Stringent engine emission regulations highlight the importance of proper engine control during transient operation. In recent years, fast emissions analyzers that measure CO and CO2 simultaneously have allowed for fast air-to-fuel ratio (AFR) calculation under steady-state engine operation. However, using a steady-state methodology to calculate AFR under transient conditions can lead to significant data interpretation errors. This research introduces an experimental cycle-by-cycle AFR calculation routine developed for transient operation using cycle-resolved CO2 and CO analyzers. Need for the new technique arises when the composition of recycled exhaust gases vary significantly from expected post-combustion products corresponding to the true in-cylinder AFR. This condition commonly occurs when AFR is changed from one cycle to the next. The peak difference between the new method and traditional methods is demonstrated to be in the range of 0.1 relative air-to-fuel ratio points, or approximately 10%. These results are for low dilution conditions where the new method should show minimal difference as compared to traditional methods. If residual gas fraction levels were increased the difference in corrected to uncorrected results would become even greater, motivating the use of the new method in high-dilution engines.

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