Announcement

Collapse
No announcement yet.

Detonation and Preignition FYI

Collapse
This is a sticky topic.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by PGT#1
    racing gas will fry your o2 sensors, and make your engine run rich.........which initally sounds like a good thing, more fuel is better for boost. I just dont like the idea of having my ECU not knowing o2 levels in a boosted engine, would just make me nervous. I dont think octane booster would be very reliable either. Since you just add a can into your gas tank, theres no way to assure that it will mix well, leaving you with a range of octanes. Which again, on a boosted engine, i wouldnt want.
    how will racegas make it run more rich ?......racegas has a much higher octane rating, wich means its less prone to self detonate as in regular gas. and the O2s are only used during regular driving, not when you race.
    Life isn't like a bowl of cherries or peaches, it's more like a jar of Jalapenos ....
    What you do today, might burn your ass tomorrow.

    Pearl '92 Audi //S4 GT3071R, running 27 psi
    Lava gray '14 Audi //SQ5, Chipwerke, 034 Intake Pipe
    For PSP Awareness click here

    Comment


    • #17
      i was saying that when you run race gas, it will burn out your 02 sensors, and since their burnt out, you ECU doesnt have imput from those sensors. So to make sure its sending enough fuel, it adds more fuel. This happened to me, i bought like 5 gallons of 118 race fuel, and after about a 50 miles of driving my check engine light came on. I had my friend run the ecu for fault codes and what came back was 02 02 02 02 02 02 02. It was runnin a little flat too after the light came on. I ran through the rest of the tank, put 93 back in, replaced the 02 sensors, light went away . Ive heard other stories similar to mine, i couldnt tell ya exactly WHY the race gas recks the 02 sensors, but apparently it does.

      Comment


      • #18
        Running boost without O2 sensors isn't a concern -- the O2 sensors are only used to run closed loop which doesn't happen when you are on boost. If it was trying to use the O2 sensors then the mixture would be bouncing around 14.7:1 and you'd be way to lean to boost safely.

        I'm not exactly sure why race gas is hard on O2 sensors, but I too have heard this before. Leaded gas will kill them too, I believe.
        Former PGT-turbo owner... now 2010 VW Golf TDI

        Comment


        • #19
          so what, do you just remove the o2 sensors? cut the cord? doesnt this send error codes and make the check engine light come on? Cause i know you want to remove the VRIS when you boost, or tie the valves open, but i wouldnt want to have that code on all the time.

          Comment


          • #20
            oh i misunderstood what you said. I thought you meant that when you boost you cant use o2 cause it would affect the air/fuel ratio, but then it clicked lol. When your boosted the ecu doesnt need to do all the open/closed loop with the vris and everything cause theres already positive pressure from the boost, gotcha.

            Comment


            • #21
              i wanted to let some people in on what causes the unique situation that detonation brings about.

              from demolitions i know about some explosives and flame fronts and a few basic things about common fuels and oxidizers.

              from physics i know about bulk modulus and sound waves.

              when the mixture is so dense and compressed it can transmit sound waves faster than flame fronts and the sound wave can be powerful enough to create combustion in many places at once.

              as one or two people described, the pressure waves go in all directions because the concussion, or sound wave travels ahead of the flame front. this is how a car can detonate but not autoignite or preignite. the original flame front can be the intial source of the concussion, but it doesnt need to be. pretty much, the more dense the mix, the more likely it will combust with a sort of fixed wave source. say the source is the spark plug being too hot and preigniting, then before the flame front can even move a fraction of the distance across the cylinder the pressure wave ignites every available fuel and oxy. if this occurs before the tdc point it can be as seen, a bit of it after tdc and after ignition can actually increase power, but is usually so drastically bad for an engine only diesels ever want to hear that ping.

              hope i didnt waste anyones time..

              Comment


              • #22
                Originally posted by ASword
                Second, the detonation temperature of 92-94 octane gas is approximately 500-860oF. Yes, this is a very wide range -- that is because it depends on a lot of factors including quality of gas, how well it is injected, A/F mixture, etc. I got the figure from Howard Chu's turbocalc spreadsheet, and I think his source was gas company publications or something like that. Your mileage may vary (so to speak).
                Yes, I looked up the Material Safety Data Sheets for unleaded gasoline from Chevron, Mobil, Arco, and a couple other brands. They all had very different ranges, and different data for summer blend vs winter blend, etc. There's a wide variety. If you're really concerned about the quality of gasoline that you're using, you can find this stuff on the companys' web sites and compare for yourself.

