Petrol fuel injectors

[Turbocharger]

Absolute numpty question from a beginner - how does a petrol fuel injector work? If I want to control a stream of fuel using electricity, can I plumb one of these up and supply 12v to spray fuel, or do I need a pump to generate pressure which is then 'released' by the injector?

[TomG]

http://auto.howstuffworks.com/fuel-injection3.htm

[Hybrid_From_Hell]

OK

My knowledge of all the leccy are not that good, but heres a poke with a stick for starters

injectors have a needle vlave held closed via a spring, additionally the valve is cooncted to a soleniod, when this gets a belt of leecy it opens and when the leecy vanishes it then snaps shut, the tip is a point and the speed and design make it atomise.

The leccy is governed via the ecu which says when to open / closeand is pulsed from the dizzy to the coil to the ECU and out to the injectiorson the flapper the 12V supply is dropped via the resistor pack to 3V

I'm sure the more knowledgeable will be along to correct me add to the above

Nige

I also know that a cracked injector caused huge misfires running problems and tears and anglosaxon for at least 16 weeks

[FridgeFreezer]

They work pretty much as Nige said - electric makes them open they don't pump fuel, they just release pressure supplied by the fuel pump and regulated by the pressure relief valve (PRV).

However, as Nige guessed, he wasn't 100% right

- The resistor pack limits the current.

Injectors are either high impedance or low impedance. High impedance injectors (usually about 12-16 ohms) can take a 12v supply directly, without a form of current control. Low impedance injectors (generally below 3 ohms) require some form of current limiting. You can use resistors to limit current, or you can use Pulse Width Modulation (PWM), which is a software solution

For some reason the low-impedance plus resistor combination works quite well

Injectors should not be used at more than 80-85% duty cycle. However, injector rates are always specified at 100% duty cycle and some nominal pressure (usually 43.5 psi = 3 atmospheres). The manufacturer leaves it up to you to determine a system pressure and maximum duty cycle in order to compute the resulting flow.

More injector info in the megamanual

[Turbocharger]

Hmm. My plan has almost imploded anyway. Since I'm about to hack about with the induction/exhaust side of my 300Tdi anyway, I was considering the benefits of adding a boss somewhere on the inlet to allow water injection using a petrol fuel injector with a 555 square wave, and turning it off/varying the mark-space ratio to control injection rate, but from a brief Googling (thanks guys) it seems they're lubricated by the fuel also (and water makes steel go rusty). This is a Bad Thing if I'm spraying it into the inlet.

[FridgeFreezer]

For water injection you need a slightly different setup:

http://megasquirt.sourceforge.net/extra/waterinj.html

You can also buy stainless steel fuel injectors (used with ethanol due to moisture content) which I'd assume would be happier with water.

[Turbocharger]

Hmm. An evening of googling this project (which only exists on my e-truck at the moment) yields the following:

1) screenwash solution is better than water since it contains alcohol

2) some sites say you need a nozzle or injector, some don't

3) most are focussed on turbo-petrol applications

4) one scary, scary hillbilly in Am-ri-ca screwed down the lid on his screenwash and fed exhaust pressure into the top and the water outlet into the inlet manifold, letting the differential pressure drive his water injection

I'm particularly paranoid about hydraulic'ing the engine, so I want to start really small and see if there's a marked benefit to be had. I'd go for manual control since I don't see a benefit in megasquirting the whole engine for just this project. I'm guessing stainless injectors might be expensive?

[FridgeFreezer]

Stainless injectors may be overkill as it seems most people use the slightly less accurate pump-valve-nozzle setup pictured above.

Instead of MegaSquirting it, why not Mircosquirt it? Cheaper, smaller, more than enough driver current for your application, and they reckon they're waterproof out of the box (designed for bikes etc.)

The size of the injector gives you a clue

Would give you enough spare outputs to drive electric fan, water pump or whatever automatically.

[RocKeR]

I'm sorry - I've obviously missed something here.... Why would you want to injet water into the inlet manifold??

Is this just a finger up at us hydrophobic V8 users to show that oil burners work even when you force water into them? B)

[Turbocharger]

Water has three four important properties with respect to this thread:

1) high specific heat capacity - so it can absorb a lot of the heat energy (of inefficient compression from the turbo, and normal combustion in the cylinder) without rising in temperature too much - giving lower cylinder temps and EGTs

2) when it turns to steam it expands considerably, taking up more space in the cylinder (which can push cyl pressures through the roof, care required)

3) it's incompressible, so if too much is injected (or ingested) it bends bits of your engine

4) it seems to render a V8 completely incapable of producing any power at all, even when waved around under the bonnet. Owners perform 'exorcisms' with strange aerosols and moaning sounds.

[Andy]

Water has three four important properties with respect to this thread:

1) high specific heat capacity - so it can absorb a lot of the heat energy (of inefficient compression from the turbo, and normal combustion in the cylinder) without rising in temperature too much - giving lower cylinder temps and EGTs

2) when it turns to steam it expands considerably, taking up more space in the cylinder (which can push cyl pressures through the roof, care required)

3) it's incompressible, so if too much is injected (or ingested) it bends bits of your engine

4) it seems to render a V8 completely incapable of producing any power at all, even when waved around under the bonnet. Owners perform 'exorcisms' with strange aerosols and moaning sounds.

No4 - total classic

[jeremy996]

Water has three four important properties with respect to this thread:

1) high specific heat capacity - so it can absorb a lot of the heat energy (of inefficient compression from the turbo, and normal combustion in the cylinder) without rising in temperature too much - giving lower cylinder temps and EGTs

2) when it turns to steam it expands considerably, taking up more space in the cylinder (which can push cyl pressures through the roof, care required)

3) it's incompressible, so if too much is injected (or ingested) it bends bits of your engine

4) it seems to render a V8 completely incapable of producing any power at all, even when waved around under the bonnet. Owners perform 'exorcisms' with strange aerosols and moaning sounds.

Back in 1991 I had a Vauxhall Nova GTE with a Chris Courtney turbo conversion and water injection. Back in those days intercoolers were rather unusual on cars, so the water injection served to reduce the charge temperature, using property 1 above. The standard car produced 100bhp, the turbo on full boost with washer fluid being injected produced 192bhp for 30 secs and about 150bhp the rest of the time. (It was limited on full noise to prevent things from melting). There was a Fiat Uno Turbo conversion with a more sophisticated arrangement, (Radbourne Racing), I think.

Mr Courtney had a big run in with Vauxhall over his interesting interpritation of the warranty terms, (at the time I worked for the administrators of Sureguard), but the car was lovely. I had to go to Germany regularly and leaving big Mercs and Beemers behind was great, if juvenile, fun. When I sold this car I bought a Morgan.