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  • Turning up the fuel

    I thought I’d start a new post carrying on from my previous “Embarrassing lack of torque” posts.

    http://www.biofuelsforum.com/threads...lack-of-torque

    The problem turned out to be a fairly simple lack of fuel via the ‘the big screw at the back of the pump’, also called the ‘smoke stop screw’ or ‘high-speed screw’…not sure what the official name is though. The pump was rebuilt about 12 months before I bought the ute, so about 3 years ago – I suppose they just tuned it very conservatively? Anyway, I had to chip off the anti tamper seal to get to it and have progressively screwed it in (clockwise) ¾ turns so far, ¼ at a time.

    I’ve been amazed at how much power has increased and it gets more powerful with every ¼ turn. The other interesting thing is that turbo lag is also decreasing and boost pressure increasing – it used to start boosting at around 2500 rpm, peaking at 12 PSI at 3500 rpm and now it starts at around 2200 and peaks at around 3200 RPM at 14 PSI (I should add that I disconnected the wastegate some time ago as it was making 11 PSI with it connected and 12 PSI without). Fuel economy also seems better, despite giving the loud pedal a hiding, but I don't have firm figures on that.

    I was warned that smoke would increase, but so far it hasn’t been an issue or even really noticeable. Also, the fast idle increases each time and that has to be adjusted down via the main throttle screw, which is very easy. Eventually I’m told I will run out of idle adjustment though. I’ve also always heard for years and years that if you keep adding fuel to a diesel, you’ll increase exhaust gas temperatures until you do some damage, like melting pistons, which is why they put the anti-tamper seal on. But I’ve also heard more recently that that is very unlikely on an engine like this.

    So can I just keep turning this screw and increasing power until:
    a) It gets too smoky; or
    b) I run out of fast idle adjustment?

    I feel like I should be happy with where I've got it to, but I'm power hungry now!
    3DB
    1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
    1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016 - SOLD
    1994 Peugeot 405 SRDT 1.9L intercooled turbo diesel (Shitbox Rally car.) - B100 since August 2019 - SOLD
    @thirddegreeburns on Instagram
    @thirddegreeburns2019 on Facebook


  • #2
    Re: Turning up the fuel

    Hi 3DB,

    stands to reason. on the too much fuel issue, you will get to a point where overfuelling occurs (too rich), after this any more fuel added will not burn, and will have a cooling effect on EGT and therefor CHT. conversely, and here is the weird bit, with internal combustion engines under constant load (I know, I know a car engine isnt under constant load), the most efficient fuel burn is at peak EGT on the lean cut. You do not want to be operating in this space though. It spells trouble for your heros. For a given power setting and load value, leaning the mixture will increase EGT.

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    • #3
      Re: Turning up the fuel

      Originally posted by Captaincademan View Post
      Hi 3DB,

      stands to reason. on the too much fuel issue, you will get to a point where overfuelling occurs (too rich), after this any more fuel added will not burn, and will have a cooling effect on EGT and therefor CHT. conversely, and here is the weird bit, with internal combustion engines under constant load (I know, I know a car engine isnt under constant load), the most efficient fuel burn is at peak EGT on the lean cut. You do not want to be operating in this space though. It spells trouble for your heros. For a given power setting and load value, leaning the mixture will increase EGT.
      That is petrol engine stuff! Quite the opposite is true when overfueling a Diesel - Excess fuel = higher EGT"s

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      • #4
        Re: Turning up the fuel

        HI 250, true, it does apply to petrol engines, but at some point the ratios will start to interrupt fuel burn and the excess fuel will start to cool the cylinders and the exhaust gases. whether or not the engine can handle the peak temperature is another thing. I would hazard a guess that most people do not want to risk their engine by finding the rich cut or the lean cut? I certainly wouldnt be.

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        • #5
          Re: Turning up the fuel

          Originally posted by Captaincademan View Post
          HI 250, true, it does apply to petrol engines, but at some point the ratios will start to interrupt fuel burn and the excess fuel will start to cool the cylinders and the exhaust gases. whether or not the engine can handle the peak temperature is another thing. I would hazard a guess that most people do not want to risk their engine by finding the rich cut or the lean cut? I certainly wouldnt be.
          What you are suggesting can never occurr when over fueling a diesel engine. In the extreme, as a result of very high combustion and EGT temperatures, the excess fuel combusts in the exhaust manifold driving exhaust gas temperatures even higher. Excess fuel in a diesel can never result in a reduction of EGT.
          Forget the petrol engine science, diesels are totally different.

