Roman

Tech Spam thread - because 1/4" BSP gets 5 hand spans to the jiggawatt

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Why couldn't you forget the exhaust venturi,  run a big fuck of turbo and turn the the fire into a blast furnace for super hot fun times/more efficient coal burn...

 

because the LP cylinder is already exhausting to atmospheric, you can put a turbine in there but you will have to raise the LP cylinder exhaust pressure which will reduce the power that makes.

 

depends on the boiler design as to what is the limiting factor in the whole system too, heat transfer area of the boiler, steam flow path, feedwater supply steam , max allowable boiler pressure. if the firebox can flow enough air to burn enough stuff to meet the rating of the boiler then blowing more air in is not going to help.

 

 

The only problem I can see with this is that if all four wheels are spinning, it's going to interpret this as though you're travelling at a higher speed, and so increase the boost and then your wheel spin increases more. Or if just front or rear wheels are spinning... How does it know which ones are or arent? (Is this for Sentras car you're talking about?)

 

Limiting per gear is probably a better option?

 

If you can look at the datalog and figure out the first rpm/load combination that the wheel spins at. Figure out how much HP this is.

 

Then apply the horsepower formula to the rpm etc of the wheel to figure out how much horsepower the wheel can put to the ground at various speeds then limit your boost to acheive approximately that amount of horsepower at each speed.

 

Im not talking of specific cars in this instance, just generally something I am interested in.

 

The idea is you set it so that you dont spin and can keep full welly and the car is just planted the whole time. another way it is done is just on timer, similar to NOS controllers first .5sec of run this much, next 0.5sec that much, then give it everything or whatever.

 

usually this is on RWD cars and the sensor is on a front wheel. even if it lifts a wheel then it doesnt see speed increase so boost doesnt go up until the wheel is back down on the ground. the 4wd all spinning issue is a bit different but you can get smart on it by looking at the rate of wheel speed increase and tuning the PID loop.

 

there are quite a few ways to skin the cat but its how you cook it that makes it taste good or something. or just get a deer, I dont know what cat tastes like but deer taste good.

 

basically its just a tool for tuning the car to the track, its not a set and forget thing

 

you tune your shocks, suspension geometry and tire pressures and whatever else to maximise your grip available,  and you tune your engine to the limit of adhesion but not past it. but its much easier and far more consistent to limit the engine power by altering you boost curve, nos delay or timing advance curve than to use your foot on the throttle

 

technical shit talking thread for technical shit talking yes?

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there are quite a few ways to skin the cat but its how you cook it that makes it taste good or something. or just get a deer, I dont know what cat tastes like but deer taste good.

 

this is brilliant. Who's up for chicken chow meow?

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Saw this guy speak last Monday, here's a previous talk:

Kiwicon 7: P0wning the Christchurch transport system

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I dont know what cat tastes like

 

technical shit talking thread for technical shit talking yes?

 

 

 

Cats taste like cat piss...... I think my brain just explodedcyd7-('suuu

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Hey so one thing I've been wanting to play with in solidworks is some of the flow modelling stuff.

 

For sake of learning the program I thought I'd draw up an intake manifold / throttle body / piping / air filter / air scoop / etc.

Then play around with some stuff and see what changes.

 

For my motor I know: Intake runner lengths, diameters

Approximate plenum size/volume

Throttle body diameter

piping diameter

How many grams per second of air the motor currently consumes at full rpm/throttle with the current length/size/etc of inlet tract (as per airflow meter readings)

 

So what I've been thinking is that it's probably outside the scope of what Solidworks can accurately acheive to try and model the pulses as each cylinder sucks etc. As although you can make time dependant flow it's not going to accurately represent an engine well enough.

 

So what I was thinking is that I've got a known Grams/second at a known pipe size (start of airbox) so perhaps I could model some different intake configs upstream of this (as realistically I'm not gonna build a new plenum or anything anyway)
and see if I can minimise the pressure drop. Or, since ideally I'd want to acheive a higher grams/second perhaps I could set an 'outlet' as vaccum or whatever at different strengths until it shows 170 grams/second as the mass flow rate with an approximation of my current intake there.

 

It will be easier that way to see changes as mass flow rate seems a lot less like reading tea leaves than pressure drop which seems less sensitive(which I guess is why they use MAF in modern cars so much) and also obviously increasing the mass flow rate is the end goal which gives an engine more power.

 

I've been thinking about whether a big bathtub looking scoop thing in front of the front radiator panel could build positive pressure past the filter at 100+ kph.... Making the intake tract up to that point 'free'.

 

I would probably need to model a reasonable amount of the front of the car but thats fine because the point of this exercise is to learn how to use solidworks more than anything else / cbf actually working on my car haha.

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Have you got just the basic package? Or all the extra modelling stuff?

 

For any serious FEA I would look at ANSYS instead, and just import the model from SW. It does fluid/solid interactions quite well. Although I hope you have a grunty computer to run it on.

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Yeah it's got the modelling stuff.

 

Jeepers, Ansys looks pretty hardcore.

 

Might check that out another time but just learning solidworks is enough to fill my brain to the brim currently!

 

And my knowledge of engineering type stuff is the bottleneck anyway, not the software.

I'll put that on the to-do list!

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Oh so as per above.

It's obviously a good plan to put an air intake into a high pressure zone.

 

I've Been wondering if there's any benefit to making a 'trough' type thing, that collects and holds air slightly pressurised for the intake pipe to pull from.

If the amount of air coming is greater than the amount of air going out then it should build some pressure.

ltqbbtj0.k1n.jpg

 

So... If you've got a certain mass of air flowing out of a hole in the back of a box/trough, (known value as per airflow meter readings) then if the trough is still lower than atmo pressure when the car is going 100kph then you just need to keep making the box bigger.
 

