Managing EGR for MPG

[MetroMPG]

Not sure if you're saying this, Rick, but EGR isn't lean burn.

With EGR, the air/fuel mixture would remain at stoich (in closed loop via the O2 sensor). It's just that with EGR active, there's less o2 in the intake charge as a proportion of total air mass, so less fuel is introduced. Then, yes, less power, and a wider throttle to compensate, with reduced pumping losses (theoretically).

[rh77]

Originally Posted by MetroMPG

Not sure if you're saying this, Rick, but EGR isn't lean burn.

With EGR, the air/fuel mixture would remain at stoich (in closed loop via the O2 sensor). It's just that with EGR active, there's less o2 in the intake charge as a proportion of total air mass, so less fuel is introduced. Then, yes, less power, and a wider throttle to compensate, with reduced pumping losses (theoretically).

Darin, I'm trying to wrap my brain around this after a long day, and probably can't offer much but uneducated inquiries -- I figured that Stoich is always the goal of the emissions system (unless in open loop) so the term "Lean Burn" should be described as a Leaner Fuel Mixture when adding an abnormally larger EG recirc. This could result in higher IATs, in leaner mixes, the higher risk of detonation, and consequently higher temps within the combustion chamber. When the ECU finds out that the lean situation is occuring does it not dump more fuel in the charge to cool things down? So in some cases the oxygen and knock sensors report to the ECU to change timing, etc. So multiple factors have to be executed to get this complicated system in good working order for optimum FE. Simply, the whole ECU would need to be replaced or reprogrammed to handle the variables. BTW, does it vary where the EG is entered into the system among vehicles -- I assume directly into the intake manifold in most/all cases?

RH77

[rh77]

Sorry about the previous rambling post -- no need to answer

I found an introduction to emission basic knowledge that I lack...

How Emissions Systems Work

I've been under the hood trying to find these items and contemplating the alteration of them for better FE/emissions, but I think Honda already figured that out when the car was made.

RH77

[MetroMPG]

Originally Posted by rh77

I think Honda already figured that out when the car was made.

"The automaker got it right" doesn't necessarily apply to all areas of design or tuning.

Witness the transmission issue. The people who've done swaps all get better FE than was originally spec'd by the automaker, though at the expense of drivability (that's a subjective term) - maybe acceleration is a better measurement.

I have no idea if higher levels of EGR will actually help FE. Still, I'd be reluctant to say the manufacturer has gone to the limit in that regard.

[rh77]

Originally Posted by MetroMPG

"The automaker got it right" doesn't necessarily apply to all areas of design or tuning.

Honestly, I'm learning here -- I had no idea what the evap canister did until today, and why the emissions routing sticker is present. I've gotten under the hood and found stuff I didn't know was there, and some that I have no clue what it does. I think I found the EGR valve, but I'm not sure. I learned this week that my hot air intake wasn't effective, but counter-effective to a degree. I finally found the starter, which I'll probably have to replace with all of the CODFISHing. No complaints -- trial, error, learning, and sacrifice for the betterment of FE and emissions. That's why I'm here.

The automaker did a good job, but perhaps "right" is too strong of a word. For us, I agree that rarely anything stock is perfect for our applications, but regarding the emission as the final product out of the tailpipe, I realized "how can we be certain that any modification to this system isn't going to hurt and not help". NOx is nasty for Asthmatics, CO2 is ruining our atomosphere, and some automakers are have done a good job and designed longevity into their emissions systems, and others haven't. We can attempt to master FE and use the Scientific Method as our guide to make changes and confirm results. Regarding the EGR...

I think I got over my head in this discussion and I'm asking questions that I could have looked up. I think I'll step aside let you guys take it from here.

-Rick H.

[MetroMPG]

Originally Posted by rh77

Honestly, I'm learning here

Me too. I'm no expert. My interest in FE, spurred on by this site, has resulted in a lot of unintended education.

The automaker did a good job, but perhaps "right" is too strong of a word. For us, I agree that rarely anything stock is perfect for our applications,

Good point. I'm willing to take a driveability "hit" for better FE. Which is saying a lot given what I'm driving.

