Combustion Characteristics of Live Fuels

142 Pages·2005·3.27 MB·English

EFFECTS OF MOISTURE ON COMBUSTION CHARACTERISTICS
OF LIVE CALIFORNIA CHAPARRAL AND UTAH FOLIAGE

by

Steven G. Smith

A thesis submitted to the faculty of

Brigham Young University

in partial fulfillment of the requirements for the degree of

Master of Science

Department of Chemical Engineering

Brigham Young University

August 2005
ABSTRACT

EFFECTS OF MOISTURE ON COMBUSTION CHARACTERISTICS
OF LIVE CALIFORNIA CHAPARRAL AND UTAH FOLIAGE

Steven G. Smith

Department of Chemical Engineering

Master of Science

Current fire-spread models are based largely on empirical correlations based on
fires burning through dead pine needles. There is a need to increase the accuracy of
modeling wildfires in live vegetation. This project investigates the quantitative and
qualitative ignition characteristics of eight live fuels, four from southern California
(manzanita, scrub oak, ceanothus, and chamise) and four from Utah (canyon maple,
gambel oak, big sagebrush, and Utah juniper). Individual leaves were observed as they
were exposed to hot gases from a flat flame burner.
The broadleaf species from both California and Utah had noticeable surface
changes during the ignition process. All fresh samples showed a color change on the leaf
surface from a light dusty color to a dark wet color. This is likely due to the melting of
the waxy protective layer. Samples of scrub oak, manzanita, ceanothus, canyon maple,
and gambel oak at moderate moisture contents (50 to 75%) exhibited bubbling under the
leaf surface. Liquid droplets were observed on the surface of Manzanita samples at
moisture contents near 75%, while bursting was observed on the surface at moisture
contents near 100%. This bursting is due to evaporation of the moisture inside the leaf
causing internal pressures to exceed the surface strength of the leaf.
Ignition was defined as the time when the first visible gaseous flame was
observed near the leaf surface. Measurements of the time to ignition and the temperature
at ignition were performed for all broadleaf species. A large degree of scatter was
observed in the quantitative ignition data, due largely to variations in leaf thickness and
moisture content. Time to ignition was found to correlate with sample thickness and the
mass of moisture in the sample. Ignition temperature was constant for varying moisture
mass but appeared to increase with thickness. The burning time, defined as the duration
of a visible flame near the leaf, was found to correlate roughly with leaf mass. Several
types of correlations were made to describe ignition temperature and ignition time as a
function of leaf thickness and mass of moisture.