22 February 2018

Notes by Noelle Goudy

Assignment for Tuesday: Think of questions for Professor Martinelli

Assignment for Thursday: Introduction and chapter 1 of Shop Class as Soulcraft

 

Announcements:

• Get stuff to be powder-coated or chromed together
  • We might be missing frame parts
  • Make sure we have anything that will be painted ready to be powder-coated
  • Example: battery box
• Next Tuesday: Professor Martinelli
  • Come up with a set of questions for him
  • Week four scribe: take notes next week
    

Housekeeping:

• Ricky: Found a taillight at the bunker and got that working; checked the spark plug on the red motorcycle
• Noelle: With Alex, assembled carburetor; flooded the carburetor and it leaked; lathed out the top plate because it was warped; reattached it and it no longer leaked
• Eric: Determined which front and back hub to use; began plugging it up for powder coating
• David: With Alex, found that half of a split-ring washer is missing (but there was one at the bunker)
• Connor: With Grace, cleaned the engine plates and put them back together; going to sandblast it today
• Charlie: Tried to disassemble the headlight; put it in a new chromed case
• Brendan: Cleaned the light; organized parts for powder coating
• Alex: Worked with Charlie
• Grace: Worked with Connor
• Jordan: With Emily, put together the jacks for the wheels
• Julianne: With Charlie and Ricky, went to the bunker; finished cleaning top end parts
• Sarah: With Ricky, attached the light and tested it; watch the dem for the spark plug
• Jake: Searched on ebay
• Hannah was out
  

Tiger Cub Engine Calculations Reading:

• Octane is C8H18
• Air is 20% O2
• Nitrogen goes in and out of engine
  • While it is a spectator, it still starts to react to form NOx
  • A problem with engines
• Sulfur present – emissions
• Carbon dioxide and water vapor are also products
• Energy release is 44,400 J per gram octane
• Air to fuel ratio is about 15:1 by weight
  • 14.7:1 grams in industry
• What limits the amount of power output is the amount of oxygen
  • Could make the engine larger
  • Compress the air
    • Super/turbocharging
  • Use pure oxygen or
    • Nitrous oxide
    • Nitromethane
• ⅕ liter -> .257 g of air and  .0171 g fuel yields 759 J
• 37,950 Watts out of the engine (100% efficiency)
• 50.9 horsepower (if the engine was fully efficient)
• Engine has about 20% efficiency in actuality
  

Demo:

• Two cylinders (pipettes) with a platinum wire
  • They are bubbling with the top open
• When the top is closed, the bubbles cannot escape
  • The gas inside the left cylinder is going down more quickly than the right
    • This cylinder holds the hydrogen (H2O -> two moles hydrogen for only one mole oxygen)
• When the hydrogen got to the bottom, a spark was lit and the ping pong ball moved upwards about a foot and a half
  • The product is water
  • The pressure increases because of heat (PV=nRT)
    • Thus, the ball is launched
• On the second launch, the ball went up about three feet
• On the third launch, the ball went up about two and a half feet
  

Brake dynamometer:

• A device that allows you to figure out the torque and power of a motor
• A rope is wrapped around the shaft of the motor (called a rope brake)
  • This motor is an electric motor
• The ropes are pulled tighter and the differences of the tensions in the ropes will allow you to find the torque as a function of speed for this motor at a certain voltage
  • The speed of the motor will also be recorded
• As the rope is pulled tighter, the engine slows down
• For an electric motor, torque vs speed is linear
  • The torque is greatest at stall
• Power = Force (Torque) * Velocity
• To get a power vs speed graph, multiply the two axes together and graph with respect to speed
  • The graph is a parabola (opening downwards)
  • The greatest power to the motor will be at the center of the parabola, which is half of the possible velocity
• Homan force vs velocity is called the Hill Curve
  • Concave and with a downward slope
• The power vs velocity graph for a human on a bike also has a peak, where it will be easiest to get up a hill
• Efficiency of an electric motor would be the power curve divided by the force (torque) curve
  • Graphed with respect to velocity, it is a straight line with a positive slope
  • The most efficient is using the least amount of energy
    

Questions for Professor Martinelli:

• Where does air flow play a role in our motorcycle?
  • Carberation
  • Cooling
  • Windage in the engine
  • Exhaust
• Aerodynamic drag
  • Streamlining shapes
  • On the wheels
• Fluid in the engine
  • Lubrication

27 February 2018

Notes by Eric: Professor Littman was not here today.  In his absence, we were joined by a guest: Professor Luigi Martinelli

•       Broad overview of the role of fluid mechanics, and more generally whatever happens when you try to move against air or water
•       Whenever you are doing mundane tasks, you are dealing with fluid flows.  Either they are opposing your motion or helping you.

o    Two regimes—organized (laminar) and chaotic (turbulent)

•       Chaotic flow will offer more resistance to the motorcycle
•       Cost of turbulent flow vs. closing the wake is a tradeoff constantly considered.
•       Distance between back of ride and wake seeks to be minimized.
•       Some helmets are designed to minimize the gap between the rider and the air flow
•       Often propulsion requires a working fluid

o    The flow rate—the amount of fluid that can go in or out—is determined by the shape of the valve.

o    The sizing of the fin is determined by the property of the flow of the engine head; therefore, the extent of the fin design of an air cool engine

•       Sometimes the two combine

o    In a sail boat, the systems are integrated—balance, steering, and other properties of the sail

o    Other, seemingly more complex systems, such as a rocket, are actually simpler.

•       Two vs. four stroke.  Two-stroke—as you draw in fresh mixture, you exhaust from the previous combustion; the two-stroke exhaust may let out unburned fuel.  If you solve the environmental problem, you would have a lighter engine because you do not need a valve. In a four-stroke engine, one stroke pulls in and compresses fuel then ignites it (power stroke), then the next stroke pushes out the exhaust.

o    The Tiger Cub has two valves to have a desirable mass flow rate.  The cam controls how quickly the valves open and close

•       Engine cooling—require heat exchange between the engine and the outside air
•       Overview of aerodynamic forces on ground vehicles

CARBURATION

•       Venturi effect: for an incompressible flow, a reduction of area causes an increase in local flow velocity and a consequent decrease in pressure.

o    Always have high velocity, low pressure

•       The carburetor then fulfills 3 primary functions:

o    Control engine power by adjusting the air intake flow

o    Meter the fuel flow in the air flow aspirated maintaining the ratio air/fuel to optimal values throughout the engine operating range

o    Homogenize the mixture of air and fuel to enable the subsequent combustion

•       It is possible to obtain optimal thickness, spacing of the fins by mathematical computations
•       There are two approaches to improving design: evolutionary and computational

External aerodynamics

•       Even with seemingly benign topics, it is hard to optimize,
•       Hybrid between electric bike and moped is most efficient
•       The speed at which the oil moves around is quite low; our motorcycle has a dry sump reduces the complexity of the system; if we had a
•       Land speed records