internal combustion enggg gpines: gas exchange processes

Internal combustion Engines: Gas exchange processes and in-g G g pcylinder charge motion-fuel injection, Carburetor

Dr. Primal Fernando

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[email protected]: (081) 2393608

Diesel engine (CI)g ( )

• The liquid fuel jet atomizes into drops and entrains air;• The liquid fuel jet atomizes into drops and entrains air; evaporates‐fuel vapor mixes with air‐air temperature and pressure are above the fuel’s ignition point. After a short delay

t i iti t tauto ignition starts.• At full load air fuel ratio is ≈ 20: 1

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Diesel fuel‐injection system consists ofj y

1. Injection pump

2. Delivery pipes

3. Fuel injector nozzles

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THE DIESEL FUEL SYSTEM

• Injection Pump usually mechanical driveB lt d ll t d d h i

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–Belts and rollers not good, use gears and chains• Note spill line from injector, pump, separator

Timing setsTiming sets

Gear setsGear sets• Cam and crank rotate in opposite directions• Noisy if not free of burrs

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• Helical and spur cut gears

Timing setsTiming sets

Timing chainsTiming chains• Single and double roller• Tensioners

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Fuel Injection Systemsj y

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General Characteristics

P t ½ i d • How does timing vary with load?• Pump runs at ½ engine speed–Controls Quantity AND timing of injectionMax fuel limited by smoke

• How does timing vary with load?–Ignition delay is SHORTER (higher density) BUT:–Although ignition delay is shorted, ll d d ll–Max fuel limited by smoke

limit–Timing varies with load and speed

still need more advance to ensure all fuel is burnt during stroke

• At max load fuel variance among cylinders should be less than 3% speed

–Timing accurate to 1o crank angle

yotherwise power limited by smoky exhaust of richest cyl.

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A pump ain’t so simple!p p p

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Valve trainsValve trains

OHV (overhead valve)Pushrod configurationgMany reciprocating partsHigher valve spring pressure required

i i d

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Compact engine size compared to OHC


OHC (overhead cam)Fewer reciprocating partsReduced valve spring pressure requiredHigher RPM capabilit

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Higher RPM capabilityCylinder head assemblies are taller


Cam in headCam-in-headNo pushrodsUse rocker arms

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Use rocker arms

Valve Locations

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Combustion process: stratified chargeCombustion process: stratified charge

jet guided wall guided inlet air guided

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Charge Stratificationg

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Combustion Chamber Designsg

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Combustion Chamber Designg

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CLASSIFICATION OF INTERNAL COMBUSTION ENGINES

CoolingCooling

1. Direct Air‐cooling

2. Indirect Air‐cooling (Liquid Cooling)

3. Low Heat Rejection (Semi‐adiabatic) engine.

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Cooling system operationCooling system operation

Engine heat is transfered . . .• through walls of the combustion chambers• through the walls of cylinders

Coolant flows . . .• to upper radiator hose• through radiator• through radiator• to water pump• through engine water jacketsthrough engine water jackets• through thermostat• back to radiator

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Cooling system operationCooling system operation

Fans increase air flow through radiator• Hydraulic fan clutches• Hydraulic fans consume 6 to 8 HP

El t i f• Electric fans

Coolant (ethylene glycol)Coolant (ethylene glycol)• 50/50 mixture increases boiling point to 227°F• pressurizing system to 15 PSI increases to 265°Fp g y

Coolant (propylene glycol)• Less protection at the same temperatures

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Less protection at the same temperatures• Less toxic

internal combustion enggg gpines: gas exchange processes

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