                Meanwhile, I've also found some data on combustion flame temperature, but I don't think I'm going to be taking any new stabs at computing the energy release...
                -- Howard Chu Chief Architect, Symas Corp. Director, Highland Sun
                17x8" BBS RC/Leda 24-way adj. coilovers/Hye-Dra-Cyl Big Brakes: Wilwood 4-piston calipers+12.2x1.25" rotors/RRE FSTB/Top-End Racing FW/MazdaSpeed-Quaife LSD/65mm TB/Autophysics CAI/Groundz/Bi-Xenon HID headlamps/Euro Clear-corners+amber LEDs/Blazer amber fogs/JVC KDMX3000+CHX1200/Pioneer 6x9s/BCT7 Scanner/etc...

                Comment


                • #23
                  Originally posted by ASword
                  Running boost without O2 sensors isn't a concern -- the O2 sensors are only used to run closed loop which doesn't happen when you are on boost. If it was trying to use the O2 sensors then the mixture would be bouncing around 14.7:1 and you'd be way to lean to boost safely.
                  I'm not sure I understand this statement.

                  I am very often in boost without being at WOT. The ECU won't go into open-loop until the TPS sees WOT, so I am in closed loop with boost from time to time.
                  JEFF ABRAMS
                  jeff@mazdamaniac.com

                  Tierbeaux Beewst:
                  ROTARY POWER!! 1.3 liter 2004 Mazda RX-8 GT Greddy E-Manage - add 30 HP!
                  TURBOCHARGED & INTERCOOLED 1.8 liter 1997 Mazda Miata
                  TURBOCHARGED & INTERCOOLED 2.5 liter 1993 Mazda MX-3 GS <== SOLD
                  http://www.mazdamaniac.com

                  Comment


                  • #24
                    Originally posted by clavier


                    I'm not sure I understand this statement.

                    I am very often in boost without being at WOT. The ECU won't go into open-loop until the TPS sees WOT, so I am in closed loop with boost from time to time.
                    I'm pretty sure that the ECU will also drop out of closed loop above a certain airflow (i.e. load)... for safety reasons.
                    Former PGT-turbo owner... now 2010 VW Golf TDI

                    Comment


                    • #25
                      Originally posted by ASword
                      Running boost without O2 sensors isn't a concern -- the O2 sensors are only used to run closed loop which doesn't happen when you are on boost. If it was trying to use the O2 sensors then the mixture would be bouncing around 14.7:1 and you'd be way to lean to boost safely.

                      I'm not exactly sure why race gas is hard on O2 sensors, but I too have heard this before. Leaded gas will kill them too, I believe.
                      O2 sensors are killed by Race gas because it is leaded. Lead coats the sensors and renders them useless, you can sometimes clean them and they come back to life, but usually they will malfunction. If you want to run race gas just pull out the 02's at the track and plug the holes with cut off bolts. Or leave them out all the time and run 02 simulators, since your 02's are only there for emissions and fuel consumption reasons, and most of you prolly don't care about that if you are boosting.

                      Comment


                      • #26
                        Originally posted by krisw
                        ok, so im wondering which of these 2 explanations is correct in describing what detonation is. is detonation when the air/fuel mixture gets so compressed and hot that it detonates BEFORE the spark plug goes off? or is detonation when a small pocket of air/fuel spontaneously combusts after the spark plug has been set off but has not completed its burn? the reason why im asking is because in Supercharged! by corky bell, he talks about how having an intercooler will cool the compressed air going into the cylendar and make it less likely to detonate. this would lead me to believe that detonation would be the first explanation. in which case if you ran nitrous while supercharging it would lower the cylendar temperature considerably, and thus reduce chance of detonation. i hope this makes sense.
                        Detonation, pre-ignition, knock... it's all the same thing - the air/fuel mixture ignites before the spark plug goes off. Once the mixture is ignited, the flame front may or may not travel optimally across the combustion chamber. If it occurs due to detonation, the flame front probably doesn't propogate across the combustion chamber like it was designed to - that would require a spark plug to light the mixture. Unless someone made a messed up head with a poor spark plug location. :-)

                        Intercooling takes out energy from the air charge, reducing the chance of detonation.

                        Running nitrous reduces the temperature, effectively doing the same thing. Except when you run nitrous, you can't control the oxygen content and since you don't want to run lean, you blast as much gas in as possible, and now you raise the chance of detonation...

                        Dan

                        Comment

                        Working...
                        X