FUEL INJECTION SYSTEMS
WITH A FOCUS ON FUEL
ATOMIZATION
By: David Shamrell
Overview

Fuel Injection Systems
 Speed
Density
 EFI


Fuel Injector Design
Fuel Atomization
 Swirl
Injectors
 Electrospray
Speed Density Fuel Injection Sys.

Fuel Flow Path:


Air Flow Path


Pump → Filter →
Regulator → Branch
Lines → Injector.
Air Filter → Throttle Plate
→ Intake Manifold
Determines Air Flow Via:



Engine Speed
Manifold Pressure
Air Temperature
EFI System

Fuel Flow Path


Air Flow Path


Same as Speed
Density
Air Filter → Air Flow
Sensor → Throttle
Plate→ Intake Manifold
Determine Air Flow
Via:


Measured Air Flow
Engine Speed
Air Flow Sensor
Fuel Injector

Electromagnetically actuated valve

Can cycle several times a second


Controlled by Electronic Control Unit (ECU)
Nozzle design affect atomization

Needle helps minimize dribble (secondary injection)
Fuel Atomization

Fuel Atomization is a function of:
 Fuel
injector geometry
 Fuel jet velocity
 Function
 Spray
type (turbulent or laminar)
 Function
 Fuel
of fuel system pressure
of nozzle type (Swirl, etc)
delivery temperature
 Fuel electrical charge
Swirl Nozzle Injectors

Multiple types, one pictured from
patent 6029913
 Filed
by Cummins Engine
Company 1998
6
curvilinear spray holes
 90 degree curvature orientation

“flow through tangential flow path
causing rapid spreading and
breakup of fuel jet spray upon
exiting spray hole”
Electrospray Injection

Installed Electrode:
 Downstream
fuel injector
 Upstream orifice

Benefits
 Reduces
surface tension
of liquid
 Shortens breakup length
 Enlarges the cone angle
of the spray
Electrospray Experimental Results
0 KV
Fuel jet
No jet
30 KV
Wider more
homogenous
spray
Electrospray Issues

Charge To Mass Ratio (of droplet)




Charge Used in Experimental = 30KV


Inversely proportional to droplet size
Step increase around 20µm (droplet diameter)
Modern techniques w/out electrode can achieve 10µm
Hard to obtain in a mobile platform
Injection velocity vs. charge (Competing Factors)

Charge imparted is a function of time


Slower velocity = more charge
However atomization is proportional to injection velocity

Thus slower velocity = less atomization