Fuel Induction Systems for SI Engines P M V Subbarao Professor Mechanical Engineering Department The...
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![Page 1: 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.](https://reader035.fdocuments.in/reader035/viewer/2022062407/56649dca5503460f94ac10f6/html5/thumbnails/1.jpg)
Fuel Induction Systems for SI Engines
P M V SubbaraoProfessor
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
1
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Isentropic Flow Through A Venturi
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p1
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Real Flow Through A Venturi
p1 p2a <p2s
pthroat
p
p1 p2a
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Practical Carburetor Venturi
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Real Air Flow Through Venturi
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Where
Fuel Flow Through Orifice
ffODOa pACm
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Carburetor Performance
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Carburetor Performance
kPap,
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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 τeva according below equation:
eva
vlv mm
dt
dm
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 numberdistribution.
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Physical Models for Spray Characterization
Entropy of a group of droplets: i
ii PPKS ln
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:(i)The sum of all probabilities must be unity:
1i
iP
(ii) the mass flow of sprayed liquid must be equal to themass of all droplets produced per unit time:
Li
iii mnVP
where n is the total number of droplets produced per unittime and mL is the liquid mass flux.