概念汽车实用英语毛矛概念汽车实用英语U8课件教学.pptVIP

PPT研究院 POWERPOINT ACADEMY * * CAR ENGINE The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move. Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an internal combustion engine — combustion takes place internally. Two things to note: * CAR ENGINE 1) There are different kinds of internal combustion engines. Diesel engine is one form and gas turbine engine is another. Each has its own advantages and disadvantages. 2) There is such a thing as an external combustion engine. A steam engine in old-fashioned trains or steam boats is the best example of an external combustion engine. * CAR ENGINE 1. Internal Combustion Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are: * CAR ENGINE 1) Intake stroke; 2) Compression stroke; 3) Combustion stroke; 4) Exhaust stroke. A device called piston is connected to the crankshaft by a connecting rod. Heres what happens as the engine goes through its cycle: * CAR ENGINE (1) The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. * CAR ENGINE (2) Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (3) When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. * CAR ENGINE (4) Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe. Now the engine is ready for th