EGR

[James Morris]

Hi Guys,
I just have a quick question on the legality of running EGR with regards to the Article 8.6.1 In order to limit the power capability from the engine, a single circular restrictor must be
placed in the intake system between the throttle and the engine and all engine airflow must
pass through the restrictor.
Does any one see any issues with feeding the EGR back in through the plenum?
Does any one know if a team has run EGR before???

James Morris
SMU Racing

[James Morris]

Hi Guys,
I just have a quick question on the legality of running EGR with regards to the Article 8.6.1 In order to limit the power capability from the engine, a single circular restrictor must be
placed in the intake system between the throttle and the engine and all engine airflow must
pass through the restrictor.
Does any one see any issues with feeding the EGR back in through the plenum?
Does any one know if a team has run EGR before???

James Morris
SMU Racing

[js10coastr]

I'm assuming that you'd have to run another valve or throttle to control the amount of EG being passed through... the restrictor would then have to be downstream of this.

[Wesley]

Just out of curiosity, why are you considering running EGR?

[Pete Fodor]

Yea I was wondering that - you thinking of using it to decrease fuel consumption?

I can only imagine it will probably give you A) a headache B) more work to do than you already have :3

[JamesWolak]

Knowing how little we are at steady state type conditions. I would be willing to state that you wont be able to gain fuel eco from EGR

[Wesley]

Additionally, why dilute some of the already restricted airflow with exhaust gas?

[Marshall.Hagen]

I am almost certain that EGR systems are intended to reduce NOx emissions by reduction of combustion temperatures, and actually has a detrimental impact on fuel economy, as you are diluting what should ideally be a uniform charge of air and fuel.

[rjwoods77]

EGR helps to get better gas economy by reducing pumping losses. It does other emissions related things but the only reason to use it in FSAE would be to reduce pumping losses but James is correct that being in and out of the throttle so much it would probably not be worth it. Shit just calibrating the control would be a nightmare without a Horiba gas analyzer just to see what the flow profile is like on so on and so forth.

[PatClarke]

Rob,
How exactly does EGR reduce pumping losses? Just curious as I had never considered that
Pat

[rjwoods77]

It was one of the first questions I asked working as a Calibration Engineer at Delphi and I still have to look at all the charts and stuff to remember what is going on since it effects a ton of things. I found a couple links that explain it well but the quick answer is it helps cylinder filling without having to draw that mass flow through the throttle which in essence reduces the pressure differential i.e. pumping losses. I used to think EGR sucked but once I saw how it helped with things I changed my mind. What's really neat is what they are doing with cooled EGR these days. I am pretty sure I read most of this out of the Heywood book if memory serves me correct.

http://www.autospeed.com/cms/A_110577/article.html

http://www.autospeed.com/A_110...p_1/cms/article.html (http://www.autospeed.com/A_110555/hDg34uLtp_1/cms/article.html)

http://www.autospeed.com.au/cms/A_110581/article.html

http://www.me.utexas.edu/~sae/...rnative_fuels_V1.pdf (http://www.me.utexas.edu/%7Esae/Files/Cooled_EGR_and_alternative_fuels_V1.pdf)

[PatClarke]

Thanks Rob,
I had never considered that the amount of gas being recirculated in petrol was sufficient to materially affect pumping losses. Obviously, I was wrong =]
These days I am mostly concerned with EGR on diesel engines where a very significant amount of EGR is used, but diesels have no throttle, so the situation is different.
We are starting to see 'reactive' throttles that choke off some air intake once the ECM has determined the fuel load. This reduces the additional air that does little but make NOx.

Incidentally, the more I have to do with these common rail turbo diesels, the more I like them!

And further incidentally, and to bring this back on topic, there is no arguable reason to use an EGR valve on a FSAE engine and many arguments why you should not!
EGR these days is commonly achieved by cam phasing. Now that is a different issue because cam phasing can very significantly reduce pumping losses and has other benefits.

