Fuel Effects on Engine-out Emissions Part 1 - Comparing Certification and Market Gasoline Fuels 2021-01-0541

Studies have shown that fuel quality plays an important role in engine-out emissions. The wide variation in composition and properties of gasoline fuels available in the market can lead to discrepancies between the expected emission levels as per set regulations and actual on-road measurements.

This study compares engine-out gaseous and particulate emission results between 5 US market fuels, 5 certification fuels and one street-legal race fuel. The market fuels were acquired from different terminals in Michigan. Tests were performed on a 4-cylinder 2.3 L turbocharged direct injection spark-ignited engine. The tests covered a wide range of steady-state operating conditions including load, injection timing and engine speed sweeps. Transient load steps were also performed under warm and cold engine conditions.

Weighting factors were assigned to the emissions results from the steady-state operating points in the study; these factors were based upon the frequency of visitation of respective point during an aggressive real drive emission cycle. This was then used to assign a ranking to the fuels.

The results from the study indicated that even within the US market-compliant gasoline fuels significant differences existed between the engine out particulate number (PN) and unburned hydrocarbon (HC) emissions, particularly at high load and under cold transient conditions—with more than 200x difference in the PN emissions and 1.5x difference in HC emissions. Furthermore, statistically significant differences existed between the engine out PN emissions of certification and market gasoline fuels, due to differences in their composition and properties. Lastly, significance of higher fuel injection pressures and optimum injection timing was demonstrated to reduce the sensitivity of the engine-out emissions to the fuel type.