Natural gas fired engines driving gensets - life expectancy
Natural gas fired engines driving gensets - life expectancy
(OP)
Hello All,
A couple of gensets will be operated at a constant load for 1500 hours a year on a 16h/day scheme. Engines are GM industrial powertrain Vortec 5.7L (350 cu.in), 8.1L (496 cu.in) and 8.1LT (496 cu.in, turbocharged), fired with Natural Gas and load is about 80%, 65% and 75% of standby rating respectively (see below).
The question is: what would be the expected engine life at the above conditions? By expected life I mean the time between major overhauls, with a decrease in the initial output power of no more than 10% to 12%. Of course, very close maintenance programs would be performed on these units. Is it nonsense to expect 13000 to 15000 hrs engine life, before having to overhaul it?
Additional application data:
GM Vortec 8.1LT-based genset
Actual Load=120kVA
Rated Standby power=163kVA
Rated Prime power=144kVA
GM Vortec 8.1L-based genset
Actual load=65kVA
Rated Standby power=94kVA
Rated Prime power=101kVA
GM Vortec 5.7L-based genset
Actual Load=60kVA
Rated Standby power=69kVA
Rated Prime power=75kVA
I've been trying to find an answer to this during the past three weeks, but I only got confused replies from prospect suppliers.
Does anybody know where I can find this info or has an answer for my question? Any help will be greatly appreciated.
Thanks!
Ernesto.
A couple of gensets will be operated at a constant load for 1500 hours a year on a 16h/day scheme. Engines are GM industrial powertrain Vortec 5.7L (350 cu.in), 8.1L (496 cu.in) and 8.1LT (496 cu.in, turbocharged), fired with Natural Gas and load is about 80%, 65% and 75% of standby rating respectively (see below).
The question is: what would be the expected engine life at the above conditions? By expected life I mean the time between major overhauls, with a decrease in the initial output power of no more than 10% to 12%. Of course, very close maintenance programs would be performed on these units. Is it nonsense to expect 13000 to 15000 hrs engine life, before having to overhaul it?
Additional application data:
GM Vortec 8.1LT-based genset
Actual Load=120kVA
Rated Standby power=163kVA
Rated Prime power=144kVA
GM Vortec 8.1L-based genset
Actual load=65kVA
Rated Standby power=94kVA
Rated Prime power=101kVA
GM Vortec 5.7L-based genset
Actual Load=60kVA
Rated Standby power=69kVA
Rated Prime power=75kVA
I've been trying to find an answer to this during the past three weeks, but I only got confused replies from prospect suppliers.
Does anybody know where I can find this info or has an answer for my question? Any help will be greatly appreciated.
Thanks!
Ernesto.





RE: Natural gas fired engines driving gensets - life expectancy
Assuming these are 1800 rpm units, you're running 100-140 psi BMEP on these engines. Turbocharged engines built to run continuously on natural gas typically operate at 145-175 psi BMEP and the heads/top ends will last 16,000-24,000 hrs. I don't know if they've beefed up the heads for this type of service but 15,000 hrs sounds a little high to me.
We do rebuild these type of engines, I'll talk to some people around the shop and see if they've got a typical lifespan for you.
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
Using your numbers (1500hrs X 60MPH =90000 miles per year)This 5X what a normal auto should see in a year.
I work for a GM industrial engine distibutor and the GM factory warrentee is for 36 months or 3500 hours.
We have some engines that have been running 24/7 for 3 to 4 years with no major problems. So,I don't think it's unreasonable to expect 7500 to 10000 hours. I think that 13000 to 15000 hours is quite a lot to expect.
If there is any thing I can do to help please let me know
RE: Natural gas fired engines driving gensets - life expectancy
All engines are 1800rpm, but there's something I don't understand: you say the heads/top ends will last 16000 to 24000 hrs, so why 15000 seem too much to you?
More or less the same question to Fmangas: 3 years @ 24/7 wouldn't mean 26000 hrs?
thanks!
RE: Natural gas fired engines driving gensets - life expectancy
Word around here is about 18 months to 2 years is best case for these engines and this may include a cylinder head swap or two in that time. Usually, the valves recess into the head which bottoms out the lifters and wipes out the cam shaft. At that point, for the price of these engines they are pulled out and replaced with an exchange long block. 15,000 hours doesn't sound unreasonable but that will likely include a top end overhaul.
