The Effects of Port Fuel Injection Timing and Targeting on Fuel Preparation Relative to a Pre-Vaporized System

The effects of port fuel injection (PFI) timing and targeting on air/fuel (A/F) control, exhaust emissions, and combustion stability at retarded spark timing were investigated on a 2.0L I-4 engine with production injectors (300-350 micron SMD droplet spray). Timings were fully closed valve injection (CVI) or fully open valve injection (OVI), and selected targetings were towards the valve or port floor. An “ideal” pre-vaporized, pre-mixed fuel system was also tested to provide a baseline with which to isolate PFI fuel preparation effects. The key findings were:

• Transient A/F excursions with PFI were minimized over the full temperature range with OVI timing and valve targeting. The X-tau modeled film mass for OVI/valve target was 50% less than CVI/valve target and 30% less than OVI/port target with a cold engine (20° C). When fully warm (90° C), the A/F response of CVI/valve target improved to near that of OVI.
• Hydrocarbon emissions and mixture homogeneity with PFI were best using CVI timing over OVI timing. With CVI timing, the injector targeting had no effect on either hydrocarbons or mixture homogeneity. Hydrocarbon emissions for closed valve PFI were identical to the vapor system at fully warm and light load conditions, but increased to 35% higher than vapor at low temperature and high load. The COV of A/F within the mixture with closed valve PFI was consistently 40-50% poorer than vapor, regardless of temperature or load.
• Combustion stability under retarded spark was best for PFI when using CVI timing, due to the much poorer fuel preparation resulting from OVI timing. With CVI timing, valve targeting improved stability slightly over port targeting, although the difference was close to test variation. Closed valve PFI stability was lower than vapor and degraded more dramatically with increased spark retard. At an engine roughness of 0.2 SDGMEP, closed valve PFI produced 25% more hydrocarbons and limited exhaust temperature by 40° C relative to the vapor baseline.