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