Ricardo Inputs

[ritwikdas18]

1)How do you measure or what input do you give to the combustion duration (10-90%) in Ricardo SI Wiebe Model?
2)Also how do you determine the speed of the turboshaft? If say we want to run cases from 1000 -12000 RPM what is the procedure to determine what turboshaft RPM has to be used at each of these cases?

[Jay Lawrence]

Ritwik,

1. Not sure. Plug some numbers in/read the tutorial and find out.
2. Turbo speed is determined by a number of factors. What turbo are you using? What do your compressor and turbine charts look like? What exhaust flow control method are you using? Do you have variable geometry? Are you running anti-lag? Do you have a turbo speed sensor to check whether it's actually spinning where it should be? Do you know what engine modifications you need to do to run a turbo successfully? Some of these questions can be answered by selecting a turbo properly and seeing how shaft speed relates to intake air mass flow and desired pressure ratio. More importantly, you are an inexperienced team and correct me if I'm wrong but you don't appear to have collected much in the way of results. Have you finished a full event, placing reasonably in all dynamic sub-events? If not, a turbo will not help you. It will do the opposite.

[Jan_Dressler]

Adding to what Jay said:

2. I don't really know how Ricardo Wave does it, but the simulations I know and work with will calculate turbo speed itself (with the help of all the data Jay mentions, which you have to input - again, read the tutorials, this can be VERY tricky sometimes to get it right). So you only have to give the software an INITIAL turbo speed for the given case. Then, it helps to play with the turbo inertia. It can help to set this to very high values for the first iteration steps, so that the initial speed will be maintained while the other simulation parameters come to realistic values. Then set it to unrealistically low values for a few steps, so that the turbo speed "adjusts itself" to correct values faster. Then back to a realistic value.

Then compare it to dyno results and find out that the simulation gives you a completely wrong picture... ;) It is really, really MUCH work to get a simulation model which actually really predicts what the engine will do, especially with a turbo.
Be happy that you don't have variable valve timing...

[ritwikdas18]

We have all the maps and answers to all the questions above. However the point of asking the query was that in Ricardo you can't specify the turboshaft rpm at each RPM of the engine. There are 3 options called balanced,fixed speed and geared off crankshaft."Balanced" is the initial turboshaft speed for that RPM. "Geared off Crankshaft" is engine RPM multiplied by gear ratio which is specified by user."Fixed Speed " is user entered fixed simulation speed of turboshaft.So the problem is that although we approximately know the turboshaft RPM at different engine RPM's we don't know how to input that into the software.Nothing can be inferred from the tutorial.

[Pat Clarke]

You don't know the turboshaft speed at different RPMs because the turbo speed is independent of engine speed!
The turbo can still be running at high RPM with the engine stopped!

Pat Clarke

[ritwikdas18]

The turbo can still be running at high RPM with the engine stopped!

Pat Clarke

But wouldn't that be due to the momentum of the shaft and not due to any torque on the shaft?Anyways my question remains how am I supposed to input that parameter in RICARDO. I am sure there are teams with turbos . I would request them to help me here.

[Jan_Dressler]

Anyways my question remains how am I supposed to input that parameter in RICARDO.
Simple: You don't input that parameter.
As you said, with your "balanced" option, you can give the software an initial turbo speed. The software will then calculate the "actual" turbo speed for the given case (RPM) and the given "hardware setup" (engine and turbo data, cam timing etc.).

Where would you want to take the turbo speeds you want enter into the software from?
Have you measured the actual turbo speeds on an engine dyno? If yes, was it a transient dyno pull, or static for a while at certain RPMs? Does your ignition timing match the ignition timing that Ricardo calculates? What about wastegate opening, what do you do in "real life" (wastegate opening based on a RPM/TPS/MAP-map, or purely dependent on MAP, or RPM/TPS/MAP plus correction map for post restrictor pressure...) - and what does Ricardo do? And so on, and so on.
This is what Pat Clarke said, there is no certain turbo speed at a certain RPM, it depends on a lot of things.

