Evaluation of Light-Duty Gasoline Vehicle Rated Fuel Economy Based on In-Use Measurements

Abstract

A study demonstrated a systematic method to assess the degree of concordance between estimated real-world and the U.S. Environmental Protection Agency (EPA) rated fuel economy for light-duty gasoline vehicles based on real-world emissions measurements. Cold engine start effects are accounted for in the real-world fuel economy and in comparison with EPA ratings. Portable emissions measurement systems were used to measure emissions of carbon dioxide, carbon monoxide, hydrocarbons, and nitrogen oxides of 122 vehicles on a specified test route consisting of various roads. Fuel economy of measured vehicles was estimated considering two cases: EPA standard driving cycles and real-world driving cycles. Average cold start emissions measurements from 32 vehicles were used in sensitivity analysis of fuel economy with respect to cold start. Real-world fuel economy estimates and comparison with rated fuel economy are not highly sensitive to cold start effects. On average, both the city and highway ratings are conservative compared with real-world fuel economy. However, there are proportions of vehicles that have lower real-world fuel economy than rated. The method demonstrated should be applied to additional vehicles and real-world driving cycles. Insights from these comparisons could motivate development of a more accurate rating scheme and identification of advice to consumers to improve their fuel economy.

Effect of Air-Conditioning on Light Duty Gasoline Vehicles Fuel Economy

“…The FTP-average rates are estimated based on a weighted combination of the three bags. The HWFET is a hot-start cycle used to simulate highway driving operation ( 19 , 37 ). The US06 and SC03 tests are referred to as Supplementary FTP (SFTP) tests ( 20 ).…”

“…Real-world measurements of the fuel-use and emission rates of 205 LDGVs were done in prior work using PEMS, an onboard diagnostic (OBD) scantool, and global positioning system receivers with in-built barometric altimeters (GPS/BA) (18)(19)(20)(21)(22). Figure 1 shows a map of the pre-defined measurement routes including 110 miles of driving between NCSU and Research Triangle Park via North Raleigh.…”

“…EPA determines FE ratings of new LDVs sold each year ( 19 ). The ratings are based on chassis dynamometer measurements on standard driving cycles used for emission compliance and FE ratings ( 19 , 20 ). For only one standard cycle, SC03, vehicles are measured with AC turned on.…”

Real-world fuel use and gaseous emission rates for flex fuel vehicles operated on E85 versus gasoline

“…EPA fuel economy, in miles per gallon (mpg), is based on chassis dynamometer measurements for FTP and highway fuel economy test (HWFET) cycles. FTP-and HWFET-based fuel economy measurements were adjusted downward by EPA to estimate the rated city and highway fuel economy (Khan and Frey 2016). The EPA city and highway ratings of the five FFVs are compared with real-world VSP modal fuel use rates weighted by the amount of time in each mode for the FTP and HWFET.…”

Vehicle Specific Power: An Alternative to Evaluate the Dynamics of Real-Driving Tests

“…The Vehicle Speci c Power (VSP) is an interesting tool because it takes into account the road grade and it is already successfully applied in mathematic models for air pollution emission from vehicles and to evaluate vehicle dynamic in road tests (Frey et al 2010; Khan and Frey 2016). This study has the objective of applying VSP to assess the dynamic of RDE tests in a more comprehensive way than the regulatory parameters from European RDE procedure.…”