A Series simulation thread.
Turbo Mini Forums

As suggested by PaulS I going to start a new topic on A series simulation.

I have EngMod4T which is based on the work of the late Prof GP Blair of QUB and which has been under development for many years now By Dr Neels Van Niekerk of South Africa. As Dr Neels has a buddy who is into A series (I think (spr)midgets) racing he made arrangement to you can construct siamese intakes and exhaust systems to use in the simulation module. It allso does turbo's but as i am sufficiently confused as it is now I'll keep it NA for now.

I made a model for a 16v K-head as well and that pretty much spits out numbers that are quite like the dyno plots i have found on the first try.

An A series model is a lot more complicated to get up and running and I have measured casts of the head to get the proper CSA down and measure the rest with calipers and such. The Cd of the head is calculated based on flow bench numbers @28 inch h2o depression (I have my own bench which is quite reasonably accurate now and regresses well ( 0.5%) through a set of flowbench tech PAPlates clones) which is the best thing you can do without making a proper rig that will pull 700mm Hg vacuum (or 374 inch depression) which will cost more than your house.

One sim run from 2k to 9k in 250prm increments takes about 90 minutes on my computer.

So I have a running model that spits out (very) interesting data (per cylinder power, charge purity,pressures traces, temperature traces) that could well be near enough to reality, but I have as of yet no way to test if the model concurs with reality.

So if anybody has data either simulated or real data I would be very interested to see if I can replicate it with some degree of accuracy. Likewise I would be very interested I measured cam files. I am planning on building a simple cam measurement set-up as a first proper lathe project , but S96 files or similar are very welcome.

Edited by Sir Yun on 19th Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I use some OEM software. I can't say what it is because I don't have a licence, just to say that it would cost me about $1000 a month if I did

I did a lot of simulations about 3 years ago. I started with my 998 turbo for which I had a rolling road curve.

The data required for the simulation is extensive, even down to port wall thickness and materials so that it can calculate the heat loss within the port itself. I had to generate Cd curves for the ports, cam lift curves, compressor and turbine maps, write the control rules for the wastegate etc, etc.

I was startled when the simulation spewed out a power curve that was very similar.


The difference at low engine revs can be explained by the difference in the way that the simulation works. It establishes a steady state condition, whereas the rolling road does not allow enough time for the turbo to spool up.

This gave me confidence to take it further.

This is the cylinder data associated with the above power curve. I'm not sure at what speed, possibly 5000rpm. You can clearly see the charge robbing happening:




I then developed the simulation for my new engine, improved head, scatter cam, tuned length manifolds, higher revs and bigger turbo:


My main interest is identifying the impact of the charge robbing and how to minimise the impact. This is a plot showing what is going on in the new engine:


Here is a plot of the VEs of the inner and outer cylinders:


Yes, there is a huge difference in the VEs, but when I separated the ports, the VEs equalised as you would expect, but not to the same level as the outers, instead around the average. What the inners lose, the outers gain.

So my conclusion is that with the right approach, the impact of the siamese can be negated.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have recently started using Ricardo WAVE, but I'm not too well versed in it yet.
But it would be nice to get a nice 1D engine model up and running for the A series engine.

Does anyone on here use WAVE?

Well the basic underlying physics are similar/ the same, the interface of engmod4t is sometimes a bit clunky and I spend a lot of time just figuring out what the heck I was actually supposed to produce to use as input (the new version has improved heat transfer as well.. have not yet figured that out). But at least I can afford it :) unlike Wave or AVLfire

I don't really see the charge robbing with shorter cams


My thoughts are like this.

you have the two pairs of cylinder with the shared intake. and the middle pair with the shared exhaust

So if you take the 3+4 intake pair and look at the mass flow traces I would expect that the mass flow of one cylinder would affect the mass flow of the other if the ''charge is robbed''.

if I take a short duration cam and you look at the mass flow at the two valves and at the beginning of the head I get this:

Now it is NA not turbo and this is an intake configuration that seems to make the inner cylinders quite a bit happier without pissing the outers off. Furthermore this a header only exhaust so LCB into atmosphere.

Attachments:

27.21kb

Edited by Sir Yun on 16th Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I assume that the red trace is the inner cylinder inlet flow, in which case you can see the charge robbing when the flow goes negative.

You wont get much charge robbing with a short duration cam.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

yep 3 is cylinder three and 4 is cylinder four .

But where does the rest of the mass go in your st2 plot ? The small negative notch does really not explain where the really big chunk goes, does it ?.

