Engine Construction and Principles of Operation

Transcription

1 Ch. 4 Engine Construction and Principles of Operation Gasoline Engine A gasoline fueled 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. 1

2 Engine Consists of: ported cylinder, piston, connecting rod, and crankshaft Piston Close fit inside the cylinder, free to slide on walls of cylinder connected to connecting rod 2

3 Simple Engine in Operation When the engine is cranked gasoline is atomized and mixed with air mixture 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 3

4 Simple Engine in Operation As the piston goes down to bottom of stroke, pressure of gases is released through exhaust port. As this is happening, new fresh air fuel 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 4

5 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, one cylinder and twocylinder engines Ethanol In 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 5

6 Gasoline must burn quickly Gasoline will not burn fast in a bucket Something needs to be done to produce an explosion Fuel is atomized The 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 6

7 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 contained To be useful, must be contained and controlled(engineered precisely) It is confined and directed to move the piston up and down 7

8 5 Categories 1. Mechanical 2. Carburetion 3. Ignition 4. Cooling 5. Lubrication Mechanical engine design and construction 8

9 Carburetion mixing of gasoline and air, admitting it to the cylinder Ignition firing the fuel charge 9

10 Cooling heat dissipation Lubrication oiling of moving parts 10

11 Cylinder Block keeps all engine parts in alignment made of cast iron or aluminum alloy Aluminum Cylinder Block Aluminum blocks are casted around steel sleeve Aluminum would wear out Light weight, ability to lose heat rapidly 11

12 Cooling Fins Engineered for efficient air circulation and heat control size, thickness, spacing and direction of the cooling fins is controlled 12

13 Cylinder Block Must be rigid and strong to contain power developed by expanding gases Crankshaft Crankshaft is the major rotating part of the engine 13

14 Crankshaft Forged 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 14

15 Crankcase Must be rigid and strong enough to withstand rotational forces of crankshaft, while keeping all parts in proper alignment Crankcase Oil for lubrication is in crankcase in some engines, used to protect internal parts, gaskets keep out dirt and oil 15

16 Pistons straight line driving member of the engine, subject to direct heat of combustion, and have enough clearance to move through cylinder Piston Provides 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 16

17 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 17

18 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 air fuel get in? Covered and exposed by piston or by using poppet valves 18

19 Poppet Valves Valve that controls the flow of fresh fuel mixture into the cylinder and provides a mean of exahusting the burned gases Valve Spring Must 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 19

20 Valve Lifter Base of lifter rides on the cam and touches the end of the valve stem Camshaft Generally 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 20

21 Flywheel Flywheel improves running quality of an engine...how? Crankshaft slows down, or stops flywheel keeps pace Keeps smooth operation till next stroke 21