Flying farther, faster, for less
New combustion technologies, including lean-burn combustion, are being investigated widely to meet the more and more stringent standards on aero engine emissions. All international standards demand reduction of nitrogen oxides (NOx) emissions, without increasing emissions of carbon monoxide, unburned hydrocarbons and smoke. In the design of low-emission combustors, lean-burn technology holds the potential for reducing NOx emissions, particularly at a high operation pressure ratio. EU-funded researchers had previously designed such a combustor adopting lean-burn technology. However, it had not been tested in rigs simulating the core engine pressure. With EU funding of the project LEVER (Lean burn control system verification rig), researchers developed the experimental facility missing for testing lean-burn combustion. To date, rigs simulate core engine pressure by means of a restrictor in the fuel delivery pipe. This concept is inadequate for simulating the high air to fuel ratios needed for stable lean-burn combustion. In the new testing facility, multiple burner simulators spray fuel, instead of passing all the fuel through a single orifice plate. Each burner simulator replicates the behaviour of the engine's fuel injectors. The latter are fitted with fuel scheduling valves and the fuel delivery pipe volumes are tuned so as to emulate the draining characteristics seen by each injector. The burner simulators are fitted with high-bandwidth transducers capable of measuring fuel dips and spikes. In the LEVER rig, the fuel is collected and recycled. The fuel level is kept stable to stop nitrogen from escaping, as the fuel flows and exits the system. For this purpose, a barrier has been added between the fuel and nitrogen space. LEVER efforts provide engineers with the ability to demonstrate that lean-burn technology is designed to reduce NOx and other emissions (smoke) while maintaining combustor efficiency. It has already been used to assess the performance of the first lean-burn control systems, which are far more complex than existing rich-burn systems, before being put to flight testing.
Keywords
Aero engines, testing facility, lean-burn combustion, nitrogen oxides, LEVER
