Lab Updates:
- Buttom End: Assembled the transmission system, cleaned crankshaft and the flywheel, printed the second and last gasket.
- Top End: Painted the triple-tree.
- Frames, Forks, and Wheels: Put the spokes into the rear wheel. They tuned the spokes by hitting the spokes with a wrench and listening to the sound. Also, if the wheel wobbles when it spins, you need to adjust it by loosening the spokes on one side and tightening them on the other.
Reading Discussion:
- Esthetics: What is meant by beautiful?
- Hip vs Square in the 1960’s.
- By keeping terms undefined, you are open to the possibility of versatile and broad definitions. In the book, Phaedrus refuses to define Quality, but still attempts to prove its existence.
- There is an inherent problem in detecting quality, and determining whether it is subjective or objective.
- If Quality Is totally subjective, then art becomes entirely shallow, without any deeper meaning other than an esthetic luxury.
- According to Pirsig, Quality is the event between the subject and the object when they recognize each other.
- However, Quality is also defined by its context (cultural, periodical, etc).
Notes by MGM
Tuesday, April 1
Visitor: Professor Ju
Mechanical & Aerospace Engineer
- Combustion and propulsion.
- Biofuels & synthetic fuels for engine design.
Readings Summary:
Set of calculations about the amount of energy per explosion in an engine.
About emissions in a Toyota.
Air / fuel ratio.
- The industry uses 14.7 ratio of air to fuel. The reason it isn’t exactly 15 is because fuel has many different components.
- For gasoline engine, you want the amount of oxygen and fuel to be stoichiometric. You don’t want any leftover water.
- Rocket engine fuel is rich, while automobile fuel is more lean. Because the temperature is very high, so they inject less fuel so that the total temperature is not as high. If you put too much fuel, the temperature will be too high.
- Nitrogen Oxide (NO) reacts with ozone, so it becomes NO2 + O2, and creates smog.
- 70% of cars in Europe use Diesel. The diesel in the USA is more expensive than gasoline. Diesel is more efficient than gasoline. The emission standard tolerates more emissions in the USA.
PPCI
- In diesel, you compress the air to a very high pressure and temperature and then inject the fuel, expecting the turbulence of the flow to mix both components.
Compression Ratio
What is compression ratio?
- When you have a piston going down, then you compress it, there’s residue volume. So the ratio is the volume being compressed. Also called the pressure ratio in gas turbines. In a gasoline engine, it’s a volume ratio.
PV = nRT
- The higher the pressure, the more capability to do the work, the higher the efficiency for expansion.
Rule of Thumb:
- Engine efficiency = Work / Heat Content (Fuel) or = 1 – [1/r^gamma] (Specific hea)
- You want to be as close to 1 as possible.
Knocking
- A premature combustion. When the piston is still coming up in the compression stroke, the gas explodes and then it wants to push the crankshaft the other way.
- The higher the compression ratio, the more this is a problem.
- Ignition occurs by itself because of high temperature and high pressure, even before the flame. This problem is called pre-ignition and can damage the piston.
Octane number
What does 87 mean?
- It is the percentage of octane vs. heptane. The higher the octane number, this means that there is more difficult to ignite.
- Numbers available: R – 87, P – 90, S – 93
Ethanol
- Ethanol is thrown into the mix to raise the octane number. However, it is no longer used because it was found out of its high pollution consequences. Ten percent of the gasoline produced in the USA is ethanol.
- The main problem with using ethanol is the friction inside the engine, because ethanol dissolves the lubricant.
CH3-CH2-OH
- You extract CH2O from this. This is toxic.
Valve Overlap
- The valve is in the intake manifold. Valve overlap is essentially that, at a certain RPM, you have a pulse, and pulse keeps going, and there’s a vacuum (negative pressure) behind it. Because of this pressure, you get more fuel being sucked into the engine, which increases the efficiency of the engine. This is the main reason valve overlap is used in engine design.
Motocross Race:
- Two-Cycle: There’s no valves, it just goes up and down. The exhaust is open. Usually, it pulls the air into the engine, compresses, and pushes out, and this is all happening at the same time. Used to be normal during the 40’s and slow. As the pulse comes out of the exhaust at a very high speed, there is this cone which expands and then contracts. This pulse pulls all the air and fuel from crankcase into the exhaust pipe and at the same time brings in the new components. Have a buzzing, bee-like sound. They are very power efficient.
- Downside: You get a strict range of RPM. Their emissions are also very bad.
- Yamaha: Made it clean by direct injection. Cost more than $10, so it wasn’t made.
Homework for Thursday: Next two chapters in the Pirsig book. (Chapters 18 & 19)
Lab
- We need to work on the brakes and paint.
- The bottom end needs to start working on putting the engine back together.
- The top end will be deputized to help the frames, forks, and wheels groups.
- Electrical will start working on the harness and make sure the distributor has all the things it needs.
Notes by MGM