Mainland High School  
WaterGates: ISTF Project #01-0224
  

 

Overview

  Introduction
ISTF Contest
Components

  One
  Two
  Three
Background
  Engines
  Environmental
  Fuels
  Legal
  MTBE
  PWC
Project
  Assessment
  Bibliography
  Glossary
  Team

 


Engines

There are many engines on the market; for example, Diesel, Wankle, Electric, Gas turbines, and rockets. However, the two most used engines are the two-stroke and the four-stroke. Both of these  internal combustion engines are made up of 4 parts; intake, where the fuel comes in; fuel chamber, where the fuel is held before used; piston, where the fuel is used; and  exhaust, where the fuel leaves. The four-stroke engine is basically the "heavy hitter" of the two, it gives power, it is large, it can give enough energy for big things, such as cars and trucks. The two-stroke engine is light, and can use fuel twice as fast as a four stroke of similar size. The two-stroke is also simpler in design, so it can be produced small enough for many uses, including small model airplanes. However, it's simplicity in design also is what contributes to it's problem of being a big polluter.


image courtesy of How Stuff Works

The four stroke engine gets its name because it has... four strokes. This is two up strokes and two down strokes. In the first down stroke, the carburetor opens the intake valve to let fuel and air into the cylinder. In the first up stroke, the fuel is compressed, because the piston decreases the volume of the cylinder, while the fuel is still inside. At the top of the cylinder is the spark plug. When the piston gets to the top of the first upstroke, the spark plug sends out a charge that ignites the fuel/air mixture, causing it to expand rapidly. This rapid expansion is what causes the second down stroke, otherwise known as the power stroke. The second upstroke (and final stroke of the cycle) is the exhaust stroke. The carburetor opens the exhaust valve, and lets the exhaust go out of the engine. The cycle is then repeated many times.

The two stroke engine is much simpler, having only two strokes. That is one up stroke and one down stroke. In the down stroke (still the power stroke) the fuel is ignited, sending the piston down. While the piston is down, fuel is let in while exhaust is let out, this also accounts for much of the wasted fuel because fuel can run straight through). In the up stroke, the fuel is compressed and ignited by the the spark plug in the same way that the four stroke engine is. the cycle is repeated from there. The only valve in the two stroke engine is a reed valve that opens while the piston is going down, due to higher pressure on the fuel intake side, and closed due to higher pressure in the engine side.  The biggest advantage of the two stroke is its weight.  A two-stroke engine is designed to give maximum energy (horse power) in minimum weight.   The intake of a two stroke engine is nothing more that a one way gate, so if the fuel chamber is empty, fuel comes in, but if the fuel chamber is full, it doesn't come out. The fuel chamber saves weight by doubling as the coolant and the lubricating system, due to the fact that the fuel has oil mixed in it.

There is many differences between the two and four stroke engine, other than the number of strokes. In the four stroke engine, oil can be directly stored in the oil pan, directly under the piston. This allows the engine to be continually oiled while the engine runs. The bad part of this is that the oil pan is heavy, so it isn't used in the two stroke engine, that tries to be as light as possible. The two stroke solves this problem by putting oil directly in the fuel, so it coats the side of the cylinder and works itself throughout the engine. However, the unused oil isn't burnt and is let out through the exhaust. Another difference is that a two stroke can burn fuel twice as fast, leading to increased power for its size. This is due to the fact that the two stroke has a power stroke every two strokes, and the four stroke has a power stroke every four strokes.   Two strokes also have the added advantage of being much easier to start than a four stroke engine, Because a four stroke engine has to go through two cycles for each time it tries to start, while the two stroke tries to start each cycle.

Combustion Stoichiometric Ratio

The lambda is the ratio of air divided to fuel, divided by the stoichiometric ratio.

The stoichiometric ratio is the ideal ratio. If the lambda is high, there is more air than fuel, which leads to inefficiency and NOx. If the lambda is low, there is more fuel than air, which leads to CO and non-combusted fuel going through.

"Gas additives ... MTBE (or ethanol)  are fuel additives that simply add additional oxygen molecules to the mixture, thus increasing heat, and pushing the engine closer to a stoichiometric ratio (14 lbs. of oxygen and 1 pound of gasoline) and burn them together - you have zero emissions. This is the definition of stoichiometric ratio. Unfortunately there are no known materials with the thermal capabilities of handling that heat." (R Haslam)

What follows is a timeline of the types of injection that has been used since 1970. This timeline also shows the difference in where and how the flue is brought into the chamber. Also as seen above as time has worn on the latest technology has been the best in terms of Fuel efficiency and maximum output. 


Images courtesy of Mitsubishi Motors

As can be seen from the above diagram the GDI engine does not only have the highest fuel efficiency but it also has the highest progress toward higher output. This means that the GDI engine will produce more power per square inch of engine capacity.

The major problem that manufactures have had with a cleaner two-stroke engine is that in low RPM situations the engine would basically die because the Volume for the air and fuel was so low that it basically suffocated. Here we see with GDI that at lower RPM's the Volume is up so therefore in our mind a revolutionary engine that has the GDI application in place could work.

Image courtesy of Mitsubishi Motors

The maker of this GDI design is the Mitsubishi Motor Company. This design can be ordered to fit most smaller sized engines ranging from our prototype Two-stroke to a Four-stroke car engine.  The price of an engine like this would more than likly range from about 2,000 and up to more than 7,500 United States dollars.

Smartplugs are a self-contained ignition system. The only time the smart plug needs any electric power is when cold starting. Once the engine heats up it doesn’t need any outside power. The Smart plugs can be retrofitted into any existing spark-ignition and compress-ignition engine. The Smartplug has a pre-chamber containing a catalytic heating element. The ignition starts within the pre-chamber when the new mixture contacts the ignition source during compression. This is due to the reduced activation energy caused by the catalyst. After reaching temperature, in compression, a "multi-point homogeneous ignition" happens. The mixture is released through holes at the bottom of the nozzle. The shape of the nozzle causes the flame to swirl filling the entire combustion chamber. In engines with a varying RPM the Smartplugs is equipped with an electronic circuit to change timing. In order to install Smartplugs in your engine the only things u need to know is how many you need the thread hole size, and compression ratio of the engine. If you have an engine with one RPM you need to know what RPM that is. The Smartplugs can be used with a variety of fuels. The advantages of the Smartplugs is an increase in output power, lower fuel consumption, reduced emissions, and simplified timing controls.



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