CFR > Title 40 - Protection of Environment > CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY > SUBCHAPTER Q—ENERGY POLICY (Parts 600–611) > PART 600—FUEL ECONOMY AND CARBON-RELATED EXHAUST EMISSIONS OF MOTOR VEHICLES > SUBPART B—Fuel Economy Regulations for 1978 and Later Model Year Automobiles—Test Procedures (§600.101-08 to §600.115-08) > 600.113-88—Fuel economy calculations.

600.113-88—Fuel economy calculations.

The Administrator will use the calculation procedure set forth in this paragraph for all official EPA tests. For the 1988 model year, manufacturers may choose to use this procedure or use the calculation procedure described in § 600.113-78. However, once a manufacturer uses this procedure, it must be used for all subsequent tests. This procedure must be used by manufacturers for 1989 and later model years. The calculations of the weighted fuel economy values require input of the weighted grams/mile values for HC, CO and CO2 for both the city fuel economy test and the highway fuel economy test. Additionally, for tests of gasoline-fueled vehicles, the specific gravity, carbon weight fraction and net heating value of the test fuel must be determined. The city and highway fuel economy values shall be calculated as specified in this section. A sample appears in appendix II to this part.
(a) Calculate the weighted grams/mile values for the city fuel economy test for HC, CO, and CO2 as specified in § 86.144 of this chapter. For tests of gasoline-fueled vehicles, measure and record the test fuel's properties as specified in paragraph (c) of this section.
(b) (1) Calculate the mass values for the highway fuel economy test for HC, CO, and CO2 as specified in paragraph (b) of § 86.144 of this chapter. For tests of gasoline-fueled vehicles, measure and record the test fuel's properties as specified in paragraph (c) of this section.
(2) Calculate the grams/mile values for the highway fuel economy test for HC, CO, and CO2 by dividing the mass values obtained in paragraph (b)(1) of this section, by the actual distance traveled, measured in miles, as specified in paragraph (h) of § 86.135 of this chapter.
(c) Gasoline test fuel properties shall be determined by analysis of a fuel sample taken from the fuel supply. A sample shall be taken after each addition of fresh fuel to the fuel supply. Additionally, the fuel shall be resampled once a month to account for any fuel property changes during storage. Less frequent resampling may be permitted if EPA concludes, on the basis of manufacturer-supplied data, that the properties of test fuel in the manufacturer's storage facility will remain stable for a period longer than one month. The fuel samples shall be analyzed to determine the following fuel properties:
(1) Specific gravity per ASTM D 1298.
(2) Carbon weight fraction per ASTM D 3343.
(3) Net heating value (Btu/lb) per ASTM D 3338.
(d) Calculate the city fuel economy and highway fuel economy from the grams/mile values for HC, CO, CO2 and, for test of gasoline-fueled vehicles, the test fuel's specific gravity, carbon weight fraction and net heating value. The emission values (obtained per paragraph (a) or (b) of this section, as applicable) used in each calculation of this section shall be rounded in accordance with § 86.084-26(a)(6)(iii). The CO2 values (obtained per paragraph (a) or (b) of this section, as applicable) used in each calculation of this section shall be rounded to the nearest gram/mile. The specific gravity and the carbon weight fraction (obtained per paragraph (c) of this section) shall be recorded using three places to the right of the decimal point. The net heating value (obtained per paragraph (c) of this section) shall be recorded to the nearest whole Btu/lb. These numbers shall be rounded in accordance with the “Rounding Off Method” specified in ASTM E 29-67.
(e) For gasoline-fueled automobiles, the fuel economy in miles per gallon is to be calculated using the following equation:

Code of Federal Regulations

mpg=(5174×104×CWF×SG)/

Code of Federal Regulations

[((CWF×HC) (0.429×CO)) (0.273×CO2))
×((0.6×SG×NHV) 5471)]
Where:
HC=Grams/mile HC as obtained in paragraph (d) of this section.
CO=Grams/mile CO as obtained in paragraph (d) of this section.
CO2=Grams/mile CO2 as obtained in paragraph (d) of this section.
CWF=Carbon weight fraction of test fuel as obtained in paragraph (d) of this section.
NHV=Net heating value by mass of test fuel as obtained in paragraph (D) of this section.
SG=Specific gravity of test fuel as obtained in paragraph (d) of this section.
Round the calculated result to the nearest 0.1 miles per gallon.
(f) For diesel automobiles, calculate the fuel economy in miles per gallon of diesel fuel by dividing 2778 by the sum of three terms:
(1) 0.866 multiplied by HC (in grams/miles as obtained in paragraph (d) of this section),
(2) 0.429 multiplied by CO (in grams/mile as obtained in paragraph (d) of this section), and
(3) 0.273 multiplied by CO2 (in grams/mile as obtained in paragraph (d) of this section).
Round the quotient to the nearest 0.1 mile per gallon.

