EER values can be compared for different vehicles where the baseline and alternative vehicle are identical models. EER values are determined for various vehicle combinations and used to calculate the fuel economy for a consistent vehicle or mix of vehicles. For example, if a diesel car operates with a fuel economy of 33 mpg and a similar gasoline vehicle operates with a fuel economy of 24.9 mpg, the energy economy is 0.00044 km/kJ (2260 kJ/km) for the diesel vehicle and 0.00033 km/kJ (3000 kJ/km) for the gasoline vehicle.
5.3 Estimating the Fuel Economy of the Alternative Vehicle
Fuel economy ratios were estimated for each technology/fuel. These ratios are indications of how much more each technology would expect to achieve in terms of fuel economy (on an energy basis) compared to the baseline conventional vehicle. Since it is not possible to obtain fuel economy data for a consistent set of vehicles with similar attributes, fuel economy is estimated from energy efficiency data and the fuel’s heating value. The Energy Economy Ratio (EER) is the ratio of alternative vehicle energy economy to the baseline gasoline vehicle energy economy (on a lower heating value basis). Baseline gasoline vehicles listed in the EPA Fuel Economy Guide are operated on Indolene during the test which has a lower heating value of 114,424 Btu/gallon. A list of EERs for the fuels and technologies examined in this study are shown in Table 5‑1. Derivation of the EERs for each technology/fuel are discussed in the following subsections.
Table 5-1: Energy economy ratios for fuel cycle analyses
Diesel, FTD DI CI
A — no data available for FUDS cycle for current vehicles
5.3.1 Baseline Gasoline Vehicles