What%20is%20mechanical%20engineering?

1
What is mechanical engineering?

• Paul D. Ronney
• Professor, Aerospace and Mechanical Engineering
• ronney_at_usc.edu
• http//carambola.usc.edu
• Slides available at
• http//carambola.usc.edu/whatisme

2
Definition of ME

• If it needs engineering but it doesnt involve
  electrons, chemical reactions, arrangement of
  molecules, life forms, isnt a structure
  (building/bridge/dam) and doesnt fly, a
  mechanical engineer will take care of it
• (if it does involve electrons, chemical
  reactions, arrangement of molecules, life forms,
  is a structure or does fly, thats OK too)

3
ME curriculum

• Basic sciences - math, chemistry, physics
• Breadth, distribution
• Tools
• Computer graphics, computer aided design
• Electronics
• Experimental engineering instrumentation
• Mechanical design - nuts, bolts, gears, welds
• Computational methods - convert continuous
  mathematical equations into discrete equations
• F ma ? F m(dV/dt) m(Vnew-Vold)/(tnew-told)
  

4
ME curriculum

• Core engineering science
• Mechanics
• Statics ?F 0
• Dynamics ?F ma
• Strength of materials
• Mechanical stress
• Vibration of beams
• Fluid mechanics - F ma applied to a fluid

5
ME curriculum

• Core engineering science continued
• Thermodynamics
• 1st Law - energy is conserved - you cant win
• 2nd Law - entropy always increases - you cant
  break even
• Heat transfer
• Conduction - q -kA(dT/dx)
• Convection - q hA(Tf - Tw)
• Radiation - q ??FA(T4 - Tw4)
• Control systems

6
ME curriculum

• Laboratory experience virtually every semester
• Synthesis
• Senior seminar
• Senior design project - capstone
• Non-credit enrichment
• Undergraduate research
• Undergraduate student paper competitions in ASME
• SAE Formula racecar

7
Curriculum
Semester
Fall 1 Math 125 Chem 105 Intro Eng Writing
Spring 1 Math 126 Phys 151 Computer Humanities
Fall 2 Math 226 Phys 152 Statics Humanities
Spring 2 Math 245 Phys 153 Dynamics Humanities
Fall 3 Engineering Math AME Lab Fluids / Gas Dynamics Heat Transfer
Spring 3 Computer Analysis AME Lab Thermo-dynamics Advanced Writing
Fall 4 Tech elective Tech elective Controls Humanities
Spring 4 Design Projects Lab Tech elective Humanities
Mathematics 19 units General Education 27 units
Science 16 units Engineering 66-68 units
8
Examples of industries employing MEs

• Automotive
• Combustion
• Engines, transmissions
• Suspensions
• Aerospace (w/ aerospace engineers)
• Control systems
• Heat transfer in turbines
• Fluid mechanics (internal external)
• Biomedical (w/ physicians)
• Biomechanics - prosthesis
• Flow and transport in vivo
• Computers (w/ computer engineers)
• Heat transfer
• Packaging of components systems

9
Examples of industries employing MEs

• Construction (w/ civil engineers)
• Heating, ventilation, air conditioning (HVAC)
• Stress analysis
• Electrical power generation (w/ electrical
  engineers)
• Steam power cycles - heat and work
• Mechanical design of turbines, generators, ...
• Petrochemicals (w/ chemical, petroleum engineers)
• Oil drilling - stress, fluid flow, structures
• Design of refineries - piping, pressure vessels
• Robotics (w/ electrical engineers)
• Mechanical design of actuators, sensors
• Stress analysis

10
Personal experience 1 - automotive engineering

• Why internal combustion engines? - alternatives
  their limitations
• External combustion - steam engine
• Heat transfer is too slow ( 100x slower than
  combustion)
• 10 B-747 engines large coal-fueled electric
  power plant
• Electric vehicles
• Batteries are heavy 1000 lbs/gallon of gasoline
  equiv.
• Fuel cells better, but still nowhere near
  gasoline
• "Zero emissions" myth - exports pollution
• Solar
• Need 30 ft x 30 ft collector for 15 hp
• (Arizona, high noon, mid-summer)
• Nuclear
• Who are we kidding ???
• Moral - hard to beat gasoline-fueled
  premixed-charge IC engine for
• Power/weight power/volume of engine
• Energy/weight energy/volume of liquid
  hydrocarbon fuel

11
Things you need to understand before you invent
the clean 100 mpg 1000 hp engine, revolutionize
the automotive industry and shop for your
retirement home on the French Riviera

• Room for improvement - factor of 2x in efficiency
• Ideal Otto cycle engine with compression ratio
  8 52
• Real engine 30 maximum
• Differences because of
• Heat losses
• Friction losses
• Throttling losses

