Hanspeter Zinn

Growth and accumulation dynamics of poly(3-hydroxyalkanoate) (PHA) in Pseudomonas putida GPo1 cultivated in continuous culture under transient feed conditions.

It has been shown that Pseudomonas putida GPo1 is able to grow in continuous culture simultaneously limited by ammonium (N source) and octanoate (C source), and concomitantly accumulate poly([R]-3-hydroxyalkanoate) (PHA). Under such growth conditions the material properties of PHA can be fine-tuned if a second PHA precursor substrate is supplied. To determine the range of dual carbon and nitrogen (C, N)-limited growth conditions, tedious chemostat experiments need to be carried out for each carbon source separately. To determine the growth regime, the C/N ratio of the feed (f) to a chemostat was changed in a stepwise manner at a constant dilution rate of 0.3/h. Dual-(C, N)-limited growth was observed between C(f) /N(f) ≤ 6.4 g/g and C(f) /N(f) >9.5 g/g. In the following, we analyzed alternative approaches, using continuous medium gradients at the same dilution rate, that do not require time consuming establishments of steady states. Different dynamic approaches were selected in which the C(f) /N(f) ratio was changed continuously through a convex increase of C(f) , a convex increase of N(f) , or a linear decrease of C(f) (gradients 1, 2, and 3, respectively). In these experiments, the dual-(C, N)-limited growth regime was between 7.2 and 11.0 g/g for gradient 1, 4.3 and 6.9 g/g for gradient 2, and 5.1 and 8.9 g/g for gradient 3. A mathematical equation was developed that compensated a time delay of the gradient that was caused by the wash-in/wash-out effects of the medium feed.

Developments and Experiences With Pulsation Measurements for Heavy-Duty Gas Turbines

The dynamical combustion processes (pulsations) of heavy-duty gas turbines must be supervised by suitable instrumentation for optimal operation of the engine regarding emissions and component life. But the hostile environment of the combustor makes it difficult to perform the measurements. There are two possible approaches to measure the combustor pulsations. Either a high temperature sensor is placed as close as possible to the combustion chamber to measure the acoustics directly (Cavity Type Probe), or the acoustic signal is led to the outside of the engine by means of a reflection free waveguide, where a dynamic pressure sensor picks up the passing signal (Long Line Probe). Both approaches were developed and investigated in detail. This paper describes the past and current efforts in refining the probe designs for use in the harsh operational environment while maintaining sensor accuracy, measurement range and lifetime as a rugged probe. Theoretical and laboratory investigations were undertaken to increase the useable frequency range of the Cavity Type Probe up to 8kHz under engine operation conditions. This was made possible with a smaller high temperature transducer, which is the result of a cooperative development project with a sensor manufacturer. Experiences with both probe concepts on Alstom’s GT26 Test Power Plant in Birr and on field engines provided clear confirmation that the Cavity Type Probe design with an advanced sensor now fulfils all initially defined requirements of acoustic combustion measurements on heavy-duty gas turbines. On the contrary, the waveguide design principle has fundamental limitations in the direct measurement of the combustion acoustics at gas turbine operating conditions.© 2007 ASME