Valve timing: its effect on emissions and fuel economy

Abstract

The effects of valve timing on exhaust emissions and fuel consumption were investigated experimentally. Emission control through the use of varied valve timing compared to conventional emissions control hardware was documented along with the effects of valve timing on emissions. Fuel consumption trends with changed valve timing were determined. The engine design of the test vehicle allowed independent adjustment of intake and exhaust valve timing. Emissions and fuel consumption were determined for steady-state speeds of 20 through 60 mph in 10 mph increments. A wide variety of intake and exhaust valve timing combinations were tested and the results compared to those of the production vehicle before modification. These results showed that valve timing has a significant effect on oxides of nitrogen emissions, but additional emissions control hardware is necessary to meet current and proposed emission regulations. Compared to emission control, varied valve timing holds more promise for reduced fuel consumption through a gain in cycle efficiency at various speeds.