Diesel engine wearing during the start up

[21121956]

Hello everybody:

For a medium speed Diesel engine, I would like to know if an equivalent exists between the wearing down that suffer at the time of the starting up and the wearing down that suffers in normal operation; i.e. one start up equals, let us say, 20 or 50 hours of operation.

Thanks in advance

 

[Zapster]

I believe you would need to factor in if they are cold startups. If cold, how cold? Also, how long will the engine sit between startups? Weeks, months, etc. If weeks or months, do you have a pre-oilier?

 

[21121956]

Hi Zapster:

Normally, the engines start/stop daily.
Before the start up, the engines are (among others) in these conditions: Pre lubrication ON during 15 minutes; lube oil temperature > 40ºC; Heavy Fuel Oil circulating at 120ºC; pre heating water (High Temperature Water) circulating at 70ºC.

 

[dgallup]

I don't have a precise number for you but in the pre-heated & lubed condition you describe I think it would be a very low number. You don't have hydrodynamic lubrication in the journal bearings but everything else should be fine.

 

[ivymike]

I agree with dgallup. Most of the wear life estimates (based on test) that I've seen have no allowance for startup wear whatsoever. It seems that they still generally err on the conservative (pessimistic) side.

 

[patprimmer]

Does the prelude lube the rings, piston skirts and groves and bores?

If not it will not help those areas which are generally the first to wear out.

Regards

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[wr180561]

With the pre-lubrication ,oil temperature and jacket water temperature you've mentioned above, I do not see that wearing at start up is an issue specially that the engine is started on no load. For these type of engines running on HFO, wearing is more related to corrosion caused by the chemical reaction of combustion products such as sulfuric acid at low exhaust temperature and the composition of sodium and titanium at high exhaust temperature. Regards
WR.

 

[CRG]

Typically, how long are the engines operated before shut down?

 

[21121956]

Hi CRG:

The engines operate during four or five full days, then comes the shut down and they remain stopped for five or six hours. After this time, they start once again.

 

[Majik]

can't idle them? seems silly to go for 120 hours then to shut down to let everything get cold and crank em up again...

 

[mrwizz]

I've heard all the theories that startup is an important cause of wear.
I replaced a non turbo diesel engine with a new crate long block. After 130,000 miles, I tore it down to inspect for wear. The main and rod bearings, cam bearings and roller rocker bearings looked new. The cylinder bores had a like new cross hatch pattern except for a bald spot (worn smooth) on the thrust side near the top of each cylinder where the rod angle pushes the piston to that side. The rocker arm pivets had signifcant wear (aluminum against steel). I junked it running at 400,000 miles because of suspension and body wear.

It's my opinion that startup wear is mostly mith. Religious attention to oil changes and cooling system maint. is the best way to get the longest service life. I use straight weight 30 or 40 seven months out of the year. and multi 15 - 40 for the few cold months. The benfit of straight weight is that it is all oil without viscosity improvers taking up volume. I mostly buy worn out and abused vehicles but still get additional long use with minor roblems. I live in coastal NC where heat is generally more of a problem than cold.

 

[Fabrico]

It's my opinion that startup wear is mostly mith. Religious attention to oil changes and cooling system maint. is the best way to get the longest service life. I use straight weight 30 or 40 seven months out of the year. and multi 15 - 40 for the few cold months. The benfit of straight weight is that it is all oil without viscosity improvers taking up volume. I mostly buy worn out and abused vehicles but still get additional long use with minor roblems.

Agree with that 110%.

 

[patprimmer]

Why do taxi cab engines where the cab runs 3 shifts outlast privately owned cars that only do short trips.

Experience would indicate to me the taxi engine has about 3 times the life.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ivymike]

oil degradation?

 

[kenre]

Only 3 times the life??

For one every taxi i have seen is on LPG, so no fuel to wash the cylinder walls down.

I did some work on one once, It had a Genuine 980,000 Km,
lpg, V8. Heads done up once, Bottom end never touched! it was never going to get a million as a taxi tho, its 7 year limit was due.

All engines are designed to operate at a certain temperature, above or below too far and wear occours more rapidly.

Ken

 

[ivymike]

All engines are designed to operate at a certain temperature

Huh? All of the engine technical specs I've seen have specified an environmental operating range of "-35F to +140F" (or so) - not "70F-90F and then they can cross their fingers."

For one every taxi i have seen is on LPG, so no fuel to wash the cylinder walls down.

Never seen an LPG taxi yet. My dad's cab was a regular ol' crown vic. Where were those LPG taxis?

 

[patprimmer]

I think he is referring to internal temperatures, not ambient temperatures.

I expect taxi engines last longer for a number of reasons.

1) Minimal number of cold starts where internal clearances are far from optimal.
2) Minimal number of starts where many parts are not lubricated for a few seconds of running.
3) Use of LPG which does not wash down bores.
4) Engine oil regularly reaches temperatures which drive of corrosive volatiles.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Isaac - Oz

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[kenre]

Thanks Pat and Greg for clearing up my post.

Yes, DownUnder i would estimate 99% or more of taxis are LPG fueled. Another reason, may be a wild thought tho, is the majority of taxis run in large cities, where dust is very uncommon, unlike rural areas where airborne dust is common.

Air filter maintanence and replacement is certainly much more critical in dusty conditions.

Ken

 

[ivymike]

That all makes more sense than what I was imagining... come to think of it, I don't think that gasoline-fueled cabs around here last all that long anyway. My Dad's was a smoky POS at about 200k-miles.