EXAMPLE
In the United States we measure with fuel economy by stating MPG (miles per gallon) or distance per unit volume. In Europe vehicles are measured with fuel consumption Liters/100 km or volume per unit distance.
FUEL CONSUMPTION
This is the metric of vehicle efficiency relating a measurement for volume of fuel consumed per given distance of travel [vol/dist]. Reductions in fuel consumption are less dramatic than the same exact increases in fuel economy.
DEFINED AS:
The volume of fuel consumed divided by the distance traveled. reported in [gal/100miles]
Scales linearly with volumetric FUEL USE (volume of fuel over time)
IS directly proportional to:
- Fuel Cost
- CO2 Emissions
(the metrics of interest for the CAFE/GHG standards)
FUEL ECONOMY
The inverse of Fuel Consumption [dist/vol], is a more commonly reported and regularly quoted metric, familiar to consumers. Describing for consumers utility of the vehicle — how far one can travel on a given quantity of fuel (like gallons).
DEFINED AS:
The distance traveled divided by the volume of fuel used, reported in [mpg],
IS NOT linear with volumetric FUEL USE (volume of fuel over time).
This non-linear relationship is NOT WELL understood by consumers, leading to misinterpretation of the benefits improved fuel economy provides for vehicles of different efficiencies.
If the GOAL is to MINIMIZE FUEL USE and MAXIMIZE ENERGY EFFICIENCY
FUEL CONSUMPTION REDUCTION is the Fundamental Metric of VEHICLE EFFICIENCY IMPROVEMENT.
FUEL CONSUMPTION RATHER THAN FUEL ECONOMY
provides an accurate comparison of technological improvements on different vehicle platforms.
The figure illustrates how increases in fuel economy (+5mpg) produce diminishing benefits to reductions in fuel consumption for increasingly efficient vehicles.