Injector nozzles

[tasdrouille]

So my 1999 A3 Jetta is gone and I got a 2000 A4 Jetta in.

The new car was a dog when floored and had no torque at 2000 rpm. It felt pretty much like my Elantra. FE appeared to be not to bad, but far from stellar.

We diagnosed a fueling problem and decided to have a look at the 200k miles nozzles.

Here's what we pulled.



Talk about atomization and spray pattern! Some of the holes were completely blocked.

I had a set of new nozzles laying around so I threw them in, problem solved. FE is probably going to be pretty good if I can keep my foot off the go pedal. They are 2 size larger than the stock nozzles. Which means more power when the pedal hits the metal, but a shorter injection duration at part load which could help FE.

[Christ]

Correct me if I'm wrong, but larger nozzle = less duration = less injection pressure = less atomization?

To a given extent, pressure is bad for atomization, but there a point where too little pressure is also bad, and adding larger injector nozzles may mean less pressure than the fuel system was designed for, causing less atomization of fuel.

This might not be a problem, since the turbulent air and heat have more to do with atomization than the injectors themselves do, but it's a consideration at least.

[Red]

Can't really tell from the crud, but is that a 4 port injector or a pintle style?

[tasdrouille]

This is a TDI nozzle used in a bosch rotary pump system. It have 5 holes and there's a spring loaded needle in the middle. Once a certain pressure is reached (220 bar) the needle pops and fuel is injected. So regardless of hole size, the injection pressure is the same.

In a diesel it is desirable to have the shortest injection duration possible for efficiency.

In a TDI proper atomization is critical and largely dependent on the nozzle design and condition. The nozzle sits tight between the valves in our flat head (yup, the head is completely flat). There is a small bowl in the piston and fuel is injected in a cone spray towards the bowl lips.

[dremd]

What nozzels did you get?

I got the pp520's in mine. But I'm having a hard time keeping my foot out of it between >$1.00 gallon fuel and bucket loads of torque I'm in the mid 40's. I have to get a better system for measuring fuel .

My used ones didn't look that bad.