Real-time inline predictions of jet fuel properties by NIRS

Significance of the Topic

Accurate and timely characterization of jet fuel properties is critical for aviation safety, engine performance and process optimization. Traditional wet chemistry methods are reliable but often slow, labor-intensive and require skilled analysts. Implementing real-time near-infrared spectroscopy (NIRS) offers a high-throughput alternative, enabling inline monitoring and immediate feedback to support quality control and process efficiency in fuel production.

Study Objectives and Overview

This Application Note NIR–25 aimed to develop robust calibration models for predicting multiple jet fuel parameters simultaneously using a NIRS XDS Process Analyzer. Key goals included:

• Establishing quantitative NIR models for parameters specified in ASTM fuel standards.
• Demonstrating inline feasibility with minimal operator training.
• Comparing model performance against established laboratory methods.

Methodology and Instrumentation

105 jet fuel samples representing various grades and sources were analyzed. Each sample was measured in triplicate over a wavelength range of 800–2200 nm using:

• NIRS XDS Process Analyzer (Metrohm) with stainless steel immersion probe (6 mm gap, 12 mm path length).
• 32 scans per spectrum with stirring between measurements to ensure homogeneity.

Spectral pretreatment involved second‐derivative transformation to reduce baseline shifts and scattering effects. Chemometric models were developed in Vision software using leave-one-out cross-validation and independent validation sets for robustness assessment.

Main Results and Discussion

Strong correlations were achieved between NIR predictions and ASTM reference methods across all parameters:

• API gravity (R2 = 0.986, SEP = 0.29).
• Density at 15 °C (R2 = 0.984, SEP = 0.0016 kg/L).
• Aromatic content (R2 = 0.962, SEP = 0.72 vol%).
• Cetane index (R2 = 0.934, SEP = 0.84).
• Boiling points at 10/20/50/90% recovery (R2 range 0.839–0.952, SEP 2.0–3.6 °C).
• Flash point (R2 = 0.925, SEP = 2.3 °C), freezing point (R2 not applicable due to narrow range, SEP ≈ 2.0 °C).
• Hydrogen content (R2 = 0.939, SEP = 0.05 wt%) and viscosity at –20 °C (R2 = 0.905, SEP = 0.23 cSt).

Model errors were comparable to or better than the precision of ASTM methods, confirming that NIRS can match laboratory accuracy while delivering results in under 30 seconds.

Benefits and Practical Applications

The inline NIRS approach provides several advantages:

• Rapid multi-parameter analysis from a single measurement.
• Reduced reliance on chemical reagents and waste generation.
• Lower training requirements for operators.
• Continuous monitoring capability to ensure consistent product quality.

This real-time feedback is particularly valuable for refinery process control, blend optimization and on-site quality assurance in fuel depots.

Future Trends and Potential Applications

Advancements in NIRS technology, such as compact fiber-optic probes and improved chemometric algorithms, will expand inline applications further. Integration with process analytical technology (PAT) frameworks and Industry 4.0 platforms can enable automated corrective actions based on spectral data. Emerging machine-learning approaches may also enhance model adaptability to new fuel formulations and broader contaminant detection.

Conclusion

This study demonstrates that NIRS, using a process analyzer setup, can reliably predict key jet fuel properties in real time with accuracy comparable to standard laboratory methods. The technique simplifies workflows, accelerates decision-making, and supports stringent quality requirements in aviation fuel production.