Multi-beam optical hardware for CO2 measurement has been developed and installed including a Tuneable Diode Laser Absorption Spectroscopy source at TRL6, a commercially available Thulium Doped Fibre Amplifier and a fibre network. A prototype of data acquisition and processing HUB unit has been developed, which will integrate firmware development. To allow the correct installation of the HUB, some modifications to the cable system have been carried out: replacement of power supply connectors around the CO2 ring; installation of new Ethernet and coaxial cables from gantry to Measurement room; a cabinet for HUBs operation was installed in the gantry. Additionally, two maintenance campaigns were carried out in M20 and in M25, to align the emitters and receivers from the CO2 system.
On the other hand, regarding the GUI software, it has been designed, and tested, integrating control/diagnostic and data acquisition of system hardware as well as control of post-processing algorithms.
By the end of the project, all required nvPM measurement hardware had been developed, installed and demonstrated in the target environment. This included a laser excitation source, an LII detection camera, and supplementary timing, recording, and measurement hardware. This final implementation features several improvements over that used in the initial stages of the project. These address: (i) the degradation in the laser output beam due to the vibration level on the gantry; (ii) reduced detection camera integration time and increased light collection to maximize SNR in the presence of testbed lighting; (iii) permanent beam profiling to support improved data interpretation; and, (iv) relocation of the system such that its use requires no change in the detuner position, increasing the system’s acceptability to engine owners. The resulting system was installed and used in engine tests during M38-40. These tests confirmed the viability of collecting LII signals from VHBR exhaust, across the full range of engine speeds in both on and off axis positions. Unfortunately, these tests ended earlier than expected (for reasons unrelated to CIDAR), before dynamic imaging (under GUI control) could be tested. Testing of the system GUI’s ability to control the system’s hardware and dynamic scanning of the laser has, however, been carried out in UNIMAN labs. The nvPM measurement system has been shown to be capable of detecting LII in the time-integrated regime within the confines of the test cell at a spatial resolution significantly better than the 10 cm objective.
An nvPM system calibration rig has been developed (at Strathclyde) to relate LII intensity measurements to nvPM concentration, using a representative source of soot (Argonaut soot generator). The soot volume fraction in the calibration rig was determined by extinction and the uniformity of the plume was verified by performing planar LII imaging. These experiments were performed for a range of laser fluences, leading to the determination of a fluence-dependent calibration factor. This calibration is adjusted for beam diameter, laser pulse energy, axial signal integration distance and signal collection geometry. LII signal generation has been modelled for this bespoke configuration (by Strathclyde), which allowed us to characterise the influence of primary particle size on time-integrated LII signals. Beam propagation models have been developed (UNIMAN) to simulate laser beam breakup due to propagation through turbulence, and LII signals generated by the resulting non-uniform beams have been modelled (Strathclyde). The resulting data have been used to inform the interpretation of experimental results but larger datasets of beam profiles recorded at the test-bed are needed to develop this further.
A test plan has been prepared to validate the CO2 and nvPM/soot measurement systems on real engine testing and evaluate the performance stability of the systems over time and environment. In the case of the nvPM system, this plan was partially implemented during the M40 trials.
The results obtained with both systems (CO2 and nvPM) are very promising. These results show the expected variation with engine speed. Besides, results obtained with nvPM system correlate well with in-stack extractive measurements. In the framework of the project, seven papers have been published and eleven conferences have been attended.
