Barometric pressure Comp

[Martin]

Is a baro fuel comp of "double pressure double fuel" applicabe to the following Effcy (fuel) calculation methods:

1. Throttle Position?

2. Manifild Pressue?

3. MAF sensor?


Example: Normally aspirated engine at sealevel and and same engine at 1500m Altitude
Baro Reading at sealevel 100Kpa, 85Kpa at 1500m
Would all the effcy calculation methods require a 15% addition in fuel when the pressure rises from 85Kpa to 100Kpa?

I know the VE of the engine will change slightly because of the increase of exhaust pressure and a lot of other variables, but that`s not the reason for my question. My question is purely about different Effcy calc methods and if the all require the +-15% Fuel increase as the air desity would be about 15% more

Thanks

Martin

[RossB]

Throttle Position:
Yes you need a Barometric compensation unless you have a MAP sensor connected to the inlet manifold. You would then calculate Efficiency using TP with MAP compensation, there would be no need for Barometric compensation.

Manifold Pressure:
You would not normally need to use Barometric compensation.

MAF Sensor:
In theory you shouldn't need to use Barometric comp with a MAF sensor but this will depend on the range and location of the MAF sensor. Using MAF for Efficiency calculation is not really suitable for high perfoermance applications but if you have to use one I would include a barometric compensation.

Going from 100 Kpa at sea level to 85 Kpa at 1500m will require a 15% reduction in fuel not addition.

[injectordynamics]

Manifold Pressure:
You would not normally need to use Barometric compensation.

Is the assumption that the fueling requirements would be the same under the following 2 conditions?

1. 70 kpa intake with exhaust exiting into 100 kpa
2. 70 kpa intake with exhaust exiting into 80 kpa

[RossB]

You would not use the Barometric Pressure comp of "double pressure double fuel" to compensate for the change to VE as a function of exhaust pressure.

[Martin]

Hi Ross,

May i suggest the follwing exmaple:
Evo 6, GrpN Rally car, MAF located right after air filter. Would you run double pressure double fuel in such a setup as a baro fuel comp?

Regards
Martin

[injectordynamics]

Sorry Ross.

I should have read the original post more carefully.

In the case of MAP sensing you would do MAP/BARO for effcy right?

[RossB]

Martin
To tune the EVO6 using MAF you would need a barometric correction but I am not sure about the setup of the comp. In reality an air flow sensor is not measuring air mass, this needs to be calculated by looking at air flow and air pressure together with air temperature. What we end up doing is using the air flow sensor input as the basis for our efficiency calculation but we need a compensation for air pressure (and temperature). I would start by using the standard barometric correction as you suggest but I would check that this compensation works when the car is taken to the higher (or lower) altitude. You may find that the barometric compensation needs to be changed to suit.

Paul
In the case of MAP sensing you would do MAP/BARO for effcy right? In the case of MAP sensing in theory for a given engine speed and manifold pressure the fuel requirement is the same so there should be no need for a barometric compensation. BUT barometric air pressure may have an effect on the VE of the engine because if its effect on the exhaust as you and Martin have pointed out. If the VE of the engine changes the fuelling requirement will also change. You could use a barometric sensor to compensate for this but the values in the table would not be as per a normal barometric compensation.