12
Things you need to understand

• Room for improvement - 8 in pollutants
• Pollutants are a non-equilibrium effect
• Burn Fuel O2 N2 ? H2O CO2 CO UHC NO
• Expand CO UHC NO frozen at high levels
• With slow adiabatic (no heat loss) expansion
• CO UHC NO ? H2O CO2 N2
• ...but we cant slow down the expansion or make
  it adiabatic
• Room for improvement - very little in power
• IC engines are air processors
• Fuel takes up little space - air flow power
• Limitation on air flow due to
• Friction
• Mechanical strength - limitation on rotation rate
• Slow burn
• Choked flow past intake valves

13
Throttleless engines

• Premixed-charge IC engines frequently operated at
  lower than maximum torque output (throttled
  conditions)
• Throttling adjusts torque output of engines by
  reducing intake density through decrease in
  pressure ( P rRT)
• Throttling losses substantial at part load

14
The TPCE concept

• Throttleless Premixed-charge Engine (TPCE)
• U. S. Patent No. 5,184,592
• Use intake temperature increment via exhaust heat
  transfer to reduce r
• Increasing Tintake leads to leaner lean misfire
  limit - use air/fuel ratio AND Tintake to control
  torque
• Provides Diesel-like economy with gasoline-like
  power
• Retrofit to existing engines possible by changing
  only intake, exhaust, control systems

15
TPCE operating limitations
16
Test apparatus

• Production 4-cylinder engines

17
USC engine lab
18
Results

• Substantially improved fuel economy (up to 16 )
  compared to throttled engine at same power RPM
• Emissions
• Untreated NOx performance
• lt 0.8 grams per kW-hr
• gt 10 x lower than throttled engine )
• lt 0.2 grams per mile for 15 hp road load _at_ 55
  mi/hr
• CO and UHC comparable to throttled engine
• May need only inexpensive 2-way oxidizing
  catalyst for CO UHC in TPCE engines

19
TPCE performance
20
Pulsed corona discharge ignition

• Collaboration with Prof. Martin Gundersen, USC
  EE-EP
• Multi-point ignition of flames has potential to
  increase burning rates (thus performance) of IC
  engines
• Lasers, multi-point sparks may not be practical
• Energy efficiency
• Multiple intrusive electrodes
• How to obtain multi-point, energy efficient
  ignition?

21
Transient plasma (pulsed corona) discharges

• Initial phase of spark discharge (lt 100
  nanoseconds) - highly conductive (arc) channel
  not yet formed (like what happens on a much
  longer time scale before a lightning bolt forms)
• Characteristics
• Multiple streamers of electrons
• High energy (10s of eV) electrons
• Enabling technology USC-built discharge
  generators having high wall-plug efficiency
  (gt50) - far greater than laser sources

22
Images of corona discharge flame

• Axial (left) and radial (right) views of
  discharge
• Axial view of discharge flame
• (6.5 CH4-air, 33 ms between images)

23
Pulsed corona discharges in IC engine-like
geometry

• Top view Side view

24
Flame ignition by pulsed corona discharges

• Rise time 2x faster with corona, with far lower
  energy input
• Have ignited with corona only (no arc) up to 10
  atm

Discharge type Delay time (ms) Rise time (ms)
Corona 20 10
Corona arc 9 19
Spark 13.2 19
25
Personal experience - micropower generation

• Hydrocarbon fuels have numerous advantages over
  batteries
• 100 X higher energy density
• Much higher power / weight power / volume of
  engine
• Inexpensive
• Nearly infinite shelf life
• Environmentally superior to disposable batteries
• 31 billion/yr of disposable batteries ends up in
  landfills
• 6 billion/yr market for rechargables

26
The challenge of microcombustion

• but converting fuel energy to electricity with
  a small device has not yet proved practical
  despite numerous applications
• Foot soldiers
• Portable electronics - laptop computers, cell
  phones...
• Micro air and space vehicles (enabling
  technology)
• Most approaches use scaled-down macroscopic
  combustion engines, but may have problems with
• Heat losses - flame quenching, unburned fuel CO
  emissions
• Friction losses
• Sealing, tolerances, manufacturing, assembly

27
Micro-scale combustion power generation

• Three projects
• Thermoelectric power generation
• Single-chamber solid-oxide fuel cell
• Microscale jet or rocket engine
• Common themes
• No moving parts
• Use common fuels in air
• Spiral counterflow heat exchanger for thermal
  management
• Thermal transpiration for pumping of fuel and air
• Non-traditional fabrication
• Collaborations with faculty industry in
  micro-fabrication, materials science,

28
Smallest existing combustion engine

• Cox Tee Dee .010
• Application model airplanesWeight 0.49
  oz.Bore 0.237 6.02 mmStroke
  0.226 5.74 mmDisplacement 0.00997 cu in
• (0.163 cm3)
• RPM 30,000
• Power 5 watts
• Poor performance
• Low efficiency (4-5)
• Emissions noise unacceptable for indoor
  applications

