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Calculating Engine Load Factor??

Discussion in 'Technical Discussion' started by golden_fox, Mar 5, 2008.

  1. golden_fox

    golden_fox New Member

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    Can I get some guidance in calculating the engine load factor?

    I am actually looking at purchasing a pair of CAT 3412E (E rating) engines and would like to get some guidance and pointers in how to calculate the load factor for the engine? It is mentioned in the engine conditions and definitions to use it upto a 30% load factor. This cannot mean an average of 30% of the rated RPM (2300)....right!!?? I am assuming that its a combination of the usage hours and the RPM ranges that the engines will be used during these hours....something like that.

    Any help would be much appreciated. Thank you all in advance.
  2. Garry Hartshorn

    Garry Hartshorn Senior Member

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    I suspect you missed a word, not that I have access to a cat manual but from memory I believe is says "up to 30% full load factor" which means you can run the engine no more than 30% of the time at full load and max RPM
  3. golden_fox

    golden_fox New Member

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    Ahhh.........how silly of me!! THANKS A LOT!! Yes it makes sense now!!!!
  4. Marmot

    Marmot Senior Member

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    Caterpillar E rating: High Performance - For vessels operating at rated load and rated speed up to 8 percent of the time, or one half hour out of 6, (up to 30 percent load factor). Typical operation ranges from 250 to 1000 hours per year.

    Refer to the fuel burn spec at 100% load at each RPM. The LOAD FACTOR is the actual fuel burn divided by the maximum rated fuel burn. If your engine is rated to burn 100GPH at WOT and you are burning 30GPH, 30/100= 30% load factor. This doesn't mean you are limited to never pulling more power out of the engine, it just means that you are limited to full rated power for 30 minutes out of every 6 hours and over the life of the engine and the amount of fuel burned should not exceed 30 percent of what it would have burned if it had been running at max rated power output.

    In a nutshell, an engine has a lifetime that can be measured in weight of fuel burned. You can run that weight of fuel through the engine in a short time period if you are extracting large amounts of power, or you can take forever to burn that much if you only extract small amounts of power. The load factor represents the relationship between fuel burn and the number of hours you are taking to burn it.

    Reading back over that it is clear as mud ...
  5. golden_fox

    golden_fox New Member

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    Thanks a lot Marmot for the very detailed explanation. Should one have to stick to this 30% load factor for all RPM ranges (actual fuel burn vs. the maximum power fuel burn for each RPM)? Or can one look at maintaining a 30% average load factor (actual burned fuel compared with the fuel burn at maximum rated power output)?

    Thanks for ur time and input!
  6. Marmot

    Marmot Senior Member

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    "Should one have to stick to this 30% load factor for all RPM ranges (actual fuel burn vs. the maximum power fuel burn for each RPM)? Or can one look at maintaining a 30% average load factor (actual burned fuel compared with the fuel burn at maximum rated power output)?"

    The load factor is based on the lifetime amount of fuel burned in relation to what the engine would have burned at max rated power. It is a moving target since you can run for a few hundred hours at low power and shift the load factor downwards.

    The amount of fuel burned is directly proportional to load, more load more fuel burned, so there is only one load that will provide an instantaneous 30 percent and we don't really care too much about that since we bought the engine because we could get 2 or 3 times the power from it than the same engine is rated at for workboats. We just can't get it for as long as they can.

    We measure every drop of fuel burned and compare that to what the engine would have burned at max rated power and that becomes the load factor.

    It is a peculiar way of rating an engine and can be confusing. Exceeding the power factor will not effect warranty, it will just shorten the time between overhauls. Cat delivers the engine with a certain number of horsepower hours stashed away in the block and fuel lets them out. Once you put a certain amount of fuel in there all horsepower hours go away and the engine is worn out ... if you stick to the 30 percent figure you should get the number of hours that Cat advertises as being available, look at it that way.
  7. K1W1

    K1W1 Senior Member

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    Hi,

    Exceeding the Load Factor will very surely affect your warranty.

    If you have a failure like a dropped valve or turbo/piston failure the Cat Tech will sure as heck look at how much fuel the engine has burned and the hours done all as a part of his paperwork to complete the warranty job. This I believe is one reason why the total fuel burn figure in the engine computer is non resettable.
  8. golden_fox

    golden_fox New Member

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    Thanks a lot K1W1! i needed to clarify that....the impact on the warranty if the load factor is exceeded and now i know that the fuel burn figure cannot be reset!
  9. K1W1

    K1W1 Senior Member

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    Hi,

    The "instantaneous" fuel burn comes and goes as the engine runs, it returns to 0 when the engine is off.

    The "trip" fuel shows how much was burned since the last time it was reset to 0

    The "Total" fuel shows how much has been burned since the very beginning of the engines life. This is the one that can't be reset (by the end user anyway)
  10. Marmot

    Marmot Senior Member

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    The total fuel burn cannot be reset because that figure is central to calculating the load factor. If it were reset the load factor number would go away.

