CLEAN : Combustion in Low-Emission And CO2–Neutral technologies -Alessandro Parente

Ensuring affordable and sustainable energy for future generations

While the world reliance on combustion is set to continue, to satisfy our energy needs, we need to advance combustion science to develop new technologies that can handle CO2-neutral fuels efficiently, and without producing pollutants. Some examples of new combustion technologies have been proposed recently, and implemented in some practical devices. However, these low-emissions combustion regimes are very complex and very difficult to predict, making impossible to transpose solutions from one industrial configuration to another. What we aim to accomplish in CLEAN is to combine the most recent advances in computer science and high performance computing, to decode the complexity of turbulent reacting flows and develop new models that can be used, with confidence, to develop fuel-flexible, efficient and clean combustion technologies.


Born in 1980. PhD in Chemical and Material Engineering (Università di Pisa), Master in Chemical Engineering (Università di Pisa). Post-docs at University of Utah and the Von Karman Institute. Associate Professor at the Aero-Thermo-Mechanics Department (ULB), Vice-president of the Belgian Section of the Combustion Institute, Chair of the ULB-VUB Research Group « Combustion and Robust Optimization ». Prof. Parente has been awared with the Fonds Renard for sustaining research (2011) and with prestigious national and international grants and programs, notably: European Research Council, Marie Curie Innovative Training Network, EU Horizon 2020.

1. Climate change, renewable energies and the storage challenge

The energy supply is one of the great societal challenges we are facing. When talking about energy conversion, we do not often recognize the role combustion plays today. If we think for a moment about our everyday life, the products we use, how we get to work or home, to meetings, to visit family and friends and go on holiday, we soon realize that almost any activity has a power signature. Most of this energy, about two thirds, comes today from combustion.

Combustion is, however, the major source of air pollution and a major contributor to CO2 and climate change. A recent UN report indicated that the concentration of CO2 in the atmosphere has reached 405.5 parts per million (ppm). If we continue on this slope, in 50 years we will pass the 500 ppm level, entering in a very dangerous zone of climate change, with temperature increase likely above 3 °C and catastrophic effects for our planet. As of today, we have almost depleted our carbon urgent to limit the temperature increase to 1.5°C, as recommended by the COP21 in Paris, to limit climate change effects. Without further ado, it is time to act.

New developments in renewable energy are fundamental to assure the energy needs of future generation, within a sustainable growth model. Yet, one fundamental challenge affects a society solely relying on renewable sources, their intrinsic intermittency. We all know that wind and solar energies are characterized by daily and seasonal changes, and they have very strong spatial dependency; likewise, geothermal and hydroelectric sources are only available at specific sites and impose precise constraints in terms of exploiting infrastructures. Thus, the intermittent nature of renewable sources requires the development of storage solutions that can guarantee the availability of the required energy supply when renewable sources are not available.

Battery-based storage is very effective for short-term storage: batteries have among the best electrical roundtrip efficiencies and they should therefore be used in case of interday and intraday storage. Their energy reservoir is however limited to a few hours by the high capacity cost.

Long-term energy storage (seasonal storage) and energy intensive processes (long-range passenger transportation and manufacturing processes) require, on the other hand, high energy densities (tens of MJ per kg), which can realistically only be provided though the transformation of chemical energy into heat and work.

We are left, then, with an apparently unsolvable paradox, namely, the awareness of the significant negative impact of combustion-based technologies and, at the same time, the acknowledgement that the world reliance on combustion is set to continue, to satisfy our energy needs. The objective of CLEAN is centered on the solution of this paradox, to show that there is no inconsistency between the renewable technologies and novel combustion technologies for new energy carriers.

2. The future energy mix and the integration of renewable sources and combustion

The future energy mix will include a variety of fuels. Power-to-X (P2X) technologies allow to store the excess renewable energy in the form of chemical compounds, characterized by the very high energy densities and, thus, representing ideal candidates for long-term storage and energy-intensive industrial processes and transportation. These chemical compounds are generally referred to as Smart Energy Carriers (SEC), and they include hydrogen (the easiest molecule that can be formed by water electrolysis), ammonia (an effective way to store hydrogen in liquid form by combining it with atmospheric nitrogen), methane (combining hydrogen with recycled carbon dioxide coming from capture and storage processes), but also methanol  and other synthetic fuels for targeted applications (for air and ground transport, power generation, …). The availability of SECs can potential lead to a seamless integration of renewable sources and combustion technologies (Figure 1), in the framework of a circular economy model, where the dependency on fossil fuel sources can be progressively dismissed, as Figure 1 indicates.

Figure 1 – A large diversity of energy carriers is expected in future years, resulting from the transformation of renewables and unconventional sources into a wide variety of compounds. The effective use of these energy carriers will require the development of CLEAN combustion technologies.

The availability of different fuel sources is an attracting opportunity. It can contribute to decarbonize the power supply, accommodate the fluctuating demand of energy and to shape a more secure energy supply for the future, with less geopolitical inhomogeneities.

Interestingly, energy storage in smart new energy carriers makes the role of combustion crucial. For the power-to-X concept to be effective and viable, novel combustion technologies shall be developed, to accommodate the expected fuel flexibility without compromising the energy efficiency and pollutant emissions. This is far from being the case today. Indeed, industrial process are optimized considering the specificity of the used fuel. Making them “fuel flexible” will be a major engineering challenge for the next decades.

