The Effects of Fuel Oxygen Concentration on Automotive Carbon Monoxide Emissions at High Altitudes

In order to improve previous estimates of the reduction in carbon monoxide achievable in Colorado for oxygenated fuels with various levels of oxygen concentration, the Colorado Department of Health has reviewed several outside studies in addition to examining an in-house data base which contains more than 400 tests on 165 vehicles. Earlier findings such as 1) considerable variability among individual vehicle reductions and 2) a nearly linear relationship between CO reduction and fuel oxygen content for non-catalyst vehicles were confirmed. However, certain other conclusions by outside researchers were not supported by the high altitude data base. These included 1) non linear relationships between CO reduction and fuel oxygen content for catalyst and closed loop vehicles and 2) the fleetwide generalization that CO reductions achievable from fuels containing 2.0 percent oxygen are eighty percent as great as CO reductions achievable from fuels containing 3.5 percent oxygen.