RE: Natural gas fired engines driving gensets - life expectancy
I used the 3 years @ 24/7 as an example of what the engines are capable of. Will all GM engines last this long no, If there taken care of (Regular preventive maintenance, quality fuel, and properly adjusted fuel system)They are quite capable of a long life.
As to why the heads are usually the first to go Natural gas and LPG are dry fuels. There is no cooling property as there is with Gasoline. This tends to make the entire combustion area hotter then normal. If the fuel quality varies and the fuel system isn't adjusted to compensate. The exhaust seat gets too hot and starts to transfer metal from the seat to the valve. When the valve cools the metal particles fall off. This is when valve recession occurs.
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
If you take care of the above problems on any engine you generally will get a good life span.
RE: Natural gas fired engines driving gensets - life expectancy
Assuming we change oil every 250hrs, install double oil filters and oversized cooling system, plus we monitor the systems remotely for temp. gas consumption, power output, running hours... will you trust these units will last up to 13000hrs? What would be the expected head life in the above scenario?
I'm pushing both prospect suppliers to give a clear indication of expected life and I'm asking a couple of other manufacturers for quotes and info... will post any relavant data I'll get.
Thanks to both of you for your help!
RE: Natural gas fired engines driving gensets - life expectancy
I think that's, um, overly optimistic.
I'd distrust anyone who said it was likely.
Mike Halloran
Pembroke Pines, FL, USA
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
Keith Cress
kcress - http://www.flaminsystems.com
RE: Natural gas fired engines driving gensets - life expectancy
We also analyzed the microturbines, but they seem to make sense financially for applications with more than 5000hrs/year.
I'm getting the sense I'll have to choose between using "cheap" engines and hope they don't fail too often or use industrial engines and not maintain them as thoroughly as I should...
RE: Natural gas fired engines driving gensets - life expectancy
You have to pay attention to your fuel composition. If the Butane levels are relatively high, then the engines can detonate, and obviously, not survive for long. If the fuel you are proposing to use is "sales gas", make sure it indeed is, and have a composition test done. This will help determine optimum ignition timing. As the engines "age", the savvy field mechanics here will retard the timing a bit at each maintenance inspection to ward off detonation. At the end of their usefull life, the power will drop off to the limit of acceptability, but at least they won't ping to death.
Same goes for A/F ratio. Have it checked once and a while, as the turbocharged 8.1L is quite sensitive to detonation, if run on the rich side.
Robin Sipe.
RE: Natural gas fired engines driving gensets - life expectancy
Not a 5.7. Then one long block will go into any one of them.
Alternatively could you get a deal on 4 sets - one as a spare.
Then if one needs service there is no panicked rush required.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Natural gas fired engines driving gensets - life expectancy
Robin: do you have any figures of how often you change the longblocks and what is their % load with respect to prime power? This info would be extremely helpful.
So far the manufacturers either don't give a straight answer or just stick to the book, i.e. they just say the engine can't be operated continuously above 65% rated prime power.
One of them said they can endorse using the genset 8hrs/day at 100% rated prime power, but above that point they want me to downrate the genset. He didn't however tell me what would be the expected life of the engine should I make it work at our conditions...
So far, the informal information I have points to what Brybik said: maximum 6000 hrs total life and one head swap in between
Later today I'll call a major GM engine integrator to see what they tell me, I'll post the reply.
Thanks again,
Ernesto.
RE: Natural gas fired engines driving gensets - life expectancy
Robin Sipe.
RE: Natural gas fired engines driving gensets - life expectancy
Yesterday I called one of the biggest GM engine integrators in the US, they told me they really don't see any problem with the units lasting up 6000 hrs, but they want me to talk to another person today.
