Standard: API 4022


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Fuel evaporated from automotive fuel systems--evaporative losses--account for a significant portion of the hydrocarbon air pollutant material from automobiles. As a result both of voluntary industry effort and of regulatory action, emissions of hydrocarbon from other sources within the vehicle have been steadily diminished in new vehicles manufactured since early in 1960. A parallel decrease has not occurrred with respect to evaporative losses and, therefore, these losses have counted for a steadily increasing percentage of vehicle emissions. It follows that evaporative losses have been the subject of technical interest as an uncontrolled emission source.

The amount of material lost from vehicles through evaporation processes obviously is sensitive to fuel volatility, and, logically, fuel volatility reduction has been suggested as a means of reducing evaporative losses. Volatility reduction would unquestionably reduce the amount of evaporative loss, but technical questions remain to be answered before the overall benefit, if any, could be assessed with acceptable confidence. Two such questions are as follows: (1) What is the effect, if any, of vapor pressure on emissions other than evaporative loss; considering these emissions, what is the overall effect on emissions from all sources within the vehicle? (2) What would be the effect upon the air pollution potential of vehicle emissions if fuels were modified to make the evaporative losses less reactive in the atmosphere?

To answer these and other questions the Bureau of Mines in cooperation with the American Petroleum Institute (API) undertook the investigation that is reported herein.

The results of other experimental work (1, 17-18)4 previous to this investigation gave some insight into the magnitude of evaporative losses that were to be expected at summertime temperatures. The current investigation extended the study to determine volatility effects at relatively cold temperatures, to determine effects of fuel changes upon exhaust as well as upon fuel system losses, and to obtain these data on a broad selection of vehicles. Inadequate or improper assessment of fuel effects could result in unwarranted fuel modifications or could prejudice the advantageous use of fuel technology in pollution abatement; misjudgment in either direction would be very costly.

The cooperative work was undertaken as a part of the Bureau's overall program to provide information on the relationship between fuels and auto related air pollution; it was coordinated with related work--done by the Bureau. Results of this study are complemented and supplemented by results of work done by the Bureau in its in-house program and in work sponsored by the National Air Pollution Control Administration.

The objectives of the test program were to determine the effect of fuel volatility and of front-end composition on quantity, composition, and photochemical reactivity of vehicle emissions including both tailpipe and fuelsystem losses. In addition to fuel volatility and front-end composition, the test variables were to include engine fuel-system features and ambient temperature.

4Underlined numbers in parentheses refer to items in the list of references preceding the appendixes.

Organization: American Petroleum Institute
Document Number: api 4022
Publish Date: 1970-02-01
Page Count: 86
Available Languages: EN
DOD Adopted: NO
ANSI Approved: NO
Most Recent Revision: YES
Current Version: NO
Status: Inactive