Search Results

The E-35 “Running Loss” program was planned in the fall of 1996, and conducted in the summer of 1997, as the third part of a series of Coordinating Research Council (CRC) sponsored evaporative emission test programs. One hundred and fifty vehicles (half cars - half light duty trucks) were recruited at a local I/M lane, and tested for running loss emissions at the ATL Facility in Mesa, AZ. The previous CRC programs had studied hot soak, and then diurnal emissions. Running loss emissions were measured in a Running Loss SHED (RL-SHED) for a 25 minute, 7.5 mile trip on a hot summer day (95°F). Vehicles from model years 1971 through 1991 were tested. A wide range in emission levels was observed - from a low of 0.13 g/mile to 43 g/mile. The test results were not able to establish whether car emissions are different, or the same, as light duty trucks. The major causes of the high emissions were liquid leaks on carburetor equipped models.

One hundred fifty-one vehicles were recruited from the I/M lane in Mesa, AZ during the summer of 1996, and their 24 hour diurnal emissions were measured in a variable temperature SHED (VT-SHED). The fleet selection included the earliest applications of evaporative emission control, and later technologies that had at least 5 years of exposure. Model years 1971 through 1991 were tested. Fifty-three percent of the sample tested had daily emissions of more than 10 grams. Five of the 151 were over 50 grams per day, and had significant liquid leaks. Twenty-six (17%) of the vehicles had emissions exceeding one gram per hour. Thirty-two of the 151 tested (21%) had identifiable liquid leaks. Carburetor systems had higher emissions than fuel injection systems. The highest emitters had resting losses of more than 0.8 g/hr. These eight highest emitters were considered outliers for the purposes of general analysis, and were not used, as is noted in the report.

The state of California has adopted a “real-time” evaporative emission procedure that will be used starting with the 1995 model year. This test, which focuses on high temperature conditions, and measures all sources of evaporative emissions, represents a very stringent requirement. Non-fuel background emissions, i.e., paint, adhesives, and even air conditioning refrigerant, can be a significant fraction of the total measured emissions. California has included a provision in their regulations that allows for the subtraction of background emissions, using a methodology to be developed in the future. This paper reviews the history of non-fuel emission regulations, provides data showing the magnitude of the problem using the new real-time procedure, and suggests a methodology for establishing a new background emission test procedure.

Closed-loop emission control systems were adopted by most motor vehicle manufacturers on a wide-spread basis in model year 1981, in order to meet the 1981 and later Federal exhaust emission standards. General Motors and the Environmental Protection Agency have conducted test programs to quantify the in-use performance of these closed-loop systems. Over 4000 vehicles (passenger cars and light duty trucks) have been evaluated covering the 1983 through 1988 model years at both low and high altitude locations. For model year 1986 and later, average emission levels, adjusted to the 50,000 mile point, are below the applicable EPA standards. The GM and EPA data indicate average emission levels have decreased during the 1980's and reflect the increased penetration of fuel injection, improvements in catalytic converter performance, and improved system and component reliability.

In recent years various parties have proposed new evaporative emission test procedures focused on controlling “excess” evaporative emissions, on hot “ozone prone” days. Studies by General Motors established the need for real-time measurements of daily emissions from parked vehicles and of “running losses” from vehicles that are driven to quantify and control the mobile source contribution to VOC inventory. “Resting losses” are shown to be a previously unidentified major source of hydrocarbon emissions. This paper describes the theories, data and development of GM's Real-Time Test Procedure.

The Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) are currently examining various proposals to modify the test procedures used to measure and regulate hydrocarbon evaporative emissions. The purpose of the proposed modifications would be to approximate the ambient conditions that vehicles can encounter on high temperature days, when many exceedances of the ozone air quality standard can occur. EPA has also developed an evaporative emissions model to support its evaluation of the proposed test procedure changes. GM has conducted tests to assess the performance of evaporative emissions control systems using the elevated temperature conditions under consideration by EPA. GM's tests used a real-time temperature cycle that extended over 24 hour time periods. The data from GM's tests indicate that on a real-time basis, evaporative emissions control systems perform better than predicted by the EPA model.

EPA and GM test programs have quantified the in-use emission performance of the GM closed-loop emission control systems. In-use exhaust emission levels, adjusted to the 50,000 mile point, show averages under the standards for the 1986 model year cars. In-use evaporative emission levels are under the standard, on average, for the 1985 and 1986 model year cars. Fuel injection systems have inherent evaporative emission performance advantages over carburetor systems. Average exhaust emission levels for the national fleet will continue to decrease as the closed-loop fleet replaces the older models. Predictions of future inventories are lower if the GM data reflecting the 1981+ emission improvements are used instead of the estimates currently in the MOBILE3 model.

The Environmental Protection Agency published a paper in November of 1985 (“Study of Gasoline Volatility and Hydrocarbon Emissions from Motor Vehicles”, EPA-AA-SDSB-85-5) suggesting that the evaporative emission test fuel be modified to reflect current “in-use” fuel characteristics. It was shown that higher evaporative emissions resulted from current vehicles when tested on higher RVP fuels. Vehicle tank fuel volatility decreases as the lighter ends in the fuel evaporate. As fuel is used in vehicle operation, the remainder in the tank becomes less volatile. The evaporative emission test procedure specifies that the test be conducted with the tank at 40% of capacity. At this level, one would expect the fuel to have “weathered” and be of less volatility than originally dispensed. This factor was not included in the EPA data.

Analysis of today's closed loop systems shows in-use emission levels - measured using the Federal Test Procedure - greatly reduced from those of vehicles produced in the mid ‘70s. The tailpipe concentration measurements (idle tests) used in I/M programs do not correlate well with in-use emissions from today's vehicles. I/M tests are not very effective in identifying emission failures and are costly compared to other control strategies. Additionally, I/M programs which do not include adequate vehicle preconditioning increase the number of false failures and cause unnecessary expense. A majority of today's closed loop vehicles have on-board diagnostic systems to identify failures. Interrogating these on-board diagnostic systems, together with parameter inspections, offers a more effective alternative to current I/M programs.

The major sources of variability of an exhaust emission test on the 1975 Federal Test Procedure (FTP) are discussed. Vehicle, driver and the ambient conditions affect hydrocarbon (HC) and carbon monoxide (CO) variability significantly. On the other hand, oxides of nitrogen (NOx) and carbon dioxide (CO2) are influenced more by the differences in vehicle loading. However, the importance of any other source of variability cannot be ignored, especially when a comparison is made between two tests. Various diagnostic aids such as the “Total Torque Tester”, a “Driver Evaluator”, an “Exhaust Bag Cross-Check”, and a “Repeatable Car”, which are used for the purpose of a better correlation between measurement systems on different test sites, are described. Designed experiments were conducted on vehicles whose emission levels were at or near the standards of 0.41 grams per mile HC, 3.4 grams per mile CO and 2.0 grams per mile NOx.