The Effects of Small Fuel Droplets on Cold Engine Emissions Using Ford's Air Forced Injection System

The effect of port injected small fuel droplets was evaluated for several different modes of engine operation. The droplets were generated by an Air Forced Injector (AFI), Figure 1, which uses high velocity air through a nozzle to produce fuel droplets on the order of 10mm Sauter Mean Diameter (SMD). AFI results were compared to those from a standard production pintle injector. Steady state data, “motored cold start” data, and injector cut-out data were collected. All three data sets illustrate functional advantages of AFI over standard Electronic Fuel Injection (EFI).

Steady state testing showed that the AFI delivers complete freedom for specifying injection timing with respect to HC emissions. This freedom is highly advantageous for transient conditions because open valve injection with small droplets causes much less port wall wetting. Therefore, less control system compensation is necessary, and more accurate air-fuel ratio control is achievable. The injector cut-out tests were used as a simple transient test and showed that roughly 75% less fuel is deposited onto the port walls with AFI vs. EFI. Motored cold start tests further showed that engine-out hydrocarbons are decreased by at least 50% in the first few seconds of engine operation using the AFI system.

The energy consumption impact of a complete system including a means of supplying pressurized air is also shown. Bench tests of injector performance coupled with engine cycle modeling show an approximate 2% increase in BSFC at 1500 RPM, 2.62 bar BMEP.