What motor lasts longer

[rd_macgregor]

Hmmm. I wonder if a closer comparison might come from Europe where the proportion of diesel automobiles is very high. The uses of these vehicles would be very similar, so a comparison of maintenance and/or lifespan would be closer to an apples-to-apples comparison.
Now the question is, "does anybody have these data for Europe?"
BOB

[Mickey_Fx]

Not a chance. Diesel x2 if not 3

Seems this discussion has taken two paths. I took the original post as more of a theoretical question and that's how I addressed it. The other path appears to be more of a comparison between typ commercially available engines which in my opinion are not apples to apples comparison, equals.

There are in the past and today examples of large industrial gas (spark ignition) engines that can and do stand toe to toe with diesel engines. Here is an example (see pic) of what is available today. Low speed, 1400-1800 rpm designed to run 24/7. Over in Salt Lake City they try and manage the lakes level by pumping water in/out. There are three I believe, gas powered engines driving pumps, large ones, ones that pump 450,000 gpm, yes per min. Think this project would use gas powered engines if reliability/dependability were not up to the task? With some applications, fuel availability dictates engine design, compression Vs spark, not reliability/durability considerations.

I have no problem if you take the path of comparing engine types if you want to compare what's available down at your local car/tractor dealer but the original question said all else being equal. I think the GE Waukesha engine is an example of a gas engine that is equal.

[SPYDERLK]

Those are engines.

[Egon]

Are those Waukeshaw engines running on natural gas?

There are many two and four cycle industrial engines running on natural gas 24-7 - 365 days a year.

[Carl Bert]

Seems this discussion has taken two paths. I took the original post as more of a theoretical question and that's how I addressed it. The other path appears to be more of a comparison between typ commercially available engines which in my opinion are not apples to apples comparison, equals.

There are in the past and today examples of large industrial gas (spark ignition) engines that can and do stand toe to toe with diesel engines. Here is an example (see pic) of what is available today. Low speed, 1400-1800 rpm designed to run 24/7. Over in Salt Lake City they try and manage the lakes level by pumping water in/out. There are three I believe, gas powered engines driving pumps, large ones, ones that pump 450,000 gpm, yes per min. Think this project would use gas powered engines if reliability/dependability were not up to the task? With some applications, fuel availability dictates engine design, compression Vs spark, not reliability/durability considerations.

I have no problem if you take the path of comparing engine types if you want to compare what's available down at your local car/tractor dealer but the original question said all else being equal. I think the GE Waukesha engine is an example of a gas engine that is equal.

I am not really sure how you are comparing apples to apples. You talk about 3 large gas engines running 24/7, but what are you comparing them to? If you had two comparable engines, one gas and one diesel, running 24/7 side by side, and one outlasted the other, that would be another story. But just to say that you know of 3 gas engines that run 24/7, doesn't prove that gas will outlast diesel. It actually doesn't prove anything. Then to say that this project wouldn't have used gas engines if they weren't reliable and dependable, well thats just your opinion. There are a number of reasons why they may have gone with gas engines, budget could have been one of them. Lastly you keep bringing up reliability and dependability. No one is saying that gas engines aren't reliable or dependable, they most certainly are. The title of this thread is "What motor lasts longer"

[daugen]

It would be hard to imagine that large a "gas" engine not being powered by "gas" and I don't mean gasoline. How could the economies work out otherwise? Diesel and Gasoline are distributed widely. But if LNG prices are especially low locally, a non-gasoline powered "gas" engine usually lasts much longer and could possibly directly compete with a diesel plant.

But I think the answer lies with rpm. And at what rpm...900 rpm ship engines last amazingly long, though they usually have quality planned long term maintenance.
Now what gasoline powered engine is going to produce full output at 900 rpm, or say to a max 1000 rpm spec? I can't think of any. Most of what I've seen is that the lower the rpm, the larger the engine is relative to output. Which adds to cost. But they last longer and are now as likely to be running the main generator for a giant electric boat as they are hooked to a propeller. Likely those Waukeshaws were running at 1200 or 1800 rpm max pumping water, which is full design load. Lastly, and never lastly is cost and budget. But I think there are ways of comparing dollars per horsepower or pound feet of torque. Ultimately, I think the answer to this question is the motor that runs at the slowest speed is likely to last the longest.

It's all just generalization unless you have a good spec. The wider the spec the more possibilities, and comparison becomes less accurate. But it does allow us to prattle on...

[DarkBlack]

If you compare it "fair" lb for lb engine material weight, and same wok done compare a 2 stoke gas to diesel.
Take a quality gas 2 stroke like a husky, or Stihl chainsaw engine where the engine alone weighs about 5lb, but can make 3-5hp for 2,000 hours. It would be atough challange for a 5lb diesel to make that kind of power for so many hours...

[Soundguy]

that reminds me of a 4" trash pump we had.. it had a pull start diesel engine.. was cantankerous.. but worked. havn't seen too many small 'lawnmower engine' sized diesels like that...

[Code54]

Diesel!

[MBTRAC]

So you're saying that the ULSD is a poor choice of fuel? Interesting, because I was recently told the opposite. I'm not saying you're right or wrong, just wish I could see some facts that would support either side of the argument.

There's lot of speculation around ULSD, the facts are hidden & manipulated to support either perspective (Ditto fgor biofuels).
IMO ULSD is not the best choice of fuel for overall engine longevity - sulphur compounds are a natural lubricant for fuel pumps/injectors, hydrofining to remove the sulphur &/or using low sulphur crude means the oil company's are substituting less effective additives/detergents (ever noticed the extra foaming of ULSD ?) as poor lubricants to meet minimum lubrication standards (which high sulphurs diesel substantially exceeded), there have also been changes in the cloud point, distillation & cetane content coninciding with the intro of ULSD globally in developed markets - The initial noticeable "impact" of ULSD is in on fuel pump seals which now degrade exceeding quickly c.5yrs & less in older gear, those with older tractors with CAV type pumps may experience increased oil consumption as the shaft seal linking the pump to the crankcase degrades...
Bio fuels (diesel & enthanol) don't sustain prior engine durability experience either, primarily as they're hygroscopic & readily absorb water & have different lubrication/catalytic properties than the fuels they're replacing- potentially unless the bio fuels are dried correctly, stored in closed environments & used within a reasonable period of time all sorts of drama/wear/contaminates can result.
The other concern with BioDiesel is by absorbing water it actually promotes the growth of algae in diesel tanks....again causing all sorts of drama.

How did I come to the conclusion of what's best for our operation? We engaged a specialist fuel engineering company to analyse & make recommendations (at a cost of $60K+)., I too have been tempted by Biofuels as use across our Truck, Farm & Earthmoving fleet & was even contemplating installing a Biodiesel plant (extremely cost effective growing/using our oil seed cropping), as just buying Biodiesel would have saved conservatively $17K+/yr in fuel costs, with a self managed plant exponetially more ..........
I elected the risks far outway any running cost benefit & though also forced down the ULSD path because of what's commercial available, on the advice of our consultants supplement with our own enhanced additives on the non road registered equipment which is not subject to emissions legislation to hopefully compensate for the lack of sulphur ........others may have a diffferent view & make other choices....