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Thread: Ricardo Inputs

  1. #21
    I am afraid it doesn't work like that. The results are different for different initial RPMs since the simulation basically does a torque balance and adds the change in rotation to the initial rotation mentioned by us.This RPM is now used as the new initial RPM for the next case of engine RPM.Setting the correct value has been the goal of this thread, so that the compressor doesn't stall early or start spooling up when it should.For e.g If I put a initial RPM of 300000 at 4000 engine RPM then it stalls immediately due to maximum RPM being 300000,while the same is not the case for 150000 or say 120000 RPM. It goes out of range at around 7000 RPM in this case which is not at all expected/possible. Hence my problem
    Last edited by ritwikdas18; 11-17-2014 at 02:15 PM.
    Ritwik Das
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  2. #22
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    Ok, so, stick it on a dyno and read the turbo speed at certain RPM. If you can't read the turbo speed then I'd suggest interpolating from measured MAP and expected/calculated (or, if you have the sensor) MAF onto your compressor map. Or, to do it theoretically: have you drawn an expected curve over your compressor map? You may have an expected maximum pressure ratio (as controlled by your wastegate........) and an expected maximum flow rate (assuming choked flow at some point) and there you have a point on your compressor map.

    If you are having problems with it going out of range then maybe it does go out of range? That's what wastegates are for. I blocked ours off once (on the dyno) for an investigation into wastegate sealing efficiency and promptly over-sped our turbo (at 4000RPM....It spooled so quickly I was lucky to be able to catch it before causing some real damage). Perhaps Ricardo is right in saying that you are over-speeding the turbo?

    Also, that compressor map has some mighty high pressure ratios on it, and you want to run without a wastegate and without an intercooler? I hope you're running E85.
    Jay

    UoW FSAE '07-'09

  3. #23
    Quote Originally Posted by ritwikdas18 View Post
    I am afraid it doesn't work like that. The results are different for different initial RPMs since the simulation basically does a torque balance and adds the change in rotation to the initial rotation mentioned by us.
    But then your simulation simply doesn't converge, like RenM said? Did you use enough iteration steps (turbo sims need way more than NA sims)? Or see below...
    Quote Originally Posted by ritwikdas18 View Post
    It goes out of range at around 7000 RPM in this case which is not at all expected/possible.
    Why should it be not expected/possible, without wastegate...? Like Jay said above, turbo speeds will go up dramatically, with the restrictor it might go into surge like crazy, very difficult for the simulation to solve.
    Jan Dressler
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  4. #24
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    Quote Originally Posted by Jay Lawrence View Post
    If you are having problems with it going out of range then maybe it does go out of range? That's what wastegates are for. I blocked ours off once (on the dyno) for an investigation into wastegate sealing efficiency and promptly over-sped our turbo (at 4000RPM....It spooled so quickly I was lucky to be able to catch it before causing some real damage). Perhaps Ricardo is right in saying that you are over-speeding the turbo?
    This is what I was trying to say. The GT06 is a tiny, tiny turbo and an academic turbine matching exercise is lying for this single-cylinder engine, even at 250 cc. At 7000 rpm it could definitely exceed 300,000 rpm with no wastegating due to the high-energy pulses. The wastegate will need to be used and, more than likely, the WG orifice will need to be enlarged.

    I'll never forget the first time I loaded the 600 ACE engine after fitting the GT1241 turbo and saw 17 psi boost at medium engine speed despite running the base WG actuator pressure of 7 psi. I backed out of the throttle immediately, did a quick googling to learn about boost creep, removed the turbine housing, and took the die grinder to the WG orifice. It required LOTS of WG porting despite the compressor match being borderline large. This was a 180 degree firing order twin, so pulse effect will be even stronger on a single.

    Ritwik, you should see what some wastegating does for your WAVE model. It's something easy to add from a tutorial model.
    Last edited by Mbirt; 11-17-2014 at 11:18 PM. Reason: addition of nostalgia
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    Matt Birt
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  5. #25
    Ok, so the Gt06 has an internal wastegate.My simulations are converging and the compressor RPM is not going out of range but I want to put in the right inputs. I used a PID Controller for wastegate actuator. I am not getting what to put in the target "field". Its the target boost pressure at each Engine RPM point since it is connected to the boost pressure sensor.Also I know that if the target boost pressure field is exceeded then the wastegate starts opening .Because of wrong target boost pressures at some engine RPM , I see a dip in the power RPM curve since more than required exhaust is wastegated. So I need help in inputting target boost at Engine RPM range of say(5000-9000 with intervals at every 500 RPM).
    Last edited by ritwikdas18; 11-24-2014 at 02:32 AM.

  6. #26
    Quote Originally Posted by ritwikdas18 View Post
    Ok, so the Gt06 has an internal wastegate.My simulations are converging and the compressor RPM is not going out of range but I want to put in the right inputs. I used a PID Controller for wastegate actuator. I am not getting what to put in the target "field". Its the target boost pressure at each Engine RPM point since it is connected to the boost pressure sensor.Also I know that if the target boost pressure field is exceeded then the wastegate starts opening .Because of wrong target boost pressures at some engine RPM , I see a dip in the power RPM curve since more than required exhaust is wastegated. So I need help in inputting target boost at Engine RPM range of say(5000-9000 with intervals at every 500 RPM).

    The target boost is entirely up to you.

    How much pressure drop will you see in your entire intake system (especially the intercoler)?


    How much boost can the engine handle? This will be likely be determined by either the knock limited point (at a certain point, adding more air and retarding spark under knock will result in less torque), which you might get into at low RPM, or the point where you reach mechanical failure of some component.

    Once you find out how much torque the engine can handle at each RPM, and if you are severely knock limited, you should be able to solve for MAP at those points. Once you add the pressure losses to this MAP, you will find your target boost pressure.
    Andrew Palardy
    Kettering University - Computer Engineering, FSAE, Clean Snowmobile Challenge
    Williams International - Commercial Turbofan Controls and Accessories

    "Sometimes, the elegant implementation is a function. Not a method. Not a class. Not a framework. Just a function." ~ John Carmack

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  7. #27
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    Ritwik,

    At UoW we had an aim boost table that our control system attempted to hit for a given RPM.

    Hopefully you are starting to appreciate the complexities of such a system, and that you can't just design a system in Ricardo and have it work in real life. As noted by Andrew ^ you will need to test this system for real and find out its limits. For detonation detection I'd suggest a simple metal tube bolted to the block as near to the combustion chamber as possible, connected to a hose that feeds into some headphones. It's simple and works very well. Obviously to do this you need to load up your system on a dyno, which is what you should have done in the first place (and with sensors in place may have quickly realised that a waste-gate and intercooler might be a good idea). If you don't have a dyno you could run it on the car, but be prepared to blow stuff up.

    Not sure why you were suggesting that you'd run without a waste-gate when the GT06 has one built into the turbine housing?
    Jay

    UoW FSAE '07-'09

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