Quality Control of Diesel

Importance of the Topic

Diesel quality parameters such as cetane index, flash point, cold filter plug point (CFPP), distillation endpoint (D95), and viscosity are critical for engine performance, fuel safety, and cold weather operation. Traditional reference methods are time-consuming and require multiple instruments and reagents, creating a need for a rapid, combined analysis approach.

Study Objectives and Overview

This study aims to evaluate the feasibility of visible and near-infrared (Vis-NIR) spectroscopy using the XDS RapidLiquid Analyzer for simultaneous, reagent-free determination of key diesel quality parameters. The goal is to compare Vis-NIR predictions against standard methods in terms of accuracy and precision.

Methodology and Instrumentation

Analysis was performed in transmission mode over 400–2500 nm at a controlled temperature of 30 °C using disposable 8 mm vials. Samples were measured on the XDS RapidLiquid Analyzer. Data acquisition and model development were conducted with Vision Air Complete software. Key instrument components:

• XDS RapidLiquid Analyzer (Metrohm 2.921.1410)
• Disposable glass vials, 8 mm path length (Metrohm 6.7402.000)
• Vision Air 2.0 Complete software (Metrohm 6.6072.208)

Main Results and Discussion

The Vis-NIR models demonstrated strong correlation with reference methods:

• Cetane index: R2=0.991, SEC=0.093, SECV=0.143.
• Flash point: R2=0.977, SEC=2.22 °C, SECV=2.50 °C.
• CFPP: R2=0.973, SEC=1.99 °C, SECV=2.24 °C.
• D95 (distillation endpoint): R2=0.861, SEC=3.07 °C, SECV=3.47 °C.
• Viscosity at 40 °C: R2=0.983, SEC=0.038 cSt, SECV=0.047 cSt.

Overall, Vis-NIR enables reliable multi-parameter screening in under one minute without sample preparation.

Benefits and Practical Applications

• Rapid analysis: complete parameter set in under 1 minute.
• No chemical reagents or sample preparation required.
• Simultaneous determination reduces laboratory workload and instrument costs.
• Suitable for routine quality control in laboratories and production environments.

Future Trends and Potential Applications

• Integration into inline and at-line process control systems for real-time monitoring.
• Expansion of calibrations to cover diverse diesel grades and biofuel blends.
• Application of machine learning algorithms to enhance prediction robustness.
• Development of portable Vis-NIR devices for field testing and on-site quality assurance.

Conclusion

Vis-NIR spectroscopy with the XDS RapidLiquid Analyzer offers a fast, accurate, and reagent-free alternative to traditional diesel quality assays. The method streamlines multi-parameter testing, maintaining comparable precision to reference standards and supporting efficient quality control workflows.

Reference

• Metrohm AG. AN-NIR-080: Quality Control of Diesel. Application Note.