NIA | Graduate Student Seminar Series

Graduate Student Seminar by Janet Convery

Date: July 8, 2005
Time: 10:30am
Location: NIA, Rm 137

An Experimental Study of n-Heptane and JP-7 Extinction Limits in an Opposed Jet Burner
Janet Convery, Virginia Tech

Propulsion engine combustor design and analysis requires experimentally-verified data on the chemical kinetics of the fuel. Among the important data is combustion extinction limit data for the fuel applied to an application. The extinction limit relates to the ability to maintain a flame in a combustor during operation. Extinction limit data can be obtained for a given fuel by means of a laminar flame study using an opposed jet burner (OJB). Laminar extinction limit data can be applied to the turbulent application of a combustor via laminar flamelet modeling. The OJB consists of two axi-symmetric tubes(one for fuel and one for oxidizer), which produce a flat, disk-like, counter-flow diffusion flame.

The paper presents results of experiments to measure extinction limits for n-heptane and the military specification fuel JP-7, obtained from the OJB. JP-7 is an Air Force-developed fuel that continues to be important in the area of hypersonics. Because of its distinct properties it is currently the hydrocarbon fuel of choice for use in scramjet engines. This study provides much desired data for JP-7, for which very little information previously existed. The interest in n-heptane is twofold. First, there has been a significant amount of previous extinction limit study and resulting data with this fuel. Second, n-heptane (C7H16) is a pure substance, and therefore does not vary in composition as does JP-7, which is a mixture of several different hydrocarbons. These two facts allow for a baseline to be established by comparing the new OJB results to those previously taken. Additionally, the data set for n-heptane, which previously existed for mixtures up to 26 mole percent in nitrogen, is completed up to 100%, pure n-heptane.

The extinction limit data for the two fuels are compared, and the application of the results to engine combustor modeling is discussed. Complete experimental results are included with conclusions.