Fuel injection plugs

[James Ballenger]

Howard Wilkinson wrote:

> James:
>     Really they don't operate at a 70x mixture...... the real purpose
> of direct injection on 4 cycle engines is to achieve true charge
> stratification so that the total mixture ratio may well be 70x, but
> the mixture which is near the plug is at the proper 14x ratio.

So the compressed air/fuel ratio pumped into the cylinder is 14.7, but the

volume injected can give a 70:1?  I am still learning, could you please
define "True charge stratification?"

> Direct injection actually results in poorer atomizaton, and direct
> injection
> engines (4 cycle) use dual mode operation with port injection at
> higher power settings, and direct injection at low power settings.

Orbital claims better atomization than mpi, a mean diameter of less than 8

microns.  High power meaning high pressure?

> The obvious advantage of the extreme lean total mixtures at lower
> power settings is that it allows a full charge or nearly full charge
> of air which means higher effective compression ratio, and more
> material in the cylinder to create pressure from the combustion
> process.

It would also mean very good fuel economy and better hc and co emissions
too right?  Also because of the quick burn of the mixture lower NOx?


>     Direct injection tends to be detrimental to max power output.

    They did a test with a ford zetec "modified" engine comparing mpi
versus their system.  At full load and 12.5:1 they had better torque
figures and VE across the range.

> Orbital if I'm not mistaken is working primarily with 2 cycle engines,
> the idea being that no fuel is blown out the port which increases the
> efficiency to about the typical .5 lb / hp/hr of a 4 cycle.  The
> Mercury Optimax has demonstrated this to work very well.

    They seem to be better entrenched in the 2 cycle market, but most of
their recent efforts seem to be with 4 cycle engines.

>     Direct injection is the first real significant improvement in gas
> engines since very nearly the beginning.  Other "improvements" such as
> overhead valves, and overhead cam, superchargers, turbos, EFI, etc...
> really didn't offer much other than slightly greater power to weight
> ratio.  Overhead valve engines for example of the same compression
> ratios didn't offer much greater efficiency or dependability, Overhead
> cam only reduced the parts count slightly and allowed higher RPM,
> boosted induction offered no benefit except a slightly better power to
> weight ratio, EFI offers a slightly improved fuel management.... In
> real life I don't see much improvement between a properly set up carb
> and an EFI system on comparable vehicles owned by people I know.  The
> main advantage of EFI is emissions control and a system where the user
> can't easily tinker with it.

    I'd have to agree with you, except for the turbo.  As evidence by
buick gn's, a significant can be seen imo.

>     Direct injection on the other hand offers an increase in
> efficiency in vehicles of as much as 30% if the numbers floating about
> are to be believed.
>     I'd love to have something  like this to play with someday....
> H.W.

Me too, I just wish I could play with it now ;-)

btw, my source for all the orbital mumbo jumbo was
http://www.orbeng.com.au/pdf/sae98.pdf

James Ballenger