195 Vs 1115 Fuel consumption

[bobansen]

I run both a 195 & a 1115, as of late I have taken the 1115 out of service to carry out checks to the top end. This has left me just the trusty 195 to carry out all my supply needs. This has left me scratching my head..
My supply demands tend to be fixed daily, that is the requirements are the same. Yet after running the 195 for over a week I have noticed some startling differences between the two engines.
  read on and give me your input on my quandary..

195..
Fuel. 50% wmo-25% diesel-25% kerosene.
Engine speed 1800rpm average
ST Head 7.50Kw
Temp- very damn hot (to ensure complete fuel gets burnt) and no smoke
Consumption over a three hour period (Loaded) 4litres

Whereas.

1115.
Fuel. WVO. 75%- Diesel. 25%
Engine speed 1200rpm average
ST Head.15kw
Temp-Hot, but a lot less than above 195.
Consumption over a three hour period (loaded) 3litres
Keep in mind that the running times and loads are the same.
Both these engine will burn what ever I put in the tanks. A few days ago I forgot to include the kerosene and she (195) still ran on the thick oil. What an engine!
Any ideas?

[mobile_bob]

the 1115 engine is likely a DI engine,  which gives it an advantage over an idi engine of about 5 percent, the larger engine is probably 3% more efficient on its own.

the st15 is about 3-4 percentage points more efficient than the st7.5

running the 195 at 1200 would result in an increase of efficiency of as much as 5%

all together maybe a 12-15% difference in the two, however...

how you are burning 25% less with the 1115/st15 vs the 195/st7.5 i can only assume as testing measurement errors.

only way to know for sure, is to measure the amount of kw/hrs produced with a given amount of fuel with each generator set

even though loads can thought to be stable and the same between each test, in practice and when measured accurately i think you
will find significant differences.

fuel composition can also shift the consumption numbers substantially, so unless you mix a large enough quantity to assure
the same mix for both tests it is hard to know how this also might factor in.  as an example my trigen will do approx 5% better fuel consumption
numbers burning 30 weight over straight pump diesel.

also measuring fuel consumption by weight instead of volume can illustrate some shift in consumption numbers, warmer fuel takes up more space, while fuel by weight is about as standard as you can get.

bob g

[Tom Reed]

The difference in fuels and the efficiency of the combustion of the WMO may be an issue too. Also how heavily loaded is the 195, especially during periods of high demand?