12-06-2013, 04:46 PM
FUEL INJECTION IN SPARK IGNITION ENGINE
FUEL INJECTION.ppt (Size: 760.5 KB / Downloads: 58)
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
Use of Greater Valve Overlap
Use of Sensors to Monitor Operating Parameters/Gives Accurate Matching of Air/fuel Requirements: Improves Power, Reduces fuel consumption and Emissions
Precise in Metering Fuel in Ports
Precise Fuel Distribution Between Cylinders (MPI)
Limitations of Petrol Injection
High Initial Cost/High Replacement Cost
Increased Care and Attention/More Servicing Problems
Requires Special Servicing Equipment to Diagnose Faults and Failures
Special Knowledge of Mechanical and Electrical Systems Needed to Diagnose and Rectify Faults
Indirect Injection
Also Called Manifold Injection or Single Point Injection (SPI) or Throttle Body Injection (TBI)
Injector Usually Upstream From Throttle (Air Intake Side) or In Some Cases Placed on the Opposite Side
Pressures are Low – 2 to 6 Bar. Maybe Injected Irrespective of Intake Process
Cost Would be Low
Semi-direct Injection
Also Called Port Injection or Indirect Multipoint Injection (IMPI) or Simply Multi-point Injection (MPI)
Injectors Positioned in Each Induction Manifold Branch Just in Front of Inlet Port
Injection at Low Pressure (2-6 Bar)
Need Not Be Synchronized With Engine Induction Cycle
Operation
Injection System Must Sense Changes to Influencing Parameters
Pass Information to a Coordinating System (Microprocessor or Computer)
Which In Turn Integrates Individual Signals and Interprets Fuel Requirements
Then Signals Injector to Open and Close