- Author
-
Varma, A.
- Title
- Spontaneous Ignition of High Voidage Fuels.
- Coporate
- University of New Brunswick, Fredericton, Canada
- Report
-
Thesis
August 1968
180 p.
- Keywords
-
fuels
|
autoignition
|
thermal decomposition
|
wood
|
mathematical models
|
equations
|
pyrolysis
|
combustion
|
air conditioning
|
thermocouples
|
radiometers
|
moisture
|
irradiation
|
humidity
- Abstract
- The object of this investigation was to determine the ignition characteristics of high voidage cellulosic fuels, which form a large part of the available fuel in a forest. The work consisted of both experimental and theoretical analysis. The fuel samples consisted of randomly oriented fuel particles packed in a cylindrical shape. The time elapsed until ignition of the fuel sample occurred, when exposed to irradiation from a gas-fired radiant panel, was measured for each of the pertinent variables over the following ranges: relative humidity of ambient air: 30-50%, fuel sample voidage : 0.0-0.867, intensity of incident radiation : 0.85-1.65 cal/ cm2-sec. A significant increase in the time of ignition was observed when the relative humidity of the ambient air increased or the intensity of irradiation decreased. Though the experimental data showed some scatter, for a fixed ambient relative humidity and a fixed intensity of incident radiation, with increase of voidage, the time of ignition increased up to a fuel sample voidage of about O.4 and then decreased continuously. Very fine thermoucouples (0.0048 inch diameter) placed at the front and rear surfaces of the fuel sample indicated that the rear surface temperature rise was negligible whereas the front surface temperature rise was approximately 325 deg C when ignition occurred. A mathematical analysis of the heat transfer within the sample was carried out for three cases using different assumptions regarding the importance of such heating effects as diathermancy of the fuel sample and internal convection. An analytical solution was obtained for each of these cases so that the temperature distribution in the sample oould be predicted as a function of time, the lntensity of incident radiation and the physical and thermal properties of the fuel sample. Using a fixed surface temperature ignition criterion of 350 dec C it was found that heat transfer model based on conduction, diathermany, internal convection and thermal inertia of the fuel sample satisfactorily correlated experimental ignition results of work.