With the introduction of the oxidation catalytic converter in 1975, improved fuel economy and reduced emissions occurred simultaneously. If the data in figure 3 were normalized to the 1978 weight mix, it would show that fuel economy improvements leveled out in 1982. The fuel economy from 1977 to 1980 improved almost exactly in proportion to the decreasing weight of vehicles. The figure also includes information on average vehicle weight. fleet combined, city, and highway fuel economy data for each model year since 1974. The period from 1968 to 1974 resulted in primary emphasis on emission control with loss of fuel economy from lower compression ratios, changes in spark timing, A/F ratio and axle ratio changes, and exhaust gas recirculation. Exploring the lean burn region is an important area of research and development because of the potential of improved fuel economy and adequate emission control with only an oxidation catalyst.įederal regulations also mandate automotive fuel economy.
The stoichiometric ratio of 14.7:1 is necessary in the Phase III control using three-way catalysts since the A/F ratio must be in a narrow window within ± 0.05 of the stoichiometric ratio to achieve high HC, CO, and NO x control efficiencies simultaneously.
The A/F ratio effects are used in all phases of control. The region where A/F ratio exceeds 17.5:1 is the lean burn region where misfires can occur along with slow flame speeds, causing increased HC concentration. Also shown is the A/F ratio for maximum power (13.5:1) and maximum fuel economy (17:1). In fact, when CO and HC concentrations are a minimum, at an A/F ratio of around 16:1, NO x production is close to a maximum. It is impossible to achieve the low emissions demanded by federal standards by A/F ratio control alone since the concentrations of the three pollutants are not minimums at the same A/F ratio. Figure 2 (Heinen 1980) is a plot of NO x, HC, and CO concentrations in the exhaust versus A/F ratio for a typical gasoline engine. 1985a.)Īir/fuel (A/F) ratio, which is controlled by the carburetor or fuel injection system, is the most important variable in determining emissions and in applying catalyst technology. (Adapted with permission from Ford Motor Co. Major phases in the reduction of automotive emissions. After current knowledge in each area has been reviewed, important gaps in our knowledge are identified and research needed to fill these gaps is described. In practice, the stringency of emission standards determines the importance of this interrelationship. Emissions and fuel economy are interrelated because both are influenced by the engine combustion system design. Fuel economy is included because achieving high fuel economy and low emissions together makes the engineering effort more difficult. This paper reviews our current knowledge of automotive emissions, including standards, control technology, fuel economy, fuels and additives, in-use emissions, measurement methods for unregulated pollutants, and models for predicting future automotive emissions. The scientific basis of this effort is the pioneering atmospheric chemistry research of A.J.Haägen-Smit, who showed that photochemical reactions among hydrocarbons (HC) and nitrogen oxides (NO x) produce the many secondary pollutants that reduce visibility and cause eye and nose irritation in the Los Angeles area. Pollution from Automobiles-Problems and SolutionsĬoncern about the automobile as a source of air pollution has been expressed periodically, but national concern was first evidenced in the 1960s when California established the first new car emission standards.
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