Testing the Dilution Rate of Diesel in Engine Oil in Accordance with ASTM D3524

Significance of the Topic

Measuring the dilution of diesel fuel in engine oil is vital for assessing lubricant performance and engine health. Excessive fuel contamination reduces oil viscosity, accelerates wear, and compromises lubrication efficiency. Accurate determination of fuel dilution helps optimize oil change intervals and prevent mechanical failures.

Goals and Overview of the Study

This study demonstrates a gas chromatography method compliant with ASTM D3524 for quantifying diesel dilution in SAE 10W-30 engine oil. The aim is to establish a simple sample preparation protocol and analytical conditions that deliver reliable results without solvent dilution or complex pretreatment.

Methodology and Used Instrumentation

Samples were prepared by blending diesel into SAE 10W-30 oil at concentrations from 0.5 to 12 mass percent and spiking each with n-decane as an internal standard. Column resolution was evaluated using a mixture of n-hexane, n-hexadecane, and n-octadecane, while the calibration endpoint was set with n-nonadecane. No sample dilution in CS2 was performed during analysis.

• Gas chromatograph Nexis GC-2030 AF coupled with AOC-20i autosampler
• Capillary column SH-Rtx-1 (5 m x 0.1 mm i.d., 0.1 µm film)
• Column program 70 °C (0 min) to 325 °C at 16 °C/min, total run 15.94 min
• Nitrogen carrier gas at 30 mL/min, split injection 1:5
• Injector temperature 300 °C, detector FID at 350 °C

Main Results and Discussion

The column achieved a resolution of 5.7 between n-C16 and n-C18, exceeding the ASTM requirement of at least 3. Calibration using six diesel standards yielded a linear response (R2 0.9967) according to y=0.0543x+0.15. Repeatability tests (n=10) at four concentration levels showed RSD values below 2.3%, confirming within-laboratory precision and accuracy meet ASTM tolerances.

Benefits and Practical Applications

The presented method offers several practical advantages:

• No need for solvent dilution or extensive sample cleanup
• Rapid analysis under 16 minutes per sample
• High repeatability and compliance with industry standards
• Applicability to routine engine oil monitoring in research and quality control laboratories

Future Trends and Possibilities

Emerging approaches include integrating backflush techniques as described in ASTM D7593 for faster throughput, automation of sample handling, and real-time online monitoring of fuel contamination. Extending the method to biodiesel blends and multicomponent fuel analysis can further enhance engine diagnostics and maintenance strategies.

Conclusion

A GC-FID method aligned with ASTM D3524 provides accurate, precise measurement of diesel dilution in engine oil using straightforward sample preparation and standard analytical conditions. The approach supports efficient maintenance decisions and ensures reliable engine lubrication performance.

References

• ASTM D3524 Standard Test Method for Analysis of Diluted Fuel in Engine Oil by Gas Chromatography
• ASTM D3525 Standard Test Method for Test of Fuel Contamination in Engine Oil by GC
• ASTM D7593 Standard Test Method for Backflush Analysis of Diesel and Biodiesel in Engine Oil
• JPI-5S-23 Test Procedures for Diesel Dilution in Engine Oil
• ASTM D4626 Practice for Determination of Fuel-Contaminated Oil
• JPI-5S-23-2017 Specification Document for Diesel Dilution Analysis