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Technical Paper

Use of a Repeatable Car to Improve Intra-Lab Variability of Emissions Tests

A Repeatable Car (REPCA) program has been developed at the Environmental Protection Agency's National Vehicle and Fuel Emissions Laboratory (NVFEL) as part of an ongoing effort to improve the precision of fuel economy and emissions measurements. This concept of using a repeatable car as an integrated system diagnostic tool is not a new idea in the emissions testing field; however, our statistical analyses and organizational approach may be different from what other laboratories are using. Furthermore, given the NVEFL's role in automotive emissions testing, we felt it appropriate to provide related industries a detailed account of our standard laboratory practices, both for informational and comparative purposes. In order to separate vehicle and measurement variability in a relatively simple manner, a process was developed to track REPCA data based on Statistical Process Control principles using the calculation of individual site offset values from two week moving averages.
Technical Paper

Test Variability of Emission and Fuel Economy Measurements Using The 1975 Federal Test Procedure

Several sets of repetitive test data using the 1975 Federal Test Procedure ('75 FTP) have been analyzed to establish the variability of each component measured during each phase of the test. The variability characteristics of four different emission control systems have been discussed and compared. The overall variabilities of the '75 FTP composite values have been assessed at ±6% for hydrocarbons and CO, ±3% for NOx, and ±1% for CO2. The extremely repeatable behavior of the CO2 emissions is utilized to calculate the fuel economy during the test. This calculation is discussed and some fuel economy results from repetitive tests are presented.
Technical Paper

Standardized Equation for Hydrogen Gas Densities for Fuel Consumption Applications1

We have established an equation for the density of hydrogen gas that agrees with the current standard to within 0.01 % from 220 to 400 K with pressures up to 45 MPa. The equation is a truncated virial-type equation based on pressure and temperature dependent terms. The density uncertainty for this equation is the same as the current standard and is estimated as 0.2 % (combined uncertainty with a coverage factor of 2). Comparisons are presented with experimental data and with the full 32-term equation of state.
Technical Paper

Passenger Car and Light Truck Fuel Economy Trends through 1980

The 4000-mile EPA fuel economy figures are presented for passenger cars from pre-emission control models through 1980, for light-trucks from 1975 through 1980, and for motorcycles for 1980. The paper accumulates most of the fuel economy analyses presented in previous papers of this kind. Accordingly, it is voluminous with data, and necessarily terse in textual material. It presupposes reader familiarity with the nature of the EPA tests and data bases, and the techniques used for the analyses, particularly harmonic sales weighting of fuel economy data. The reader must refer to precursor papers for such descriptions. Some aspects treated are: stratification by weight class, vehicle size class, manufacturer, and MPG range; domestic vs. import, gasoline vs. Diesel, and 49-states vs. California models.
Technical Paper

Passenger Car Fuel Economy as Influenced by Trip Length

Data from the Nationwide Personal Transportation Study (NPTS) and other sources have been used to generate distributions of vehicle miles traveled (VMT), average speed, and fuel consumption as a function of trip length. Approximately one third of all automobile travel in the U.S. is seen to consist of trips no more than ten miles in length. Because short trips involve more frequent stops and a smaller percentage of operation during warmed-up conditions, nearly half of the fuel used by automobiles is consumed during the execution of these short trips. The typical trip of approximately ten miles in length has been shown to result in a fuel economy that is equal to the average fuel economy achieved for all trips combined.
Technical Paper

Passenger Car Fuel Economy Trends Through 1976

The fuel economy data compiled by the U.S. Environmental Protection Agency (EPA) have been analyzed to determine the trends in passenger car fuel economy beginning with model year 1957. This paper adds the 1976 model year data to the historical trend and concentrates on comparisons between the 1976 and 1975 models. Calculation procedures which allow the changes in fuel economy to be determined separately for system optimization, new engine/vehicle combinations, and model mix shifts have been employed in the analysis which compares 1976 models with 1975 models. A wide range of percentage changes was seen for the fifteen manufacturers who were certified in time to be included in the analysis performed for this paper. The net change in fuel economy for the 1976 new car fleet has been estimated at +12.8% compared to the 1975 new car fleet. System optimization is responsible for 8.8% of the improvement and model mix shifts are projected to account for +3.1% of the change.
Technical Paper

