Advanced PFI is a Bosch system innovation for gasoline port fuel injection. Innovations such as pressure increase, twin injection, PFI scavenging, and open valve injection deliver impressive system benefits and redefine the technical possibilities of this propulsion principle. In combination with turbocharging, further reductions in fuel consumption and CO₂ emissions can be realized – with no impairment to torque or performance.
To support air-fuel mixture formation during a cold start, the pressure in the fuel low-pressure system is raised temporarily to up to 6 bar. This increases the mass of the vaporizing fuel, reduces the spray droplet size SMD, and lessens manifold wall fuel condensation. As a result of the increase in pressure, the maximum volume of fuel that can be metered goes up, which supports injection synchronous with induction. The demand-driven provisioning of the amount of fuel and fuel pressure also reduces the average power draw of the fuel supply pump.
Using two injectors per intake port optimizes spray alignment and targeting in the cylinder, while spray targeting combines insights from the field of fluid physics with engine know-how. The spray geometries are modified optimally to the requirements of the specific intake port.
Distributing the fuel through two injectors reduces the spray droplet size (SMD) thanks to a lower static flow rate, a lower spray density (due to the larger cone angle), and an optimized internal flow in the valve (single tapered spray). Overall, this improves vaporization, reduces manifold wall fuel condensation, and increases ignition stability. Further advantages include later ignition angles in cold-engine running and faster attainment of the catalytic converter's conversion point.
PFI scavenging is a technology developed by Bosch that is used in the turbocharging of downsized engines. During the period when both the intake and the exhaust valves are open, pure fresh air – without any fuel – is flushed through the combustion chamber. Fuel is injected only once the exhaust valve has closed. The injection period is set such that no unburned fuel leaves the combustion chamber.
The scavenging effect achieves a higher exhaust gas flow rate even at low engine speeds, thereby shifting the operating point of the exhaust gas turbocharger to a lower so-called "base speed." The resulting increase in cylinder charge at low speeds improves the power output of gasoline port fuel injection engines specifically in the starting-off range.
Open valve injection (OVI)
What distinguishes this injection method is that fuel is injected into the incoming fresh air from the intake manifold only when the intake valve is open. This injection synchronous with induction occurs at low to medium speeds under engine full load and therefore in the knocking risk range. Thanks to the reduced wall contact of the air-fuel mixture, the fresh charge is cooled more effectively, reducing the knock tendency. As a result, the compression ratio of the basic engine can be increased by a factor of between 0.5 and 1.0 and fuel consumption falls in the part-load range. Using OVI in conjunction with twin injection enhances the OVI effect by means of improved atomization and vaporization and optimized targeting.