[Stugotz99]

I just spoke with my college combustion sciences professor. He has done significant research on direct injection engines at Univ of Texas. His work began several years ago on the J-spec engines that could not meet US emissions requirements. Then, they were using injection technology called "spray guided" direct injection which aimed the spray at the spark plug. Also there was "wall guided" which sprayed the piston and/or cylinder wall.

His research showed that spraying the fuel on any surface in the combustion chamber produced large amounts of particulate emissions. He is not totally familiar with the Mazda design but assumes they are using the now popular "air guided" injection (not sure what that implies). Still he said that if their system was not perfect and fuel was coming into contact with any surface, high particulate emissions would result. He also reinforced that they would not be using an overly rich mixture when not needed; only high load periods. Therefore, unless you're hard in the throttle all the time (me?...never), the sooty tailpipe is likely due to the injection method.

Anyways, somewhat trivial information, but I thought I would pass it on.

 

[GT1]

[quote author=stugotz99 link=topic=67428.msg1159886#msg1159886 date=1169326222]
He also reinforced that they would not be using an overly rich mixture when not needed; only high load periods. [/quote]
It seems that he is stating the obvious unless I am missing something.

It is common knowledge that virtually all modern fuel injected engines run with a stoichiometric air/fuel ratio (i.e. closed loop with O2 sensor) unless under high load.

 

[Stugotz99]

[quote author=GT1 link=topic=67428.msg1159938#msg1159938 date=1169328858]
[quote author=stugotz99 link=topic=67428.msg1159886#msg1159886 date=1169326222]
He also reinforced that they would not be using an overly rich mixture when not needed; only high load periods. [/quote]
It seems that he is stating the obvious unless I am missing something.

It is common knowledge that virtually all modern fuel injected engines run with a stoichiometric air/fuel ratio (i.e. closed loop with O2 sensor) unless under high load.
[/quote]

Thank you for re-pointing out the obvious...That's why I said "reinforced". :thinking: A lot of people think it is a continuously rich mixture causing the soot.

The prior two paragraphs are the less obvious points...

 

[Boother]

[quote author=GT1 link=topic=67428.msg1159938#msg1159938 date=1169328858]
It is common knowledge that virtually all modern fuel injected engines run with a stoichiometric air/fuel ratio (i.e. closed loop with O2 sensor) unless under high load.
[/quote]

That common knowledge really only applies to port fuel injected cars. With direct injection, it is possible to run A/F ratios much leaner than stoich by stratifying the charge around the sprak plug. The swirl control valve on the intake manifold helps create this stratified charge by controlling how the air behaves in the intake and as it enters the combustion chamber.

While I agree with the prof about the fuel burning off a surface, I must also point out that very lean fuel ratios do tend to release more particulate emissions (re: soot) than stoich as well.

 

[GT1]

[quote author=Boother link=topic=67428.msg1160247#msg1160247 date=1169348491]
[quote author=GT1 link=topic=67428.msg1159938#msg1159938 date=1169328858]
It is common knowledge that virtually all modern fuel injected engines run with a stoichiometric air/fuel ratio (i.e. closed loop with O2 sensor) unless under high load.
[/quote]

That common knowledge really only applies to port fuel injected cars. With direct injection, it is possible to run A/F ratios much leaner than stoich by stratifying the charge around the sprak plug. The swirl control valve on the intake manifold helps create this stratified charge by controlling how the air behaves in the intake and as it enters the combustion chamber.

[/quote]
In the case of our engine, I've never seen it running lean. By monitoring the first (wideband) O2 sensor, I've found that the mixture is always stoichiometric (when cruising or idling) or richer.

 

[Boother]

[quote author=GT1 link=topic=67428.msg1160406#msg1160406 date=1169358361]
In the case of our engine, I've never seen it running lean. By monitoring the first (wideband) O2 sensor, I've found that the mixture is always stoichiometric (when cruising or idling) or richer.
[/quote]

I see. Seems weird that Mazda wouldn't take advantage of this with the MS3 engine, as every other manufacturer is with theirs. They must still be using the swirl valve to promote good fuel atomization and not for charge positioning.