volumetric efficiency?

[bozothenutter]

what is the Ve of the f4r 738?
does the RS2 increase it?

where would I find this type of data? been looking all over the net, but it not something that seems to be mentioned anywhere (only that it's really good or improved....:S)

 

[reedy107]

Lol. What do u need the v.e for ??

Ben

 

[bozothenutter]

just reading some books with calculation in them.....

 

[Chip-mk1]

I dont think you will find any particularly reliable figures published for an F4R to be honest mate.

The RS2 IME improves VE for most of the rev range but actually lowers its a little around 5K and just over.

 

[Steven103]

Highly doubt the numbers are available anywhere besides Renault or anyone who has raced an F4R with a serious budget, not just bolting tried & tested stuff on (i.e. works teams). And then of course is the "what are you going to do with it?" Unless you have the money to CFD & develop a new head/intake manifold there's not much point in working it out.

There are a few people keen on numbers who may have worked it out? MG cup NorthloopCup?



However you could be an awfully good club member and do some little experiments & work it out for us? I apologise if you already know all of this, but you'll need:

Engine speed (easy - look at the dash for an estimate!)
Manifold air pressure, P (can you see this via cheapy OBD chip?)
Intake temperature, T (you definitely can see this via a cheap OBD!)

Air density, Rho (google)
Molar mass of air, M (google)
Bore & stroke of an F4R (google)

PV=nRT can be substituted with density & rearranged to give the actual volume of air in the manifold:

V=(Rho*R*T)/(P*M)

Then stick that into the volumetric efficiency formula (google) and Bob's your uncle!



(Again apologies if you know all of this)

Be careful with units. They all need to be SI so temperature in Kelvin, engine speed in Rad/s etc.

For extra man-in-shed points do it across the rev range. Volumetric efficiency changes with engine speed and if you were to graph it, it should virtually mimic the shape of the torque curve (IIRC). Obviously at high revs when you've got high mechanical losses (due to friction) and a very different thermal efficiency (due to each cycle taking 1/7th of the time that it does at idle) you may find the curve differs a little from the torque curve.



EDIT: Need to learn to type faster...

 

[Chip-mk1]

Its easier to measure than to attempt to calculate steven given that the engine already exists, the whole point of trying to model is when you havent yet built the engine, and its a lot more complicated to get anywhere close than you are imploying there, especially given youve not even mentioned cam specs for example let alone inlet or exhaust, to get anything like accurate figures from theory alone is going to take a lot more detail and some very expensive modelling software.

 

[Steven103]

How is actual volume in cylinder generally "measured?" Actual volume flow rate must be reasonably accurate with a MAF surely? Compared to say heat loss through cylinder walls, energy loss on intake system must be relatively small (not negligible, but small in the big scheme of things)?

Presumably actual volume could also come relatively easily from exhaust analysis calculations that you could do by hand once you know how much fuel went in and how much HC, CO, Nox etc. came out?

Slightly needless questions I'm sure as the exact answer is no doubt do preliminary hand calcs to verify they're not great, do better hand calcs/combustion analysis to verify CFD is in the right ballpark, then use CFD "properly" before putting it all into a 10 page SAE paper titled "measuring volumetric efficiency of a modern passenger vehicle 4 stroke DISI engine."


Fair point about valves opening. In your experience and being as broad as possible how close (as a rough % maybe) is the old Vin/Vdisp compared to a proper simulation?

I.e. in comparison (I'm sure you know, but just by way of making my question clearer) regarding vertical wheel loads & weight transfer: a 5 minute excel spreadsheet comes within 5% of both a 3000 word Matlab script and a full 7DOF model in proper simulation software which itself it impressively close to a 4/5/7 post rig (I appreciate weight transfer isn't really what post rigs are usually used for, but that's another topic).


EDIT: Sorry silly (well not silly but you know what I mean) question... Instantly remembered the nice graph of in-cylinder pressure you get from a spark-plug-mounted piezoelectric (completely appreciate VE & in-cylinder pressures etc. are only really used for OEM development) sensor on the intake stroke the moment I hit "post." Would be relatively easy to get the actual volumetric efficiency from that - obviously once you've built the thing and put it on a dyno...

I ramble too much. This forum is bad.

 

[Chip-mk1]

Easiest way to retrofit something to measure with would be just attaching a MAF inline after the filter TBH mate, anything else is going to be complexity for no gain.

I dont think you will get anywhere close on a simulation for an F4R given that they vary by about 5% from the factory even for supposedly identical engines, lol.

 

[Steven103]

It seems to be common knowledge that MAF is better than MAP for fine tuning, but is there anything else that makes MAF so much better than calculating the same parameter via P and T? There are loads of things we can't measure directly, but by measuring other bits & doing a bit of maths we can get a perfectly useable "approximation."

That sort of suggests that if you had a MAF and T sensor, the calculated P would be miles off what would be read by a MAP sensor - which sort of makes MAP sensors seem a bit s***?

 

[bozothenutter]

thanks for the reply guys...me and my questions. Steven...it is only rambling if nobody listens....

 

[Chip-mk1]

It seems to be common knowledge that MAF is better than MAP for fine tuning, but is there anything else that makes MAF so much better than calculating the same parameter via P and T? There are loads of things we can't measure directly, but by measuring other bits & doing a bit of maths we can get a perfectly useable "approximation."

That sort of suggests that if you had a MAF and T sensor, the calculated P would be miles off what would be read by a MAP sensor - which sort of makes MAP sensors seem a bit s***?

MAF is actually measuring how much air has flowed into the engine, so if you have this, and you have the rpm and the engine size then you actually know exactly what the VE is (subject to a few corrections like temp and atmospheric pressure etc)

All MAP is doing is telling you what pressure is in the inlet, its telling you nothing really about how much air is flowing or what the VE is, obviously there is a relationship, but only one you can work out if you already know the VE, it cant be used as a starting point to work out the VE.
For example, silly extreme example, but block all the inlet ports up and then drill a 2mm hole in them so thats your new port, the MAP reading is going to think loads of air is flowing into the engine like its at full throttle even though now almost nothing does.

 

[Chip-mk1]

Are you trying to achieve something Bozo, or is it just an "out of interest" type question?

If you want to know how the VE compares to other engines, just look at torque figures is your best bet from published data, its not a bad link between the two.

What you'll find is that VE drops a hell of a lot at high rpm on these compared to something decent like a honda of course!

 

[bozothenutter]

just out of interest basically.
trying to learn about engines and what works and doesn't and why....the main reason i'm on this forum now actually.

funny that, i had already deduced that honda's would probably have better Ve than a F4R, is that to do with the rod ratio or the bore/stroke? (or valve size/cam profile etc......soo many variables!)

 

[Chip-mk1]

It's to do with all of the above basically mate.

The f4r is quite good for VE at around 5krpm though.

 

[Steven103]

Oh dear. It would appear that I've had a moment of complete lunacy

m dot. aka dm/dt.

p without a dot. aka just p