Diesel Engine Testing Questions 1

[mikeneal]

I am doing some real world testing using a 7.3liter TD (Ford/International) with the intent of gathering information to perform some exhaust CFD modeling.
Any exhaust experts have any advice as to best way to measure flow? I plan in placing numerous temp and static pressure taps along the system. Since it is a diesel can I use the intake mass flow and correct for temperature, how do I correct for the boost? Is a pitot tube best approach? Any way to accurately get the flow ?

 

[MikeHalloran]

Unless there's a leak somewhere,
(intake mass flow + fuel mass flow = exhaust mass flow).

The turbo just increases mass flow beyond what a NA engine would flow, but measuring the intake mass flow takes care of that.




Mike Halloran
Pembroke Pines, FL, USA

 

[1gibson]

MAF sensor is a hot wire anemometer, it will measure MASS flow, so already accounts for increase in density due to boost.

 

[ivymike]

especially if you use it upstream of the turbo, the way we typically do. would recommend measuring T&P downstream of the compressor, as well as up&downstream of the turbine.

don't forget that you "leak" up to about 2% of your mass flow out the crankcase ventilation system (if it's not recycled into the intake)

 

[mikeneal]

I have found out some aftermarket gauge monitors /tuners have the ability to report MAF but I am having trouble getting any applications people are the various manufactures to sign up if they can definitely do that. If by chance I cannot get that data from OBDII port anyone have suggestions on how to best record flow data. I was initially thinking since it is diesel (w/o air throttle body) that I could use displacement and speed , but the turbo makes that a non-solution I suppose.

 

[mikeneal]

I found out there is not a MAF sensor on the 7.3PSD and actually there is very little data available too me via the OBD-II port, so it seems I must gather the flow data the old fashioned way. Open to suggestions if anyone has been down this road before and had any lessons learned /advice they can offer. Thnaks

 

[tbuelna]

mikeneal,

Diesel exhaust flows present a very complex flow condition to model dynamically, since the temperatures, pressures, velocities, gas compositions, etc. can vary widely at any given instance, at any given point in the exhaust system.

Real time dynamic pressure data can be collected using a water cooled piezo pressure transducer with a high enough sampling rate.

As others noted, exhaust mass flow is simply intake air mass flow plus injected fuel mass flow. Diesel engines don't require intake air mass flow sensors, since they don't need to run at stoichiometric AF ratios. If you need mass air flow data, most dynos have intake airflow measuring equipment available.

Hope that helps.
Terry