A number of approaches to the development of low emissions engines have been reported in the literature. Many of these approaches, however, have reduced emissions by retarding ignition timing. This increases exhaust gas temperatures for more complete HC oxidation in the exhaust system but results in a fuel economy penalty.
Previous studies by the authors indicated that NOx can be effectively reduced with judicious use of EGR. While this may result in increased HC emissions, under some conditions it also can result in improved fuel economy.
The data reported in this paper demonstrate that the use of EGR is capable of reducing NOx emissions and octane number requirements while improving fuel economy. Any resultant increase in HC emissions can be controlled with an efficient HC/CO oxidation catalyst.