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:  Pump → Filter → Regulator → Branch Lines → Injector.  Air Flow Path  Air Filter → Throttle Plate → Intake Manifold  Determines Air Flow Via:  Engine Speed  Manifold Pressure  Air Temperature

EFI System  Fuel Flow Path  Same as Speed Density  Air Flow Path  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 of fuel system pressure  Spray type (turbulent or laminar) Function of nozzle type (Swirl, etc)  Fuel delivery temperature  Fuel electrical charge

Swirl Nozzle Injectors  Multiple types, one pictured from patent  Filed by Cummins Engine Company 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 No jet Fuel jet0 KV 30 KV Wider more homogenous spray

Electrospray Issues  Charge To Mass Ratio (of droplet)  Inversely proportional to droplet size  Step increase around 20µm (droplet diameter)  Modern techniques w/out electrode can achieve 10µm  Charge Used in Experimental = 30KV  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