          Comment


          • #6
            Re: Turning up the fuel

            Originally posted by Captaincademan View Post
            or the lean cut? I certainly wouldnt be.
            A diesel engine always runs to what you call 'the lean cut' every time you lift your foot off the loud pedel.
            You lift your foot, the governor closes off the fuel, no fuel or very little fuel be injected until engine revvs fall and the goveror decides to open up and inject a bit more fuel.

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            • #7
              Re: Turning up the fuel

              This topic is getting very interesting, please keep it going and most of all please be nice to each other

              What I always thought is a diesel "eats" what you give it to him, more fuel equals more power that is why I never understood is the black smoke equals unburned fuel theory.

              Have a good night Gentleman
              1990 Toyota Hilux LN106 with ATG 2 tank system (sold after running 150.000 ks on mainly WVO)

              1993 Toyota 75 Series with 1 HDT conversion, 75l factory tank and a custom 170l under tray tank. (Retired with 680.000ks on the clock mostly running on BIO and on WVO)

              2006 Landcruiser Troopcarrier 1HZ with DTS Turbo Kit, 170ltr long range tank currently not converted, running on B100

              "him who never made a mistake, made no discovery either"

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              • #8
                Re: Turning up the fuel

                Originally posted by Bueff View Post
                This topic is getting very interesting, please keep it going and most of all please be nice to each other

                What I always thought is a diesel "eats" what you give it to him, more fuel equals more power that is why I never understood is the black smoke equals unburned fuel theory.

                Have a good night Gentleman
                You are correct, up to the stoichiometric ratio of fuel to air. After that point, there is not enough air to burn the fuel completely, resulting in black smoke from the partly burned fuel.
                Now, I believe that it is possible for the fuel to be burning hotter as it leaves the combustion chamber, even though there is not enough oxygen to combust it completely.
                I do know that over fueling a diesel does increase EGTs.
                Regards,
                Tony

                Regards,
                Tony
                Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

                Current Vehicles in stable:
                '06 Musso Sports 4X4 Manual Crew Cab tray back.
                '04 Rexton 4X4 Automatic SUV
                '2014 Toyota Prius (on ULP) - Wife's car

                Previous Vehicles:
                '90 Mazda Capella. (2000 - 2003) My first Fatmobile. Converted to fun on veggie oil with a 2 tank setup.
                '80 Mercedes 300D. 2 tank conversion [Sold]
                '84 Mercedes 300D. 1 tank, no conversion. Replaced engine with rebuilt OM617A turbodiesel engine. Finally had good power. Engine donor for W123 coupe. (body parted out and carcass sold for scrap.)
                '85 Mercedes Benz W123 300CD Turbodiesel
                '99 Mercedes W202 C250 Turbodiesel (my darling Wife's car)[sold]
                '98 Mercedes W202 C250 Turbodiesel (my car)[sold]
                '06 Musso Sports Crew Cab well body. [Head gasket blew!]
                '04 Rexton SUV 2.9L Turbodiesel same as Musso - Our Family car.
                '06 Musso sports Crew Cab Trayback - My hack (no air cond, no heater).

                Searching the Biofuels Forum using Google
                Adding images and/or documents to your posts

                Comment


                • #9
                  Re: Turning up the fuel

                  Fair enough, I guess you learn something everyday eh? I guess the question that comes out of this is what is more important to measure for what you are doing? If turboed then EGT will be very important for life of the Turbo, but CHT is critical for engine life? If over fuelling ups EGT's as several people here point out, is that enough to counter the cooling effect of unburnt fuel in the cylinder?

                  Where does the additional oxygen come from to support continued combustion in the exhaust manifold / turbo / pipe / muffler etc?or is there oxygen left over from the initial burn? if so then I would have thought there would have been enough to burn more fuel? or is there that much oxygen left over because we are never really approaching the maximum magic stoichiometric ratio?

                  or is the fact that it has been demonstrated that the EGTs keep climbing only because no one here has "snuffed" a diesel engine out with fuel? thinking about it, I would imagine this would need a severe amount of fuel.

                  I think all of this is telling me that the limiting factor (which I always thought to be the case anyway) on a diesel engine is RPM on a heavy piston with a relatively long stroke. If you could build a robust diesel that could handle crazy high RPM, then you might have a power plant capable of developing enormous power, as it can 'eat' as Bueff so eloquently put it, as much as you give it.

                  Obviously you blokes know a heck of a lot more about diesel's than I do, I am just thinking out load here.

                  Comment


                  • #10
                    Re: Turning up the fuel

                    it can 'eat' as Bueff so eloquently put it, as much as you give it.
                    Up to a point. I mean remember your compression ratio. There is not a lot of room in the combustion chamber of a diesel engine. A 3 litre diesel has 750 cc or ml per pot.
                    With a compression ratio of say 22:1 that means at top dead centre you have 34cc or ml space. So if you tried ti inject 40 ml of fuel you would have hydraulic lockup and start bending con rods.
                    Have a look on youtube at some of the tractor/truck pulls and see how much smoke they blow out.
                    For normal driving we are not going any where near these types of settings, or you would be arrested and thrown at the EPA for sure.

