Faculty of engineering applied science memorial

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Unformatted text preview: able power output. Faculty of Engineering & Applied Science Memorial University of Newfoundland ENGI 1030 Lawnmower Disassembly/Assembly Exhaust Stroke By the time the piston is forced most of the way down the cylinder, nearly all of the usable energy created from the burning fuel has been used. At this point, the exhaust valve begins to open and as the crankshaft rotation continues, the rising piston forces the spent gases out of the cylinder and into the exhaust system. Just prior to the piston reaching TDC, the exhaust valve closes and shortly thereafter, the intake valve reopens to start the process over. Two Cycle Engine Operation Intake/Compression Stroke A two cycle engine actually accomplishes two things per cycle while running, whereas a 4 cycle completes one task per cycle. This is possible by making use of both the combustion side and the crankcase side of the piston. Following the flow of fuel, we'll start with the engine intake from the carburetor. As the crankshaft rotates, the piston is pushed upwards. This does two things. One, the rising piston generates a vacuum in the sealed crankcase, which pulls a fresh air/fuel charge from the carburetor into the crankcase (thus the reason for having to add lubricating oil to the gas for 2 cycle engines). A small reed valve (a one way valve) allows the mixture to enter the crankcase, but not leave by the same path. At the same time, the rising piston is also compressing the previous charge in the combustion chamber. As the piston nears the top of the stroke, the ignition system ignites the charge in the combustion chamber. Power/Exhaust Stroke Once the air/fuel charge is ignited, the pressures generated by the burning mixture force the piston down, again accomplishing two things. The downward motion of the piston turns the crankshaft, providing power output. In addition, the downward motion is pressurizing the air/fuel mixture previously loaded in the crankcase. As the piston continues its travel down the cylinder bore, it will first expose the exhaust port in one side...
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