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  • EGR

    Interesting item here http://www.bbc.co.uk/news/business-36589106 about diesels which only conform to euro 5 spec. These of course are what Toyota sells to the Australian market.
    I wish it were more informative although it does say that manufacturers keep how their vehicles are programmed close to their chest.

  • #2
    Good read. Can see the slow demise of the city based diesel passenger car. Fortunately petrol engines have become more efficient in recent years. The argument does not apply to the bush but I doubt down the track the politicians will be able to see the difference.
    2009 120 GXL D4D, TJM Bull Bar, Winch, Safari Snorkel, ARB Lift, ARB Lockers, Black Widow Drawers

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    • #3
      That seems to shoot down the reason for having EGR in the first place.

      As I understand it EGR cools down the burn to reduce the amount of NOx, yet that article reports that the cooler the burn the more NOx is produced.

      I had previously read that the cooler the burn the more CO2 is produced, which is what all the climate people want to stop.

      Makes me wonder why we have been inflicted with the EGR in the first place, perhaps more research should have been done before putting them in.

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      • #4
        Yes we need someone to explain the principles as it has always seemed contrary to common sense that a cooler burn can be achieved by injecting hot exhaust. We know that an intercooler gives more power and increases efficiency by cooling the air which has been heated by being compressed by the turbo.
        This makes sense to me but introducing hot exhaust gas does not, or is it because it contains less oxygen?
        The article says that manufacturers are allowed to restrict the EGR valve when the (presumably ambient) temperature is too hot or too cold to "protect the engine" and this is the loophole that is being used.
        I have no idea why temperatures would make any difference to injecting hot exhaust back into the inlet manifold with consequent soot and crap forming. So a reason from some of the brains on here would be appreciated.
        Vehicles (IMHO) are too complicated now, I used to run Isuzu troopers in the UK, the 3.0 litre Cat based engine had its EGR operated by vacuum, it was a simple job to add a ball bearing in the pipe to keep the valve shut. There were no fault codes etc produced, oh for the old days!

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        • #5
          As taken from wikipedia

          In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline and diesel engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. This dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures. NOx is produced in a narrow band of high cylinder temperatures and pressures.

          In a gasoline engine, this inert exhaust displaces the amount of combustible matter in the cylinder. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.[1] Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates (though at some loss of engine efficiency).[2] Gasses re-introduced from EGR systems will also contain near equilibrium concentrations of NOx and CO; the small fraction initially within the combustion chamber inhibits the total net production of these and other pollutants when sampled on a time average. Most modern engines now require exhaust gas recirculation to meet emissions standards.

          Regards
          Doug
          2018 150 Series Crystal Pearl Prado VX 2.8l. 2 inch King springs and Bilstein shocks, Airtek TJM snorkel.

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          • #6
            So after reading Wiki, how come Nox is worse when cold air gets sucked in, does not seem to add up to me but I am very definitely not mechanically minded

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            • #7
              Originally posted by ozimacca View Post
              So after reading Wiki, how come Nox is worse when cold air gets sucked in, does not seem to add up to me but I am very definitely not mechanically minded
              The NOX levels are higher with cold air because it contains more O2 than recirculated exhaust gas which has already burnt most if not all of its oxygen content. The lower the O2 level going into the engine the lower the NOX emission.
              2018 150 Series Crystal Pearl Prado VX 2.8l. 2 inch King springs and Bilstein shocks, Airtek TJM snorkel.

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              • #8
                Thanks Doug for posting the Wikipedia explanation, looks like I was on the right track by thinking that the EGR valve allows in already burnt air which contains less oxygen causing lower combustion temperatures. The combustion temperature is the important part here, not how hot the air was when entering the engine.
                The article suggests that regulations allow less EGR valve intervention if the ambient temperature is too low or too high, this is to "prevent engine damage"
                This is where the confusion starts for me, how could damage be caused if the EGR opens out of a certain temperature range? Has anyone ever monitored a Prado valve to see when it is opening? as I don't expect this information would be available from any manufacturer let alone Toyota.

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                • #9
                  Originally posted by cuda View Post
                  The NOX levels are higher with cold air because it contains more O2 than recirculated exhaust gas which has already burnt most if not all of its oxygen content. The lower the O2 level going into the engine the lower the NOX emission.
                  OK thanks, I have got that now, oxygen is the culprit !

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