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This paper describes the development of an ultra low NOx (i.e. sub 10 ppmvd) combustion system from the successful completion of a high pressure rig programme, to the installation of the system on a gas turbine in commercial operation. It includes a detailed description of early screening tests for DLN concepts and an explanation of how these were developed on both rig and engine test bed. Specific discussions include the concepts and technology for: 1) NOx reduction 2) Optimisation of premix turndown for carbon monoxide control at part load conditions 3) Control of combustion driven pressure oscillation (combustor dynamics) and the failures resulting from the lack of control. In addition to the DLN aerothermal development, an outline description of the combustor mechanical design and the control and systems modification from the conventional combustion system is given.

A flat bladed axial swirler of 0.7 swirl number has been investigated in a 76 mm diameter combustor with all the combustion air passing through the swirler. Both liquid and gaseous fuels were used with eight injection points on the combustor wall just downstream of the swirler. This wall injection was aimed at the exploitation of centrifugal mixing forces acting on the burnt gas pockets at the wall to send them towards the centre and to displace higher density unburnt gas pockets to the wall and so promote mixing. For both kerosene and propane fuels there was a significant improvement in the combustion efficiency and NOX emissions compared with central fuel injection. For kerosene the NOX emissions were lower than for propane and very close to those for premixed fuel and air. However, for gas oil there was little improvement in performance with wall injection compared with central. This was attributed to the slower vaporisation rate with gas oil coupled with the centrifugal action on the liquid droplets with central injection.

Experimental combustion and NOx emissions results are summarized for a range of jet shear layer combustion systems that have rapid fuel and air mixing, short intense flames, a high turn-down ratio and low NOx characteristics. Two burner sizes of 76 and 140 mm are investigated for propane and natural gas. Three jet shear layer burners are compared with axial and radial swirlers. The combustion techniques were developed for application to low NOx combustion systems for industrial gas turbines, where NOx emissions as low as 10 ppm at 15 per cent oxygen have been demonstrated. It is shown that at one bar pressure, gas turbine combustors and high-intensity burners operate at similar air flow, blockage and pressure loss conditions.