i need help choosing between two marine gensets. 3

[WafaB]

This will be a stupid question, but this is the only way one can aqcuire basic knowledge.
So i'm studying a case of replacement of a marine genset.
i have my boundaries for the frequency, the generator output, the size of the genset...
My research has brought several results, but i will focus on the wartsila 8W20 genset and the MAN l21/31 genset.
the two are pretty close, they fit the requirements, they use the same type of fuel, the two are medium speed, so i'm having trouble comparing the two.
How can i compare the performance of the two diesel engines to decide which one will be more efficient ?

 

[davidbeach]

Fuel consumption rate at the same constant load would be one comparison.

At some point the two options become similar enough that you base your decision on other factors, such as which will provide better field service, or which has more readily available spare parts.

 

[waross]

Fuel consumption: Further to David's post, read the fine print and determine what Specific Gravity fuel was used for the fuel consumption tests.
Years ago I was making recommendations for a new gen set and of course fuel consumption was a big issue. The set was to be used for prime power in the Yukon Territory where fuel is always expensive.
The fuel consumption of all but one set was virtually identical save for one brand.
One set, a well known North American brand, showed 10% less fuel consumption than every other set on the market.
Then I read the fine print. The odd set was tested with a fuel with 10% higher specific gravity than all the other sets.
as you know, diesel fuel energy is almost directly related to the specific gravity.

I will second David's suggestion;
Consider field service, availability of spares, service intervals and cost of service. Are filters proprietary or are replacement filters available on the open market.
Are the windings copper or aluminum?
Is the main breaker included in the comparison price?
Are the supplied protection packages comparable?

You may also want to consider the hours per month or hours per year required for at sea maintenance of each engine.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[catserveng]

Both of these engines have excellent service records in marine applications, looks like the MAN is a two stroke optimized for HFO fuels, the Wartsila is a four stroke designed for a broader fuel range. So to make a good comparison, need to know what your typical fuel use would be. Also, do you need to meet emissions regulations, like from IMO? Fuel efficiency all by itself isn't the primary performance factor for a lot of marine engines anymore, depends on where you plan to operate.

In general terms, I have found over the years that Wartsila seems to have a larger worldwide presence for service and spares. Based mainly on electric power applications it seems both manufacturers provide a very good product. The MAN in that series has (as I remember) a unitized base frame that supports both the engine and the generator, makes installation by the yard easier I'm told, and in some cases provides better torsional stiffness for the package overall.

For marine genset operations you need to look at the fuel efficiency over the entire expected operating load range, marine gensets usually spend a lot of their life at loads well below rated, so need to compare fuel consumption at multiple load points.

Hope that helps, MikeL.