EGR now very important…

Posted on May 20th, 2008 in Driving Emotion,Economy,Engine Management by Julian Edgar

Today’s AutoSpeed article – EGR Comeback – is far more important than an initial glance might suggest.

In fact, it is the first of three stories that we will have on exhaust gas recirculation (EGR), a technique that is increasingly important in the chase for better emissions and fuel economy.

Next week we start a two-part series on modifying electronically-controlled EGR. The guinea pig is my hybrid Honda Insight, but I think that the shown techniques (certainly in broad-brush application, if not the specifics) are applicable to any spark ignition engine.

The key point to realise when considering EGR is that the exhaust gas is fed back into the intake after the throttle blade.

Therefore, in part-throttle conditions, recirculated exhaust gas can help fill the cylinders, so reducing the amount of air that needs to be drawn past the throttle. The result of that is reduced pumping losses, and so potentially better fuel economy.

While I have never seen anyone modify EGR in the way covered in the articles, I think the technique has enormous potential for custom tuning, especially of modified cars where ignition timing and part-load mixtures have been altered.

Without giving away what is still to come, in my Honda I can accurately and steplessly adjust the real-time EGR from within the cabin, tuning its action to suit the prevailing requirements. I’ve also chosen to do it for nearly no cost and with all the tuning done on the road, but it’s an approach that also lends itself perfectly to engine management changes via software re-writing (or an interceptor) and dyno tuning.

And I think cooling the EGR opens up a whole new field of potentially better part-throttle fuel economy in spark ignition engines.

So have a close look at today’s background article on EGR, and shed the mind-set that EGR is just some horrible old fashioned emissions band-aid…

34 Responses to 'EGR now very important…'

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  1. Stewart said,

    on May 20th, 2008 at 8:44 am


    My wife used to own a cheapy Mazda 323 (1982) which my brother in law had plugged up the EGR outlets to the inlet manifold with cut down bolts!! not knowing why EGR was there, i left it alone and complained incessantly about its poor fuel economy and its poor running ability..

    the benefits of hindsight

  2. doctorpat said,

    on May 20th, 2008 at 10:56 am

    If I interpret this correctly, one can see EGR as yet another way to vary the effective displacement of an engine.

    A two litre motor running 40% EGR is really acting like a 1.2 litre motor, with the associated fuel consumption. (The effect on emissions is an additional effect.)

    Hence we have the ability to vary the displacement from 1.2 litres (effective), to two litres, and then add 1 barr of boost to get 4 litres. That’s got to be more efficient than lugging a 4 litre donk around all the time, when you only use the power 1% of the time.

  3. Brent said,

    on May 20th, 2008 at 11:54 am

    I’m really keen to see what can be done with regards to cooling the gases? I wouldn’t imagine it would be too easy to cool a turbo exhaust from the almost 1000 degrees to 21 degrees mentioned in todays article.

    As always I look forward to seeing what Julian has found out for us but I hope he follows it up better than the water injection articles. Anything that will get better part throttle emissions and economy is welcome in my books.

  4. Ben said,

    on May 20th, 2008 at 12:03 pm

    The diagram of the honda EGR system in the EGR comeback article appears to show a linear potentiometer being used as the valve opening sensor. Have you altered this signal, or are you controlling the valve directly?

    I’m guessing you altered the valve lift sensor signal to get the ECU to open the valve more or less. The computer would still have the ability to alter the EGR, but you would then be able to say whether you want it to be open more or less. Or am I on the wrong track completely?

    Another issue I have is that wouldn’t altering the EGR amount alter mixtures on a car without an air-flow meter? Because the pressure in the inlet manifold would rise without actually getting more fresh air into the engine. Or is the closed loop on the insight able to deal with the changes you are making?


  5. Ben said,

    on May 20th, 2008 at 12:15 pm

    Brent – What was wrong with the water injection article? Apart from not advancing the timing more to get more out of the water injection (which he has proven he can do with the 5c modification). Leaving the system installed on either car for a fuel economy benifit would have either meant some kind of variable flow design (and all of the water going into the intake) or a large tank.

  6. doctorpat said,

    on May 20th, 2008 at 12:51 pm

    I too found that the water injection article wasn’t quite finished. It really needed a few more weeks of work: a before/after Insight fuel economy measure and direct injection into the Pug.

    However I was perfectly aware that the practical considerations brought up in the article were not going to allow that (at least not yet).

    And therefore we have the choice between an unfinished, tantalizing article, or no article at all. I’ll go for the unfinished article every time.

  7. Lionel said,

    on May 20th, 2008 at 1:11 pm

    Temperature reduction can be accomplished by water injection into a cooling chamber for the exhaust gases. If the water injection system with a fine mist is sprayed into the chamber and the water is at a relatively cool temperature to begin with as it goes through the latent heat of vaporization stage it will absorb heat from the exhaust gases. If it turns to steam–great! Now you have steam injection which provides a power boost along with the exhaust gases reducing pumping loses and engine displacement. Sounds good to me. Can’t wait to see what Julian comes up with!

