In accordance with the present invention a disposable fuel cartridge for use in fireplaces that self regulates the shape, height, width, depth and burn time of the flames produced when the fuel inside the cartridge, such as alcohol gel, is exposed to ambient air and ignited, where the cartridge makes efficient use of fuel so as to produce a desirable, generally rectangular flame pattern without the need for any additional components, such as rectangular “fuel cells” or rectangular damper lids placed over the “fuel cells”.