Quality Control of Diesel

Importance of the Topic

Diesel fuel can accumulate water during production, transport, and storage. Excessive moisture fosters microbial growth, leading to corrosion, sludge formation, filter clogging, and potential damage to fuel injection systems. Monitoring water content is essential to ensure compliance with standards (maximum 200 mg/L per EN 590) and to maintain engine performance and longevity.

Study Objectives and Overview

This application note evaluates near-infrared spectroscopy (NIRS) as a rapid, cost-effective alternative to Karl Fischer titration for quantifying water content in diesel fuel. The goal is to develop a robust prediction model enabling moisture determination within one minute.

Methodology and Instrumentation

Diesel samples with water levels from 103 to 379 mg/L were analyzed using the following equipment:

• DS2500 Liquid Analyzer (400–2500 nm) with integrated 40 °C temperature control
• 8 mm pathlength disposable glass vials
• Vision Air Complete software for data acquisition and model development

Spectra were acquired in transmission mode, and a calibration model was built correlating NIR spectra to reference Karl Fischer measurements.

Main Results and Discussion

The NIR-based model demonstrated high accuracy and precision:

• Coefficient of determination (R²): 0.9776
• Standard error of calibration: 16 ppm
• Standard error of cross-validation: 21 ppm

The strong correlation between predicted and reference values confirms the method’s reliability. Spectral features in the NIR region effectively capture water absorption signals, enabling fast quantification.

Benefits and Practical Applications

• Rapid analysis: moisture content determined in under one minute versus five minutes for Karl Fischer titration
• Cost savings: no reagents required beyond disposable vials
• Non-destructive: preserves sample integrity for further testing
• Robust operation: suitable for laboratory and production environments, resistant to dust, moisture, and vibrations

Future Trends and Opportunities

Advances in NIR instrumentation and chemometric algorithms will further enhance sensitivity and expand applicability to additional fuel parameters. Integration with automated sampling and data management systems can streamline quality control workflows. Potential applications include inline monitoring during production and real-time tank surveillance.

Conclusion

Near-infrared spectroscopy using the DS2500 Liquid Analyzer provides a fast, accurate, and cost-efficient method for diesel moisture determination. It offers significant advantages over conventional Karl Fischer titration, supporting stringent quality control and operational efficiency in the fuel industry.