Cat Spark-Ignited Recip Engine - Effect of Exhaust dP on Output and HeatRate

[RebaBB]

I am working on a prpject with an 1800 kW Caterpillar spark-ignited reciprocating engine, where we will be installing a CO catalyst and silencer on the exhaust system. This will increase the exhaust pressure drop by 10 inches H2O. What will be the effect on engine output and heat rate? I am not able to find performance curves which indicate the effect of the higher back pressure on engine output and heat rate. I am not even able to find generic curves for such! Can anyone help?

 

[ivymike]

The allowable exhaust backpressure for Cat gas-fueled engines varies, but if you're talking about a G3516 then the allowable limit is about 20" water. Within that range they will be able to deliver full power.

 

[catserveng]

Ask the CAT dealer involved with your project to provide you a current copy of the Application and Installation Guide, it has information to help in desgning the exhaust system and impacts of higher back pressures. There is a module specific to exhaust systems.

The stated maximum for most turbocharged SI engines 29 inches H2O, that being said, some of the more highly turbocharged engines and Miller cycle engines see a slight reduction in efficiency when the back pressure exceeds 16 inches H20 at full load, but usually within the stated performance tolerences. Make sure the provider of the catalyst provides both the "clean" restriction, and maximum restriction at end of catalyst service life.

There are a large number of engines operating with oxidation catalysts, SCR's and heat recovery units all in one system with no performance problems, just takes a bit of care to get it right.

Have you also been provided with the TMI (Technical Marketing Information) data for the engines selected for you application? at the end of the data sheet is a reference section that lists the limits and tolerences. While it doesn't provide a curve for various back pressures impact on engine performance, it does provide some information which you would find helpful.

Hope that helps, Mike L.

 

[MikeHalloran]

I'd be _very_ suspicious of an assertion that a catalyst _and_ a silencer will add only 10 inches of water to the backpressure. Ten inches is more believable for a silencer alone, and a vestigial one at that.


Mike Halloran
Pembroke Pines, FL, USA

 

[Hoxton]

For us Europeans, 10in water is equal to about 25mbar.
(Sorry, just thinking aloud!)

As others above say, typical maximum DIRTY pressure drop is about 50mbar - 20in. This is measured from the outlet flange of the turbo(s) to atmosphere.

The MWM engines I dealt with also has a minimum pressure, usually 30mbar.

With respect to all above, you have to start with the desired back pressure, say 45mbar, then design the exhaust system and specify the required clean (new) design back pressure for silencers, catalytic converter, heat recovery (if any), Exhaust runs, bends etc.

We always started with 15mbar total for silencer and cat (since we often bought then as a package). We then might have to adjust this once design has verified the complete exhaust.

As catserveng says, refer to the caterpillar application guide. The MWM one is on the MWM website. MWM.net - downloads - layout of power plant.

The CAT document I last saw two years ago, a good document, we always looked at other engine makers application guides, since they often overlap in their recommendations.