    I will look for the Cat reference to warranty and post it unless someone else finds it or calls Cat first. Running higher load factors just uses up the engine faster, it doesn't damage the engine as long as the engine is operated within its rated power output and operating parameters so there is no connection between dropping a valve and running higher load factors.
  11. Marmot

    Marmot Senior Member

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    Found it! Cat has an online Marine Selection Guide with the following information:

    Time at Full Throttle: “E” rated engines in typical pleasure craft
    applications normally record less than 1% - 2% of operational time at full
    throttle. Caterpillar develops engines with this rating to operate for up to
    8% of the time at full throttle. Exceeding this amount of time at full throttle
    operation will cause engine overhaul life to be reached sooner than
    anticipated, but will not affect warranty. Please refer to the Marine
    Engine Selection Guide (LEDM3457) for all other rating definitions.
  12. K1W1

    K1W1 Senior Member

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    Hi,

    CAT literature doesn't always mean what it says.

    CAT will also have you believe there is no de rate at up to 50 Deg C.inlet air temp.

    If there should be a failure- make a claim and then see how the Dealer who by the way is CAT's customer (not you the owner) and see how the whole process works.
  13. Marmot

    Marmot Senior Member

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    I'm not interested in getting into a pissing match trying to defend Cat but if they say there is no warranty issue then there is no warranty issue. Why would they waste their time making up and publishing something like that in a document intended to educate engine users or buyers about the meaning of their engine ratings and applications?

    The other side of the issue is, as I wrote earlier, if the engine is operated within its rated power range and within its operating parameters, it is not overloaded or abused and will last for the number of horsepower hours it is designed to produce. Operating it at higher load factors does not overload the engine, it merely "wears out" the engine in less time.
  14. golden_fox

    golden_fox New Member

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    It is true that there is nothing specified in the rating conditions (LEDM3457) and nor in the CAT Marine Warranty description that the warranty will become void if the rating conditions are not followed. But at the bottom of the Marin Warranty description, under the limitations, it does state that CAT is not responsible for 'Failures resulting from improper use or installation'. I guess this provides them the grounds to void a warranty for not using the engines within the rating conditions. I have also discussed this with the CAT distributor in my area and they have specifically said that if I do not follow the rating definitions for the engine (30% load factor, 1000 hours, etc.) then the warranty will become void....
  15. Marmot

    Marmot Senior Member

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    If I were going to buy an engine from them I would make sure they put in writing that they are placing warranty conditions on the engine beyond what Cat is publishing. I wonder if they will do that? Considering that they also added an hour limit well under Cat's published specification adds to the issue. Have you contacted Cat headquarters to obtain a definitive statement on what conditions would void the warranty? Until you have that the issue is moot.
  16. K1W1

    K1W1 Senior Member

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    As I tried to point out above you the end user are not buying from or having any dealings with CAT Corporation. You deal with their Dealers who are the only people CAT recognise as their customers, you are a customer of the dealer not CAT themselves.


    They will refer you to your dealer to answer all these questions. If as Golden Fox says it states in the Marine Warranty Description and he has been told by his distributor that failure to follow rating or installation instructions/definitions can have a negative affect on any warranty I would be inclined to believe that especially when coupled with my extensive experiences battling with CAT Dealers mis representation of product, performance and reliability issues and the CAT Corps sloping shoulders when it comes to accepting responsibility for a lot of what their dealers say and or do.
  17. golden_fox

    golden_fox New Member

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    I don't think i was actually very clear before. The CAT dealer meant 250 to 1000 hours per annum, which is also what's mentioned in the E Rating by CAT. When I have contacted CAT, I get referred to the regional 'head quarter', which for Asia Pacific Region is in Singapore. Will let you know if they tell me something different, but I do doubt it though.
  18. Marmot

    Marmot Senior Member

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    I was the one who was not clear on the hours, 250 to 1000 p.a. is what Cat state as "normal", for some reason when I responded I had another figure in mind so pardon the confusion, it originated with me.

    I spoke to Pantropic Power Systems in Miami today and their warranty person stated unequivocally that exceeding the load factor will not effect the engine warranty. Doing so is not considered abuse or improper operation. I am waiting for a written response and will post it when (and if) it arrives.
  19. Marmot

    Marmot Senior Member

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    K1W1 wrote:

    "CAT will also have you believe there is no de rate at up to 50 Deg C.inlet air temp."

    Cat very clearly states that the rating conditions for 3500 and smaller engines are based on either SAE or ISO standard conditions of either 25 deg. C or 27 deg. C inlet temperature. Power will drop off above those temperatures.

    3600 series and C280 engines are rated at 45 deg. C to the turbo.
    Power will drop off above that temperature.

    The specs are very clearly defined and there isn't much faith based engineering involved so it is unclear where the misunderstanding could have come from.
  20. K1W1

    K1W1 Senior Member

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    Hi,

    Marmot- 12 yrs ago I was involved in a boat with 3306 Gensets rated at 160 ekw @ 1500 RPM. These were ok with the wet manifolds but in an effort to clean up the exhaust stack which was fed into UNIKAT Catalytic converters the wet manifold and turbo turbine casing were exchanged for dry ones off a 66Z Engine ( Industrial). The engines were never bench tested with this arrangement. The temps in the box were extreme and as the Air Cleaner inlet was also in the box the inlet temperature was often 50 Deg C which just made the exhaust gas hotter. The manifold used to glow cherry red under heavy load and we had numerous failures of turbos and the manifolds (11turbos were done on 2 engines in the first 12 months in service)

    At the time the published CAT Data sheet gave the rating as being normal up to 50 Deg C.

    The whole lot was eventually changed for the original style wet ones and we did not have anymore failures although the soot filters did require cleaning occasionally after this.

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