If you really have measured actual turbo speeds, well, all the better, then you can verify your simulation results better.

[RenM]

Hello Ritwik,

1) get the engines burn duration you need to run a pressure indication system and calculate the burn rate from the sensed pressure signal. This will however require a very expensive indication system most teams dont have access to. In the end you´ll probably end up using some reasonable estimations, and adjust the parameter to fit your engine imep. As long as you use reasonable estimations it is not a very important factor if you are only looking for a relative comparability when adjusting your gas exchange.

2) The turbo speed is determined by your intake system and your desired charge pressure. I am not familiar with wave, however the only useful way is to use a wastegate controller which adjusts the wastegate throat diameter to control the turbo speed and hence the pressure ratio of the compressor. This method will also result in the correct turbine back pressure which you dont get if you simply lock the turbo to a certain speed and dont actuate the wastegate.

[ritwikdas18]

Simple: You don't input that parameter.
As you said, with your "balanced" option, you can give the software an initial turbo speed. The software will then calculate the "actual" turbo speed for the given case (RPM) and the given "hardware setup" (engine and turbo data, cam timing etc.).


We are not using a wastegate(After analysis we have understood that we don't need to).You are right ,In the tutorials , they have given the software an initial turbo speed at each RPM (initial turbo speed being same for a range of bit higher end RPMs (3000-5000 RPM in the simulation case)). I don't have a clue and neither can it be inferred as to how they got to the initial RPMs for different turbospeeds.I know that's the right thing to do, but how do we calculate the initial turbo RPM at each RPM of our simulation? Approximate numbers will do.

[Mbirt]

We are not using a wastegate(After analysis we have understood that we don't need to).
Free-floating huh? This is not going to go well. I highly suggest diverting your resources from modelling to physical testing so you can quickly learn about pulse flow and turbine matching with single cylinder engines.

You are right ,In the tutorials , they have given the software an initial turbo speed at each RPM (initial turbo speed being same for a range of bit higher end RPMs (3000-5000 RPM in the simulation case)). I don't have a clue and neither can it be inferred as to how they got to the initial RPMs for different turbospeeds.I know that's the right thing to do, but how do we calculate the initial turbo RPM at each RPM of our simulation? Approximate numbers will do.Read the compressor map.

[Pat Clarke]

Ritwikdas18

1. What University do you represent?
2. Has there been a team discussion about this topic?
3. Is your Ricardo suite licenced?

Pat Clarke

[ritwikdas18]

Read the compressor map.


Tried it. The compressor map starts around 120000 RPM. So I set that at 4000 Engine RPM.Around 7000 RPM the shaft RPM reaches 300000 after which the compressor stalls. Also the sensor attached to the turboshaft shows negative power(instantaneous) generated. There is definitely something wrong.

[ritwikdas18]

Ritwikdas18

1. What University do you represent?
2. Has there been a team discussion about this topic?
3. Is your Ricardo suite licenced?

Pat Clarke

1.BITS,India
2.Yes
3.Yes

[RenM]

You should really rethink your turbo matching. If you don't need a wastegate, your turbine will be way to big to get a good transient response which is VERY VERY important in FSAE.

Perhaps your simulation hasn't converged yet and you will need more iterations for your turbine speed to converge. Thats a common problem when simulating a turbo charged engine. You should also check your turbos inertia.

[Mbirt]

Tried it. The compressor map starts around 120000 RPM. So I set that at 4000 Engine RPM.Around 7000 RPM the shaft RPM reaches 300000 after which the compressor stalls. Also the sensor attached to the turboshaft shows negative power(instantaneous) generated. There is definitely something wrong.The simulation could be fine and the issue could have something to do with the high energy of the exhaust pulses that you're not wastegating relative to the low mass flow rate. Considering the compressor map starts at 120000 rpm, I'm sure it's a very small turbine match for a single cylinder engine bigger than 250 cc. This is why you need to start physical testing as soon as possible. Turbocharging a low cylinder count engine is not something that academics and industry professionals have a ton of experience with, so we have to learn things the hard way.

