Gas engine misfire torsional study & affect on power provided 2

[genRman]

Hello,
I'm an electrical engineer in need of some direction pointing!
Has anyone got information on high horsepower natural gas engines, where a study of torsional analysis has been completed to discover the effect of cylinder misfire on the power provided to a shaft driven, direct coupled AC generator?

I konw it's a specialist area, but any help would be very much apreciated.

Thanks

 

[MachineryWatch]

Hi,

I'm not sure if my experience is relevant because I didn't really understand your question. I have done torsional analysis on a large natural gas engine that was direct coupled to a centrifugal chiller with an integral gearbox/speed increaser.

The torsional analysis was requested because of repeated catastrophic failures of the coupling. We did some of the torsional data acquisition, but terminated the effort when inspection revealed that one of the cylinders was misfiring. This was indicated by removal of the rocker arm covers where the valve stems and springs for the cylinder were covered in carbon, indicating burnt valves. The ignition system was then inspected. Spark plugs were found to be in poor condition, especially the cylinder in question.

It was found that the maintenance on the relatively new (<2 years) engine had been very poor. The group contracted to provide the maintenance was a local rep/dealer of the engine manufacturer. It was also discovered that simple recommended procedures for checking valve lash/clearance prior to initial starting of a newly delivered engine were not followed by the same local service organization when the system was commissioned. This lack of initial checking for proper valve clearances led to the valve being burned and the misfiring.

The engine manufacturer in this case delivers 99.9+% diesel engines. The delivery set-up procedures for the natural gas engines are quite different from the diesels. This also led to the total neglect of the ignition system which, of course, diesels do not have.

Oddly, the misfire was audibly discernable to us who came to the site as diagnosticians for the chiller manufacturer, yet went unnoticed by the engine manufacturer's rep and the local on-site maintenance people.

The misfire imparted enough torsional energy to the coupling to destroy it in about 2 hours running time! This happened in quick succession with 2 new replacement couplings.

I hope this helps even though it is not about a generator.

Skip Hartman

http://www.machinerywatch.com

 

[kplim1178]

Hi,
I did some studying of IC engines years ago, you may find these 2 books useful:

Kerr Wilson, &quot;Practical Solutions to Torsional Vibration&quot;, Chapman & Hall, 3rd Edition. 1963.

E J Nostorides, B.I.C.E.R.A., &quot;An Handbook of Torsional Vibration&quot;, Cambridge University Press, Cambridge, 1958.

If you can lay hands on the books by Kerr Wilson, it has all the examples and calculations, very detail analysis etc, it comes in 4 or 5 volumes. Sadly it is out of print. Perhaps the publisher can make a cd-rom copy someday. Hope this help.

Cheers,
KPLim1178

 

[VibEngr]

Poor engine maintenance and cylinder misfire can definitely create torsional vibration problems. In fact, I'm giving a short course on how to avoid torsional vibration problems in reciprocating equipment at the GMRC next month. If you are interested, you may download our paper at

http://www.engdyn.com/download/GMRC2002.pdf

You will need Adobe Acrobat to view the file. It covers engine misfire and gives several interesting case histories. At the end of the paper is a long list of technical references. Two excellent ones have already been mentioned: Torsional Vibration Handbook by BICERA and Practical Solutions to Torsional Vibration Problems by Ker Wilson. The Diesel Handbook is another good one. I hope this helps.

Troy Feese, P.E.

 

[kplim1178]

The paper by VibEngr is certainly worth reading and no doubt your short course is definitely a worthwhile investment for those who are interested in IC engines and reciprocating machineries. I have a request regarding the strain gauge telemetry system for measuring torque. Would it be possible for you provide a sample calculation of the torque and how the signal looks like. I have never stick a strain gauge. It unfortunate that I am too far away from you and my present job do not involve engines or strain gauging. I believe it is an art by itself. Thank you in advance.

 

[genRman]

VibEngr,
Troy Thanks for your assistance & an advance copy of your paper, it looks very interesting & I will be taking some time to read it in detail. Thanks also for the reference notes, I appreciate the time & effort taken to reply.

 

[VibEngr]

A strain gage telemetry system can be used to evaluate actual transmitted and dynamic torque in a shaft. A full bridge arrangement (4 gages) can measure torsional strain while negating strains due to bending, axial and temperature effects. The voltage signal proportional to strain can be converted to torque or shear stress. The measured stress can then be compared to allowable levels. If possible, the gages should be located where maximum twist occurs, which requires knowledge of the torsional mode shapes of the system. Depending on the particular mode shape, this installation location may not be feasible. Installing the gages on the shaft near the coupling hub (but away from any keyways) is usually adequate.

For torque measurements, I use Micro-Measurements strain gages and Binsfeld telemetry systems. See links below.

http://www.vishay.com/brands/measurements_group/strain_gages/mm.htm

http://www.binsfeld.com/

Also, for anyone taking strain measurements, I highly recommend The Strain Gage Primer by Perry & Lissner. This book contains all the necessary formulas for converting strain readings to torque or stress.