A series of tests were performed on a gasoline powered engine with a Dedicated EGR® (D-EGR®) system. The results showed that changes in engine performance, including improvements in burn rates and stability and changes in emissions levels could not be adequately accounted for solely due to the presence of reformate in the EGR stream. In an effort to adequately characterize the engine's behavior, a new parameter was developed, the Total Inert Dilution Ratio (TIDR), which accounts for the changes in the EGR quality as inert gases are replaced by reactive species such as CO and H2. By calculating the TIDR and using this factor, rather than the reformation ratio or EGR rate, the results of the testing and sources of combustion improvement in the engine can be segregated into improvements due to the presence of reformate, such as initial kernel formation periods and unburned hydrocarbon emissions, and improvements due to the reduction in the total inert dilution levels, such as the emissions of the oxides of nitrogen and the fully turbulent combustion period.