I agree with your points on emissions. We could all find ways to hack our cars to lean out the A/F mixtures and gain MPG, but we'd be increasing oxides of nitrogen in the exhaust. With carb'd cars, you just had to introduce a vacuum leak between the carb and the cylinders.

---

Another bit of EGR / MPG info:

Air induction, EGR, and fuel economy (John De Armond; Bob Hale)
http://yarchive.net/car/air_induction.html

I looked up your reference (Internal Combustion Engine Fundamentals,
Heywood, page 837,838). Very interesting. Appears from his chart
that BSFC minimizes at about 25% EGR.

It should be pointed out that the chart in question shows large gains
for fast burn chamber designs. On the same chart is a line for slow
burn chambers that shows much less improvements and then only at
low (5-10%) EGR injection.

[rh77]

Originally Posted by MetroMPG

Me too. I'm no expert.

Many of us here would disagree.

My interest in FE, spurred on by this site, has resulted in a lot of unintended education.

Unintended, but that's a good thing.

I'm willing to take a driveability "hit" for better FE. Which is saying a lot given what I'm driving.

Bingo. I've been trying to de-tune my car for better FE. I'll take a huge hit in power if I have to. 145hp is too much for the Integra, and 200+ is a lot for the TSX, but it's starting to get the mileage of the 'Teg, with LEV status. I admittedly lack any knowledge of the how the Honda K24 engine and its TbW system works. Much more complicated than '98 emissions components.

We could all find ways to hack our cars to lean out the A/F mixtures and gain MPG, but we'd be increasing oxides of nitrogen in the exhaust.

Something I didn't realize until the last month or so.

Thanks for the link -- I'll dive in and see what happens.

Honestly, I've made some careless errors in posts lately, mostly because I'm home this week, have more time to post and just plain didn't have the facts straight. It's like cramming for an exam -- the brain is designed to actively forget, but when you put too much information into it, what's lost isn't up to the person.

RH77

[omgwtfbyobbq]

I've posted this before, and when using a 1.9L TDI modified for SI and PFI, the maximum EGR rate was ~50%, and peak BTE ~43% on methanol, and ~41% on ethanol, which is much better than the Prius' 37%, and more importantly, on ethanol 38% efficiency is seen as low as ~7 bar from ~1.2-1.8k rpm (fig.4), which means that efficiency is ~1.5 times that of the best gasoline engine available during he EPA highway cycle.

Since the price of E85 seems to correspond to it's lower energy rating per gallon, this implies that a Prius powered by one of these engines, running on E85, would probably get ~55mpg of E85 on the EPA highway cycle, or a fuel content adjusted rating of ~77mpg. So as long as the price of E85 is less than 87 octane gas, it would be more efficient, and definitely cheaper, to have this type of engine.

It appears that the limit in terms of minimizing pumping losses via EGR is primarily engine design, and then probably the octane of the fuel. Is anyone else thinking about an intercooled EGR valve?

edit- Oh wait, the University of Wisconsin already did for some parallel diesel hybrid project. But no mention of it's use for gassers, I wonder why...

[rh77]

Holy guacamole, I just found something out, the TSX has NO EGR!

About the K24 engine...

Quote from:

http://www.vtec.net/articles/view-ar...icle_id=401733

"Cam Timing Mechanism

The biggest gift Honda has given to tuners of the K-series engine is the VTC mechanism. Located on the end of the intake camshaft, the VTC mechanism, via hydraulics, allows 25 [crank] degrees of continuous movement on the TSX and 50 degrees on the RSX. [snip] For emissions, the ability for Honda to rotate the cam to zero at idle to dial out all overlap makes for a very clean engine with no need for EGR. EGR porting is in place on the head, but is blocked off."

I guess that's one way to do it...

RH77

[Sludgy]

Originally Posted by MetroMPG

I wonder what makes higher cylinder temperatures: lean burn, or high rates of EGR.

EGR always makes cylinder temperatures lower. That's how it reduces NOx formation.