Testing the Dilution Rate of Gasoline in Engine Oil in Accordance with ASTM D7593

Significance of the Topic

It is critical to monitor fuel dilution in engine oil because contamination with gasoline or diesel reduces oil viscosity and compromises lubrication performance. Accurate and rapid quantitation of fuel dilution informs maintenance schedules and ensures engine longevity.

Objectives and Overview

This study demonstrates a gas chromatography approach compliant with ASTM D7593 to measure gasoline dilution in engine oil using an automated backflush system. The aim is to shorten analysis time while maintaining accuracy and repeatability, aligning with standard requirements for gasoline, diesel, and biodiesel detection.

Used Instrumentation

• Nexis GC-2030 gas chromatograph with AOC-20i autosampler
• SH-Rxi-1ms capillary column (15 m × 0.25 mm I.D., 0.25 μm film)
• Backflush system including a backflush element and APC electronic flow controller
• Carrier gas nitrogen
• Flame ionization detector

Methodology and Instrumentation

Standard oil samples containing 0 to 5 percent gasoline were prepared in a 75 mm2/s base oil. Calibration used the n-C12 elution at 0.74 minutes to trigger backflush, removing high boiling components. Analytical conditions included a column temperature of 225 °C, injector and detector temperatures of 350 °C, split injection (1 to 100), nitrogen carrier gas at 2.3 mL/min under constant pressure control, and an injection volume of 0.1 μL.

Main Results and Discussion

The backflush method reduced analysis time to under 2 minutes per sample compared to over 20 minutes in conventional runs. Calibration curve linearity was excellent with R2 at or above 0.9995 across 0 to 5 percent gasoline. Ten repeat injections demonstrated RSD values below 1.5 percent. Blank CS2 injections confirmed efficient removal of oil matrix components.

Benefits and Practical Applications

• High throughput with cycle times under 3 minutes
• Standards compliance without solvent dilution or extensive sample preparation
• Lower carrier gas consumption and reduced labor input
• Dual-channel configuration possible to double sample throughput

Future Trends and Potential Applications

Future enhancements may include automated backflush control, integration with advanced detectors for multi-fuel analysis, and application to biodiesel blends. This method is well suited for engine oil condition monitoring and predictive maintenance systems.

Conclusion

The described GC backflush technique delivers rapid, accurate fuel dilution measurements in engine oil, fulfilling standard requirements while increasing laboratory efficiency and reducing costs.

References

• ASTM D7593-14 Standard Test Methods for Determination of Gasoline, Diesel, and Biodiesel Content in Used Lubricating Oils by Gas Chromatography
• Shimadzu Application News G310 through G314