GERMAN SCIENTISTS are preparing to rig-test an auxiliary power unit (APU) fuelled by gaseous hydrogen as part of a study aimed at reducing the nitrous oxide component of aircraft-exhaust emissions.
The tests, scheduled to begin later this year, will be carried out on an AlliedSignal GTCP 36/300 APU modified with new combustion-chamber technology, known as Micro-mix, developed by the aeronautics department of Aachen's university of applied sciences.
According to the institute's Professor Guenter Dahl, the system could open the way towards creating an alternative to crude- oil-based aviation fuels.
A typical turbofan engine running on kerosene produces quantities of unburned hydrocarbons, soot, carbon monoxide and nitrogen oxide (NOx). All emissions, apart from NOx, have been reduced to comparatively low levels over the past few years. Now the spotlight is on NOx, which is known to contribute to the formation of ozone and smog.
Dahl's team will monitor APU behaviour and emission gases for NOx content, comparing parts per million combustion product values with those produced by a standard un-modified GTCP 36/300 unit fuelled by kerosene.
The next step in the programme will be to run the APU with a standard design combustor fuelled by injected gaseous hydrogen, instead of liquid aviation kerosene. This stage will serve as a control test for comparison against a third series of trial runs, in which the engine will be equipped with the Micro-mix diffusing combustor fuelled by hydrogen.
Dahl claims that by distributing the diffusion flames and making them microscopically small, the formation of NOx can be reduced significantly. This is achieved, he says, by increasing the number of injection ports in the burner, which results in a larger number of smaller diffusion flames and a more homogeneous fuel consumption - the basis of the Micro-mix concept.
The test programme, which will be completed by the end of this year, is funded by the German Government and International Aerospace Companies.
Source: Flight International
