Measurements of Hydrogen-Enriched Combustion of JP-8 in Open Flame

Abstract

Hydrogen enrichment is presented as a control parameter to improve JP-8 combustion. Research in fuel reforming gives an opportunity for hydrogen production at the point of use. Hydrogen-enriched combustion of JP-8 seeks to take advantage of the energy density of JP-8 and the combustibility of hydrogen. At low power output (<2 kWe), technologies such as Stirling engines, thermoelectric, and thermophotovoltaic generators have the potential to compete with diesel engines, but require reliable JP-8 combustion. Experiments were conducted with atomized JP-8 in a 5 kWth open flame, based on a 500 W power source. JP-8 is sprayed through an air-atomizing nozzle. Hydrogen was added to either the atomizing air or to a concentric tube supplying the main combustion air. In these experiments, hydrogen represented up to 26% of the fuel energy contribution (EC). During hydrogen enrichment, JP-8 flow rate was reduced to maintain constant fuel energy input. Temperature is measured vertically and laterally through the flame. Temperature profiles show that combustion shifts toward the nozzle as hydrogen is added. Hydrogen in the secondary air maintains diffusion flame behavior, but earlier in the flame. Hydrogen in the nozzle air creates a premixed pilot flame structure in the center of the flame. This premixed hydrogen and air flame provides initial energy to speed droplet heating and vaporization, producing higher peak temperatures than the other cases studied. Gaseous emissions are measured above the visible flame. Hydrogen enrichment by both methods reduced unburned hydrocarbon emissions by up to 70%. The advantages provided by hydrogen enrichment represent opportunities for reduced size, improved operational reliability and control, and reduced pollutant emissions.