In this 13-part series of articles, The Combustion Institute recognizes the 2023 Distinguished Papers selected from among the scientific papers presented during the 39th International Symposium on Combustion. Congratulations to Leonardo Castellanos, Francesco Mazza, and Alexis Bohlin for winning the DPA in the Diagnostics colloquium.

Dr. Bohlin and the members of his team authored their distinguished paper, “Water vapor in hydrogen flames measured by time-resolved collisional dephasing of the pure rotational N2 CARS signal,” because they believe that further development and refinement of sustainable hydrogen technologies will play an important role in achieving a smooth energy transition and more climate-friendly propulsion and power systems. In this research they have explored a new diagnostics strategy to make scalar determination in highly reactive mixtures – with hydrogen – complete and more accurate. New insight into the critical transport mechanisms in hydrogen flames is developed through rigorous testing and quantification. Thus, the team believes that additional experiments are necessary.

Castellanos, Mazza, and Bohlin found interest in this study because the common forms of light-matter interaction (i.e. fluorescence and absorption) are not very efficient on hydrogen. They developed ultrafast laser diagnostics (based on light scattering of the molecules) to perform spatially resolved probing of temperature and key-species in hydrogen reacting flows. The team used a new diagnostic strategy, which uses the sensitivity from species-specific collisions manifested in the time-domain as a marker of the presence of water vapor in the flow. This was necessary, as they also wanted to measure the concentration of water vapor which is a progress variable for the reactions in the flow. This is a nearly impossible task with conventional pure-rotational coherent Raman spectroscopy detection, which suffers from a relatively low scattering cross-section of H2O. With their rather unconventional method, the mole fraction of H2O in the high-temperature region of the flame can be quantified with a relative experimental uncertainty down to a few percent. The researchers were almost surprised to see that it turned out to be this successful.

There are several benefits to the team’s findings. The immediate benefit of this new diagnostics strategy is that it can be used to measure the complete scalar fields in hydrogen reacting flows. In a follow up measurement campaign, the technique made it possible to retrieve a direct experimental observation of both preferential and differential diffusion effects, which are unique transport properties of highly reactive mixtures with hydrogen. In the long-term, the team is convinced that many research groups will continue to explore these capacities for new applications and develop ultrafast laser diagnostics that will become even more powerful as a research tool. This is quite recent technology, but this team (and colleagues) have shown that it allows for powerful recordings of multivariate data. Some related discussions have raised uncertainty about the transmission of short (and obviously more delicate) laser pulses obtained through optical windows, possibly resulting in hesitation among the managers and researchers at large-scale research facilities to invest in these new capabilities, despite being very interested in amplified short-pulsed laser systems. Castellanos, Mazza, and Bohlin hope that the current findings, together with their other recently published results, help to inspire and convince others about the feasibility of robust use of these ultrafast regenerative amplified lasers.

In this team’s opinion, the beneficiaries of powerful measurement capacities are also builders of models in flow physics and chemical kinetics, as well those that are interested in validation data to improve the fidelity of numerical simulations.

This research of water vapor in hydrogen flames began in mid-2021 and was completed during the fourth quarter of 2022. The experiments were performed in the laboratory at Delft University of Technology in the Netherlands, in collaboration with Luleå University of Technology in Sweden.

Over 1,500 papers were submitted to the 39th International Symposium on Combustion. All papers were categorized into one of 13 colloquia, and then distributed to Colloquium Coordinators and Co-Chairs. Each paper received at least three reviews from qualified individuals through the peer-review process. Less than 50 percent of the papers submitted were accepted for presentation.

Following the symposium, one paper presented in each colloquium is awarded the distinction of Distinguished Paper. Visit here to view the presentation. The 13 Distinguished Papers undergo committee review for consideration for the Silver Combustion Medal. A paper selected for this honor exemplifies quality, achievement, and significance to advance a field of combustion science, and will be awarded during the 40th International Symposium in Milan, Italy.