Engine Dissection - University of Washington

Engine Dissection - University of Washington

Engine Project Your team is going to dissect and assemble a 3.5 HP single cylinder, 4 cycle engine, made by Briggs and Stratton in Milwaukee, Wisconsin These engines are typically used in lawn mowers, snow blowers, go-carts, etc (ref. 2, Used by permission of Briggs and Statton, 1992, all rights reserved) Engine Project

Start engine. Disassemble engine. (Follow the instruction exactly!) Review parts and functions Ask questions! Answer questions about engines. (group assignment) Reassemble engine. Re-start engine. Write individual report on how engines work. (individual assignment) What is an engine? - a machine which converts chemical energy into mechanical energy Types of engines: *External combustion engine. -Ex: steam engine Figure source:http://www.tpub.com/machines/12.htm

*Internal combustion engine. -Ex: car engine Internal combustion engines Reciprocating engine - 4 stroke engine - 2 stroke engine Rotary engine - Wankel engine - Turbine engine Reaction engine

- Rocket engine The very basic of an engine The ideal gas law: PV = nRT P: pressure; V: volume; n: mole number; T; temperature - Gas will expand upon the application of heat. - The application of heat upon the gas will increase its pressure (if gas is confined in a volume). - The compression of the gas will increase its temperature We try to create heat (through burning) to the gas, so the gas can push the piston, thereby cranking the engine, and output the movement to useful work. 4 stroke Cycle 1

Intake Valve Intake Manifold Cylinder 2 Exhaust Valve Exhaust Manifold 3 4 Spark Plug Piston

Connecting Rod Intake Stroke Intake valve opens, admitting fuel and air. Exhaust valve closed for most of stroke Crank Crankcase Compression Stroke Both valves closed, Fuel/air mixture is compressed by rising piston. Spark ignites mixture near end of stroke.

Power Stroke Exhaust Stroke Fuel-air mixture burns, Exhaust valve open, increasing temperature exhaust products are and pressure, expansion displaced from cylinder. of combustion gases Intake valve opens drives piston down. Both near end of stroke. valves closed - exhaust valve opens near end of stroke 1. Intake 2. Compression

3. Power 4. Exhaust Animation Questions : 1. How do we have the mixture of fuel and air into the cylinder? 2. How do we initiate the combustion? 3. Anything else important related to the combustion? 4. How do we out put the work into useful energy? 5. Anything else to notice? How do we get the mixture of fuel

and air? Venturi-type Carburetor The carburetor of our engine Choke Venturi Higher Pressure Outside Engine Fuel Bernoulli Effect: P+1/2 V2 = Constant Throttle

Venturi-type Carburetor in the car Air/Fuel Mixture To Engine Bernoulli Effect: P+1/2 V2 = Constant Throttle Plate Atomized Fuel Valve Stem Fuel Inlet Float Venturi Choke Plate Bowl

Constant level is maintained in bowl -as float moves down, valve stem moves down, allowing more fuel into bowl, float moves up and closes valve Fuel Nozzle Inlet Air Metering Orifice Ref. Obert How do we initiate the combustion?

Image resource: http://www.nhsnowmobilemuseum.com/ burdicksledshed/1974%20Alouette%20Super%20Brute %20440.htm But how do we get the spark plug spark? Megneto system ( which our engine uses) Mechanical ignition Electronic ignition Engine management system . Anything else important related to the combustion? Think about following situations:

-What will happen if the intake or exhaust valve are not closed during the compression stroke (just before the power stroke)? -What will happen if the intake or exhaust valve open during the power stroke? These situations are not desirable. Need solutions to avoid these. Solution? Right timing of the valves. The valve mechanism. rocker Valve Mechanisms: How you get the right timing valve push rod

Image from : Automotive mechanics, 8 ed. By William H. Crouse th piston valve lifter camshaft cam crankshaft Timing marks So now you think you can prevent all the leaking from the cylinder? Piston

Image from: www.rbracing-rsr.com/ 113orca.htm darryl.hudson.home.mindspring.com/ ww.eng.iastate.edu/explorer/topics/car/engine.htm How do we output the work into useful energy? Reciprocating to rotary motion Crankshaft Image from : toyotaperformance.com/crankshaft_kits.htm Anything else to notice? Piston, crankshaft, & fly wheel Image from: http://www.eng.iastate.edu/explorer/topics/car/engine.htm

Output torque time Have a better idea how engines work? How does the engine complete these Primary Functions? Hint

Get started? Suck in fuel/air? Mix air and fuel? Ignite the mixture (at the right time)? Make the combusting gases do work? Make the work available to somebody? Exhaust the gases? Shut off? Think about the parts and processes involved for each. Have a better idea how engines work? How does the engine complete these Secondary Functions?

Hint Stay lubricated? Operate the valves at the right time? Smooth out the power pulses? Store the fuel? Keep cool? Make it easy to start? Think about the parts and processes involved for each.

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