The paper will describe the results of an experimental investigation on the effect of diluents premixed with either the jet or co-flowing air stream on the blowout limits and flow field structure of jet diffusion flames. Experiments were conducted for a range of co-flowing air stream velocities with methane as the primary jet fuel, and nitrogen and carbon dioxide as diluents in the jet fuel; carbon dioxide was also used in the co-flowing air stream.
The addition of a diluent to the surrounding air stream had a much stronger effect on the blowout limits than the addition of the diluent to the jet fuel. The effect of partially premixing air with the jet fuel on the blowout limits was also investigated. The addition of air (to up to 30%) to the methane jet significantly reduced the blowout limits of lifted flames, but it had little effect on the blowout limits of attached flames, which was rather unexpected.