Fuel Injection vs. Carburetors

Fuel Injection System

• Fuel injection is a crucial component affecting the performance and operation of internal combustion engines (specifically, CI engines).
• Both fuel injection and carburetors aim to prepare and deliver a combustible mixture to the engine, per its needs.
• However, their methods differ.

Fuel Atomization

• Both systems require fuel atomization before ignition for proper mixing with air.
• For carburetors, incoming air velocity needs to be higher than fuel velocity.
• Injectors require the fuel velocity to be greater at the injection point.

Fuel Supply

• In carburetors, fuel supply depends on the amount and velocity of air passing through the throat.
• Injectors rely on pump pressure for fuel supply.

Carburetor Problems

• Maldistribution of fuel in multi-cylinder engines.
• Loss of volumetric efficiency due to passage restrictions.
• Freezing at low temperatures.
• Surging in the secondary tank due to tilting.
• Risk of fire from backfires.
• Vapor leakage in extreme heat.
• Excessive fuel supply.

Injector Advantages

• Correct and uniform mixture distribution.
• Improved volumetric efficiency.
• Freedom from icing issues.
• Better starting and acceleration.
• Absence of tilting problems.
• Better fuel control.

Injector Disadvantages

• Higher initial cost and complex design.
• High maintenance costs.
• Bulkier and heavier.
• More noisy.
• Requires a specific fuel type.

Fuel Injection System Objectives

• Meet engine demand for fuel volume.
• Distribute fuel evenly to all cylinders.
• Inject fuel at the correct time and rate.
• Inject fuel with proper pattern and atomization for the combustion chamber design.
• Inject fuel with abrupt start and stop to avoid dribbling.
• Injection timing should adapt to engine load and speed.
• System requires high reliability throughout its operation.

Functional Elements of Fuel Injection System

• Pumping element: Moves fuel from the tank to the cylinder.
• Metering element: Measures and supplies fuel at the rate determined by engine demand.
• Metering control: Adjusts the rate of fuel metering according to engine needs.
• Timing control: Adjusts the start and end of the injection process.
• Mixing element: Atomizes and distributes fuel inside the combustion chamber.

Classification of Injection Systems

• Air Injection Systems: Fuel is forced into the cylinder using compressed air. This is less common today, requiring multi-stage compressors.
• Solid/Air-Less Injection Systems: Liquid fuel only is injected directly into the cylinder.

Injection Pump Governor

• The injection pump governor regulates fuel delivery based on injection pump characteristics, air intake, and engine demand.
• The governor adjusts fuel supply to match engine speed changes and load to prevent issues like stalling or excess fueling.

Fuel Injector

• Fuel injector design impacts the rate and completeness of fuel combustion.
• Atomizing fuel into small droplets increases surface area for better mixing with air and rapid vaporization.
• This improves combustion speed and effectiveness.

Nozzle

• The injector nozzle is crucial for liquid fuel spraying into the combustion chamber, ensuring atomization, and proper fuel distribution.

• Factors affecting distribution of fuel include Injection pressure, air density in the cylinder, and fuel properties.

• Preventing fuel from striking the combustion chamber walls is crucial to avoid carbon deposits.

• Efficient fuel injection ensures proper mixing of air and fuel for optimal combustion.

• Specific factors like fuel velocity, and areas like droplet size, should be accounted for in determining these rates.