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, 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, 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 < Piston moves downward.
The speed of the piston

27. 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.

28. 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?

29. The Ultimate Goal of Thermodynamic Modelling

30. Cold Period of Operation
Hot Period of Operation

31. Combustion Generated Pressure-Crank Angle Diagram

32. In-cylinder Processes in a Diesel Engine

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

34. Engine Cylinder – Piston system
/injector

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

36. 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

37. 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.

38. 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.

39. The Piston

40. 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.

41. 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

42. Geometry of Connecting Rod

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

44. 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.

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

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

47. 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.

48. 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

49. 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.

50. 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

51. Bending Loads Buckling Load about X-axis: Buckling Load about Y-axis:
A = Cross-sectional area of the connecting rod,
l = Length of the connecting rod,
σc = Compressive yield stress,
Ixx and Iyy = Moment of inertia of the section about X-axis and Y-axis
respectively, and
kxx and kyy = Radius of gyration of the section about X-axis and Y-axis
respectively.

52. Crank Shaft

53. Design Concepts for Crank Shaft
The crank shaft is designed considering two positions of the crank:
When Crank is at Dead centre (Maximum Bending Moment).
When Crank is at angle where Twisting Moment is maximum.

54. When Crank is at dead centre
Stepwise procedure:
Draw a Free Body Diagram of the Crankshaft with various horizontal and vertical forces.
Calculate the piston force.
Industry assumptions while calculation of forces in FBD.
Find all the horizontal & vertical reactions

55. When the crank is at an angle of maximum twisting moment
The twisting moment on the crankshaft will be maximum when the tangential force on the crank (FT) is maximum.
The maximum value of tangential force lies when the crank is at angle 30º to 40º for constant pressure combustion engines (i.e. diesel engines).
When the crank is at angle at which the twisting moment is maximum, the shaft is subjected to twisting moment from energy stored by flywheel.
The above design parameters can be cross checked for the factor of safety while designing by considering the crankshaft at an angle of maximum twisting moment.

56. Design Procedure for Crankshaft
The following procedure is adopted for designing a crankshaft.
Find the magnitude of the various loads on the crankshaft.
Determine the distances between the supports and their position with respect to the loads.
For the sake of safety, the shaft is considered to be supported at the centres of the bearings and all the forces and reactions to be acting at these points.
The distances between the supports depend on the length of the bearings, which in turn depend on the diameter of the shaft because of the allowable bearing pressures.
The thickness of the cheeks or webs is assumed to be from 0.4 ds to 0.6 ds, where ds is the diameter of the shaft..
Now calculate the distances between the supports.
Assuming the allowable bending and shear stresses, determine the main dimensions of the crankshaft.

57. Design of Central Crankshaft

58. Hierarchical causes and modes of crankshaft failure

59. Crankshaft reliability improvement strategy