Discovery Magazine

Oxygen - Enriched Combustion of JP-8

Oxygen-enriched combustion (OEC) has shown the ability to improve the fuel efficiency and power density of burner-based power systems and diesel engines as well as micro-power generation systems. By minimizing problems with flame quenching, OEC is also expected to greatly improve the performance of MEMS-based micro-combustors needed for micro-power generation. A solid fundamental understanding of oxygen-enriched combustion chemistry and associated flame properties (e.g., flame structure, laminar flame speed, flammability limits, quenching distance, thermo-acoustic noise) is needed to push the development of these power systems forward. This fundamental understanding is now sorely lacking. For example, existing combustion reaction mechanisms, which are generally tailored to describe combustion in ambient air, do not predict the correct trends for the flame speed of oxygen-enriched mixtures of methane, the simplest hydrocarbon. An accurate physical description of the combustion processes is needed to design micro-power generation systems that are efficient and reliable.

Using a flat-flame burner, this study will experimentally investigate the flame structure, flame speed, flammability limits, quenching distance and thermo-acoustic noise of premixed, oxygen-enriched flames of JP-8 and a JP-8 surrogate. A well-established surrogate (n-decane) was selected for study in addition to the actual fuel because JP-8 is a complex mixture that cannot currently be modeled computationally. The measured data will be used to construct and validate a skeletal reaction mechanism for the combustion of the JP-8 surrogate under elevated oxygen concentrations. That combustion mechanism will then be used to design an oxygen-enriched, micro-scale combustor for a micro-power generation system.

The overall goal of this program is to develop an experimentally validated reaction mechanism for oxygen-enriched JP-8 combustion that accurately predicts flame structure and properties and is suitable for the design of oxygen-enriched MEMS-based micro-power generation. Specific objectives that support this overall goal are to determine the flame structure (temperature and gaseous species) as a function of the height above a flat-flame burner in order to produce a validation data set for oxygen-enriched combustion of JP-8 and a JP-8 surrogate; determine the laminar flame speed, flammability limits, quenching distance, and thermo-acoustic noise for oxygen-enriched flames burning JP-8 and a JP-8 surrogate; demonstrate a skeletal reaction mechanism that accurately predicts flame structure, laminar flame speed, flammability limits, and quenching distance for oxygen-enriched combustion of JP-8 and a JP-8 surrogate; and demonstrate a preliminary design for a MEMS-based, oxygen-enriched micro-combustor for a 20-W micro-power generation system.