Passenger Car Fuel Economy During Non-Urban Driving

The use of fuel economy data from the Federal Test Procedure (FTP) has provided a substantial amount of data on the fuel economy of passenger cars in urban driving conditions. Since the FTP does not represent the type of driving done in rural areas, especially on highways, a driving cycle to assess highway fuel economy was a desirable supplement to the FTP. The new Environmental Protection Agency (EPA) “highway” cycle was constructed from actual speed-versus-time traces generated by an instrumented test car driven over a variety of nonurban roads and highways. This cycle reflects the correct proportion of operation on each of the four major types of nonurban roads and preserves the non-steady-state characteristics of real-world driving. The average speed of the cycle is 48.2 mph and the cycle length is 10.2 miles, close to the average nonurban trip length.
Technical Paper

Passenger Car Fuel Economy - Trends and Influencing Factors

This paper discusses some trends and influencing factors in passenger car fuel economy. Fuel economy and fuel consumption were calculated by a carbon balance method from HC, CO, and CO2 emissions measured by the 1972 Federal Test Procedure. The information presented was derived from nearly 4000 tests of passenger cars ranging from 1957 production models to 1975 prototypes. Data are presented for various model year and vehicle weight categories. Trends in fuel economy are discussed on an overall sales-weighted basis and for each individual weight class. Some of the factors that influence fuel economy are quantified through the use of a regression analysis. Particular emphasis is placed on the differences in fuel economy between those vehicles that were subject to federal emission regulations and those vehicles that were not. Three ways to characterize vehicle specific fuel consumption are presented and discussed.
Technical Paper

Fuel Economy of the 1975 Models

The fuel economy data obtained from the emission tests run by the U.S. Environmental Protection Agency (EPA) have been used to show passenger car fuel economy trends from model year 1957 to present. This paper adds the 1975 model year to the historical trend and concentrates on comparisons between the 1975 and 1974 models. Methodologies which allow different 1975 vs 1974 comparisons to be made have been developed. These calculation procedures allow the changes in fuel economy to be determined separately for emission control systems, new engine-vehicle combinations and model mix shifts. Comparisons have been calculated not only for the fleet as a whole but for each of the 13 manufacturers who were certified as of the time this paper was prepared. The net change in fuel economy for the fleet has been estimated at +13.8% comparing the 1975 models to the 1974 models assuming no model mix change occurs.
Technical Paper

Exhaust Emissions 1966-1972 Model Year Light Duty Motor Vehicles

This report describes the results of a surveillance study initiated by the U.S. Environmental Protection Agency to measure gaseous exhaust emissions from 1020 light-duty motor vehicles. This project was the second effort in a continuing program using the CVS Federal Test Procedure. Selected privately-owned vehicles, drawn randomly from six metropolitan areas, were tested in as-received condition. The emissions data obtained from these 1966-1972 model-year vehicles are reported in grams per mile of unburned hydrocarbons, carbon monoxide, carbon dioxide and oxides of nitrogen while fuel economy is reported in mpg as determined over the Federal Driving Schedule.
Technical Paper

Development of Greenhouse Gas Emissions Model for 2014-2017 Heavy- and Medium-Duty Vehicle Compliance

Of all existing modes of transportation, onroad motor vehicles are the largest contributor to greenhouse gas emissions and fuel usage. The Environmental Protection Agency and the National Highway Traffic Safety Administration finalized regulations in April 2010 to reduce greenhouse gas emissions and improve fuel economy for 2012-2016 model year light-duty vehicles. In November 2010, both agencies jointly proposed the first ever greenhouse gas standards for medium- and heavy-duty trucks which are expected to take effect for model years starting in 2014. Vehicles of light-duty families are subject to mandatory testing for certification and compliance. Unlike the light-duty sector where a vast majority of vehicles are mass produced for generally similar purposes, medium- and heavy-duty vehicles are commonly custom-made.