Fuel Induction Systems for SI Engines

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Fuel Induction Systems for SI Engines

• P M V Subbarao
• Professor
• Mechanical Engineering Department

The Pace of Net Heat Addition Influence the Area
of the Engine Cycle ..
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Induction of Fuel in SI Engine

• The task of the engine induction and fuel systems
  is to prepare from ambient air and fuel in the
  tank an air-fuel mixture that satisfies the
  requirement of the engine.
• This preparation is to be carried out over entire
  engine operating regime.
• In principle, the optimum air-fuel ratio for an
  engine is that which give the required power
  output with the lowest fuel consumption.
• It should also ensure smooth and reliable
  operation.
• The fuel Induction systems for SI engine are
  classified as
• Carburetors.
• Throttle body Fuel Injection Systems.
• Multi Point Fuel Injection Systems.

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The Carburetor A Natural Fuel Induction System
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Isentropic Flow Through A Venturi
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Real Flow Through A Venturi
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Practical Carburetor Venturi
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Real Air Flow Through Venturi
Where
Fuel Flow Through Orifice
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Carburetor Performance
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Carburetor Performance
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Carburetor Performance
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Control of Equivalence Ratio using Carburetor
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Modern Carburetor
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Artificial Induction of Fuel

• The fuel-injection systems for conventional
  spark-ignition engines inject the fuel.
• There are both mechanical and electronically
  controlled injection systems.
• Better volumetric efficiency
• More uniform fuel distribution
• More rapid response to changes in loading
  conditions
• More precise control of the equivalence ratio.

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Standard Gasoline Injectors
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Anatomy of EFI
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Serviceable Parts of A EFI
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Filters for EFI
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Overview of Electronic Fuel Injection System
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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.
• 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

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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)
• Increased power and torque.

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Port Fuel Injection System
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Modeling of Fuel injection

• The models needs to predict the spray process,
• the distribution and evaporation of droplets and
• the fuel layer formation and transmission in the
  port.
• The governing equations of motion and droplet
  evaporation are used to develop a model.
• The rate of evaporation of liquid fuel is
  calculated by first determining the fuel mean
  drop diameter (SMD) and characteristic
  evaporation time teva according below equation

where ml is the liquid fuel mv is the mass of
the fuel vapor. ?eva is time factor
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Time Factor

• Time factor calculated based on the energy
  balance between the surrounding air and the
  liquid droplet and the assumption that the heat
  transferred is a fraction of the available
  energy.
• The size of droplet and its energy will decide
  the rate of evaporation.

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Droplet Size Distribution

• The droplet size distribution in sprays is the
  crucial parameter needed for the fundamental
  analysis of the transport of mass, momentum and
  heat in evaporation. Engineering
• Parameter determines the quality of the spray and
  consequently influences to a significant extent
  the processes of emissions in combustion.
• Detailed experimental data is used to develop
  distribution functions.
• To obtain the detailed quantitative information
  of the sprays, a two-component Phase Doppler
  Anemometry (PDA) is used.
• This performs the simultaneous measurements of
  the droplet velocity and size and the volume
  flux.

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Measurement of Quality of Injection
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Diagnosis of EFI Health Quantity of Injection
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The Spay Pattern Generated by an Injector
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Instability of Fluid Ligament in Ambient Air
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Mean diameter distribution of droplets (micron)
in 100 mm downstream and 300 Kpa, 25o C
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Distribution of droplets velocity (m/s) in 100 mm
downstream and 300 Kpa, 25o C
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Frequency diagram of droplets mean diameter
D is the droplet diameter and N is the
normalized number distribution.
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Physical Models for Spray Characterization
Entropy of a group of droplets
where S is the information entropy, the name used
when the information concept is applied to
problems in physics and engineering. In this
equation K is a constant and Pi is the
probability of the occurrence of a certain
result, in terms of number fraction. Maximum
feasible entropy corresponding to physical
conditions will decide the droplet distribution.
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Physical Constraints

• The following physical and mathematical
  constraints must be obeyed
• The sum of all probabilities must be unity

(ii) the mass flow of sprayed liquid must be
equal to the mass of all droplets produced per
unit time
where n is the total number of droplets produced
per unit time and mL is the liquid mass flux.