3Engine Terminology: Stroke and Displacement amount of vertical travel of the piston from bottom dead center (BDC) to top dead center (TDC)Displacement (D)space displaced by thepiston during a strokeTDCBDCD = (stroke)(p)(Bore)2/4Bore
4Engine Terminology: Compression Ratio Compression ratio (CR):ratio of total volume to the volume of the combustion chamberspark ignition engines have CR = 7-12CR = (C + D)/Cwhere C = volume ofcombustionchamberD = displacement
5Classification of Engines External vs. Internal CombustionSpark Ignition vs. Compression IgnitionCylinder ConfigurationValve Location2 Stroke or 4 Stroke
6Engine Classification: External vs. Internal Combustion External combustioncombustion of an air-fuel mixture transfers heat to a second fluid which becomes the motive (working) fluid that produces powerE.g., steam driven engineInternal combustionthe products of combustion are the motive fluid
7Engine Classification: Spark vs. Compression Ignition Spark ignition (SI) enginesa compressed, homogeneous air-fuel mixture (15:1 ratio of air to fuel by mass) is ignited using a sparkCompression ignition (CI) enginesrapid compression of air to a high pressure raises the temperature so that fuel, when delivered into combustion chamber, spontaneously ignites without need for a sparkoften referred to as a Diesel engine
16CarburetorsPurpose of the carburetor is to produce a mixture of fuel and air on which the engine can operateMust produce economical fuel consumption and smooth engine operation over a wide range of speedsRequires complicated device rather than a simple mixing valve; price is very important!
17Venturi (nozzle)Use force of atmospheric pressure and artificially created low pressure area to mix fuel and airUse a venturi nozzle to lower air pressure in carburetor to create suction to “pull” fuel into airVenturi (nozzle)Bernoulli Principle:P+1/2 V2 = Constant
18Venturi-type Carburetor Air/Fuel Mixture To EngineThrottle PlateAtomized FuelValve StemFuel InletIn 1797, Giovanni Battista Venturi, an Italian hydraulics engineer, observed that that as water flowed through a constriction in a pipe, its velocity increased and its pressure decreasedFloatChoke PlateVenturiBowlConstant level is maintained in bowl -as float moves down,valve stem moves down, allowing more fuel into bowl, float moves up and closes valveFuelNozzleInlet AirMetering OrificeRef. Obert
19Flo-Jet Carburetor Fuel tank is above carburetor Fuel is fed directly to carburetor by gravityWhy the vent?
20Flo-Jet CarburetorAir-fuelmixtureFuel from tankAir flow
21Pulsa-Jet CarburetorIncorporates a diaphragm type fuel pump and a constant level fuel chamber
22Pulsa-Jet Carburetor Operation Intake stroke of piston creates a vacuum in carburetor elbowPulls cap A and pump diaphragm B inward and compresses springVacuum thus created on “cover side” of diaphragm pulls fuel up suction pipe S into intake valve D
23Pulsa-Jet Carburetor Operation When engine intake stroke is complete, spring C pushes plunger A outwardGasoline in pocket above diaphragm to close inlet valve D and open discharge valve EFuel is then pumped into fuel cup F
24Pulsa-Jet Carburetor Operation Venturi in carburetor is connected to intake pipe I which draws gasoline from fuel cup FProcess is repeated on the next stroke, keeping the fuel cup fullSince fuel cup level is constant, engine gets constant air-fuel ratio
25Name as many parts as you can Parts of an IC EngineName as many parts as you canName: ________________CROSS SECTION OF OVERHEAD VALVE FOUR CYCLE SI ENGINE