SMALL ENGINES ENGINE OPERATION FOR A FOUR STROKE ENGINE
SMALL ENGINES • An engine is a device which converts energy into mechanical motion to do work. • Small engines are described as internal combustion engines rated up to 25 horsepower. • A small engine has either a spark ignition or a compression ignition based on how the fuel is ignited. • Small engines are classified as either four-stroke cycle engines or two-stroke cycle engines.
PARTS OF THE ENGINE • CYLINDER BLOCK Engine component which consists of the cylinder bore, cooling fins, and valve train components. Made of cast aluminum alloy that are lightweight and dissipate heat rapidly. • CYLINDER HEAD Engine component made out of cast aluminum alloy fastened to the end of the cylinder block farthest from the crankshaft. • COOLING FINS An integral thin cast strip designed to provide efficient air circulation and dissipation of heat away from the engine cylinder block into the air stream. • HEAD GASKET A filler material placed between the cylinder block and cylinder head to seal the combustion chamber. Made of soft metals and graphite layered together. • SPARK PLUG Component that isolates the electricity and produces the spark for the engine
PARTS OF THE ENGINE • PISTON A cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process. • CONNECTING ROD Engine component that transfers motion from the piston to the crankshaft and functions as a lever arm. • CRANKSHAFT An engine component that converts linear (reciprocating) motion of the piston into rotary motion. • FLYWHEEL A cast iron disk that is mounted at one end of the crankshaft to provide inertia for the engine. • COUNTERWEIGHTS A protruding mass cast into the crankshaft which partially balances the forces of a reciprocating piston.
PARTS OF THE ENGINE PISTON PISTON: A cylindrical engine component that slides back and forth in the cylinder bore by forces produced during the combustion process.
PARTS OF THE ENGINE PISTON PISTON: DIFFERENT PISTON TYPES: FLAT IRREGULAR DISHED DOMED
PARTS OF THE ENGINE PISTON PISTON RINGS: An expandable split ring used to provide a seal between the piston and the cylinder wall Three types: • COMPRESSION RING • WIPER RING • OIL RING 1 2 3
PARTS OF THE ENGINE VALVE TRAIN VALVE HEAD MARGIN VALVE FACE VALVE SEAT VALVE NECK VALVE GUIDE VALVE SPRING VALVE ROTATOR VALVE SPRING RETAINER
FOUR STROKE CYCLE ENGINE • INTAKE STROKE • COMPRESSIONSTROKE • POWER STROKE • EXHAUST STROKE
INTAKE STROKE • Occurs from TDC to BDC • Intake valve opens • Air-Fuel that was previously mixed in the carburetor is now sucked into the combustion chamber due to the low pressure created inside.
COMPRESSION STROKE • Compresses the Air-Fuel mixture • By compressing the Air-Fuel mixture: • Allows for more energy to be released. • Increases fuel vaporization • Allows for more complete burning
POWER STROKE • Spark occurs igniting compressed air-fuel mixture • Spark occurs 20 degrees before TDC so the flame front can spread throughout combustion chamber • Gases ignite pushing piston away from the cylinder head • Linear motion from the piston is transferred into a rotary motion on the crankshaft
EXHAUST STROKE • Exhaust valve opens • Inertia from the flywheel and other parts push the piston back up toward TDC, pushing the spent gases out of the combustion chamber.