6/24/2009

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A pump ain’t so simple! Layout of conventional fuel system

In‐Line Pumps (most common)‐a set of cam driven plungers (one for each cylinder)

• Driven from crank ½ speed• Multi‐lobe cam• This example uses rack, not lever• Rack rotates plunger assy and 

controls flow• Governor and advance coupling 

driven by rotating weights acting against a spring (like mechanical advance on distributor)

l d i h l i• Fuel trapped in the plunger is forced through a check valve into the injection line. The injection nozzle has one or more holes through which the fuel is sprayed to cylinder. 

Plunger Design – Traditional Injection Pump

• Plunger forces fuel through fitting• Rotating Lever controls how much spills back – lever controls fuel flow (no throttle)

• All run by cam driven by crank

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Plungers

• Operation:

Plunger moves up and blocks inlet–Plunger moves up and blocks inlet

–Fuel is allowed to escape through spill port (notice helical grove)

–Reminder of fuel forced out outlet port

–Stroke is constant by delivery varied by rotation

Rotary Pump

• M ch less complicated b t lo er press res• Much less complicated but lower pressures• Few moving parts• Fed by transfer pump• Metering through governor mechanism – rotor slides• Pressurization via sliding pistons

Typical Rotary Pump Fuel Injectors• Nozzle type dictates performance• Single Hole

–Good for ID–1mm hard to clog

• Multi hole–Better misting–Easy clog as size ‐> 0.1mm

• Clogs caused by decomp of leaked fuel• Differential pressures cause opening• Note needle design – pressure OPENS nozzle• Differential pressures 

–f(needle diameter vs. seat diameter)Spring closing–Spring closing

–Harder to open than to keep open• Smaller seat contact area and strong spring 

enhance sealing, eliminate dribble• Dribble leads to emissions and deposits

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Operation of needle

• This is why it’s easier to keep a needle open than to open it initially

• Good idea to provide pressure release mechanism to fast and accurate closing

Pintle Nozzle

• Excellent disbursement, provides conical spray patternconical spray pattern

• Looks Similar to that used in CIS systems

• Opens UPWARD• Excellent clog resistance

More Injector Considerations• Aux hole to bleed excess fuel and prevent deposits• 4V Heads:

–Upside• Vf Up• Central injector position

–Downside• Less swirl• More nozzle holes for good disbursion/combustion, as small as 0.1 mm 

• Nozzles cooled by fuel–Cooling important to maintain tolerances and sealing

• Spray Pattern Critical!–Aspect Ratio of 2‐8Aspect Ratio of 2 8–Larger Aspect Ratio – more penetration–Larger Aspect ratio – Smaller cone–Atomization up –w‐ velocity, but restricts penetration as well

Pilot Injection• Small Amount of fuel early to initiate flame front• Allows for large advance• Eliminates knock and corresponding problems associated with high peak pressures and• Eliminates knock and corresponding problems associated with high peak pressures and 

wave impingement• 2 Spring Special injector needed for 2 mode operation

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Electronic Unit Injection

• Electronic Unit Injection

Solenoid Controlled–Solenoid Controlled–So fast pilot injection can be used–Expensive to produce–Widely used in heavy truck where emissions and economy are critical

–Controlled just like SI EFI

• Variation is HEUI

Moving Components• Valves

– Intake: open to admit air to cylinder (with fuel in Otto cycle)(with fuel in Otto cycle)

– Exhaust: open to allow gases to be rejected

• Camshaft & Cams

– Used to time the addition of intake and exhaust valves

– Operates valves via pushrods & rocker armsarms

Valve trains

OHV (overhead valve)Pushrod configurationMany reciprocating partsHigher valve spring pressure requiredCompact engine size compared to OHC

Valve trains

OHC ( h d )OHC (overhead cam)Fewer reciprocating partsReduced valve spring pressure requiredHigher RPM capabilityCylinder head assemblies are taller

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Valve trains

Cam-in-headNo pushrodsUse rocker arms

Valve Locations

Combustion process: stratified chargeCombustion process: stratified charge

jet guided wall guided inlet air guided

Charge Stratification

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Combustion Chamber Designs Combustion Chamber Design

Combustion Chamber Design Combustion Chamber Design

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Combustion Chamber Design Combustion Chamber Design

Combustion Chamber Design CLASSIFICATION OF INTERNAL COMBUSTION ENGINES

Cooling

1. Direct Air‐cooling

2. Indirect Air‐cooling (Liquid Cooling)

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

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Cooling system operation

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

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

Cooling system operation

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

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

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