Diesel Generator Exhaust 3

[joan271273]

I would like to check if a designed exhaust stack for a diesel generator is OK and will not affect the unit. I think I need to have the generator backpressure as part of the data for the calculation.

Can someone give me a step by step for the calculation, any help is appreciated.

Thanks

 

[ChasBean1]

Before going through all the engineering involved with analyzing the diesel cycle and reduction of efficiency, etc., have you contacted the manufacturer? If it's a new unit, submit them a sketch and see if they'll still warranty it with the stack.

If you need to go further, as a general rule for stacks, ACGIH recommends no less than a 2,600 feet per minute stack velocity to keep out rain and over 3,000 fpm to better "shoot the plume" so to speak (vertical stacks only). I recently did an exhaust re-entrainment analysis and found that the diesel stacks had discharged exhaust at about 5,300 fpm.The higher this velocity gets, the more backpressure there will be. Find out the displacement of the engine & RPM, and use the exhaust pipe size to determine the stack velocity. It might be a good idea to keep this velocity low (e.g., under 2,000 fpm) until it has to discharge, at which point the diameter can be reduced to add velocity (again, mainly for straight-up discharge).

Don't forget thermal expansion. A carbon steel stack will expand 0.8 inches (if I remember right) per 100°F heatup per 100 feet of pipe. Also don't forget stack pitch and drainage, and potential re-entrainment. We would typically recommend a worst case 10,000:1 dilution at any nearby air intake. If necessary, have someone do a mathematical model such as the Halitsky model (1989) described in ASHRAE.

I don't know if this is what you needed, but hopefully some of the info will help. Good luck!

 

[joan271273]

Thanks for the response, I am not a mechanical Engineer and wanted to have a way of reviewing this on my own.My HVAC contractor is stating a 6,646 ft/min of stack velocity. The stack overall lenght might be 300' with four 90 degree elbows in the path.

I would like to avoid dependance on the subs to review the data. I also have the engine data available.

 

[rsvenkat]

We have a three cylinder,four stroke diesel engine. There is a silencer attached to it. How can we find out that the existing silencer is suitable for the engine?

 

[rsvenkat]

we have a three cylinder, four stroke diesel engine with a silencer attached to it. there is much of noise. how do we find out that the existing silencer is of required size or not?

 

I write to ask if someone could be of assistance with the following:-

With Petrol Engines it is easy to test the CO2 presents in the Cooling System (Water) using Gas Detection Liquid.

Hence should a petrol engine have the early stage indicators of a blown head gasket, the CO2 gas can be monitored in the Radiator top tank, indicating combustion gases are leaking from the combustion chamber to the water cooling system.

Correct me if I am wrong, the CO2 content in diesel exhaust fumes contain only about 40 parts per million, making it extremely difficult to detect using the same simply method as a petrol engine.

My questions are:

(1) What would be the main gas in diesel exhaust fumes ?

(2) What chemical or solution can be used to detect that gas using the same or similar method as mentioned above ?

(3) Perhaps there is another test that can be carried out within the water cooling system to indicate diesel combustion gases?

(4) Is there a simple in-the-field test to indicated the above when there are no bubbles in the water of the cooling system?

NOTE: The top Radiator tank maintains water & the system runs at operating temperature (80-88 Deg C) & can travel many klms on the highway with no problem.

As soon as the engine is backed off, water is displaced from the top tank to the header tank & does not draw the water back from the header tank when required.

Additional water then has to be added again to the top tank. This problem has been existed since the engine was completely overhauled.

Radiator has been cleaned, all hoses & clamps replaced, luminus die has been used in the water to find any fine leakage, new radiator cap, new header tank, the cooling system has been pressure tested & yet the problem still persists.

Email: qas1@bigpond.com (&/or) airdry55@hotmail.com

Many Thanks & Kind Regards to all.

 

[ivymike]

Your statement about the CO2 content of diesel exhaust sounds wrong to me, but I'm in no mood to "think hard" right now.

 

Thank you ivymike, I look forward to your thoughts.

 

[ivymike]

Okay, I've looked at my response from last night again, and I still think you're wrong about the CO2 content of diesel exhaust. Excluding N, CO2 should be the largest fraction of the exhaust, with H2O a close (often ignored) second. CO, HC, and NOx are produced in much smaller quantities than CO2 (a couple of orders of magnitude - 100x smaller).

I'm not sure what your cooling system configuration is, but it's my guess that it's similar to the following:

There is a "closed" (pressurized) system that can only be safely filled when the engine is cold. The radiator cap regulates pressure in this portion of the system

There is an "open" (non-pressurized) recovery (or "expansion&quot tank that captures coolant that is vented past the radiator cap.

The problem you're having, if I read it right, is that coolant that goes into the recovery tank is not being sucked back into the radiator?

If I've gotten all that right, my suggestions are:

Check the radiator cap to make sure it's not allowing leaks to atmosphere (you've replaced it, so check that off the list)

Check the hose from the radiator outlet to the expansion tank for leaks

Check that the expansion tank end of the hose is at the BOTTOM of the tank, so that it is completely submerged in coolant.

 

[stony]

I agree with all of ivymikes' suggestions with the exception of the rad cap. Having worked as a mechanic for over 20 years, I feel qualified to say that NEW parts aren't necessarily GOOD parts.

 

[ivymike]

I'll agree with that - seen it a few times myself. The reason I posted "you've done it, check it off" in the first place was just to acknowledge that he thought he'd already addressed the potential problem w/ the radiator cap. Perhaps I should have worded it differently.