The contribution of intermediate-temperature heat release to octane sensitivity

Jonathan Peterson, Abdulrahman Mohammed, Inna Gorbatenko, Eshan Singh, Mani Sarathy

Research output: Contribution to journalArticlepeer-review


Carbon footprint reduction can be achieved by increasing the efficiency of combustion engines. For spark-ignition (SI) internal combustion engines (ICE), fuel octane sensitivity (OS)—defined as the difference between a fuel's research octane number (RON) and motor octane number (MON)—can help identify ideal fuels for avoiding unwanted knocking conditions. Moreover, it will help to extend the range of operating conditions that can be used in next-generation high-efficiency engines. Presently, there is a controversy over whether high or low OS fuels are beneficial for increased efficiency of next-generation engines depending on application and technology, e.g. high OS fuels are advantageous for down-sized and turbocharged spark-ignition (SI) engines, whereas low OS fuels are superior in novel systems such as pre-chamber engines. This work aims to improve the understanding of the impact of OS on the combustion performance of engines by analyzing the contribution of intermediate-temperature heat release (ITHR) to OS. The heat release of several mixtures of toluene, iso-octane, and n-heptane with similar RON but varying OS were studied under homogeneous charge compression ignition (HCCI) conditions in a cooperative fuel research (CFR) engine. This method gives insight into the heat release of the auto-igniting fuel without the obfuscation of the spark-ignited flame. At RON conditions, ITHR was a marker of OS. Furthermore, a new parameter called ITHR sensitivity was defined as the difference between the ITHR measured at RON conditions and the ITHR measured at MON conditions. ITHR sensitivity decreased with increasing octane sensitivity. This shows that non-sensitive fuels experience a greater change in the amount of ITHR as compared to sensitive fuels when changing from MON conditions to RON conditions. Thus, for engines requiring high OS fuels, it is recommended that components with high ITHR sensitivity are used and vice-versa for engines requiring low OS fuels.
Original languageEnglish (US)
Pages (from-to)129077
StatePublished - Jul 3 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-07-19
Acknowledgements: The authors of this paper would like to express their gratitude to the Clean Combustion Research Center at King Abdullah University of Science and Technology for the funding and equipment that made this research possible.

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Organic Chemistry
  • Chemical Engineering(all)
  • Fuel Technology


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