Designing

Describe about the Small Scale Engine Design?

In this project, we continue our designing process, as completed in the semester 1, with the manufacturer changes as specified.

The project specifications in the part-1 of project were:

a) Miniature two stroke, compression ignition engine (to be used in an Unmanned Arial Vehicle)

b) Brake horse power = 0.06bhp (45W) when speed = 14,000rev/min

c) Capable of driving a propeller of  a 200mm x 100mm diameter pitch

d) Drive shaft greater than 5mm

e) Air cooled

f) Production of 500 engines per year

The changes that our consultancy has been asked to incorporate are:

a. Design changes for production of 2000, 5000, 10,000 engines per year

b. Assembly planning for

i. Crankshaft assembly

ii. Piston assembly

iii. Fuel line assembly

c. Process planning for crankcase, crankshaft, cylinder head or piston.

d. Engine life cycle analysis.

Assembly Planning

Crankshaft Assembly

The crankshaft is the part which rotates in the main bearings, which is inside the crankcase. There are connecting rods are attached to “throws”. This is the area which is attached to offset, where the change of reciprocating motion of the piston into rotary motion takes place.

Fig. 2: Crankshaft Assembly

In this project, we have been asked to assemble the crankshaft assembly. Running the data given as thresholds on the CES EduPack, we have arrived at the conclusion to use Machining Process for the assembly. It has to be machined using stainless steel.

Fig. 3: CES EduPack Machining Planning

PLANING is a process of machining category, which is used for removing metal from surfaces in vertical, horizontal, or angular planes. In this process, the work piece is reciprocated in a linear motion against single-point tools, which can be one or more. This planning process is most widely used for producing flat surfaces on large work pieces. But, the process can also be used to produce a variety of irregular shapes and contours, like helical grooves, deep slots, and internal guide surfaces. The machining processes which is used to remove metal from surfaces are called SHAPING and SLOTTING. They do this with a single-point tool mounted on a reciprocating ram.

Shape
Solid 3-D

Non-circular prismatic
Circular prismatic
Physical attributes
Roughness 0.4 – 25 µm
Range of section thickness 10 – 500 mm
Mass range 0.01 – 100 kg
Tolerance 0.013 – 0.5 mm
Process characteristics
Prototyping
Discrete
Economic attributes
Relative equipment cost medium
Labour intensity medium

Economic batch size (units) 1 – 100
Relative tooling cost low

Fig. 4: Piston Assembly

This has again been designed using Machining, in which turning, boring and parting process is used.

Fig. 5: EduPack Details on Turning, Boring and Parting

TURNING is the process that generates external surfaces of revolution. It does so by removing material from a rotating work piece, which is done using a single-tipped cutting tool. The rotory motio to the work piece is provided by chuck mounted which is gripped in a lathe. BORING is this same action applied to internal surfaces of revolution. It is commonly used process for finishing or enlarging holes or other circular contours. Although most boring operations are done on straight-through, simple holes (ranging upward in diameter from about 6 mm), tooling can be designed for holes with bottle-shaped configurations, boring blind holes and bores with undercuts, steps, and counter bores. The process of boring is used after drilling, which is done to increase dimensional accuracy and finish This is also done for finishing holes too large to be produced economically by drilling, like large pierced holes in forgings or large cored holes in castings. The process of PARTING is the process where the separation of a turned object from the stock from which it was made by turning the section down to zero.

Assembly Planning

Shape
Circular prismatic
Hollow 3-D

Solid 3-D
Physical attributes
Tolerance 0.013 – 0.38 mm
Mass range 0.001 – 5.5e4 kg
Roughness 0.5 – 25 µm
Process characteristics
Discrete
Cutting processes
Machining processes
Prototyping
Economic attributes
Relative equipment cost high
Relative tooling cost medium
Economic batch size (units) 1 – 1e7

Fig. 6: Fuel Line Assembly

The fuel tank has to be manufactured by Seam Welding, according to EduPack.

