Ethylene combustion products obtained over a range of conditions regularly show peaks with retention times and mass spectra expected for C20H10 polycyclic aromatic hydrocarbons (PAH) when analyzed by gas chromatography/mass spectrometry (GC/MS). Analysis by high-performance liquid chromatography with spectrometric diode-array detection (HPLC/DAD) yields three distinct peaks over the C-20 PAH elution interval whose UV-vis spectra differ from those of known PAH, These results, highly characteristic of ethylene flames, strongly suggested the presence of at least three C20H10 PAH. Recent progress in PAH synthesis permitted the comparison of chromatographic and spectrometric data for flame samples with those of authentic dicyclopentapyrenes : dicyclopenta[cd,fg]pyrene, dicyclopenta[cd,mn]pyrene, and dicyclopenta[cd,jk]pyrene. The comparative analysis established that the three C20H10 PAH long observed in ethylene flames were indeed the three dicyclopentapyrene isomers, Additional analysis of samples from a range of flames showed that the dicyclopentapyrenes are present in fullerene-deficient flames, but are absent in fullerene-producing flames. The dicyclopentapyrenes are notable for being isomers of corannulene, a possible fullerene precursor also found in a range of flames. The significance of these findings in relation to the flame production of fullerenes is discussed.