发动机英文.ppt

Internal Combustion Engines *Introduction *Fuels *Four Stroke Engine *Parts of a four stroke engine About this Lesson This lesson contains hypertext links to . If you are connected to the internet, click on the link icon and scroll to the animation at the sight. Introduction Fuels Why are nearly all vehicles and engines powered by gasoline? extremely high energy density cheap (relative to other sources) easy and safe to move around Fuels Why not use other fuels? Size of engines needed to utilize these fuels is impractical for automobiles lawnmowers etc. Convenience it takes 15 seconds to pump a gallon of gas vs. several hours to recharge batteries (i.e. electric cars) Fuels What are other types of fuels that can be used? Wood- steam engines Coal- steam engines Oil Electricity Internal Combustion Where do we get internal combustion? The idea here is to take a fuel (gasoline for example) and burn it in an engine to create movement of cars and other gas powered machines. This is where we get internal combustion engines. Internal Combustion A cannon uses the basic principles of internal combustion engines. If you take a small amount of high energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. The four-stroke cycle Almost all engines use a four-stroke combustion cycle to convert gasoline into motion. This is also known as the Otto cycle in honor of Nikolaus Otto who invented it in 1867. This process takes the basic example of a cannon several steps further. The four-stroke cycle The four stroke combustion cycle consists of: 1. Intake 2. Compression 3. Combustion 4. Exhaust The four-stroke cycle The piston starts at the top, the intake valve opens and the piston moves down to let the engine take in a full cylinder of air and gasoline during the intake stroke The piston then moves up to compress the air/gasoline mixture. This makes the explosion more powerful. The