Fig. 7: EduPack details of Seam Welding

In seam welding, circular wheel-like electrodes press the overlapping sheets to be welded together and while rolling conduct a series of high current-low voltage pulses to the work. These produce overlapping spot welds which become a continuous seam. No fluxes or filler material is required. The electrodes are made of low resistance copper alloy and are water-cooled.

The carburettor has to be manufactured using High Pressure die casting.

Fig. 8: EduPack details of High Pressure die casting

In the process of PRESSURE DIE CASTING, molten metal is injected under high pressure into a metal die. This is done through a system of runners and sprues. During this solidification, the pressure is maintained. Then, the die halves are opened to inject the casting.  As high pressures is involved here, the two die halves are held together by a high force. They are then locked with toggle clamps also. The dies are precision machined from heat resistant steel. They are then cooled with water. They often include several movable parts and are therefore expensive and complex. The die casting machines are of two types, which are generally used. They are: hot chamber and cold chamber. In the ‘hot chamber’ process, which is also known as gooseneck process, the molten metal is held in a furnace in which a gooseneck chamber is submerged. Upon each cycle, the gooseneck is filled with metal. It is then forced into the die. Because of the prolonged contact between the injection system and the metal, this process is restricted to zinc-base alloys. In the ‘cold chamber’ process, metal is melted in a separate furnace. It is then transported to the die casting machine. The cold chamber process can be used for a variety of alloys, whereas the hot chmaber process cannot. Die castings cannot be heat-treated because of internal porosity. The process is very competitive for producing large quantities of thin-walled castings.

Shape
Non-circular prismatic
Hollow 3-D

Solid 3-D
Circular prismatic

Physical attributes
Roughness 0.8 – 1.6 µm

Mass range 0.05 – 15 kg
Tolerance 0.15 – 0.5 mm
Range of section thickness 1 – 8 mm

Fig. 9: Cost modelling of High Pressure die casting

We have here analysed the two materials that can be used to manufacture crankcase. They are:

1. Aluminium C355.0
2. Aluminium S319.0

Material Processing footprint for Aluminium C355.0: (according to CES EduPack)

General properties
Designation
Al-alloy: C355.0, T6
UNS number A33350
Density 2.7e3 – 2.73e3 kg/m^3
Price * 1.69 – 1.85 USD/kg
Composition overview
Composition (summary)
Al/4.5-5.5Si/1.0-1.5Cu/.4-.6Mg/.2Fe/.2Ti/.1Mn/.1Zn
Base Al (Aluminium)
Composition detail
Mn (manganese) 0.1 %
Si (silicon) 4.5 – 5.5 %
Ti (titanium) 0.2 %
Zn (zinc) 0.1 %
Al (aluminium) 92 – 94 %
Cu (copper) 1 – 1.5 %
Fe (iron) 0.2 %
Mg (magnesium) 0.4 – 0.6 %
Mechanical properties
Bulk modulus 68.3 – 71.8 GPa
Poisson’s ratio 0.33 – 0.343
Shape factor 28
Yield strength (elastic limit) 193 – 276 MPa
Young’s modulus 70 – 73.6 GPa
Shear modulus 27 – 28.4 GPa
Hardness – Vickers 90 – 95 HV
Fatigue strength at 10^7 cycles 62 – 97 MPa
Tensile strength 255 – 345 MPa
Elongation 1 – 3 %
Fatigue strength model (stress range) * 42.9 – 80.2 MPa
Parameters: Stress Ratio = 0, Number of Cycles = 1e7
Compressive strength 193 – 276 MPa
Flexural strength (modulus of rupture) 193 – 276 MPa
Fracture toughness * 18 – 23 MPa.m^1/2
Mechanical loss coefficient (tan delta) * 1e-4 – 0.002
Thermal properties
Maximum service temperature 130 – 200 °C
Minimum service temperature -273 °C
Melting point 545 – 620 °C
Thermal expansion coefficient 22.3 – 23.5 µstrain/°C
Thermal conductivity 152 – 165 W/m.K
Specific heat capacity 963 – 1e3 J/kg.K
Latent heat of fusion * 384 – 393 kJ/kg

