How does a diesel fuel injector work?

Answer 1

A typical gas injector will use a solenoid to move a pintle vavle to allow relatively low fuel pressures to flow past, forming an injection "cone". Typical Multi-Port Fuel injection pressures are 45-80PSI. Throttle Body injection pressures are typically 10-20PSI.

A classical diesel injection system works quite differently.

A "distributor-style" or "inline-style" injection pump takes up fuel, either with the aid of a supply pump (called the lift pump) or occasionally they have a built in lift pump. The pump pressures to the injection pump off of the lift pump are usually 4-10PSI. Inside of the injection pump, fuel is pressurized to 2000-6000PSI typically. In the classic injection system, this pressurized fuel will flow through a high-pressure injector tube from the injection pump to the injectors. The injectors have internal detents and spring mechanisms set up to allow them to "pop" or open at a certain pressure. This style of injector has ZERO electronic assistance. Once pressure is built to the "pop" point, it is injected into either a pre-chamber (Indirect Injection) or directly into a bowl in the piston (Direct Injection) and stays open until pressure in the tube is bled down below the "pop" point at which the pintle closes again.

There are other methods of injection in a diesel engine, one of which which is also unassisted by electronics utilizes a central injection pump that pressurizes all injectors to roughly 20-35000 PSI. A dedicated lobe on the camshaft (occasionally an entire dedicated camshaft) wil then actuate the injector. Many heavy-duty diesel engines use this system, and the VW TDI Pumpe-Duse uses a variant of this system.

Then we hit into electronically assisted setups.

One of which is the HEUI- Or, Hydraulic Electronic Unit Injector. The 7.3L Powerstroke is the most notable engine to use this method. I am not 100% on HEUI theory, but I'll do my best.

In this, fuel is supplied via a rail to the injectors at relatively low pressure (45-75PSI typically) and high pressure oil (600-3500PSI, engine load variable) is supplied via a separate rail to another port in the injectors. When the injectors are signalled to turn on, the high pressure oil flows in on top of an "intensifier" piston and the fuel flows in below. Off, and the fuel is allowed to flow out of the nozzle. The differential in sizes of the piston in contact with the oil and in contact with the fuel causes a multiplication force, where the fuel exiting the nozzle is roughly 20-30,000PSI.

One notable feature of the HEUI injector is that it is several times larger than any other diesel injector design.

The most recent addition to the familiy is the Common Rail injection system. Again, a central pump pressurizes the fuel rails to roughly 30,000PSI. There are 2 types of injector used in this setup. Either A) the solenoid injector. Very similar in principle to a gas injector, but much burlier, as we are dealing with tens of thousands of PSI pressure, not tens of PSI. Or B) The Piezoelectric injector. I am not quite sure how the Piezoelectric injectors work, but I do know they are the fastest, most precise control-system for injectors currently available. They allow for much better control of the fuel injection cycle, allowing for a quieter, more powerful, more fuel efficient, and lower emissions engine.

If you have the older style with an injection pump leading to the non-eletronic injectors, do some research on things like pop-test calibrations. Also, hit up some diesel forums and use the search function.