Fuel injection plugs

[Howard Wilkinson]

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

-----Original Message-----
From: James Ballenger <jballeng at vt.edu>
To: diy_efi at efi332.eng.ohio-state.edu
<diy_efi at efi332.eng.ohio-state.edu>
Date: Tuesday, April 27, 1999 3:37 PM
Subject: Re: Fuel injection plugs


>
>
>Gary Derian wrote:
>
>> What is the point of direct injection?
>
>Superb fuel atomization.
>
>> All it does is make the operating conditions on the injector more
severe.
>> Direct injection requires injecting only during the intake stroke.
>
>    Not if you inject the fuel into another high pressure air
injector.  The
>orbital version of direct injection works very very well imo.  The
mixture that
>is fired out of the air injector is supposedly below 10 microns 80%
of the
>time.  It makes for a super quick, clean burn.  They quote being able
to run a
>70:1 mixture at light load, dunno about that one though, and huge
peformance,
>emmissions, and fuel economy improvements.  They are making
automotive
>applications now too, sounds very good to me.
>http://www.orbeng.com.au/index.htm
>Though I'm not sure how to get my hands on a system like this one.
>
>    James Ballenger
>
>
>