29
Some power MEMS concepts - gas turbine (MIT)

• Friction heat losses
• Made from silicon - very high thermal
  conductivity - heat transfer along casing
  rotor, from turbine to compressor
• Very high rotational speed ( 2 million RPM)
  needed for compression (speed of sound doesnt
  scale!)
• Manufacturing tolerances

30
Worlds smallest operational gas turbine - Ewald
Schuster, USC-AME

• Mass Flow..... .049KG/s
• RPM .. 220k
• Weight..... 6.5 ounces
• Thrust...4 Pounds
• Fuel consumption...2.6 oz /min
• Fuel .Jet-A
• Pressure ratio ... 21

31
Testing and first flight of 2.25 Turbine
32
Direct methanol fuel cell
Methanol is easily stored compared to H2, but has
6x lower energy/mass and requires a lot more
equipment! (CMU concept shown)
33
Thermal management

• Swiss roll heat recirculating burner -
• minimizes heat losses
• Toroidal 3D geometry
• further reduces losses -
• minimizes external temperature
• on all surfaces

2D Swiss roll combustor (Weinberg, 1970s)
1D counterflow heat exchanger and combustor

34
Approach for thermal-fluid design

• Key issue SCALING - if it works at the
  macroscale, will it work at the microscale?
• Test macroscale versions of mesoscale combustor
• Use experiments to calibrate/verify computer
  simulations at various Reynolds number (Re)
• Demonstrate
• Scale down process (macro ? meso)
• Ability to model (macro, meso) over a range of Re
• Use computer models to optimize mesoscale device
  (difficult to use diagnostics at small scales)

35
Macroscale experiments

• Initial 2-D inconel designs - high thermal
  conductivity (poor performance at small scales)
  thermal expansion (warpage)
• Titanium - 2x lower conductivity expansion than
  inconel
• Implementation of experiments
• PC control and data acquisition using LabView
• Mass flow controllers for fuel air
• Thermocouples (7)

36
Mesoscale experiments

• Wire-EDM fabrication
• Pt igniter wire / catalyst

37
Numerical model - Swiss roll

• FLUENT, 2D, 32,000 cells
• Conduction (solid gas), convection (gas),
  radiation (solid-solid only)
• Chemical reaction

inlet
outlet
38
Reaction zone structure

• Reaction zone centered at low fuel because
  maximum heat recirculation needed for high enough
  T for flame survival
• Higher fuel, less recirculation needed - flame
  moves away from center
• High fuel
• Low fuel

39
Power generation - thermoelectrics

• Same principal as thermocouple, material
  optimized for power generation
• Imbed in wall between hot (outgoing product) and
  cold (incoming reactant) streams
• US Patent No. 6,613,972 (9/2/2003)

Typical thermoelectric configuration -
alternating n- and p-type elements
Overall configuration - Wall itself is electrical
conductor
40
Thermoelectrics

• Widely used in deep space missions, some
  commercial applications
• TE efficiency typically 15 of Carnot with same DT

41
Thermoelectric microgenerator problem

• TE wall material thermal conductivity k 1
  W/mC
• Gas k 0.025 - 0.1 W/mC
• ? Thermal resistance between gas TE wall gtgt
  resistance across TE
• ? Most ?T between gas TE wall, not across TE
• ? No power generation!
• Macroscale devices - strong turbulence,
  convective heat transfer, low thermal resistance,
  but microscale Reynolds too low!
• Need dirty tricks for microscale devices!

42
Dirty tricks

• Integrated TE wall T-fin design greatly reduces
  Rgs/RTE - without massive pressure drops due to
  aggressive fins in flow channel
• Metal fins (blue) have high thermal conductivity
  - act as thermal short-circuit
• Air acts as thermal open-circuit
• Elongating base of T-fin and TE walls reduces
  Rgs/RTE
• US Patent No. 6,613,972 (9/2/2003)

43
Power generation - SOFC in a Swiss roll

• PI Sossina Haile, CalTech
• Solid Oxide Fuel Cells (SOFCs) use hydrocarbon
  fuels directly, but need high T
• Swiss roll for thermal management
• Patent pending

44
Single Chamber Fuel Cell in Swiss roll

• Maximum power density 375 mW/cm2 at T 540C
  demonstrated with hydrocarbon fuel, unlike PEM
  fuel cells that use hydrogen or (maybe) methanol

 
Cell voltage (V)
Cell power (mW/cm2)
45
Anode supported cell in Swiss roll
 
46
Fabrication of microscale parts

• EFAB (Electrochemical Fabrication)
• Micromachining process developed at USC
• Commercialization by Microfabrica Inc., Burbank,
  CA
• Analogous to macroscale rapid prototyping,
  solid freeform fabrication
• Produces arbitrary 3-D structures by stacking
  layers
• JPL (Pasadena, CA) process for electrochemical
  deposition of TE elements
• Can electrodeposit materials with structural,
  sacrificial, catalytic, thermoelectric, magnetic,
  etc. properties
• Enables device fabrication using a single
  monolithic process
• No clean room required for device fabrication

