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Location:
South Australia
Registered:
July 2002
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NOx emissions & 3S-GE
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Mon, 18 October 2004 04:06
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Okay - this is the easy part of this post - does anyone have any information on the level of NOx emissions from a 1st gen 3S-GELC.
Harder part, this is sort of related to both N/A Single Throttle Body Design and EFI Design - 4cyl GE L-Jetronic. Okay - I'm making a custom throttle body for 1st gen 3S-GE head...I'm hoping to run a high compression ratio engine (around 10.0:1 - 10.5:1) and still have legal emissions (haha I hear you say).
I spent a couple of hours searching around in the Barr Smith library, I had a look around at the specific legalities of emission levels in cars and sort of had luck (my car will more than likely have to go through quite a round of testing once I re-register it) but I wanted to know if anyone has any thoughts on the following
NOx emissions can be reduced by achieving one of the following, however it would seem that all are inter-related
- highly rich/lean mixture
- low peak cylinder pressure
- low peak flame/flame front temperature
1. Highly rich or lean mixture
A highly rich mixture is out of the question, although the option of running slightly rich may be available (catalytic convertors would take care of the CO emissions) anything highly rich won't be possible, and anything highly lean won't be possible due to the design of the 3S-GE head being insufficient to support lean-burn conditions. (swirl ports, VVT or direct injection)
Lean mixtures can be 'simulated' to an extent though by introduction of inert mass (water, exhaust gas) into the intake charge, meaning the oxygen content of the gas is reduced but more importantly the inert matter present will absorb the heat at the flame front.
2. Low peak cylinder pressure
Well, I'm running high compression aren't I? That's a bummer, but the peak pressure can be reduced by retarding ignition timing (flame front propogation occurs during less of the compression up-stroke and more of the expansion down-stroke) however this clearly reduces power. Other options are to reduce the mass in the cylinder, which isn't practical for power purposes either.
I'm wondering if the rod/stroke ratio would affect this, as a faster accelerating piston during expansion would surely reduce the peak cylinder pressure. A low rod/stroke ratio would be required for this, right? However that might kill some revvability (I guess I'm only aiming for around 7000rpm anyway, with a nice wide torque band)
3. Low peak charge/flame temperature.
Better fuels can help in this regard (98 octane burns 'colder' than 91 octane fuel for example), and as above, inert matter can be introduced into the charge to absorb the heat of the flame front.
Basically, I'm thinking that either some form of water injection or some form of exhaust gas recirculation. Exhaust gas recirculation is interesting as there have been many developments in this area allowing much higher levels of exhaust gas into the cylinder without incurring knock penalty or loss of fuel economy (I think I read something about allowing egr to enter only one port, however unfortunately this isn't truly possible with the GE head, I imagine an EGR outlet near the manifold side of the port wouldn't suffice). Water injection is also interesting, however I'm wondering if anyone has actually bothered using it on an N/A engine and how annoying it actually is.
Increased intake/exhaust overlap can also help the level of NOx emissions however obviously this wouldn't be as precise-a-method of controlling the exhaust gas present in the cylinder as a good EGR system would be.
So finally - what are other peoples suggestions or opinions? I need a bit of a push in the right direction at this stage!
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