How To Calculate Diesel Efficiency At Different Loads

"what other inputs do I need"

You need inputs from every diesel generator manufacturer whose data you want to include.

There is NO easy way to calculate this, without accumulating fuel consumption vs power output data for every generator on the market.

It takes work that you must do yourself. Get busy gathering your data. Noome's going to do it for you.

Not sure what type of data I need hence my question here. Simply looking for some direction in how to go about setting up a generic spreadsheet to do this.

You need fuel consumption vs electrical power output data for all the generators you want to include.

This is NOT rocket science.

It is simply a data acquisition exercise.

No one else is going to gather the data for you.

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Look for the data the various manufacturers list, that should provide you with a start.

Without any hard data all you can use is an efficiency factor or an array of factors for all given loads.

Of course to arrive at the efficiency array you will have to have hard data. . .

Try to play a bit with energy in and out calculations and you know what I mean!

It is not possible to calculate efficiency without knowing the fuel used and the work delivered during the fuel consumption period. Get realistic!

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You need to install a fuel flow meter.

https://www.google.com/#q=fuel+flow+meter

http://www.dieselserviceandsupply.com/Diesel_Fuel_Consumption.aspx

50% efficiency is probably the best you can hope for with average~35% ballpark...

Each installation will have different efficiency characteristics and will require real time measurement of fuel in and power out over a period of time for accuracy...more time=more measurements=more accuracy

It's like diagnosing how much food was eaten of a certain organism by its constituent of excretion.

One way of quantifying it ,is measuring the flue gas quality or proportions at the exhaust pipe or stack and also its flue velocity (volumetric rate).

The following would constitute the proportions of flue gases

• CO%
• CO2%
• H2O%
• HC
• SOx%
  

Then, by basic Chemistry you would be able to find the mass rate or mole rate of fuel that was combusted by summing up the constituents. Say,

2H+1/2O2=>H2O; 2mole H

C+1/2O2=> CO; 1mole of C

S+x/2 O2 => SOx; 1mole of S

The sum of H,C,S in the flue gas is the approximate fuel mass/volume used to produce energy at a certain rate.

It's quite not a straight forward solution and appear to be bothersome if you are not well acquainted with but, rest assured you'll find the solution.

I am open as a contractor/consultant if you have the budget and additional data as stated.

Some flue analyzers has analytics on the combustion efficiency alone it's quite different on the total thermal efficiency of the engine (@BHP).

I would surmise the easiest way to find the generator efficiency is by:

1) Convert the generator KVA output into BTU.

2) Convert the diesel energy content into BTU.

3) Measure and record the diesel consumption rate for/at various generator output loads for a definite time period. (At least four (4) different test points 0%, 25%, 50%, 100%. Keep in mind that the more sampling points taken over the generator output rage, the more accurate the calculations will be.)

4) Divide the BTU output by the BTU input to identify efficiency for each measured point then average readings to identify overall efficiency.

If you are simply looking for cost factors I would meter/measure the fuel consumption rate for a defined period of time and a given load then divide the fuel consumption by the KVA output to identify the cost of fuel per KVA or VA.

If accuracy is critical then do not forget to consider maintenance costs in the equation.

Item 1) not a good idea. You will have 20% error at standard power factor of 0.8. Small gensets commonly work on almost resistive loads, which alters the AC generator efficiency significantly.

As to the original posted question, starting off by wanting power rating in kVA and efficiency in kWh/liter suggests a confusion about the relevant factors. The old practice of pounds per kWh was better. A set maker would qualify the fuel as a certain kWh thermal per kg to a final temperature which would be in a fuel standard specification.

The fuel mass per litre varies with temperature. Fuel suppliers often vary constituents by season.

You would have to decide whether the design criteria were :-

• cost per hour, including maintenance, overhaul and repair costs.
• power to weight ratio.
• Fuel Efficiency.
• reliability.
• dependable running time without maintenance.
• size.
• etc

Even if you had the figures for every available genset, a single kWh/litre figure would be useless for a specific requirement.

If you do not have actual site recorded temperature compensated fuel consumption data that you can correlate with load, then you can only really quantify a theoretical value based on what the engine manufacturer states in their data sheets. Engine suppliers will usually provide a stated g/(Brake)kWh or l/kWh of diesel at percentage loads. Using weight & not volume is more accurate as 1 kg will always weigh 1 kg, but the weight of 1 litre will vary dependning on the temperature. Efficiency of the genset will also vary based on the efficiency of the alternator at different loads (genset load profile). These values can be interpolated from the alternator efficiency curves correlating with percentage & power factor, found in manufacturer data sheets. To get an accurate load profile, you will need to look at historical data from your site, & determine what percentage of times your genset/s ran at certain load ranges.

EG: If engine manufacturers power at 100% is 531 (BkW), engine manufacturer stated fuel consumption @ 100% is 193.9 (g/BkWh), & alternator efficiency @ 100% is 94.9%, then genset kW (electrical) is 531 * 94.6% = 502.3 (kWe) & fuel consumption (g/kWh.e) is 193.9 (g.BkWh) / 94.6% = 205 (g/kWh.e)

Genset efficiency @ 100% is 1/(42,900 [kj/kg] * 205 [g/kWh.e] / 3600000) = 40.94%

Repeat for other load percentages.....

Just got back from a month of leave so hopefully I haven't messed anything up in there.

Hope that helps.

Cheers,

Clarity.