by Jon Inge – NW Alfa Romeo Club Communications Director (published with permission)

Let’s look at how the fuel actually gets into the engine. One gallery provides fuel to the front side of the plungers; another provides oil to their rear, so that even though they’re working in liquid fuel, they have an oil supply immediately the engine starts rotating.

The belt-driven crankshaft drives the plungers up and down, sending pulses of fuel into the delivery lines to the injectors. The amount of fuel contained in each pulse is controlled by rotating each plunger to expose more or less of the helical slot at its top to the fuel gallery. This rotation is achieved via a toothed collar clamped onto each plunger engaging with a rack moved laterally under the control of the 3D cam in the pump’s logic
section.

Each plunger forces fuel at 400 psi through a check valve and into the metal delivery line; the check valve prevents it flowing back into the barrel as the plunger descends for the next stroke. Fuel at 400 psi is thus delivered to the injector in the inlet manifold, where it’s held in check by a spring-loaded pintle valve; imagine a tiny poppet valve, such as the inlet valve in the main cylinder head. The pressure of the next delivery from the pump plunger forces the pintle open, spraying fuel in an atomized cone (restricted by a shroud so that it doesn’t wet the inlet tract walls) until the pintle spring shuts it off again as the pressure drops. A disc with a tiny orifice is fitted in the input end of the injector to damp out oscillations in the fuel flow.

There’s enough internal volume in each injector and fuel line that, on
average, fuel will be in them for something more than 10 engine revolutions, up to as much as 100 at idle. This gives the fuel time to
reach a temperature close to that of the engine coolant which surrounds
the injector; the high pressure suppresses vapor formation inside the
injector. This means that the fuel charge, when released into the intake air passage, has high temperature as well as high pressure to assist with its atomization. The air volume in the inlet tract, similar to the swept volume of the cylinder, doesn’t linger to get the same heat exposure, so the engine runs with a cold air charge and a hot fuel charge. That’s pretty elegant. We’ll wrap this up next month.