Fuel injection plugs

[Howard Wilkinson]

James:
    I didn't say that very well..... What I meant to say was that due
to fuel charge stratification the area in which the spark plug is
located where combustion is initiated is at normal ratio, but the
surrounding area may be extremely lean.
    The ideal engine (in terms of efficiency) is like a diesel where
power output is controlled by fuel supplied not by air fuel mixture
being supplied under a vacuum (throttling) which results in lower max
pressure prior combustion.  Basic thermodynamic theory shows that for
a given amount of thermal energy the pressures will be higher if a
full charge of air is available for expansion.  We are after all
developing power from the pressure, so any way we can achieve more
pressure from a given amount of fuel will improve our efficiency.
    My comments on 4 cycle direct injection were not relating to the
Orbital system.  It's been awhile since I chased this info down on the
web.  I believe Mitsubishi or some other Japanese company is at the
forefront of direct injection 4 cycle engines and may actually have a
car on the market by now.  This type of system was the one I described
with the two injectors, one being direct, and one port.  I believe
they are using the same basic Siemens type injector as is used by
Orbital, and info on these developments is probably to be found from
the Siemens web site.  Try the link below... I'm not sure if it's
current.
http://www.frostbyte.com/siemens/siemens/powertrain/

H.W.

Date: Wednesday, April 28, 1999 5:34 AM
Subject: Re: Fuel injection plugs


>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
>
>