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Engine OperationChapter 3
Engine Components • Four-Stroke Cycle Engines • Two-Stroke Cycle Engines • Valving Systems • Diesel Engines • Turbo Chargers • Engine
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Chapter 3 — Engine OperationChapter 3 — Engine Operation
The engine block is the main structure of the engine which helps maintain alignment of internal and external engine components.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Engine displacement is determined by the bore and stroke of the engine.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The crankcase breather functions as a check valve to maintain crankcase pressure and to route gases to the carburetor.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Cast aluminum alloy cylinder blocks with cast iron cylinder sleeves combine the light weight of aluminum with the durability of cast iron.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The head gasket is placed between the cylinder block and cylinder head to seal the combustion chamber and to provide even heat distribution.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The crankshaft is the main rotating component of the engine and is commonly made of ductile iron.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The piston acts as the movable end of the combustion chamber and is designed to utilize the forces and heat created during engine operation.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Piston rings commonly used on small engines include the compression ring, wiper ring, and oil ring.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
A connecting rod is designed to withstand sudden impact stresses from combustion and piston movement.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Bearings and bearing surfaces are subjected to radial, axial (thrust), or a combination of radial and axial loads.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Small engines commonly have two main bearings to provide a low-friction bearing surface on each end of the crankshaft.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Rod bearings provide a low-friction pivot point between the connecting rod and the crankshaft and the connecting rod and piston.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The flywheel supplies inertia to dampen acceleration forces caused by combustion intervals in an engine.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The intake event occurs when the air-fuel mixture is introduced into the combustion chamber as the piston moves from TDC to BDC.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The compression event is an engine operation event in which the trapped air-fuel mixture is compressed to form the charge.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The compression ratio of an engine is a comparison of the volume of the combustion chamber with the piston at BDC and TDC.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
During the ignition event, atmospheric oxygen and fuel vapor in the charge are consumed by the progressing flame front.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
During the power event, hot expanding gases force the piston head away from the cylinder head.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
During the exhaust event, piston movement evacuates exhaust gases to the atmosphere.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Valve overlap is the period between the exhaust event and the intake event when the piston nears TDC.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
A two-stroke cycle engine completes five events in one operating cycle.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Two-stroke valves are widely used in the outdoor power equipment industry for hand-held equipment applications such as chain saws, trimmers, and leaf blowers.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Valves seal the combustion chamber to control the flow of air-fuel mixture into the cylinder and exhaust gases out of the cylinder.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Valve location determines whether an engine is an L-head or OHV engine.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Timing marks on the cam gear and crankgear indicate the proper gear teeth mesh required to prevent damage to engine components.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Valving systems on two-stroke cycle engines require fewer parts and are less complicated than four-stroke cycle engine valving systems.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Diesel engines use an injection pump to deliver pressurized fuel to the cylinder at precise intervals.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The injector is hydraulically activated by the pressurized fuel delivered from the injection pump.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Heat in the glow plug is created by resistance to current passed through a heating coil.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Load is increased or decreased by adding or removing water from the impeller housing of a water dynamometer.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The electric dynamometer measures brake horsepower by converting mechanical energy into electrical energy.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The eddy current dynamometer measures engine torque using load from the magnetic field produced by current in eddy current coils.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
The prony brake dynamometer measures engine torque using an adjustable brake that exerts pressure on a spring scale.
Chapter 3 — Engine OperationChapter 3 — Engine Operation
Engine horsepower decreases 3 1/2% for each 1000′ above sea level.
