Direct Injection - very simple model

[Robert Harris]

Middish sized V-8.  Use a standard 4 barrel carb manifold.   Start with
mounting a standard throttle plate from a Holley vacuum secondary ( or other
brand ).   Connect the primaries to the foot feed.  Connect the diesel pump
"throttle" to the foot feet.  Throw away everything above the throttle plate
and plug the non sensor holes in the throttle plate.

Basic Stamp or similar computer.

Inputs - MAP, air temp, EGO, coolant temp, RPM.  throttle position from the
diesel injector.  Output - stepper motor position for the secondaries.  

In this scenario, using the primaries tied to the diesel pump, the mixture
will vary from rich to pig rich depending on the air flow to pump flow
relationships.  The computer compensates by adding AIR to the engine ( leaning
it out ) from some simple tables and measurements.   The EGO fine tunes it.

Notice the complete lack of injector timing or pulse widths or cylinder to
cylinder stuff.  Since the calculation is not time critical in respect to
crank angle, the algorithm needs only to loop at some speed necessary to
update the single output - stepper motor position - in near real time to the
engine.

Next observe that the fuel flow  LEADS the air flow.  The computer is always
in catch up mode - leaning the mixture back to set-point after an increase in
fuel flow.   This natural behavior eliminates any need for computer aided
enrichment "accelerator pump" stuff as it is built into the design.  

Stanameyer makes a number of diesel pumps and injectors for mid range V-8
engines that is compact enough to work well and the older GM units are
reasonably available in  pre-owned parts palaces.

To placement of the injector - an enlarged sparking plug hole.  There was a
thread about plasma jet ingnition.  There is was also one about stratified
charge.  The model to look at is fuel scavenged prechamber stratified charge.

Essentially a small pre-chamber which couples the fuel injection and the
sparking plug into a smallish chamber that leads to the main chamber.  The
fuel is injected past the sparking plug and straight into the main chamber.
The prechamber is extremely rich.  Since the sparking energy is an order of
magnitude or more less in a still chamber, it is extremely easy to get a
plasma jet effect.  Also, the firing phase of all spark ignitions cares less
about the "mixture" at the plug as every thing is stripped below its corporate
atoms.  The optimum is excess hydrogen from fuel rich conditions as it is the
hydrogen atoms after the plasma explosion ( all spark ignitions ) that travel
furthest into the "mixture" and initiate the chemical / thermal reaction of
the fuel.  

Don't agree?  Argue with John B. Heywood, Director Sloan Automotive
Laboratory, M.I.T Internal Combustion Engine Fundamentals, ISBN 0-07-0286-37-x
Chapter 9  Combustion in Spark-Ignition Engines - with emphasis on flame jet
pre chamber stratified charges. Bought the book and actually read it.

>From the above. a mechanical direct injection based on a diesel pump and
injectors is not out of the reach of a moderately competent fangler - once you
rescrew your hat and think "Control The AIR".  

Using the GM/Ford diesel pump will force the fuel into the chamber at about
1800 psi and during a relatively small number of crankshaft degrees - about
any time you want it.  Think vaporization - screw atomization.

This also should qualify as a doable in your lifetime DIY_EFI because its not
going to work without a simple computer to control the air like conventional
EFI controls the fuel.   Think about it - its not that hard to do.



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