Crankshaft Assembly

Durability: fluids and sunlight
Weak alkalis Acceptable
Strong alkalis Unacceptable
Water (fresh) Excellent
Strong acids Excellent
Organic solvents Excellent
Water (salt) Acceptable
UV radiation (sunlight) Excellent
Oxidation at 500C Unacceptable
Weak acids Excellent
Primary material production: energy, CO2 and water
CO2 footprint, primary production 11.9 – 13.2 kg/kg
Water usage 125 – 375 l/kg
Embodied energy, primary production 209 – 231 MJ/kg
Material processing: energy
Conventional machining energy (per unit wt. removed) * 4.16 – 4.6 MJ/kg
Non-conventional machining energy (per unit wt. removed) * 31.8 – 35.2 MJ/kg
Metal powder forming energy * 7.97 – 8.81 MJ/kg
Vaporization energy * 17 – 18.8 MJ/kg
Casting energy * 2.39 – 2.64 MJ/kg
Forging, rolling energy * 3.02 – 3.34 MJ/kg
Material processing: CO2 footprint
Vaporization CO2 * 1.36 – 1.5 kg/kg
Forging, rolling CO2 * 0.242 – 0.267 kg/kg
Metal powder forming CO2 * 0.638 – 0.705 kg/kg
Conventional machining CO2 (per unit wt. removed) * 0.333 – 0.368 kg/kg
Casting CO2 * 0.143 – 0.158 kg/kg
Non-conventional machining CO2 (per unit wt. removed) * 2.54 – 2.82 kg/kg

Material Processing footprint for Aluminium S319.0: (according to CES EduPack)

Designation
Al alloy: S319.0; LM21-M (cast)
UNS number A03190
Density 2.78e3 – 2.84e3 kg/m^3
Price * 1.65 – 1.81 USD/kg
Composition overview
Composition (summary)
Al/6Si/4Cu/Zn
Base Al (Aluminium)
Composition detail
Si (silicon) 6 %
Cu (copper) 4 %
Al (aluminium) 90 %
Zn (zinc) 0 %
Mechanical properties
Hardness – Vickers 85 – 90 HV
Fatigue strength at 10^7 cycles * 55 – 65 MPa
Bulk modulus 65 – 86 GPa
Poisson’s ratio 0.32 – 0.36
Young’s modulus 71 – 75 GPa
Yield strength (elastic limit) 124 – 137 MPa
Tensile strength 190 – 210 MPa
Compressive strength 124 – 137 MPa
Shear modulus 26 – 28 GPa
Shape factor 38
Flexural strength (modulus of rupture) 124 – 137 MPa
Elongation 1.9 – 2.2 %
Fatigue strength model (stress range) * 41.2 – 50.8 MPa
Parameters: Stress Ratio = 0, Number of Cycles = 1e7
Fracture toughness * 24 – 26 MPa.m^1/2
Mechanical loss coefficient (tan delta) * 1e-4 – 0.002
Thermal properties
Thermal conductivity 119 – 123 W/m.K
Minimum service temperature -273 °C
Melting point 520 – 615 °C
Thermal expansion coefficient 20.5 – 21.5 µstrain/°C
Specific heat capacity 944 – 982 J/kg.K
Maximum service temperature 130 – 200 °C
Latent heat of fusion 384 – 393 kJ/kg