So I started out with a box 100x100 with an outlet that's sucking 170 grams per second of air. Tested at 100kph... Lower than atmo pressure in the box.

 

Made it 100x500. Still lower

 

Made it 100x1000. Now gets to about atmospheric. (This could fit in the car, could take up the whole lower inlet panel thing)

 

I then drew some piping and an airbox type thing off the back of it, to represent air filter box. To see if that could get slightly above atmo.

 

Yes and no, the trough thingy gets above atmo but having a 72mm dia hole outlet is where the pressure drop happens.

 

Increased the size of this, and increased the size of the box to 200x1000

 

Now it's getting above atmo pressure inside the airbox at 100kph...

 

However it was above atmo pressure by something like 0.001 PSI. Haha. Not bad I suppose if it means you could get the entire inlet tract including air filter for 'free' in terms of restriction.

 

It seems the name of the game is to make any pipe pre-throttle body as bigger diameter as you can get away with.

In my case I'm stuck with a MAF sensor that needs to be inside a certain diameter pipe and it's got a 72mm throttle body so those seem to be the bottlenecks.

 

I wonder what the intake pressure drop is at the moment IRL... I've really gotta get a pressure differential gauge at some point for nerdy experiments like this.

I guess another thing is that 170 grams per second is peak airflow meter reading, but because the engine operates through a powerband it's only reaching this at certain speed/rpm combos. It would only get to this reading currently at 50kph, 80kph, 130kph, ~185kph.
So at the real life 100kph MAF reading it may very well make positive pressure there. Even if it only did so 'off peak' it just means it would broaden the powerband instead of increasing the peak.

I might run it a a few more times at the grams/second rating for the rpm it drops to on gear change.

And yes I realise this all seems stupid compared to just getting a turbo or supercharger.

However engine bay simplicity is a set in stone goal for my car.
If I made a contraption as per above it fits into a part of the car that's currently unused and completely out of the way of everything else. (and doesnt cost me any money hah)

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http://en.wikipedia.org/wiki/Ram-air_intake

 

From elsewhere:

...discussed this in class one day. The professor started with the basic equation for dynamic pressure:

ec8ec06139093baceb1cd1af74fd3a3f.png

And everyone agreed they understood how that worked. So then he had a student come up to the board and work out the pressure at various speeds. The punchline is you have to go 170mph to get half a psi of pressure. Yes, this is just for non-compressible fluid, but the basic magnitude is there.

 

But:

146-9910-ram-12-zoom.jpg

sportrider caption said:

 

KAWASAKI ZRX1100: As a test control, we fitted the Pi System to a non-ram-air-equipped motorcycle. If you think figures like 17mb seem insignificant, take a look at how much vacuum is present in a regular airbox and you'll realize even that amount of positive pressure can make a huge difference. With a pressure of -27mb, it's obvious that power gains can be realized by converting that vacuum into positive pressure.

Read more: http://www.sportrider.com/tech/146_9910_ram/photo_12.html#ixzz1tcC01mzq

 

 

TLDR: CBR1100 +6% hp

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Ansys will be way better than the SW CFD module (like using sketchup vs SW for solid modelling) but it can be done.

 

 

You should note that you're going straight to the big leagues with running CFD on intake manifolds. A project on optimising an intake manifold with CFD would easily be a year long project for a 4th year engineering student.

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Ansys will be way better than the SW CFD module (like using sketchup vs SW for solid modelling) but it can be done.

 

 

You should note that you're going straight to the big leagues with running CFD on intake manifolds. A project on optimising an intake manifold with CFD would easily be a year long project for a 4th year engineering student.

Yeah I've seen that vid, its easy enough to vary the flow between runners like that with a time dependant analasys.

But yeah there are too many variables and assumptions to use it for anything apart from cool animations.

But as per my rant above, knowing the MAF sensor value in grams per second gives me some useful info regarding what's good for anything upstream of the throttle body.

It's a real life value which can be applied to known pipe sizes etc.

 

Rather than making assumptions about how much flow/volume/blah blah comes from the valves/cams/etc. which is what's required to reinvent the intake manifold which is already good.

 

Everything I've done so far (not much) seems to point to that the bigger the pipe the better, for minimising pressure drop.

Which is useful info.

Rookie - As I've mentioned briefly before, my car used to have quads on it.

But to get a runner length that's good with a straight pipe, I had to cut some of the bonnet support things out. This caused an  irrepairable bonnet warp and I had to source another one before painting the car.

Having a bonnet cutout or whatever isnt an option for what I want with the car.

If the car needs bent intake runners then the only real advantage of quads over single TB is that you can have a much larger plenum volume and no step down to the diameter of the single TB.

Which is beneficial, but if I had $2-3k to throw around then I'd be buying tires and other things first.

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Just use another harmonic and then you can have quads that fit and are better than stock?

 

You make everything so difficult Roman....

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Also what are you talking about?

I did a quick calculation and the 3rd harmonic will put the intake length at ~15cm for 7000 rpm, how can you not fit this in your car?

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Are the stock intake runners 40 cm long?

 

If it was me I would happily compromise 7000 rpm 2nd harmonic for 4-5000 rpm 3rd harmonic, you are going to use it heaps more. One thing velobikes have taught me is that you are always overly ambitious with rpm/speed numbers which always works out to your detriment.

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It's been proven already that longer the runners the better for these motors, even glenn's ones with ~190kw atw run long curved runners to get enough length.

 

Apart from how it sounds, and how it looks (which is irrelevant because I'll never run open throttles anyway)

 

What do you think is going to be better about quads? And in your mind how much better is it going to be for the $2-3k expense.

 

When I had quads before it was about a grand in parts from memory, to get bolted to side of motor. Not including ECU / tuning / etc.

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