Sunday, January 1, 2012

Power and Fuel Consumption Estimation of Gasoline and Diesel Generator

Some manufacturers include the consumption of fuel per hour for a specific power output in specification. For example a generator set will consume 6.5 liters of diesel per hour when working at 25 kva. But some other manufacturers do not include fuel consumption in specification.

How to estimate of fuel consumption? 
Based on the calculation of the total power load, we can estimate fuel consumption for generator set. By these calculations we can see on fuel consumption of gasoline-driven generator set compared to diesel-driven generator set.

Specific Fuel Consumption (SFC)
Specific Fuel Consumption of a generator, based on the amount of fuel consumption divided by the motor output power. In calculating the estimates made here, the motor output power (brake horsepower, flywheel horsepower) is considered equal to the power consumed (load power), efficiency factors are not calculated.

If not written on the generator manufacturer's specifications, we can use the following SFC data.
Otto (gasoline) engine: 273-227 g/kw/hr, the average value = 250 g/kw/hr
Diesel engine: 209-178 g/kw/hr, the average value = 194 g/kw/hr
http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption

Fuel density
The density of fuel depends on the temperature and its contents, can generally be taken as the average value as belows by wikipedia:
Gasoline          0.745 kg/l
Diesel fuel       0.832 kg/l

Calculation
If the electrical load is 10,000 watts or 10KW, and used continuously for 24 hours a day. Please note the unit measurement of power, if using kva then it needs to be multiplied by  power factor to get the power in watts. Then based on the average value of Specific Fuel Consumption, fuel consumption is:

For gasoline motor generator: 250 x 10 x 24 = 60 000 g/day = 60 kg/day
If the specific gravity of gasoline is 0.745 kg/l, then consumption in liters is:


60 / 0.745 = 80.54 liters per day

For diesel motor generator: 194 x 10 x 24 = 46 560 g/day = 46.56 kg/day
If the specific gravity of diesel fuel is 0.832 kg/l, so fuel consumption in liters is:


46.56 / 0.832 = 55.96 liters per day


These calculations show that the diesel motor generator has much better fuel efficient. Gasoline motor generator consumes 44% more fuel. But of course must also consider the price of fuel where generator works.

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