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Converting Brake Specific Fuel Consumption in Pounds of Fuel per
Horsepower Hour into Watt Hours per Horsepower Hour
A tale of two vehicles, one electric with a rated BSFC of 0.15 lbs. of fuel-e per HP Hour, and a gasoline engine with a BSFC rated at 0.45 lbs. of fuel per HP Hour. This is a good metric and a dramatic way of expressing the comparative efficiency of these two drive trains but unfortunately we are still looking at the world through fossil fuel colored glasses and we are in need of a better metric to express these values.
A gallon of gasoline contains 32,777 watt hours of energy so all we need to do is use this metric to convert both vehicle drive trains to watt hours per horsepower hour and we will have a metric that looks at the world through electric vehicle colored glasses instead. On the plus side it will be a more direct way of computing and of looking at the new world we are now entering.
There are six pounds in a gallon of gasoline (E-85 unleaded with ethanol) this means there are.
32,777/6 = 5,462.8 watt hours per pound of gasoline.
BSFC = 0.15 lbs. x 5,462.8 = 819.42 watt hours per HP Hour for our electric vehicle.
32,777/6 = 5,462.8 watt hours per pound of gasoline.
BSFC = 0.45 lbs. x 5,462.8 = 2,458.27 watt hours per HP Hour for our gas powered vehicle
This new metric was included in my new blog titled Electric Vehicle Energy Conversions and I felt it was in need of explanation as not everyone might have made the conjectural leap of understanding how I arrived at these figures.
I think it is important as we enter this new age of electric drive to stop thinking in terms of gallons of gas, pounds of fuel, or pounds of fuel equivalent. We could use the term pounds of fuel equivalent but this is an abstractions. Watt hours per Horsepower Hours is not an abstraction for either a gas or electric car in this instance since one Horsepower is by definition 747 watts and a Horsepower Hour is by definition 747 watt hours.
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