Water in diesel fuel and petrol (gasoline)

Importance of the topic

Rapid and accurate water determination in diesel and petrol is critical to ensure fuel quality, prevent corrosion, and maintain engine performance. Even small amounts of water can lead to phase separation, microbial growth, and damage to engine components. Therefore, reliable methods for trace water analysis are essential in fuel analysis and quality control laboratories.

Objectives and overview

This study presents a procedure for quantifying water in diesel fuel and petrol using coulometric Karl Fischer titration. Due to the low water content in these samples, the coulometric approach was selected for its high sensitivity and precision.

Methodology

The procedure involves direct injection of the fuel sample into a titration cell containing Hydranal Coulomat AG-H reagent. Key steps include conditioning the cell to achieve a stable drift below 10 µg/min, precise sample weighing by difference, and automatic titration initiation.

Instrumentation used

• 737 Karl Fischer Coulometer with a diaphragm-free cell
• 728 Magnetic Stirrer
• Sample syringe
• Printer for result output

Key results and discussion

The method was applied to diesel fuel T105 and two petrol grades (313 and T51). Average water contents were determined as follows:

• Diesel T105: 94.3 ± 2.3 ppm
• Petrol 313: 45.9 ± 1.5 ppm
• Petrol T51: 108.8 ± 3.5 ppm

These results demonstrate the method’s reproducibility and suitability for low-level water detection in hydrocarbon matrices.

Benefits and practical applications

• High sensitivity allows detection of trace water levels
• Automation reduces operator error and improves throughput
• Minimal sample preparation speeds analysis time
• Applicable to quality control in fuel production and compliance testing

Future trends and opportunities

Advances may focus on integrating inline Karl Fischer sensors for real-time monitoring, miniaturization of titration cells, and enhanced automation through robotic sample handling. Emerging reagents and cell designs could further lower detection limits and expand applications.

Conclusion

Coulometric Karl Fischer titration with Hydranal Coulomat AG-H provides a robust and precise approach for quantifying water in diesel and petrol. The method’s sensitivity, automation capabilities, and ease of use make it well suited for routine fuel quality assessments.