LAUSR

Abstract The effects of up to 30% H 2 O and CO 2 replacement of N 2 in air on the structure and shape of laminar coflow syngas (CO H 2 ) diffusion flames were experimentally and numerically studied. Temperatures along the flame centerline were measured using a type-B thermocouple. The OH*-chemiluminescence and flame luminance were captured respectively by an intensified CCD camera and a CCD camera to determine the flame height and radii. The syngas diffusion flames were numerically modeled using detailed thermal and transport properties and the chemical reaction mechanism of Davis et al. (2005). Four pairs of artificial species were introduced in additional numerical calculations to isolate the chemical, thermal, transport, and radiative effects of H 2 O and CO 2 . The experimental and numerical results show that H 2 O and CO 2 replacement of N 2 in the oxidizer reduce the peak flame temperature, but they influence the flame centerline temperature distributions differently. The thermal and radiative effects of both H 2 O and CO 2 addition decrease the flame temperatures. The chemical and transport effects of CO 2 and H 2 O affect flame temperatures differently. H 2 O addition promotes the OH concentration though H + O 2  = O + OH and O + H 2 O = 2OH, while CO 2 addition decreases the OH concentration by suppressing those reactions. The higher concentrations of OH under H 2 O addition signify higher combustion intensity and hence lead to decreased flame height and radius. In contrast, the addition of CO 2 suppresses flame temperature and the overall combustion process, resulting in increased flame height and radius.