fuel injection in the spark ignition engine

7/29/2019 Fuel Injection in the Spark Ignition Engine

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FUEL INJECTION IN

SPARK IGNITION ENGINE


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Merits of Fuel Injection in the SI

Engine

Absence of Venturi No Restriction in

Air Flow/Higher Vol.

Eff./Torque/Power

Hot Spots for Preheating cold air

eliminated/Denser air enters

Manifold Branch Pipes Not concerned

with Mixture Preparation (MPI)

Better Acceleration Response (MPI)

Fuel Atomization Generally Improved


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Merits (Continued)

Use of Greater Valve Overlap

Use of Sensors to Monitor OperatingParameters/Gives Accurate Matching

of Air/fuel Requirements: ImprovesPower, Reduces fuel consumptionand Emissions

Precise in Metering Fuel in Ports Precise Fuel Distribution Between

Cylinders (MPI)


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Merits (Continued)

Fuel Transportation in Manifold not

required (MPI) so no Wall Wetting

Fuel Surge During Fast Cornering or

Heavy Braking Eliminated

Adaptable and Suitable For

Supercharging (SPI and MPI)


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Limitations of Petrol Injection

High Initial Cost/High Replacement Cost

Increased Care and Attention/More

Servicing Problems

Requires Special Servicing Equipment toDiagnose Faults and Failures

Special Knowledge of Mechanical and

Electrical Systems Needed to Diagnoseand Rectify Faults


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(Continued)

Injection Equipment Complicated,

Delicate to Handle and Impossible to

Service by Roadside Service Units

Contain More Mechanical and

Electrical Components Which May Go

Wrong

Increased Hydraulic and Mechanical

Noise Due to Pumping and Metering

of Fuel


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(Continued)

Very Careful Filtration Needed Due toFine Tolerances of Metering andDischarging Components

More Electrical/Mechanical PowerNeeded to Drive Fuel Pump and/orInjection Devices

More Fuel Pumping/Injection Equip-ment and Pipe Plumbing Required-May be Awkwardly Placed and Bulky


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Indirect Injection

Also Called Manifold Injection orSingle Point Injection (SPI) or ThrottleBody Injection (TBI)

Injector Usually Upstream FromThrottle (Air Intake Side) or In SomeCases Placed on the Opposite Side

Pressures are Low

2 to 6 Bar. MaybeInjected Irrespective of Intake Process

Cost Would be Low


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Semi-direct Injection

Also Called Port Injection or IndirectMultipoint Injection (IMPI) or SimplyMulti-point Injection (MPI)

Injectors Positioned in Each InductionManifold Branch Just in Front of InletPort

Injection at Low Pressure (2-6 Bar) Need Not Be Synchronized With

Engine Induction Cycle


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Direct Cylinder Injection

Also Called Direct Multi-pointInjection (DMPI) or Gasoline DirectInjection (GDI)

Injection May be During Intake orCompression Process

Increased Turbulence Required

To Compensate For Shorter PermittedTime For Injection/Atomization/MixingInjection Pressure Must Be Higher


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Major Features With Petrol

Injection

There is Separate Air and Fuel

Metering

Fuel Metering is Precise

Under All Engine OperatingConditions


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Methods of Discharging Fuel Into

Air

1. CONTINUOUS INJECTION

Injector Nozzle and Valve arePermanently Open While Engine is

OperatingAmount of Fuel Discharged as aSpray is Controlled by

a. Varying Metering Orifice, orb. Varying Fuel Discharge Pressure, or

c. Both


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Comparing Pulsed and

Continuous Injection

Assume Engine Operates Between 750(Idling) and 7500 rev/min (Max. Speed)

(1:10 ratio)

In Continuous Fuel Injection:

Fuel Flow has to vary by a Factor of 1:50by Volume using Variable Area Orifice

Injection Pressure has to Vary by aFactor of 1:2500 using Fixed Orifice

Or a Combination of Both Variables


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Types of Injection For MPI

1. Timed Injection

Start of Fuel Delivery For Each CylinderOccurs at the Same Angular Point in

Engine Cycle

Could be 60 or 90Deg. ATDC of Induction Stroke ofEach Cyl.

2. Non-timed InjectionAll Injectors Programmed to Discharge

Fuel at Same Time. Each Piston Willbe on a Different Part of the Cycle


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Operation

Injection System Must SenseChanges to Influencing Parameters

Pass Information to a Coordinating

System (Microprocessor orComputer)

Which In Turn Integrates Individual

Signals and Interprets FuelRequirements

Then Signals Injector to Open andClose


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Controlling Parameters to Sense(Some of the Parameters)

1. Engine Speed

2. Amount of Inlet Air (Engine Load)

3. Throttle Position

4. Air Temperature5. Coolant Temperature

6. Altitude

7. Cranking Speed

8. Exhaust Oxygen Concentration

9. Battery Voltage

fuel injection in the spark ignition engine

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