Code of Federal Regulations

[51 FR 37851, Oct. 24, 1986]
The Administrator will use the calculation procedure set forth in this paragraph for all official EPA tests. For the 1988 model year, manufacturers may choose to use this procedure or use the calculation procedure described in § 600.113-78. However, once a manufacturer uses this procedure, it must be used for all subsequent tests. This procedure must be used by manufacturers for 1989 and later model years. The calculations of the weighted fuel economy values require input of the weighted grams/mile values for HC, CO and CO2 for both the city fuel economy test and the highway fuel economy test. Additionally, for tests of gasoline-fueled vehicles, the specific gravity, carbon weight fraction and net heating value of the test fuel must be determined. The city and highway fuel economy values shall be calculated as specified in this section. A sample appears in appendix II to this part.
(a) Calculate the weighted grams/mile values for the city fuel economy test for HC, CO, and CO2 as specified in § 86.144 of this chapter. For tests of gasoline-fueled vehicles, measure and record the test fuel's properties as specified in paragraph (c) of this section.
(b) (1) Calculate the mass values for the highway fuel economy test for HC, CO, and CO2 as specified in paragraph (b) of § 86.144 of this chapter. For tests of gasoline-fueled vehicles, measure and record the test fuel's properties as specified in paragraph (c) of this section.
(2) Calculate the grams/mile values for the highway fuel economy test for HC, CO, and CO2 by dividing the mass values obtained in paragraph (b)(1) of this section, by the actual distance traveled, measured in miles, as specified in paragraph (h) of § 86.135 of this chapter.
(c) Gasoline test fuel properties shall be determined by analysis of a fuel sample taken from the fuel supply. A sample shall be taken after each addition of fresh fuel to the fuel supply. Additionally, the fuel shall be resampled once a month to account for any fuel property changes during storage. Less frequent resampling may be permitted if EPA concludes, on the basis of manufacturer-supplied data, that the properties of test fuel in the manufacturer's storage facility will remain stable for a period longer than one month. The fuel samples shall be analyzed to determine the following fuel properties:
(1) Specific gravity per ASTM D 1298.
(2) Carbon weight fraction per ASTM D 3343.
(3) Net heating value (Btu/lb) per ASTM D 3338.
(d) Calculate the city fuel economy and highway fuel economy from the grams/mile values for HC, CO, CO2 and, for test of gasoline-fueled vehicles, the test fuel's specific gravity, carbon weight fraction and net heating value. The emission values (obtained per paragraph (a) or (b) of this section, as applicable) used in each calculation of this section shall be rounded in accordance with § 86.084-26(a)(6)(iii). The CO2 values (obtained per paragraph (a) or (b) of this section, as applicable) used in each calculation of this section shall be rounded to the nearest gram/mile. The specific gravity and the carbon weight fraction (obtained per paragraph (c) of this section) shall be recorded using three places to the right of the decimal point. The net heating value (obtained per paragraph (c) of this section) shall be recorded to the nearest whole Btu/lb. These numbers shall be rounded in accordance with the “Rounding Off Method” specified in ASTM E 29-67.
(e) For gasoline-fueled automobiles, the fuel economy in miles per gallon is to be calculated using the following equation:

Code of Federal Regulations

mpg=(5174×104×CWF×SG)/

Code of Federal Regulations

[((CWF×HC) (0.429×CO)) (0.273×CO2))
×((0.6×SG×NHV) 5471)]
Where:
HC=Grams/mile HC as obtained in paragraph (d) of this section.
CO=Grams/mile CO as obtained in paragraph (d) of this section.
CO2=Grams/mile CO2 as obtained in paragraph (d) of this section.
CWF=Carbon weight fraction of test fuel as obtained in paragraph (d) of this section.
NHV=Net heating value by mass of test fuel as obtained in paragraph (D) of this section.
SG=Specific gravity of test fuel as obtained in paragraph (d) of this section.
Round the calculated result to the nearest 0.1 miles per gallon.
(f) For diesel automobiles, calculate the fuel economy in miles per gallon of diesel fuel by dividing 2778 by the sum of three terms:
(1) 0.866 multiplied by HC (in grams/miles as obtained in paragraph (d) of this section),
(2) 0.429 multiplied by CO (in grams/mile as obtained in paragraph (d) of this section), and
(3) 0.273 multiplied by CO2 (in grams/mile as obtained in paragraph (d) of this section).
Round the quotient to the nearest 0.1 mile per gallon.

Code of Federal Regulations

[51 FR 37851, Oct. 24, 1986]