Energy transfer Processes at gas/wall Interfaces under extreme Conditions

Project Information

EPIC

Grant agreement ID: 759546

DOI

10.3030/759546

Project closed

EC signature date 20 October 2017

Start date 1 December 2017

End date 31 May 2023

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 351,00

EU contribution

€ 1 499 351,00

Coordinated by

THE UNIVERSITY OF EDINBURGH
United Kingdom

Periodic Reporting for period 4 - EPIC (Energy transfer Processes at gas/wall Interfaces under extreme Conditions)

Reporting period: 2022-06-01 to 2023-05-31

Summary of the context and overall objectives of the project

EPIC is designed to develop and utilize a suite of advanced laser diagnostics to study transient heat transfer associated with flame-wall interactions (FWI) at gas/wall interfaces. In particular, EPIC is designed to investigate the fundamental thermo-chemical and thermo-physio processes that describe the heat and momentum transfer within boundary layers. This research is important as these processes must be well understood for further development of new high efficiency (low emitting CO2) engines for ground transportation, marine, and aerospace sectors. One of the leading reasons why we lack knowledge in this subject is the lack of experimental tools to measure spatially-resolved gas-phase temperature fields for near-wall reacting flows. EPIC utilizes hybrid fs/ps rotational coherent Anti-Stokes Raman Spectroscopy (referred to as HRCARS) to provide 1D spatially resolved gas-phase temperatures normal to walled surfaces. This is a relatively new diagnostic, which was previously not exploited for near-wall heat transfer. In EPIC we combine HRCARS with a suite of other laser diagnostics such as phosphor thermometry (PT) to measure wall temperature, laser induced fluorescence (LIF) to measure flame and other species distributions normal to walls, and particle image velocimetry (PIV) to measure the near-wall velocity field. With these tools, EPIC is uniquely designed to provide fundamental ground-breaking experimental research outcomes as a first step to solve these critical problems.
EPIC objectives include:
O1) Development of a novel experimental facility to investigate the highly transient and highly variable processes at the gas/wall interface using novel measurements in O2-5.
O2) Experimentally measure, for the first time, the temporally and spatially transient thermal-boundary layer under transient pressure rises to identify leading mechanisms of heat loss as fluid pressure increases.
O3) Experimentally quantify, for the first time, the local flame and fresh-gas heat loss that defines flame quenching at high pressures for single- and two-wall passages.
O4) Simultaneously measure surface temperature and flame distribution to establish correlations that describe the relationship between flame quenching and surface heat flux for single- and two-wall passages.
O5) Advanced diagnostics for fundamental studies of hydrodynamic- and thermal boundary layer development in reacting flows.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We have accomplished the sought objectives and have progressed further than anticipated.
The experimental facility was manufactured in 2018/9, satisfying O1, and providing the test-rig used in EPIC.
We developed a 1D HRCARS approach to measure gas-phase temperature at high pressures and temperatures. We then used 1D HRCARS to resolve 1D gas temperatures within the thermal boundary layer during gaseous compression and expansion events within facility. HRCARS was combined with PT and LIF to study the transient gaseous heat loss for three important processes occurring at gas/wall interfaces: (a) unburnt gas polytropic compression, (b) FWI, and (c) post-flame gas expansion. Findings are the first of their kind that resolve single-shot, transient heat loss measurements within a developing boundary layer, which satisfy objectives O2 and O3. We have also advanced N2 linewidth models used in Raman spectroscopy.
For O4, we have succeeded the original objective. We measured wall temperature and flame front distributions in a two-walled crevice to investigate transient heat transfer and flame quenching. We collaborated with partners from Princeton University (US) and ONERA (France) to synthesize a new phosphor (ScVO4:Bi3+), providing precise wall temperature measurements at high repetition rates. Our work led to the development of a two-wall quenching model. We further extended our work to 2D high-speed PT. In this work, we discovered new attributes of heat fluxes associated with intrinsic flame features of a flame, including those associated with thermodiffusive instabilities imposed from lean H2-air flames. We have further expanded PT into the field of fire science to study the heat transfer mechanisms responsible for the rate of flame spread along solid surfaces.
We achieved O5 objectives during EPIC, however, the full progression of O5 finished shortly after the duration EPIC in Oct. 2023. This delay was due to the ambitious nature of EPIC and the limitations of COVID protocols. In O5, we developed a novel wavelet-based Optical Flow (wOF) algorithm for ultra-high spatial resolution velocity fields in wall bounded turbulent flows. This effort has enabled the impressive ability to resolve momentum and mass transport within boundary layers. This work was extended further to resolve the evolution of the turbulent boundary layer during FWI, which combined wOF, CARS and LIF diagnostics. Findings describe deviation from canonical boundary layer flows, and provides a priori information for correct modelling of these unique boundary layer flows. Additional measurements of HRCARS, PT, and PIV were conducted during EPIC, and publications resulted shortly after the conclusion of EPIC. In that work, for the first time we resolved the thermal flame structure (flame temperature, thermal flame gradients) in response to wall heat loss.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

EPIC has pushed the state of the art to study transient heat transfer and FWI. Development of HRCARS within EPIC has enabled new insight of the effects of wall heat loss within thermally driven flows. In HRCARS, we have also developed a novel approach to measure precise gas-phase pressure alongside temperature and O2 concentrations. This approach resolves precise pressure gradients associated relevant to a variety of aerodynamic applications.

The progress within PT has pushed the state-of-the-art to study transient heat transfer. PT is often used as a 0D measurement technique. While applications of 2D PT exist, high-speed 2D PT was previously unavailable. EPIC has allowed us to expand PT into a unique high-speed 2D methodology. This work has yielded new insights into heat flux signatures associated with FWI and thermodiffusive instabilities for carbon-free e-fuels. Expansion of PT into the field of fire science has provided exciting opportunities to understand the underlying modes of heat transfer that govern the rate of flame spread, which was previously inaccessible.
Another improvement in PT has yielded from the use of multi-photon excitation of thermographic phosphors, which allow the ability to suppress unwanted fluorescence signals. Multi-photon excitation for PT was unexplored before EPIC, and provides future research opportunities in a variety of applications in manufacturing, medicine, and fire science.

For velocity, the development of wOF has gone well beyond the state-of-the-art of PIV. Not only does our wOF provide a spatial resolution four times greater than PIV, it also provides has higher accuracy up to 15%. We have expanded our use of wOF to investigate particle-turbulence interactions at the particle scale with our collaborators at TU Darmstadt (Germany). This work is an extension to the gas/wall research from EPIC, and was initiated in Feb. 2023. We have since published our findings after the conclusion of EPIC, and have two more publications on the way.

Summary of simultaneous measurements for thermal boundary layers and flame-wall interactions