I looked at a EAE649isch cammed version of this same engine and in my trace you see more more effects but it does not lose a chunk like that

I just received a S96 file for a NZ mini seven cam I will give that a go shortly. maybe it is just input related

cheers
JR

Edited by Sir Yun on 16th Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

We are only looking at a few percent difference in VE, not a "really big chunk".

You need to consider the area under the curve. The outer cylinder is filling for longer as well as getting a helping hand at the start of the valve opening.

EDIT: I'm not sure what the black line shows, but I can see that you may be looking at the difference between it and the cylinder traces. I guess that the black line is the mass flow at the inlet to the carb? What you are seeing is some compression of the flow within the port.

Edited by Paul S on 17th Oct, 2014.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I used it for my fianl year uni project. I looked at inlet manifold and drivetrain optimisation for our formula student car.

I want to make an A-series model but never got round to it.

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Edited by Sir Yun on 19th Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

I can't see anything missing. Do you mean the part when it flattens out?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

yeah I mean that bit.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Charge robbing can only occur when both inlet valves on the port are open, so on my trace that is where the green line is visible.

If you compare the start of the inner cylinder flow with the start of the outer cylinder flow, the gradient is much steeper with the outer cylinder, meaning the outer cylinder gets a helping hand from the inner, initially filling quicker, then levelling off before increasing again.

By the time the green trace ends, charge robbing has stopped.

I can't remember what rpm that trace represents but I think it is at around 7000rpm when the difference is VE is not so great.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Just found the latest data for the simulation. It has been developed since that plot, but the shape is much the same.

It is at 7000 rpm and the flattening of the mass flow is due to the relationship between cylinder pressure and port pressure i.e. differential pressure across the valve.

What you also have to take into account is that the outer cylinder exhaust valve is also open during the charge robbing. With the tuned length runners, this is running at a lower pressure than the inlet, so some flow is going straight through into the exhaust.

Edited by Paul S on 19th Oct, 2014.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Way below the intellectual level of the previous posts, but in some other engines it is quite common to have different rocker ratios for inlet and exhaust, so has anyone modelled larger diameter exhaust on two cylinders or someother such workaround to get the inner and outers to behave more similarly?

I haven't yet as i first want to know if the sims can match data on a relatively simple case. I might try to model a generic 7 port just to have a look at the siamese exhaust behaviour in isolation. And model 10 cm stubs (RR merlin style) as they are quite neutral with regards to tuning for the 5 porter

So far the kelford F11 camfile is giving me a hard time as it is plain weird .

Edited by Sir Yun on 20th Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I read it in Blairs book somewhere . .

what duration is your cam ? is it the 274 you mentioned a few times ?

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

You may be right about the 10cm runners, particularly on the inner cylinders. Impractical though.

It is the 274 cam on the original 998Ti, but when actually measured, it's more like 250 inlet, 260 exhaust degrees duration.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

found where I read it. page 653..used as a tuning neutral exhaust for the examining the fundamentals of intake tuning.

idea it just to take a look at the effect of the intakes without the exhaust doing too much interfering.

it is indeed not very practical

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Sounds like a good starting point.

Trouble is that the short exhaust runner on the centre branch may have a significant effect on VE compared with the outer branch.

I started by building the model of what I already have a RR curve and developed it from there.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I have some (engine ? not shure anymore) dyno data for the seven. The s96 cam data should be functional .

now i'll have to see how well it wants to match reality :)

the guy that is working on the engine is a WC level two stroke pro and he has some interesting ideas . my first tests mainly show that it is a challenge to get it tuned as you have even more variables but it does seem to do something quite interesting.

Edited by Sir Yun on 23rd Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

Well, first tries are not matching the dyno . general shape is pretty decent but i make way too much power. adjusted the dcr to 8 which helps a lot to get it in the neighbourhood (10:1 static CR with a kelford f11 cam). Have to revisit the burn models and fmep if they need tweaking to see if i can get it nearer .

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

My software gives gross crank power, so you need to account for some losses.

How does your software account for ancillaries driven off the crank - cam, oil pump, water pump, alternator, fan etc?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

You are right. turns out you can use a more extensive friction loss model where you specify engine main parameters, oil type, valve train type, bearing sizes and diameters and some more stuff. Then it calculates the losses for the components vs rpm.

You have to make some compromises like for the different sizes for the cam bearings, I could only use a single size for all three.

This is my data so far for the narrow band used for racing as i got for the dyno. Correlation is pretty good given that a few parts are definitely not matching the actual engine yet. Burn Eff was a tad high i think as well.

Attachments:

20.02kb

14.15kb

Edited by Sir Yun on 23rd Oct, 2014.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/