Diesel consumption test

[vic008 17]

Anyone got a nifty little way of?

(2 cylinder)Using dipstick not too accurate with a bit of swell. Thanks

[Island Time 1,252]

Fuel consumption test. Fill the tank right to the top. Run set revs 30 mins, refuel to top. Consumption x2 = per hour at those revs. The issue is that fuel consumption to maintain revs is variable due to loading. But it will give you a start point. 

[wheels 543]

Or have you looked on line for the info on your engine. They usually have a fuel use chart or some kind of figure stated. Usually a difference between fuel use under no load and at full load is about 20% increase.

[vic008 17]

Hoping you might have invented something , say involving a gallon jug in cockpit, and a length of hose.? ? Not wanting to bleed engine either

[wheels 543]

That would work too.
The only way to do a proper accurate test is with an electronic Fuel Flow meter. Navman/Northstar had one on their big GPS/Plotter and it was the only one available in what I would call amateur world, that was actually a very accurate device for diesel. There are many available for Petrol, but Diesel was always a problem because there is a return line and the temperature has a huge impact on Fuel expansion for Diesel. They can sometimes be found second hand. I have a spare Head unit, but I don't have the sensors that need to be plugged into the fuel lines.
It could be that how Navman did this has now been copied into other brands.
Why are you wanting to find out Vic008 ?? Just as a interesting to know, or have you a problem?
You can get a ruff rule of thumb of use by a simple calculation.
Diesel Engines will use a range between 0.380 & 0.450 lbs/hp hour; 172 & 181 grams/hp hour; 231 & 243 grams/kW hour.
Or
GPH = (specific fuel consumption x HP)/Fuel Specific Weight
A close enough average for SPC is 0.4
Or

diesel-fuel-consumption-nat-aspirated.pdf

[Guest 000]

Wheels, I have had a copy of your downloaded chart for some time, trying to figure out consumption of any new boat we buy.

But, don't understand it.

My present boat has a Perkins Parama M30 3 cyl diesel engine - 29.5hp at 3600rpm. I cruise at 2000rpm and from the power curves the engine is delivering 18hp at that rpm. From the chart I should be burning 3 litres/hour. In reality I am burning about 1.8 litres/hour.

[w44vi 17]

Wheels, I have had a copy of your downloaded chart for some time, trying to figure out consumption of any new boat we buy.

But, don't understand it.

My present boat has a Perkins Parama M30 3 cyl diesel engine - 29.5hp at 3600rpm. I cruise at 2000rpm and from the power curves the engine is delivering 18hp at that rpm. From the chart I should be burning 3 litres/hour. In reality I am burning about 1.8 litres/hour.is 

Your motor is able to produce 18 hp at 2000 rpm that would burn 3 l/hour but your prop is not using 18 hp  

[Guest 000]

Your motor is able to produce 18 hp at 2000 rpm that would burn 3 l/hour but your prop is not using 18 hp

 

OK thanks. I understand.

That means then that to produce a data sheet saying that a diesel engine will consume X amount of fuel whilst producing Y amount of HP is pointless because the compiler of the data does not know what the end loading on the engine is, anymore than the average yachtie knows how much HP his propeller is actually using for any given revs.

[Island Time 1,252]

you can more think of it as UP To 18hp, which is the max at those revs...

[wheels 543]

Chris, Ummmm, yeah nah sort of maybe not close but could be...perhaps
A diesel is unique in that it's Hp is related to the engine revs. Basically, the Injector pump delivers a set dose of Fuel to each cylinder. That dose of fuel as a certain calorific value, which results in a certain amount of power available when it fires in the Cylinder. The RPM is governed and that happens by moving the Fuel rack to alter the dose of fuel in relation to the RPM. As a Load comes on, the governor moves the rack to allow a little more fuel in so the RPM stays the same. The max difference between unloaded and fully loaded is usually around 20% increase in fuel, before the RPM is increased, or the Engine cannot produce anymore power.
So if it takes little effort to propel the Boat forward at lower RPM, then the fuel saving could be 20% off the figure in the list for a starter.
The next part is the actual Hp. There are several different ways Hp is measured. SAE, BHP, DIN, SHP, Max intermittent, Continuous and I think that is it. You can be sure that a Manufacturer is always going to use the best figure possible for selling the engine. For a for instance, my Perkins 6.354 has 3 ratings I can think of off the top of my head. 130Hp, 105Hp and 95Hp. The 95Hp is the real McCoy actual. I can't remember what the 105 was for.
So in answer to your situation, your 18Hp may not be the same 18Hp that the fuel is calculated with. Or in other words, you can be sure the glossy brochure the Sales guy uses would have the best possible Hp with the least possible Fuel consumption, less that 20% and you just might get yourself to the value stated.
By the way, I used the figure stated on the page of 172 grams/Hp/hr x 29Hp and I get 4.988 ltrs. I quickly compared that to my engine and it's 130Hp rating x .172 is 22ltrs, which is about right. I run our engine at 1600 RPM that gives us about an 8 to 10ltr/hr consumption.