Cheers
Pat

[rjwoods77]

Pat,

I remember when doing PVET for CARB I had to create failures codes by manipulating all sorts of equipment to fake the ECM into thinking stuff was bad. One of those was the EGR pintle. Just driving along and pushing the thing in different ways caused different codes. If memory serves me correctly under high IMEP conditions the pintle was closed. It was only on low to mid IMEP that the pintle fluctuated. If a FSAE car is in low to mid IMEP then the driver/car sucks. The only condition I could see this used is when you are downshifting but that would be some weak downshifting. More the reason to go to a cvthttp://fsae.com/groupee_common/emoticons/icon_smile.gifEGR control is very complicated in terms of ECM control to since it is a PWM controlled device based off a number of different inputs.

[Charlie]

Simply described an EGR system is a displacement reducer. Although exhaust may have *some* fuel or oxygen, it is basically an inert gas as it's been through the combustion process already. Add it into the cylinder and it dsplaces fresh air, allowing you to put less fuel into the cylinder and advance timing without risk of overheating the chamber (and reduces the risk of knock).

I don't see the pumping losses to be significant, but it should reduce them by some amount. I suppose that at part throttle, the throttle body is the most significant pumping loss and you are bypassing it with EGR.

I think EGR is a good tool but I don't see it being useful on any petrol racing car. It might be a hard thing to get through the rules, though technically I would think it's legal, since all the air going into the intake would still go through the restrictor first.

[VFR750R]

As mentioned there is no advantage at WOT and part throttle power or efficiency does not decrease lap times.
That should end the debate for fsae.

I do find it interesting the idea of EGR for diesels. Do you want it as hot or cool as possible? It also seems that throttling a diesel for the purpose of decreasing NOx is backwards. Turbos are often installed to decrease combustion and exhaust temperatures for a given amount of fuel. Which i would assume lowers NOx. I would expect hotter combustion temps and worse efficiency throttling a diesel. Seems like cylinder deactivation would be more desireable then throttling.

[overdrive535]

If I understand it correctly, one would want the EGR gas at or lower than the temp of the charge air after it has passed through the intercooler. I doesn't make much sense to me to cool the charge air and then heat it up again.

The only reason for EGR on a diesel is to reduce the NOx to Tier 4 required levels.

[VFR750R]

The reason I would assume hot rather then cold is diesels are not knock limited and will run higher efficiency when they are run hotter. Intercooling reduces efficency of burn for volumetric efficiency. If EGR is a low loading efficiency improver, i'd imagine the gases being hot is no big deal.

[Damon Pipenberg]

My experience is that for gasoline engines, EGR is used to dilute the intake charge, which lowers the combustion temperature while maintaining a stoichiometric AFR (required for the catalyst to work properly). The lowered combustion temperatures reduces NOX production. There might be some advantage in terms of pumping losses as well, but I'm not aware of it.

I don't believe that there is a fuel economy benefit, I'm pretty sure its the opposite. Simply running a lean mixture would be much better for fuel economy, but it is difficult to make the emissions system work for lean burn, as least for a port injected engine.

Of course with direct injection and phased cams, a stratified charge can be achieved, and lean burn can take place without high combustion temps and associated emissions.

As far as race cars go, its not something to worry about - we're lucky we don't have to think about emissions.

[overdrive535]

2010

That's all I can say...

[Charlie]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Damon Pipenberg:
I don't believe that there is a fuel economy benefit, I'm pretty sure its the opposite. Simply running a lean mixture would be much better for fuel economy, but it is difficult to make the emissions system work for lean burn, as least for a port injected engine.
</div></BLOCKQUOTE>

You are right that EGR is primarily a NOx reducer, but it does result in better fuel economy, because it reduces effective displacement. This means you can put less fuel in the charge without worrying about lean misfire. Effectively, you can get an acceptable A/F ratio with less fuel than necessary if the EGR system was not operating.

[Wesley]

While I agree that the associated loss from the throttle body is sidestepped, increasing the amount of inert gas also reduces the specific heat ratio of the motor. You do see reduced heat rejection from the lower temperatures, but it seems for every advantage there's a drawback that keeps efficiency around the same.

[bhatia]

EGR increses specific heat of mixture. so rise in temperature are lesser which reduces chances of self ignition. so calibrator may use more advanced ignition timing and improving the efficiency.