Browse Publications Technical Papers 2000-01-1171

Evaporative Leakage from Gas Caps 2000-01-1171

The AirCare® vehicle emissions inspection and maintenance program is briefly described, together with the benefits which the program has already achieved. Additional benefits have been projected should the program include some more sophisticated assessment of evaporative emission control systems.
The feasibility of including such an assessment has been investigated, and a pilot study has been conducted in the regular inspection lanes. The operational and systems implications are described. The pilot study has resulted in an analysis of the incidence of faulty gas caps in the Lower Fraser Valley light-duty vehicle fleet, and how this relates to other vehicle characteristics such as vehicle make, model, model year, mileage etc.; and inspection data including emission control system components tampering and tailpipe emissions.
Approximately 10% of all gas caps tested failed the pressure test, compared to the 1% that were failed by visual inspection. Correlation with other vehicle and inspection data showed that the likelihood of a leaking gas cap cannot be accurately predicted without a functional test.
The second part of this paper describes the operation, construction and testing results of a Gas Cap Leakage Rate Tester. The Leakage Rate Tester is capable of precisely measuring the mass flow rate out of a leaking gas cap at specific pressures. Over 170 fuel caps were tested on this unit and results separated into three groups; those that fail the EPA Pressure Test, those that passed, and anomalous Honda fuel caps. These results are analysed as a precursor to larger-scale fleet projections.
This work has formed the first and second parts of a more comprehensive evaporative emissions assessment and modelling project.


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