Detailed Hydrocarbon Analysis of Spark Ignition Engine Fuels by GC using ASTM D6729

Significance of the Topic

Spark ignition engine fuels demand precise characterization to guarantee performance, emissions compliance and consistent blending in refinery operations. Detailed hydrocarbon analysis (DHA) under ASTM D6729 provides a full-species breakdown, enabling accurate quality control and regulatory adherence.

Objectives and Overview of the Study

This application note demonstrates the implementation of ASTM D6729 for detailed hydrocarbon profiling of C5–C14 components in gasoline and related refinery streams. Emphasis is placed on calibration, chromatographic separation, repeatability studies and data reporting using dedicated DHA software.

Methodology and Instrumentation

• Calibration: n-alkane mixture used to determine Kovats retention indices.
• Sample types: Gasolines with oxygenates (MTBE, ETBE, TAME, ethanol) and blending stocks (naphthas, reformates, alkylates) up to 225 °C.
• GC Conditions:
  
  • Injector: Split/splitless at 250 °C, split flow 200 mL/min.
  • Column: 100 m × 0.25 mm ID × 0.50 µm film.
  • Oven program: 0 °C hold 15 min; 1 °C/min to 50 °C; 2 °C/min to 130 °C; 4 °C/min to 270 °C, hold 10 min.
  • Carrier gas: Helium at 43.1 Psi.
  • Detector: FID at 300 °C.
• Data processing: Eclipse DHA software groups hydrocarbons (normal, iso, cyclic saturates; unsaturates; aromatics; oxygenates) and reports weight/volume percent by carbon number.

Results and Discussion

• Peak identification: Kovats indices matched database entries for reliable assignment of C5–C14 species.
• Chromatograms: Reformate and gasoline samples exhibited clear separation, with critical pairs fully resolved.
• Group composition (reformate): 60.03% n-paraffins, 11.31% naphthenes, 9.71% aromatics, 18.96% unknowns by mass.
• Repeatability: Sixteen injections of a gasoline sample yielded RSDs below 3% for key analytes, meeting the ≤0.1 specification (standard deviation/average) of ASTM D6729.
• Resolution: Critical pairs (benzene/methylcyclopentane; m-xylene/p-xylene; n-tridecane/1-methylnaphthalene) exceeded the minimum resolution factors, confirming robust chromatographic performance.

Benefits and Practical Applications

• Enables detailed species-level profiling for blending optimization and regulatory reporting.
• Quantifies oxygenates and hydrocarbon classes to support performance and emissions assessments.
• High precision and repeatability ensure confidence in routine quality control workflows.

Future Trends and Possibilities for Use

Emerging developments may include fast GC methods for higher sample throughput, GC-MS integration for enhanced structural confirmation, and advanced data analytics such as machine learning for automated peak identification and reporting.

Conclusion

The described GC-FID method with ASTMD6729 protocol and Eclipse DHA software delivers accurate, precise and comprehensive hydrocarbon analysis of spark ignition fuels. Exceptional peak resolution and repeatability affirm its suitability for industrial and research laboratories.

Instrumental Setup

• Gas chromatograph with split/splitless injector
• Flame ionization detector
• 100 m × 0.25 mm × 0.50 µm capillary column
• Helium carrier gas
• Eclipse DHA data processing software