Acidity in aviation turbine fuel according to ASTM D3242

Importance of Assessing Acidity in Aviation Turbine Fuel

Acidic constituents in turbine fuels, even at trace levels, can corrode metal components of fuel systems and impair phase separation from water, compromising engine performance and safety.

Objectives and Overview of the Study

This study demonstrates the full automation of ASTM D3242 for acidity determination in aviation turbine fuel by integrating an automatic titrator with an Optrode photometric sensor, aiming to streamline sample degassing, titrant delivery, and endpoint detection while meeting precision criteria.

Methodology

The automated procedure follows ASTM D3242 with key steps:

• Sample Preparation: 100 ± 5 g of fuel mixed with 100 mL of solvent and 0.1 mL p-naphtholbenzein indicator.
• Degassing: Continuous purging with dry, CO₂-free nitrogen at 400–450 mL/min for 3 min under stirring to eliminate dissolved gases.
• Titration: Monotonic endpoint mode (MET U) introduces alcoholic KOH titrant in fixed increments; after each dose, the Optrode monitors absorbance at 610 nm and the first derivative identifies the equivalence point.

Used Instrumentation

• OMNIS Professional Titrator with magnetic stirrer
• OMNIS Dosing Module
• 20 mL OMNIS special Cylinder Unit
• Optrode photometric sensor (610 nm)
• OMNIS Stand-Alone software license

Main Results and Discussion

Triplicate analysis (n=5) of three fuel samples produced mean acidity values of 0.0219, 0.0478, and 0.0839 mg KOH/g with absolute standard deviations between 0.0001 and 0.0005 mg KOH/g (relative deviations ~0.6 %), in compliance with ASTM D3242 precision limits. The photometric endpoint detection delivered sharp inflection signals, minimizing subjective interpretation.

Benefits and Practical Applications

Automating the titration workflow reduces manual handling and potential operator bias, enhances throughput, and ensures consistent data quality. The integrated degassing and Optrode sensor enable reliable acidity monitoring for quality control in fuel production and certification labs.

Future Trends and Possibilities

Future developments may include real-time data integration for continuous process monitoring, cloud-based result management, and multi-wavelength photometric detection to analyze additional fuel impurities simultaneously.

Conclusion

The automated ASTM D3242 titration method using the OMNIS system and Optrode sensor provides precise and reproducible acidity measurements in aviation turbine fuels with minimal user intervention, meeting standard requirements and streamlining QA/QC operations.

References

• ASTM International. ASTM D3242: Standard Test Method for Acid Number of Aviation Turbine Fuels.