[Jan_Dressler]

You should really rethink your turbo matching. If you don't need a wastegate, your turbine will be way to big to get a good transient response which is VERY VERY important in FSAE.
Indeed! I never worked on a turbocharged FSAE engine, but on Group N / R4 rally engines now... Which is basically FSAE x 3: 33 / 34 mm restrictor, turbo, thottle after turbo, 2l engine. Okay, plus some nice things like variable cam timing on both camshafts with the Evo X.
But again, it is basically "scaled up" FSAE... So we are running the stock turbo, according to the rules, have max torque (700 Nm+) at about 3000 rpm, max power (360 hp+) at about 4000 rpm, driver should shift below 5000. But as soon as we get to peak torque (=flow limit of the restrictor, and at that moment about 3,xx bar absolute MAP), we have to gradually open the wastegate. After that moment, it is balancing additional boost vs. too much exhaust back pressure / post restrictor pressure. All the time playing with exhaust cam timing, and so on (and while trying to get to the point of peak torque, there are some pretty advanced anti lag strategies...).

Perhaps your simulation hasn't converged yet and you will need more iterations for your turbine speed to converge. Thats a common problem when simulating a turbo charged engine. You should also check your turbos inertia.
That's what I said on the first page of this thread, have your shaft inertia way high for the first couple of iterations while everything "adjusts itself", than lower it dramatically so that your simulated turbo can match the speed, then go back to realistiv values.

[Jay Lawrence]

Ritwik,

Can you post a picture of your compressor map? I would definitely support what RenM said above ^
I hope you understand what is required to successfully run a turbo for this competition. Can you provide information about your setup (engine, turbo, intercooling, management, oiling, etc.)?
As mentioned above, Ricardo will not just spit out your desired engine package. There are a great many parameters that require you to already have a certain engine package running and covered in sensors. Ricardo is then used to try to 'optimise' your existing package. If you don't have these parameters (or at least logical approximations) then all you have is garbage in = garbage out.

[ritwikdas18]

The compressor map is attached herewith.417(http://turbochargerspecs.blogspot.in/2013/03/garrett-gt06-gt0632sz-32-trim-80-hp.html for any additional info you need)
The engine is a Honda CBR250R (250cc).The turbo used is a GT06 which is the smallest turbo in the market. Intercooler is not used.The oil drain and feed lines are on the same side of the turbo and an oil pump is used.The rotor inertia(2.4E-06) is obtained from the manufacturer so I am sure about that.
Also the goal is to find the engine RPM at initial turboshaft RPM(In other words it is approximately when the turbo starts spooling).Also this can't be done physically to an extent because what we input in Ricardo is the initial RPM, the actual turboshaft RPM at a particular engine RPM is calculated by doing a torque balance from compressor and turbine sides divided by inertia.(In the tutorials they had an initial turboshaft RPM for each engine RPM with initial RPMs being same after 2500 engine RPM, again this is not the actual turboshaft RPM at that engine RPM)

[ritwikdas18]

That's what I said on the first page of this thread, have your shaft inertia way high for the first couple of iterations while everything "adjusts itself", than lower it dramatically so that your simulated turbo can match the speed, then go back to realistiv values.

Shaft Inertia can only be input as a constant in Ricardo

[RenM]

I am sorry, i really dont understand your question : "Also the goal is to find the engine RPM at initial turboshaft RPM "

If you are running a static simulation the initial turboshaft rpm doesnt really matter since it will converge because of the power balance of compressor and turbine. Setting the right turboshaft rpm will only help speed up the convergence but doesnt change the results. Just start with a reasonable guess, run the simulation and use the resulting turbo speed as new initial rpm.

If you are running a transient simulation you can with a high rpm, then let your vehicle brake and then accelerate again.

[ritwikdas18]

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

[Jay Lawrence]

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.

[Jan_Dressler]

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...

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.

[Mbirt]

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.

[ritwikdas18]

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).

[apalrd]

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.

[Jay Lawrence]

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?