Fuel consumption

[Squeaky]

Good morning:

I have a new engine and the manual indicates the following for fuel consumption:

268 g/kW.h
(196 g/hp.h)
6.9 oz/hp.h
@ 2500 rpm.

What the heck does this mean when applied to liters per hour?

It is a 16 hp diesel.

Cheers

Squeaky

 

[ghostlymoron]

My 16hp Yanmar uses approx 1/3 gal/hr

 

[ghostlymoron]

Proper answer

Diesel fuel weighs approx 885grammes/litre (less than water)
If your engine uses 196 grammes/horsepower/hour the consumption in litres per hour is
196x16/885=3.543502825litres/hour
There are 4.55litres in a gallon so that equates to 0.77879183gal/hr that is higher than I would have thought where did the consumption figures come from?

 

[PuffTheMagicDragon]

I take diesel as being 760 grammes per litre. This means that your engine, at 2500RPM uses 196/760 litres per horse power per hour. If you round the figures you could say 200/800, which would give you 1/4 of a litre /hp/hr.

Thus, if to maintain that number of revs your engine is having to produce 12 hp, (e.g. against a strong wind and/or current) then your consumption would be 12 x 0.25 = 3 litres per hour. OTOH, if the wind and/or current is with you, the engine will not need to work so hard in order to keep to the same revs. Say it needs to produce only 6hp. In that case your consumption would be only 6 x 0.25 = 1.5 litres per hour.

You probably have charts in your engine manual that show you these figures.

 

[Squeaky]

Good afternoon:

I got the figures quoted from the manual which was supplied with the engine but it might as well be written in Chinese as far as I am concerned.

I used the figure of about 2 ltr an hour for my former 21 hp engine and I guess I am going to have to work out the new consumption by trial and error as 3 ltr an hour seems well over the top to me for 16 hp.

Thanks for your efforts though.

Cheers

Squeaky

 

[PuffTheMagicDragon]

I think that something might not be sufficiently clear. The fact that a diesel engine is rated at 16 horse power does not mean that you are actually taking 16 hp out of it all the time. What power it actually produces depends on the load that it has at a given time; this is then reflected in the consumption. If your boat is clean and you are motoring through flat calm, you might only be taking 3hp out of your '16hp' engine.

 

[Ex-SolentBoy]

Good morning:

I have a new engine and the manual indicates the following for fuel consumption:

268 g/kW.h
(196 g/hp.h)
6.9 oz/hp.h
@ 2500 rpm.

What the heck does this mean when applied to liters per hour?

It is a 16 hp diesel.

Cheers

Squeaky

Love maths things.

Red diesel is specified at between 0.83 and 0.88kg per litre, lets call it 0.85 average.

You use 0.196/0.850 litres per hp, that is to say 0.23 litres.

So, according to your figures at 2500rpm the engine generates 16hp and uses 3.7 litres per hour.

Interestingly, my 85 hp engine uses 0.21 litres per hp at max rpm and this ties in my understanding that all marine diesel engines use roughly the same amount of fuel to produce a horsepower at full throttle.

You need the graphs for your engine though. At half throttle for us (1400rpm) we use 15% of the fuel at full throttle (2800rpm).

Of course, how fast you go depends on drag, but it is interesting to graph the whole thing. It really show you what speeds are best when motoring.

 

[Tranona]

As already noted, you are unlikely ever to take 16 hp (which is probably only 14.5 if you look at the power curves). Cruising at about 2500 revs you are using around 7 or 8 hp. I expect you will average somewhere between 1 and 1.25 litres per hour. As Solentboy has said, the specific fuel consumption of different makes of diesels varies very little. Consumption is a function of power demanded which can be influenced by a number of factors - prop, weight, weather (windage and seas etc.) You have probably already discovered the last knot of speed is very expensive on fuel. Easy to explain when you see the extra HP required.