  8. Julian Edgar said,

    on May 20th, 2008 at 2:50 pm

    Just a general comment: the more complex a DIY article is, the less people will ever do it. It therefore behoves me to keep my DIY articles as technically simple as possible.

    Ten times as many people will try a water injection system where the nozzle can simply be placed in front of the engine air intake than will ever do so if a pressure-tight attachment needs to be made into the inlet manifold. If better intake air temp reduction can be made by simply squirting the nozzle on the intercooler core than injecting the water pre filter, then most people will be happier to do that than try to inject water into the intake post turbo.

    Perhaps 100 times as many people will try a very simple technique for altering EGR than would attempt to build a water injection system integrated with the EGR system!

    By far the most popular DIY articles over a decade of AutoSpeed have been those that are very simple, cheap and easy to do, even if the results are not quite as good as would be achieved with much more complex and expensive modifications.

  9. Andrew said,

    on May 20th, 2008 at 6:58 pm

    To those who have access (probably most likely through a university library) this combination of EGR and heated intake air on an SI engine may be interesting:

    Effects of Inlet Air Heating and EGR on Thermal Efficiency of a SI Engine At Part Load – SAE Paper 901713.

  10. Julian Edgar said,

    on May 20th, 2008 at 7:00 pm

    Well found – I didn’t find that one in my research. If anyone has a copy, I’d like to see it…

  11. Michael said,

    on May 20th, 2008 at 8:53 pm

    I have questioned this for a while now, you hear about reducing oxides of nitrogen as the primary purpose, but does it not at the same time, technically force you to use more throttle and reduce pumping losses as against a system without egr or egr removed?

    I questioned my brother who removed it from his SR20DE pulsar after fitting a import plenum about economy, but claims no significant reduction noticed.

    I am unsure of how these pollutants as such effect combustion or if at all in anyway…

    Should be interesting to hear results, but my guess is it will be hard to measure.

    I mean most of the engines with cylinder deactivation are only claiming up to 10-15% at best and thats with multiple cylinders shut down entirely.

  12. Blair said,

    on May 21st, 2008 at 3:56 pm

    Isn’t an EGR integral to the anti-lag systems used in World Rally Cars?

    I do not know if this is what they do but taking the exhaust after the turbo and injecting it after the throttle butterfly seams to be the best strategy to me. It allows the turbo to keep spinning, and indeed the motor, ready for instant response once the throttle is opened again.

  13. Jake C said,

    on May 22nd, 2008 at 7:48 am

    Some anti lag systems linked the intake, pre throttle plate, to the exhaust manilfold. when the trailing throttle occured which could be defined as roughly <25% throttle and <2200rpm the (modified?) egr valve was opened, allowing the boost pressure to flow directly into the axhaust manilfold, while the ecu would also increase fueling by say 20%. The air and fuel now in the exhaust manifold would burn and expand, spooling the turbo.
    other methods exist now, but this one relates to this blog the most.

  14. Howard said,

    on May 23rd, 2008 at 10:53 am

    Excellent concept Julian, I look forward to seeing what the out come is.
    It’s already got the grey matter ticking over as to how it can be retrofitted to cars without EGR.
    I think Ben made an excellent point about using such a system on a car with MAP sensed load measuring.

  15. Wayne said,

    on May 25th, 2008 at 11:43 am

    I too am very keen to see the articles and give it a go. I was also thinking about an airflow meter bypass which can be used to chase a particular AFR when in lean cruise (like your Insight does as standard!) as lean cruise on my commodore is open loop. Iny thoughts of such a project in the future? I recently managed 10L of LPG per 100km for the recent trip to Brisbane (760km avg speed 89km/h). As I do 46,000 km per year (95% in lean cruise), a 2% improvement would mean a $80 saving per year.

  16. Ben said,

    on May 25th, 2008 at 9:56 pm

    Wayne, a simple method of altering the airflow meter output is to use a potentiometer between the output voltage and ground. The wiper arm (the one that varies in voltage) then becomes your new air-flow meter output. Wound all the way one way, you have normal air-flow meter output, the other, none. As you can see it’s a very powerful tool… It’s also much simpler than bypassing the air-flow meter.

    This article deals with the exact modification, along with a way to force open loop (DIY lean burn?). Read the whole series.

    Julian – Have you ever come across anyone making their own lean burn system?

  17. Julian Edgar said,

    on May 25th, 2008 at 10:53 pm

    Only if it’s an airflow meter that doesn’t have a variable frequency output…

    I haven’t come across anyone doing a lean burn modification. I spent Friday working on an (unsuccessful) system.

  18. Chris said,

    on May 26th, 2008 at 9:36 am

    What proportion of exhaust gas is water vapour? I seem to recall it’s over 50%. Well-cooled EGR = water injection, give or take… like the exhaust-water recycling systems on late piston-engined airships.