Durability: fluids and sunlight
Strong acids Excellent
Weak acids Excellent
Water (salt) Acceptable
Organic solvents Excellent
Water (fresh) Excellent
UV radiation (sunlight) Excellent
Strong alkalis Unacceptable
Weak alkalis Acceptable
Oxidation at 500C Unacceptable
Primary material production: energy, CO2 and water
CO2 footprint, primary production 11.9 – 13.2 kg/kg
Embodied energy, primary production 209 – 231 MJ/kg
Water usage 125 – 375 l/kg
Material processing: energy
Casting energy * 2.3 – 2.54 MJ/kg
Forging, rolling energy * 2.41 – 2.67 MJ/kg
Conventional machining energy (per unit wt. removed) * 4.08 – 4.51 MJ/kg
Metal powder forming energy * 7.65 – 8.46 MJ/kg
Vaporization energy * 16.4 – 18.1 MJ/kg
Non-conventional machining energy (per unit wt. removed) * 30.8 – 34 MJ/kg
Material processing: CO2 footprint
Forging, rolling CO2 * 0.193 – 0.214 kg/kg
Casting CO2 * 0.138 – 0.152 kg/kg
Conventional machining CO2 (per unit wt. removed) * 0.326 – 0.361 kg/kg
Vaporization CO2 * 1.31 – 1.45 kg/kg
Metal powder forming CO2 * 0.612 – 0.677 kg/kg
Non-conventional machining CO2 (per unit wt. removed) * 2.46 – 2.72 kg/kg

Conclusion

The changes has been done according to the requirements. The analysis has been done on CES EduPack, taking the number of parts manufactured as 200, 500 and 10,000.

The cost threshold has been set to $100 in each case.

According to the CO2 footprint, the material suitable for use in crankcase of the crankshaft assembly should be Aluminium S319.0., though it is not they fuel efficient is terms of energy produced, but eco audit suggests Aluminium S319.0 for low carbon dioxide emission.

References

George E. Dieter (1997). “Overview of the Materials Selection Process”, ASM Handbook Volume 20: Materials Selection and Design.

Ashby, Michael (1999). Materials Selection in Mechanical Design (3rd edition ed.). Burlington, Massachusetts: Butterworth-Heinemann. ISBN 0-7506-4357-9.

“Material Grapher”. Materials Digital Library Pathway MatDL.org.

“Granta Design”. Granta Design.

Ashby, Michael F. (2005). Materials Selection in Mechanical Design. USA: Elsevier Ltd.

Frank Jardine (Alcoa): “Thermal Expansion in Automotive-Engine Design”, SAE paper 300010

G P Blair et al. (Univ of Belfast), R Fleck (Mercury Marine), “Predicting the Performance Characteristics of Two-Cycle Engines Fitted with Reed Induction Valves”, SAE paper 790842

G Bickle et al. (ICT Co), R Domesle et al. (Degussa AG): “Controlling Two-Stroke Engine Emissions”, Automotive Engineering International (SAE) Feb 2000:27-32.

BOSCH, “Automotive Manual”, 2005, Section: Fluid’s Mechanics, Table ‘Discharge from High-Pressure Deposits’.

https://www.epa.gov/nonroad/proposal/r01049.pdf

“Suzuki LJ50 INFO”. Lj10.com. Retrieved 2010-11-07.

“Lotus, QUB and Jaguar to Develop Variable Compression Ratio, 2-Stroke OMNIVORE Research Engine”. Green Car Congress. 2008-08-12. Retrieved 2010-11-07.

“Lotus Engineering Omnivore Variable Compression Ratio Engine to Debut in Geneva”. Wot.motortrend.com. Retrieved 2010-11-07.

Korzeniewski, Jeremy (2008-08-12). “Lotus developing efficient two-stroke OMNIVORE engine”. Autoblog. Retrieved 2010-11-07.

Gordon Jennings. Guide to two-stroke port timing. Jan 1973

Irving, P.E. (1967). Two-Stroke Power Units. Newnes. pp. 13–15.

“junkers”. Iet.aau.dk. Retrieved 2009-06-06.

Junkers truck engine 1933.

BHE – Stepped Piston Engine

Ross and Ungar, “On Piston Slap as a Source of Engine Noise,” ASME Paper

Sherman, Don (December 17, 2009), “A Two-Stroke Revival, Without the Blue Haze”, New York Times.

Walshaw, T.D. (1953), Diesel engine design (2nd ed.), London, England: George Newnes Ltd.

Kalpakjian, Serope; Steven Schmid (August 2005). Manufacturing, Engineering & Technology. Prentice Hall. pp. 22–36, 951–988.