, and so on.

  47. Inertia Bending Forces • The perpendicular (or transverse) components produces bending action (also called whipping action) and the stress induced in the connecting rod is called whipping stress. • Resultant inertia force: Maximum bending moment

  48. Design of Connecting rod • In designing a connecting rod, the following dimensions are required to be determined : • Dimensions of cross-section of the connecting rod, • Dimensions of the crankpin at the big end and the piston pin at the small end, • Size of bolts for securing the big end cap, and • Thickness of the big end cap.

  49. cross-section of the connecting rod • The connecting rod is considered like both ends hinged for buckling about X-axis • and both ends fixed for buckling about Y-axis. • A connecting rod should be equally strong in buckling about both the axes. • Use Rankine’s formula

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