                    Comment


                    • #11
                      Re: Turning up the fuel

                      The reason a rich mixture in a petrol engine cools things down is that the petrol evaporates and it takes in heat to do that (latent heat of evaporation) the difference with a diesel engine is that the fuel does not evaporate but atomises (turns to droplets of liquid fuel), so has minimal cooling effect.
                      The one thing I have yet to find out is which engine can produce the most power, diesel or petrol, given the same displacement. Some of those modified engines (diesels) used in sled pulling comps. put out enormous power. I think they have turbo boost pressures up to 20psi? Of course a F1 engine uses petrol so for comparison we should look at the same engine speed as well
                      Diesels certainly have the lead as far as torque goes. eg. the new V8 Range Rover diesel produces 700Nm
                      Johnnojack
                      4WD Isuzu Jackaroo 3.1 200000km on WVO,(2020) 2 tank home built system 6 solenoids FPHE, heated filter fuel line and tank pickup for thicker oil. Mk. 9 version now and no changes planned as trouble free.
                      Mercedes W201 190D 1986 model: 2 tank system, bigger fuel line from tank, no heat exchanger, electric pump for diesel 22000km so far sigpic

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                      • #12
                        Re: Turning up the fuel

                        Originally posted by Johnnojack View Post
                        The reason a rich mixture in a petrol engine cools things down is that the petrol evaporates and it takes in heat to do that (latent heat of evaporation) the difference with a diesel engine is that the fuel does not evaporate but atomises (turns to droplets of liquid fuel), so has minimal cooling effect.
                        The one thing I have yet to find out is which engine can produce the most power, diesel or petrol, given the same displacement. Some of those modified engines (diesels) used in sled pulling comps. put out enormous power. I think they have turbo boost pressures up to 20psi? Of course a F1 engine uses petrol so for comparison we should look at the same engine speed as well
                        Diesels certainly have the lead as far as torque goes. eg. the new V8 Range Rover diesel produces 700Nm
                        20psi would be very modest. I run an F250 [7.3l V8] fitted with a 4" turbo that will easily boost to 30 psi.
                        It needs to be driven with one eye on the EGT gauge and the other on the tacho - redline is only 3250 rpm and it gets there awfully quick! I don't often use that tune [switchable from the cockpit] for obvious reasons.

                        Comment


                        • #13
                          Re: Turning up the fuel

                          Just did a bit of research on sled pulling engines - 100 to 200 psi boost is common and up to 300 psi using 4 turbos was mentioned. They tear engine blocks apart quite frequently!

                          Comment


                          • #14
                            Re: Turning up the fuel

                            Ive allways been a fan of drift racing and a team that has been getting A lot of attention in Europe is black smoke racing https://www.youtube.com/watch?v=hf5lLMCWWYc
                            yeap its diesel, and its an old mec wagon and yeap it did come first in Epua Drift – Seinäjoki, Finland.

                            absolutely amazing!
                            http://www.blacksmokeracing.com/abou...er-2012-setup/

                            Comment


                            • #15
                              Re: Turning up the fuel

                              Smithy - That Black Smoke 300TD is awesome. It would be great to build a bio / SVO version!

                              250 - I think the EGT gauge must be a necessity if you start seriously adjusting boost & fuel? I have considered investing in one. Any recommendations? And how hot is too hot?

                              I also fitted a water-to-air intercooler, made out of bits and pieces I bought on ebay or scavenged, before I started all of this fuel & boost adjustment stuff as I thought hot air was the problem. It didn't make much difference before I turned the fuel up, but it really works well now.

                              I've saved some pics here - I hope this works as I haven't been able to upload anything for a while:

                              https://www.dropbox.com/sh/negjarj0o...wrehQY5Aa?dl=0

                              Before installing it, I couldn't touch the cross-over pipe between turbo & inlet manifold without burning my hand after a run at full boost. Now it never gets over about 40C, no matter how hard you push it…….unless in heavy traffic where there is no airflow through the water radiator. I need to add a thermofan before summer.
                              3DB
                              1995 Holden (Isuzu) Rodeo 2.8TD 4X4 - B100 since April 2013
                              1976 Mercedes 300D Turbo 'The Coal Grenade' - B100 since May 2016 - SOLD
                              1994 Peugeot 405 SRDT 1.9L intercooled turbo diesel (Shitbox Rally car.) - B100 since August 2019 - SOLD
                              @thirddegreeburns on Instagram
                              @thirddegreeburns2019 on Facebook

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