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This study presents a methodology to predict particle number (PN) generation on a naturally aspirated 4-cylinder gasoline engine with port fuel injection (PFI) from wall wetting, employing numerical CFD simulation and fuel film analysis. Various engine parameters concerning spray pattern, injection timing, intake valve timing, as well as engine load/speed were varied and their impact on wall film and PN was evaluated. The engine, which was driven at wide open throttle (WOT), was equipped with soot particle sampling technology and optical access to the combustion chamber of cylinder 1 in order to visualise non-premixed combustion. High-speed imaging revealed a notable presence of diffusion flames, which were typically initiated between the valve seats and cylinder head. Their size was found to match qualitatively with particulate number measurements. A validated CFD model was employed to simulate spray propagation, film transport and droplet impingement.

With Advanced PFI, Bosch has demonstrated that gasoline port-fuel injection is becoming significantly more energy-efficient by means of innovative system development. Advanced PFI combines fuel pressure increase, twin injection, PFI scavenging, and open valve injection. The use of Advanced PFI makes it possible to reduce consumption by 12%, with a corresponding decrease in CO2 emissions. The higher compression in the part-load range alone accounts for 2% of the reduction. The remaining 10% come from downsizing with turbocharging and PFI scavenging. At the same time, Advanced PFI allows a reduction in hydrocarbons (HC) emissions. Thanks to more homogenous air-fuel mixture formation and reduced manifold wall fuel condensation, HC emissions fall by 20% in the test cycle. And Advanced PFI also permits an increase in specific engine power output, with PFI scavenging achieving significantly higher low-end torque.