An Approach for Controlling Vehicle Emissions 680400
Using 1966 and later model vehicles equipped with crankcase and exhaust hydrocarbon and carbon monoxide controls, prototype systems were installed to control evaporative emissions from the tank and carburetor and nitrogen oxides in the exhaust. The systems selected were the ARCO vehicle vapor recovery, and the nitric oxide reduction.
Baseline evaporative emissions were determined for two of the vehicles operated over-the-road and on the chassis dynamometer. The proposed federal evaporation loss test technique was used for evaluating the performance of the vehicle vapor recovery system.
Evaporation losses from the equipped vehicles were less than 1 g per test -- well below the proposed federal standard of 6g. However, carbon monoxide in the exhaust from one car increased by approximately 0.1%. The system had no effect on exhaust hydrocarbons.
The mechanism by which the vehicle vapor recovery system functions was investigated briefly. Depending upon the particular vehicle and the design of the control system, tank vapor flowed to either the carburetor bowl, the crankcase vapor storage area, or both during diurnal soak. During hot soak, vapor generated in the carburetor flowed primarily to the crankcase for storage, although with one of the vehicles a small amount went to the fuel tank.
Modifications to the system were made to alter the ultimate destination of the vapor during the diurnal and hot soak test cycles.
The nitric oxide reduction system used for controlling nitrogen oxides is an improvement of the internal type. The system has been designed to recirculate exhaust during part throttle acceleration and cruise, but to shut off the flow during idle, full throttle acceleration, and deceleration. Approximately 15-22% of recycle is used. Exhaust without added air is a necessity for recirculation. A source of air free exhaust must be provided for vehicles equipped with manifold air injection.
Reductions of nitrogen oxide emissions ranging upwards from 80% were achieved. The concentrations of hydrocarbons and carbon monoxide in the exhaust were held within the existing standards of 275 ppm and 1.5%, respectively, and in several instances were reduced below these levels.