One possible solution is to imagine to tailor fuels to technologies, but this might have limitations depending on the local availability of fuel building blocks (e.g. carbon dioxide). A better approach is to develop technologies that can operate efficiently and without harmful emissions regardless of the fuel. We collectively indicate these technologies with the name of MILD combustion.

3. Novel combustion technologies

Figure 2 – The energy trilemma: our society needs an affordable, secure and environmentally friendly energy supply.

To meet the long-term objective of CO2 neutrality and mitigate the effects of global warming, the combustion field requires profound innovation. MILD combustion technologies potentially offer a solution to this, for the ability of guaranteeing fuel-flexibility, while ensuring very high energy  efficiency and virtually zero pollutant emissions (figure 2).

MILD combustion originates from a change in perspective in combustion science, cultivated in the last decades. Previously, it was not considered possible to obtain both high efficiency and low pollutant emissions and a trade-off had to be accepted between the two, because the problem was only studied from an energetic perspective. Nowadays, combustion is treated and controlled as a chemical reactor, which allows to simultaneously meet environmental and energetic needs, and to accommodate the flexibility of fuel resources expected in future years (Figure 3). Some examples of MILD combustion technologies have been designed in recent years, and implemented in some devices. However, these low-emissions combustion regimes are very complex and very difficult to predict, making impossible to transpose solutions from one industrial configuration to another.

Figure 3 – Using comventional technologies, a trade-off exist between the NOx concentration and the efficiency of a combustion process. Advances in computational science and energy systems allow today to overcome this limitation, with systems that can deliver simultaneously very high efficiency and virtually zero emissions. MILD combustion furnace


CLEAN aims at developing advanced simulation tools for realistic combustion systems that can be used with confidence to predict the behavior of existing systems, to optimize their operation and develop new solutions. Multi-scale and multi-physics approaches will be developed to accurately describe all the relevant physics involved, from the molecular scale where the fuel conversion takes place, up to the macro scale of the system. Both experimental and numerical data will be used, in an integrated approach, where experiments and simulations feed each other in a virtuous cycle (Figure 4), generating the high-fidelity data required for the development of digital twins. To this end, machine learning inspired techniques will be used to recognize patterns and classify the information in the form of reduced-order models.

Figure 4 – Digital twins are bridges between real systems and digital world. The development of digital twins requires a strategy based on experiments and simulations, at different scales and levels of complexity, tied together with a methodology able to extract the system key features and to encode them in predictive, reduced-order models.

The approach will be demonstrated with three proofs of concept, though the development of the first-of-their-kind digital twins for a variety of systems, including a combustion furnace, a micro gas turbine for heat and power generation, and a piston engine bench. The availability of all these three technologies with the BURN Joint Research Group[1] offers the unique opportunity of proving the effectiveness of digital twins for a variety of applications, and their potential use of in decision-making and regulation.

CLEAN represents the first attempt to use high-fidelity data to directly develop models, i.e. the digital twins, to control, optimize and develop new energy systems. Engineers have always developed lumped models and correlations for design and optimization, based on empiricism and theory. It is time to bring the numerical simulations into the picture, to drive the development of novel technologies.

[1] The ComBUstion and Robust OptimisatioN research group is a joint ULB-VUB group,

5. Requested Budget

6. Research environment

The research activity of the Principal Investigator (PI), Alessandro Parente, is articulated around the following axes:

  • Turbulent/chemistry interaction in turbulent combustion and reduced-order models.
  • Non-conventional fuels (solar fuels, renewable sources).
  • Novel combustion technologies, e.g. MILD combustion, with virtual zero pollutant emissions.
  • Numerical simulations of turbulent reacting flows.
  • Uncertainty quantification in computational fluid dynamics.

Professor Parente has authored to date more than 60 journal papers in peer reviewed journals (h-factor of 18, more than 1000 citations), around 100 contributions to International Conferences, 4 book contributions and 1 patent. He has been recently awarded a prestigious ERC Starting Grant for his project VADEMECOM: the project aims to drive the development of modern and efficient combustion technologies, by means of accurate and adaptive models. In January 2015, he has founded with Prof. Contino, the BURN group (, which involves 7 full time professors and more than 40 researchers (PhDs and PostDocs), with the aim of developing a world-class research group in combustion simulations and experimental investigations.

Prof. Parente has a wide range of national and international collaborations, thus indicating the breadth and depth of his research activities. This is reflected in his implication in several research projects and networking actions with the most renowned research institutes in the combustion field. In particular, it is worth mentioning his implication in the CLEAN-Gas Marie Skłodowska-Curie Action ( with Politecnico di Milano, Technische Universität Darmstadt and Centrale Supélec, and his participation to the COST Action SMARTCATs (, as official representative for the Walloon Region as well as Working Group leader. The funding received by the BURN group since 2010 consists of more than 15 research projects, with a global budget of more than 7 million euros. In terms of supervision experience, Prof. Parente is currently supervising/co-supervising 2 post-doctoral researchers, 20 PhD students, 14 of which in co-tutelle with European and International partners.

The present research proposal shows many synergies with the ongoing research projects and could fully benefit from the knowledge, resources and network available in the group. In particular, the group disposes of experimental means (furnace test bench, engine bench, gas turbine bench, advanced diagnostic & measurement tools, and computing facilities) with a total value exceeding 3M euros.