Measuring Back Pressure Without an Engine
Measuring Back Pressure Without an Engine
(OP)
There are many techniques on how to measure backpressure in an exhaust system that is already connected to an engine. How can you measure the backpressure in an exhaust system if it is not going to be connected to one though? What could you use to represent the airflow and backpressure to match what the engine would create (or something proportional) to see if the backpressure is within the specifications? The engine is a 3.0L V6 VM Turbo Diesel. Thanks for the help!





RE: Measuring Back Pressure Without an Engine
The blower would pretty regularly trip a 15A/115V breaker because of its instantaneous starting current of ~49A. I added a timed relay so it started at reduced current (~35A) for 6 seconds, which was enough time to get it mostly spun up.
If I had it to do over, I'd have bought a 3phase motor and a VFD that could run it from a single phase input and ramp it up to speed while limiting the current a bit more.
To use a blower like that, you'll have to measure your pressure with some precision (think Dwyer Instruments) and extrapolate along the assumed system curve from the one point you can measure with the blower.
Oh. A round car air filter glued to the blower inlet will keep birds out of it and reduce the noise a little. An acoustic labyrinth on inlet and outlet will help more.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
Chris
RE: Measuring Back Pressure Without an Engine
You need to have a way to check your calculations on an actual engine, at least once. Regularly would be even better.
If you're limited to a 115V supply, you're limited to a ~1HP motor, unless you can deal with the noise and maintenance issues of a brushed universal motor, in which case you can probably get to ~2HP. ... Okay, with a 3ph motor and a VFD, you might be able to get to 2HP. At least get a 20A circuit.
Back up there. Do check the facility; the tin shop I worked in had only one 115V outlet on the factory floor; everything else was higher voltage and 3 phase.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Measuring Back Pressure Without an Engine
Yeah true, I will give the facility I belive there might be higher voltage outlets. I wonder how much mass flow a 1 or 2 HP motor can create?
We have to measure parts from certain batches before they leave the plant to make sure they are within the backpressure specifications. There is the DOC/DPF (DOC – Diesel Oxidation Catalyst ; DPF – Diesel Particulate Filter) and the SCR (Selective Catalyst Reduction) components that together make the exhaust system.
The full assembly backpressure can have no more than 850 mbar. The question is how to create the pressure in which to be measured.
RE: Measuring Back Pressure Without an Engine
RE: Measuring Back Pressure Without an Engine
I'm getting at least 4HP, neglecting all losses and uncertainties,
to feed 900 kg/hr of standard-ish air
against a backpressure of 850mbar,
and omitting any attempt to account for the engine's actual
turbo exhaust temperature, not revealed.
That's a huge backpressure limit.
Much larger turboDiesels have limits as low as 50mbar.
I hope some number somewhere includes a little budget for the exhaust system outside of the DPF,etc.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
850 mbar of backpressure does seem quite high but hey I'm not going to question Chrysler's specs.
The engine's actual exhaust temperature is 450 degrees Celsius.
Does there need to be some sort of conversion of numbers since the 900 kg/hr involves the different gasses in the exhaust while the 4 HP blower will only be using air (different density gasses)?
RE: Measuring Back Pressure Without an Engine
Leaving the resistance unchanged, it takes 1.98HP to push 900 kg/hr of 70F air through it and the backpressure is 349 mbar.
This would be a good time for you to talk to Chrysler to reach agreement on the specifics of a test that will be agreeable to everyone.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Measuring Back Pressure Without an Engine
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Back Pressure Without an Engine
Use a modest compressor to charge a big air tank.
Dump the tank contents through a large fast acting valve connected to the UUT, and measure the pressure at the connection point.
The pressure will not be static of course, but will be a decay curve starting near the initial tank pressure and decaying to zero. It will probably decay very quickly, because we have been working here with a very high backpressure limit that is probably not even close to representing a new, clean system.
The tricky part, IMHO, is that Chris will have to work with Chrysler's Engineering and Quality organizations to develop a test procedure and a limit curve that all will find acceptable.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
850 mbar represents a new, clean system and 1100 mbar represents an aged system with ash and soot accumulated. These seem like accurate representations of the backpressure for an entire system at maximum exhaust gas flow rate.
I really do like the idea of a compressor and an accumulator actually. I would need a compressor that could build up over 1100 mbar of pressure, so lets say 1500 mbar to be safe, and that also could keep up with the air flow rate of 900 kg/hr. Those seem like very high pressure and flow rate numbers to achieve though.
RE: Measuring Back Pressure Without an Engine
RE: Measuring Back Pressure Without an Engine
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Measuring Back Pressure Without an Engine
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Measuring Back Pressure Without an Engine
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Measuring Back Pressure Without an Engine
For 100% testing, filtered pipeline natural gas as a fuel for the microturbine should be acceptable.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Measuring Back Pressure Without an Engine
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
dgallup, everything you just described seems very plausible. This article describes the operating principles of sonic nozzles very well for someone interested. [link http://www.trigasfi.de/pdf/Sonic-Nozzle-Brochure.p...]
I don't have any experience/knowledge with sonic nozzles. Is the pressure ratio mentioned achieved soley by pressurizing the inlet of the nozzle?
RE: Measuring Back Pressure Without an Engine
"The mass flow rate is primarily dependent on the cross-sectional area A of the hole and the upstream pressure P"
RE: Measuring Back Pressure Without an Engine
http://us.kaeser.com/Products_and_Solutions/Rotary...
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Measuring Back Pressure Without an Engine
RE: Measuring Back Pressure Without an Engine
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Measuring Back Pressure Without an Engine
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Measuring Back Pressure Without an Engine
They can come complete with sound insulation and controls.
As for a way to produce a specific backpressure out of the PD blower, have a tee between the blower and test bench that will feed a pipe submerged in a water tank at the level of water corresponding to the pressure desired (want to test at lower pressure, remove water), the pressure to the test bench will build up to the static water head and excess flow will bubble through the bypass providing a reliable pressure source.
Hydrae
RE: Measuring Back Pressure Without an Engine
Big ol' Roots blower and a submerged branch pressure vent.
You _will_ want the sound insulation.
Mike Halloran
Pembroke Pines, FL, USA
RE: Measuring Back Pressure Without an Engine
You still would need to figure out & engineer an electric motor drive, as well as the conversion from exhaust conditions to equivalent air flow @ temperature.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz