basic plumbing for pulsed fuel injection

[16Victor]

In the process of re-plumbing my underhood fuel lines to convert my car to pulsed fuel injection, I am debating the best plumbing scheme.

Engine is an I4, all four injectors will fire simultaneously. Calculated injector size is 26#/hr.

In most systems, the main fuel flow follows this route:
Pump -> Filter -> Rail -> Regulator -> Tank (in series)

In order to clean up the underhood plumbing, I am considering:
Pump -> Filter -> Regulator (tee to Rail), -> Tank

This would eliminate the fuel return line from the rail and physically clean up the installation. I am concerned about rail pressure pulsations and the possibility that the far-end injectors may starve (since I'd be feeding one end of the rail vs the center). Are these valid concerns? Can an accumulator/damper/snubber be effectively used at the end of the rail to reduce pressure pulsations?

Or should I just stop thinking and do it like everybody else?

Thx -

Ron

 

[patprimmer]

The return from the far end aids in purging vapor from the ststem.

It requires a bit longer fuel line, so OEM's would not do that if they thought they could save a few cewnts worth of line.

Regards
pat

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

It also has the advantage that the returned fuel will be cooler, so we'd do it if we could.

Cheers

Greg Locock

 

[dgallup]

Please note that the traditional fuel pressure regulators maintain a constant pressure differential between the fuel rail and the intake manifold. Therefore, if you remote mount the pressure regulator back at the tank you still have to run a line from the manifold back to the pressure regulator. Also, I think that setup will not give you good pressure regulation at the rail during throttle transients. Much better to put the pressure regulator at the end of the fuel rail.

Note that some modern systems use a returnless system. These are much harder to program as they do not maintain a constant pressure drop across the injectors and thus the injector flow is no longer just a function of pulsewidth. The ECU has to calculate the injector flow rate based on MAP sensor input. This is a cheaper system in high volume production since processing power is getting cheaper all the time and any hardware eliminated saves cost. These systems tend to run higher rail pressures to eliminate hot start problems caused by fuel vapor in the injectors/rail.

 

[Flowczar]

Ron,

Some pressure pulsations, especially when group firing, may be hard to get rid of. I posted last month with a problem we were having on a custom fuel rail set-up. We applied 4 dampers to the system to get things managed. Testing shall prove worthwhile.

I would suggest returning from one end of the rail and damping the other end.

Happy Wrenching!

 

[16Victor]

Thanks for your message - I am having the conventional in-one-end, out-the-other rail made up.

Oh well, if we don't think...we don't think.

Thx,

Ron