engine construction and principles of operation...ch.4.notebook 1 february 04, 2014 ch. 4 engine...
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February 04, 2014
Ch. 4
Engine Construction and Principles of Operation
Gasoline Engine
A gasolinefueled engine is a mechanism designed to transform chemical energy into mechanical energy
It is an internal combustion engine. Combined with air and burned inside the engine.
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EngineConsists of:
ported cylinder, piston, connecting rod, and crankshaft
Piston
Close fit inside the cylinder, free to slide on walls of cylinderconnected to connecting rod
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Simple Engine in Operation
When the engine is cranked gasoline is atomized and mixed with airmixture is forced through intake port and into the cylinder, where it compressed and ignited by electrical spark
Simple Engine in Operation
Burning rapidly, gases expand and apply pressure to the top of the piston and make piston go downward, causing the crankshaft to turn
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Simple Engine in OperationAs the piston goes down to bottom of stroke, pressure of gases is released through exhaust port. As this is happening, new fresh airfuel enters the cyclinder and starts another upstroke of the piston
Gasoline
Hydrocarbon fuel refined from petroleum(dark, thick liquid extracted from earth by oil wells)
Gasoline should; ignite readily, burn cleanly, resist detonation(violent explosion), vaporize easily, without being subject to vapor lock, be free of dirt, water, abrasive
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Gasoline
Assigned to OCTANE number that corresponds to its ability to resist detonation
Premium Gas burns slower than regular gas
Regular grade burns faster and has a lower octane number
Regular gas is used in small, low compression, onecylinder and twocylinder engines
EthanolIn the 1970's, a 10% ethanol blend of gasoline was introduced.
Alcohol can corrode fuel tank linings, shrink carburetor floats and seals, increase carbon deposits
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Gasoline must burn quickly
Gasoline will not burn fast in a bucket
Something needs to be done to produce an explosion
Fuel is atomizedThe more surface area of gasoline exposed to air, the faster the amount will burn
Gas is broken into tiny droplets and mixed with air=atomizing
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Fuel is Atomized
Given a spark and all the atomized particles in the "chamber", the gas will flash into flame almost instantly causing a sudden explosive release of heat energy
Explosion must be containedTo be useful, must be contained and controlled(engineered precisely)
It is confined and directed to move the piston up and down
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5 Categories
1. Mechanical
2. Carburetion
3. Ignition
4. Cooling
5. Lubrication
Mechanical
engine design and construction
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Carburetion
mixing of gasoline and air, admitting it to the cylinder
Ignition
firing the fuel charge
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Cooling
heat dissipation
Lubricationoiling of moving parts
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Cylinder Blockkeeps all engine parts in alignment
made of cast iron or aluminum alloy
Aluminum Cylinder BlockAluminum blocks are casted around steel sleeve
Aluminum would wear out
Light weight, ability to lose heat rapidly
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Cooling Fins
Engineered for efficient air circulation and heat control
size, thickness, spacing and direction of the cooling fins is controlled
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Cylinder Block
Must be rigid and strong to contain power developed by expanding gases
Crankshaft
Crankshaft is the major rotating part of the engine
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CrankshaftForged from cast steel
Counterweights are used to
balance the weight of the connecting rod
Crankshaft
End of crankshaft and flywheel have matched tapers providing good holding power
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Crankcase
Must be rigid and strong enough to withstand rotational forces of crankshaft, while keeping all parts in proper alignment
CrankcaseOil for lubrication is in crankcase in some engines, used to protect internal parts, gaskets keep out dirt and oil
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Pistons
straight line driving member of the engine, subject to direct heat of combustion, and have enough clearance to move through cylinder
PistonProvides seal for combustion chamber and crankcase
Piston Rings fit the grooves with slight side clearance and produce tension on walls, rings prevent blowby of gases and oil leakage into combustion chamber
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Piston
Hollow to reduce weight
Top may be flat, domed, or contoured to reduce weight
Piston Pin or Wrist Pin
Hole in each side of the piston
through which a piston pin or wrist pin is placed
Acts as a hinge between the connecting
rod and piston and holds the two together
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Connecting Piston to Crankshaft
piston connected to crankshaft by connecting rod
Big end connects to crankshaft, small end to Piston pin or wrist pin
Intake and Exhaust Ports
How does airfuel get in?
Covered and exposed by piston or by using poppet valves
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Poppet Valves
Valve that controls the flow of fresh fuel mixture into the cylinder and provides a mean of exahusting the burned gases
Valve SpringMust be used to hold it firmly against the seat. Placed over the valve stem, compressed to provided tension
Spring allows valve to be opened when necessary
For engine to function, valves must be opened at right time and for right amount of time
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Valve Lifter
Base of lifter rides on the cam and touches the end of the valve stem
CamshaftGenerally located in crankcase, directly below valve stems and valve lifters
Driven by crankshaft through gears
Camshaft gear is always twice as large as its crankshaft gear
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Flywheel
Flywheel improves running quality of an engine...how?
Crankshaft slows down, or stops flywheel keeps pace
Keeps smooth operation till next stroke