  19. Ben said,

    on May 26th, 2008 at 9:58 am

    At least you now know what doesn’t work. Are you going to put this information in an article? I would love to hear about it. As you have said, one experiment is better than any number of opinions, whatever the outcome. Or could you post it here?

  20. doctorpat said,

    on May 26th, 2008 at 10:23 am

    I’ll second Ben’s comment.

    And Chris, any on line content on the airship motors?

  21. Julian Edgar said,

    on May 26th, 2008 at 10:28 am

    It’s part of a series I am working on that is scheduled for 10 weeks’ time.

  22. Ben said,

    on May 26th, 2008 at 10:49 am

    Now that’s a long wait…

    Incedentally you might want to have a look at this forum:

    I know you don’t normally like forums, but this one appears to to have a lot more people who actually do experiment with mileage.

  23. Chris said,

    on May 26th, 2008 at 5:39 pm

    doctorpat: There’s a few figures mentioned in this report. Their motivation was different, though: they needed to balance out the weight of the fuel they were burning, to avoid having to vent expensive helium.

  24. Ben said,

    on May 26th, 2008 at 6:43 pm

    As opposed to the hydrogen blimps, which vented hydrogen (through the diesel engines) to counteract the lost weight of the diesel fuel. Increasing their range by some 25% apparently.

    Kind of proves the worth of using hydrogen as a supplemental fuel in some engines (Much like LPG is used occasionally in diesels). Of course a hydrogen on demand setup is a little more difficult to do properly.

  25. Jake C said,

    on May 27th, 2008 at 7:50 pm

    I don’t know if this works, but it supposed to be able to ofsett the o2 sensors output voltage.

    Maybe an op amp with a gain of 1 could be used (voltage follower) and by using a potentiometer on the offset null circuit a variable offset voltage could beacheived?

  26. Jake C said,

    on May 27th, 2008 at 7:56 pm

    Oops, i didn’t include the link.
    (sorry for the terrible typing, broken wrist)

  27. Wayne said,

    on May 28th, 2008 at 5:18 pm

    For those Aussie Commodore Drivers out there, VY II V6 has an EGR system similar to the Insight. Active just off idle for a fair percentage of throttle, and seems to be active in lean cruise (on holiday and left the EGO indicator at home Doh!). Frequency 128Hz and duty cycle from 40 to 60%. If anyone has a wiring diagram id like to see it.

  28. Julian Edgar said,

    on May 28th, 2008 at 6:33 pm

    If there is no feedback circuit, the Digital Pulse Adjuster (starts at would be ideal to modify EGR valve operation.

    (Or just apply full power to it via a dashboard switch [with a dropping resistor to limit current flow] and do some initial testing!)

  29. Wayne said,

    on May 29th, 2008 at 12:40 am

    As with the Honda, there is a 5 pin plug on the commodore valve. I have not tested the range and relative direction of the signal change yet. What are your thoughts about back probing all three wires with a trimpot and to give the feedback signal a bias? Obviously it would make the whole setup much more sensitive, but reverting back to standard would be much simpler.

  30. Andrew said,

    on May 29th, 2008 at 1:54 pm

    If it truly is open loop when in lean cruise and not chasing a specified mixture on a wide band, might a digital pulse adjuster be used to lean out the LPG using the fuel control valve? How you might switch it in and out (lean cruise vs stoich.) I don’t know.

    For a car not originally fitted with EGR, the control of the valve might be done by using an SC independent boost controller to operate the valve using injector pulse width as a load indiactor.

  31. Wayne said,

    on May 30th, 2008 at 9:57 pm

    More testing on the commodore today showed among other things that at 100km/h and near constant the egr valve is between 70% and 90% open depending on the throttle position. Coasting down big hills it tapers right off to closed. When I get home and have all my tools, i am going to mod the feedback signal and see in there is a change in the fuel consumption.
    Thanks Andrew for the suggestions. As it is a brand new (earlier this month) gas system, I am not keen to tamper with it and void its waranty.

    Julian, Did you look into upsizing / upgrading egr valve at all while working on the article?

  32. Julian Edgar said,

    on May 31st, 2008 at 10:47 am

    EGR could be increased to the point of causing poor car behaviour. Therefore, a larger valve would not have been of any use.

  33. BG said,

    on June 3rd, 2008 at 1:14 pm

    Random thought – might get more noticeable changes to varying EGR on an engine without variable valve timing ?

  34. Bob Sheeley said,

    on May 28th, 2009 at 5:00 am

    I’m running a turbo’ed Hayabusa motorbike engine in a car here in the uk, only for track use. I’m running at low boost (8psi) and do have a little lag on low revs (to about 4.5k – engine revs usefully to about 9.5k). I’m seeing articles on EGR but cannot find out quite how this could help me with my issue, although I believe that there is a solution in there somwhere. I’m using a Motec ECU, which is quite powerful and has quite a lot of ability. Any ideas?