Engine exhaust gas pressure
Engine exhaust gas pressure
(OP)
Hello everybody:
In our Diesel power plant it is planned to use the engine exhaust gases to generate energy by cogeneration.
For medium speed (514 rpm) twin turbocharged Diesel engines, delivering 17.000 kW, it is required to know the exhaust gas pressure.
As we all know, once the exhaust gases exit the cylinders, they end up in the exhaust manifold, from here the gases flow into the turbines of the turbochargers and then, they flow out to the heat recovery boiler (if any) or directly to the stack (if no boiler is installed).
It is in that zone, between the outlet of the turbocharger and the entrance to the boiler that the pressure of the gases is required.
Is there, besides the direct measurement of course, any method to ascertain/calculate this pressure? In that point of the stack there is no pressure gage.
Your opinions or comments are thanked in advance
In our Diesel power plant it is planned to use the engine exhaust gases to generate energy by cogeneration.
For medium speed (514 rpm) twin turbocharged Diesel engines, delivering 17.000 kW, it is required to know the exhaust gas pressure.
As we all know, once the exhaust gases exit the cylinders, they end up in the exhaust manifold, from here the gases flow into the turbines of the turbochargers and then, they flow out to the heat recovery boiler (if any) or directly to the stack (if no boiler is installed).
It is in that zone, between the outlet of the turbocharger and the entrance to the boiler that the pressure of the gases is required.
Is there, besides the direct measurement of course, any method to ascertain/calculate this pressure? In that point of the stack there is no pressure gage.
Your opinions or comments are thanked in advance





RE: Engine exhaust gas pressure
Have you tried to obtain the turbo's performance map?
RE: Engine exhaust gas pressure
RE: Engine exhaust gas pressure
The pressure at the point you describe (downstream of the turbo) will be determined by the mass flow rate, the temperature (giving density and thus volume flow rate), and the restrictiveness of the downstream exhaust ducting. Backpressure includes restrictions due to pipe size, silencer, system configuration, boiler, rain cap, and other exhaust-related components.
Old engine application guide calculations:
P(kPa) = (L*S*Q^2*3.6E6)/D^5 + P.s + P.b
or
P (in. H2O) = (L*S*Q^2)/(187*D^5) + P.S + P.b
Where:
P = Back pressure (kPa), (in. H2O)
psi = 0.0361 x in. water column
kPa = 0.00981 x mm water column
L = Total Equivalent Length of pipe (m) (ft)
Q = Exhaust gas flow (m3/min),(cfm)
D = Inside diameter of pipe (mm),(in.)
S = Density of gas (kg/m3), (lb/ft3)
P.s = Pressure drop of silencer/raincap (kPa),(in. H2O)
P.b = Pressure drop of boiler (kPa),(in. H2O)
RE: Engine exhaust gas pressure
RE: Engine exhaust gas pressure
RE: Engine exhaust gas pressure
Thanks to all for your advise. I have found this site: http
RE: Engine exhaust gas pressure
In order to get the pressure, I wonder if it is technically acceptable to install a standard pressure gage?, or we have to take into account some particular points besides the temperature of the exhaust gases of around 700º F?
Your comments are appreciated. Thanks.
RE: Engine exhaust gas pressure
RE: Engine exhaust gas pressure
Thanks dgallup for your support.
RE: Engine exhaust gas pressure
RE: Engine exhaust gas pressure
We measure this constantly on all of our on-road Diesels that have exhaust particulate traps. There is a high temp 1/4" ID braided line about 30" long that runs from the exhaust pipe to a small, chassis mounted pressure switch manifold.
RE: Engine exhaust gas pressure
The backpressure _limit_ on engines of that size is usually less than a foot of water, so you need a really sensitive pressure gage, like a Magnehelic, or an actual water manometer.
As mentioned, a couple of feet of metallic tubing will radiate enough heat to keep from melting the gage.
Mike Halloran
Pembroke Pines, FL, USA