You would imagine its all about scaling right?

 

Wow, great read. Im very excited to try this out. ETA on this?

 

Well I am waiting for an temp sensor to show up then I will install it and then begin really coding it up...

 

Yeah, you could scale things to make it work. I was just suggesting to base the airflow calcs off the ideal gas laws.

I'm not sure what Tephra meant by "so it will try to target 8.3 like normal." I assumed he meant he would try to setup the program so that a target AFR of 8.3 would give you the same AFR you would get on the factory ECU with 8.3 AFR programed in?

I would think it would be better to just use the ideal gas law and mass balance equations to setup everything. Thus a target AFR of 11.0 in the target AFR table would give you a real 11.0 AFR provided your VE table was correctly setup. VE is also based on the ideal gas law. It means that at 100% VE, you have the air mass in the cylinder that you would according to the ambient conditions and engine displacement if the cylinder was filled completely.

Also, it is very possible to exceed 100% VE. Larger turbo setups can often run at 115% VE or higher even under substantial boost pressures. Particularly if a good effort is put into resonance tuning of the intake and exhaust manifolds.

 

yeah I dont understand how you can run at higher than 100% VE...

 

Its all about air velocity, as air enters the chamber the velocity of the air is great enough that the chamber is actually pressurized a little bit when the valve closes. Thus you've filled the chamber with more air than it would hold at static pressure, IE 100% VE.

 

Yep

If you want to know the mechanism behind it, look into Helmholtz resonant tuning or other wave prorogation theory with regards to internal combustion engines. It's very well documented that you can far exceed 100% VE. 4-valve motors are pretty efficient designs and it really doesn't take much to push them past 100% VE.

The idea of Volumetric Efficiency is a little funny though. Typically, you can not possibly over come 100% efficiency in anything because of conservation of energy, mass balance, blah blah blah. But in regards to engine VE, all you are doing is trying to apply a coefficient to relate dynamic response to the expected system response when negating these other parameters of engine dynamics.

 

Statically speaking the engine consumes say 2.0L of air in 4 rotations correct? Lets say we are at standard temperature and pressure in the room, we can then do math and find out that we have 1 million air molecules in 2.0L and STP.

Now at higher boost a turbo engine compresses the air charge. Unfortunatley this makes heat, reduces charge density, and the air molecules are further apart. Thus we might have more than 1 million air molecules in the same 2.0L but not much. If we intercool this and make the charge more dense we can really add a lot more air molecules, perhaps 2 million air molecules in the same 2.0L and 20psi of boost. (for the advanced I know this technically isn't more VE, but the math that Tephra is doing in the ecu isn't smart).

Also, you can tune things like the intake and cylinder head ports, as well as the camshaft lobes such that the air going into the engine is "tuned". Many NA cars from hondas can achieve over 100% VE from the factory these days using principles like.

Just make sure your math allows for much more than 100% VE. Depending on how you do it much, much, much more than 100% VE.

 

A 2.0l motor running an additional atmosphere of boost is not 200% volumteric efficient though. Post 45 shows a map that is similar to what danl is talking about where it is showing 138% VE at 4800 RPM and 210kPa absolute manifold pressure. That is what I'm suggesting avoiding by using a little bit more intelligent math so that your numbers are realistic.

Just to put it into perspective of roughly how the 4G63 performs. My stock cammed 2G 4G63 with a GT2871R was showing a VE of ~98% from 4500-5500 RPM then dropped off to ~80% VE by 7000 RPM. That same motor with some FP2 cams and a T67 was sitting around 105% VE from 5500-6500 then dropped to ~98% VE by 7800 RPM. Point is, it doesn't take much to make the 4G63 have a VE higher then 100% at peak torque when it's nearly there in stock form. Thus the maps definitely need to accommodate VE>100% if you are going to be using anything based on the ideal gas laws.

 

To me - 100% means that the engine can suck-in-and-push-out 100% of the air available to it.

You can't get more than 100% of something...

I will however make the map able to go higher than 100% just incase hehe

 

Tephra, I agree with your and that's how I always have used VE. VE is based on your pressure reference, which should be atmospheric pressure. You can't have more than 100% of something. In the case of volumetric efficiency, if you do, then your pressure is changing, and ur reference was from the unchanged pressure. In turbo engines, that's obvious because we run turbocharges. In NA engine, it can be done because of the few points mentioned in the above posts. But, you still aren't getting over 100% VE. The pressure is changing....and maybe you are getting 100% at that pressure, but most likely, you aren't even at 100%.

Many people look at VE from different angles. But in the case of this thread and the SD patch, VE should be looked at as a curve of how well the engine flows it's air, without the aid of a turbo or increasing pressure above atmospheric. The max should be 100%.


Eric

 

yeah... Well I think it doesn't matter how people treat their VE - I will make allowance for the table to go higher than 100%, probably upto 200% just incase.

Once its out and people are testing it then the "best way" to tune it will come forwards

 

If you are using the ideal gas law to find mass flow rate, it is very possible to have greater then 100% VE.

If you decide to go this way, maybe this attachment will help out. It would be best if somebody double checked it, as I did it in about 15 minutes. I threw in some rough numbers and the outputs seemed pretty reasonable though.

The last two equations are about all that I think are important. The constant to describe the engine displacement, fuel type, and injectors is a powerful little constant.

Going from a 2.0L to a 2.3L? Change the scaling constant.

Changing from Unleaded to E85 or a low specific gravity race fuel? Change the constant.

Rescaling for injectors (negating response characteristics) is done with a simple change to this constant.

It saves a TON of time on major changes like that in one neat and clean little constant. It obviously won't give you a perfect tune, but it will get you real close real quick, which I'm sure the professional tuner using ECUflash would really appreciate.

I didn't get this from any manuals or anything and I'm just doing it off the top of my head, but I can say for certainty this is how a lot of the higher end standalones deal with fueling calculations. With this method, you basically use straight MAP and RPM for the desired AFR and VE table look up then use the scaling constant and the last equation to calculate IPW. From here, you apply your compensations for coolant temp, acceleration enrichment, etc. Do them as percentages with zero correction being 100% and it's all straight forward multiplications. This automatically accounts for density changes due to intake temps and the intake temp compensation is strictly to change the AFR based on detonation threshold, ie. enriching when the intake temps are hot to prevent detonation from excess heat.

 

mmm well I wanted to leave the fueling system the same so things like injector scaling are changed like they currently are.

my formula takes into account engine displacement, so 1997 cc can be changed to whatever really quick, obviously i have imposed a 3000cc limit - I dont think anyone has a 3L+ engine?? :P

 

Yeah, I keep getting stuck in thinking how to make an ECU work from the start, instead of adapting to already existing code. Although, there is a "load" calc (g/rev) in those equations that would probably drop right in and I'm assuming it is similar to what you already have implemented?