47
Instant Masking

• Pre-fabricated masks serve as reusable printing
  plates
• Polymer mask patterned on anode using
  conventional photolithography

48
EFAB process flow
Selectively deposited material (usually
sacrificial)
Blanket deposited 2nd material (usually
structural)

Blanket deposit 2nd material
Selectively deposit 1st material Using Instant
Masking
Planarize layer
Repeat for all layers
Etch sacrificial material
49
EFAB highlights

• Minimum isolated feature 20 x 20 µm, maximum
  feature size 5000 µm

12-layer chain, 290 ?m wide (worlds narrowest?)
Nickel micro-combustor 38 layers, 300 µm tall
2nd generation folded micro-combustor
50
Application of ME concepts to bacteria

• Collaboration with Prof. Steven Finkel, USC
  Molecular Biology
• Propagating fronts are ubiquitous in nature -
  flames, solid rocket propellants, some acid/base
  polymerization reactions
• Flames Fuel Oxidant Heat ? More heat
• Two essential ingredients
• Reactive medium (e.g. fuel-air mixture)
• Autocatalyst - product of reaction that also
  accelerates the reaction (e.g. thermal energy)
• Self-propagation occurs when the autocatalyst
  diffuses into the reactive medium, initiating
  reaction and creating more autocatalyst, e.g. A
  nB ? (n1)B

51
Bacterial fronts

• What about bacteria? Nutrient bugs ? more
  bugs?
• Many bacteria (e.g. E. coli) are motile - swim to
  find favorable environments - diffusion-like
  process - and multiply (react with nutrients)
• Two modes run (swim in straight line) tumble
  (change direction) - like random walk
• Longer run times if favorable nutrient gradient
• Suggests possiblity of flames

52
Motile bacteria

• Bacteria swim by spinning flagella - drag on rod
  is about twice as large in crossflow compared to
  axial flow (G. I. Taylor showed this enables
  propulsion even though Re 10-4) (If you had
  flagella, you could swim in quicksand or
  molasses)
• Flagella rotate as a group to propel, spread out
  and rotate individually to tumble

http//www.rowland.org/bacteria/movies.html
53
Propagation rates of motile bacteria fronts

• As agar concentration increases, motility of
  bacteria and thus the propagation speed (s)
  decreases substantially

54
Quenching limit of bacteria fronts

• Quenching limit min. or max. value of some
  parameter (e.g. reactant concentration or channel
  width) for which steady front can exist
• Quenching channels made using filter paper
  infused with antibiotic - bacteria killed near
  the wall, mimics heat loss to a cold wall in
  flames
• Bacteria can propagate through a wide channel but
  not the narrow channel, indicating a quenching
  limit
• Quenching described in terms of a minimum Peclet
  Number
• Pe sw/D (w channel width)
• For the test case shown s 1.75 x 10-4 cm/s, D
  3.7 x 10-5 cm2/s, w at quenching limit 2.1 cm ?
  Pe 9.8 - similar to flames and polymer fronts

55
Quenching limit of bacteria fronts
6 mm wide channel 35 mm wide channel E. coli,
0.1 agar, 100 µl of kanamycin per side, 6.5
hours after inoculation
56
Comparison of fronts in Mot and Mot- bacteria

• Switching from Mot to Mot- bacteria decreases
  the bacteria diffusivity (Dautocatalyst) by
  1700x but nutrient diffusivity (Dreactant) is
  unchanged - decreases propagation speed and the
  effective Lewis number
• Mot- fronts cellular but Mot fronts smooth -
  consistent with Lewis number analogy of flames

Mot 5 hr 30 min after inoculation Mot- 50
hr after inoculation 0.1 (left) or 0.05
(right) Agar dyed with a 5 Xylene Cyanol
solution (Petri dish 9 cm diameter)
57
Biofilms

• Until recently, most studies of bacteria
  conducted in planktonic (free swimming) state,
  but most bacteria in nature occur in biofilms
  attached to surfaces, e.g. on teeth, clogging in
  water and oil pipelines, infections in catheters
• Recently many studies of biofilms have been
  conducted, but the effects of flow of the
  nutrient media have not been systematically
  assessed

58
Biofilm experiments - laminar flow in tubes
59
Biofilms - images
Experiments show an effect of flow velocity or
shear rate on growth rate and upstream spread
60
Summary - ME

• Perhaps broadest engineering discipline
• Everybody needs MEs
• Core material permeates all engineering systems
  (fluid mechanics, solid mechanics, heat transfer,
  control systems, ...)