Here in Italy the gas quality should be good, but I'm asking the distribution company for a composition sheet to be sure
RE: Natural gas fired engines driving gensets - life expectancy
If you haven't already, you may want to talk to the guy's at Rama Motori. They have experience in your country with Industrial (GM,John Deere, and Briggs) gensets
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
And you may consider reviewing your loads and reporting in kW instead of KVA. Not the same. Depends on the characteristics of the load. KVA describes the capacity of the alternator but kW describes the power of the motor and the load on the motor. Generator/alternator KVA is typically 125% of engine kW. That's the rating. The actual values depend on the load and its characteristics.
kW will never by more than KVA but KVA is often more than kW. Sometimes a lot more.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Natural gas fired engines driving gensets - life expectancy
On the other hand, I've been reporting kVA power because, as far as I know, the engine will have to supply it and not only the real component (kW). It made sense to me, since the total energy (which should be real+reactive) has to come from somewhere and that's the prime mover. I'm not an expert in electricity issues... can someone confirm this?
Ernesto.
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
Be careful of anyone who says they change the heads or any components on a new engine. This will immediately void the GM warranty. I have came across the integrator you are talking about. I have taken there heads apart and they have standard GM parts.
The heads that come from GM are already equipped with hardened seats, different valves, and different springs.
RE: Natural gas fired engines driving gensets - life expectancy
RE: Natural gas fired engines driving gensets - life expectancy
They retrofit a wide deep sump oil pan with a 15 qt oil reservior.
The lean setup saves fuel but they did not care, the lean closed loop setup is more reliable and costs less per hr.
RE: Natural gas fired engines driving gensets - life expectancy
We are not sure of using the engines in lean burn mode, as NOx will increase and we'll be near the permitted emission limit, but closed loop makes a lot of sense to me...
On the other hand and as promised, here's some feedback from distributors and integrators:
Integrator 1: "Engines at those conditions will last 10 years, if properly maintained"
Integrator 2: "Standar Engine life is 25000 hrs, at your conditions and with proper maintenance, you should get at least 18-20k hrs"
Both integrators said no head replace would be necessary...
Local distributor 1: "About 10000 hrs before you replace the head, then another 10000 hrs"
Genset manuf. 1: "17000 hrs, you will have to swap heads at 8000hrs"
Genset manuf. 2: "Don't even think about using the 8.1L turbo at 120kVA (they offered Doosan engine instead and said it'll last >20000hrs). The 8.1L nat. asp. will do for 60kVA and will last >13000 hrs"
My conclusion is that integrators trust the engines more than the distributors/genset manuf... maybe because the genset manuf. don't know the engines as well as the integrators. Maybe it's just a very unusual application we have here.
I'll try to knock on GM's door directly, but they are not having a great time lately, so I'm affraid it'll be harder than usual.
Thanks to everybody!
RE: Natural gas fired engines driving gensets - life expectancy
Mike Halloran
Pembroke Pines, FL, USA
RE: Natural gas fired engines driving gensets - life expectancy
One grenaded at 2K due to a coolant leak but they run about ~9k hrs, annual replacement. They run substantially derated for longevity.
As for lean burn, if the system is well designed then Nox is low without need for much aftertreatment. Real low. They use a large commercial three way cat for nmhc due to high oil consumption. One of the keys to longer valve life is to let the valve guides leak more than usual and bleed off a little air from the turbo to increase crank case ventilation which is not a problem with port injection.
My invlovement has been limited to the fuel system. The injectors do not seem to fail due to wear but to keep the engine running they filter and dry the fuel with a regenerating dessicant system that costs as much as the engine/compressor.
I think the life expectancy would be less with a genset in your application. Just my 0.02 dinars
RE: Natural gas fired engines driving gensets - life expectancy
Once againg, real life experiece (turbocohen's) suggests that the information from the integrators and genset mfgr. is at best not reliable...
RE: Natural gas fired engines driving gensets - life expectancy
If TBO or uptime is that important to you, maybe it's time to find or develop a spreadsheet to balance out the lifecycle costs of:
- extended warranty
- service contract
- preemptive replacement/ planned downtime
- on condition maintenance
- more expensive engines
- fancier monitoring equipment
- cost of unplanned outages, including collateral damage
Surely someone has done it before.
It's all a crapshoot anyway, but if you've got an MBA beating on you, well, they love spreadsheets.
Mike Halloran
Pembroke Pines, FL, USA
RE: Natural gas fired engines driving gensets - life expectancy
h
RE: Natural gas fired engines driving gensets - life expectancy
Thanks!
Ernesto.
RE: Natural gas fired engines driving gensets - life expectancy