Scirocco
Imft Cerfacs Erc

EXPERIMENTS AT IMFT:

 

 

 

 

 

The experimental work planned at IMFT is focusing on three types of flames:

 

WP1: Small laminar flames controlled by H2 injection.

Premixed laminar flames are found in stoves, domestic heaters, industrial process heating burners. They are interesting prototypes for SCIROCCO because making these burners compatible with PtG strategies (iebeing able to burn H2 in these systems) would be a great improvement in many regions of the world. The problem addressed in SCIROCCO can be formulated as follows:

Examples of burners targeted in WP1: a stove (left) and a domestic heater (right). The laboratory flames studied at IMFT will mimic the features of these devices.

‘Having a burner designed to burn methane or propane, similar to those above, can we modify it to inject hydrogen “somewhere” to make this system more efficient: less prone to instabilities, able to operate in ultralean conditions with extended LBO limit, with controlled noise and pollutant emissions (NOX, CO, soot) ? Can we also ensure ‘fuel flexibility’ which means being able to go from 0% of H2  to 100 % of H2with minimal changes in the burner geometry ?’.

The answer to the last question is critical for PtG strategies where H2 would be produced locally (in a farm for example) and burnt locally too, either in conjunction with another gas or pure if no fossil fuel is available.  

These studies also require to consider the effects of H2 injection on pollutants such as NOx which may be adversely affected by H2addition and must be kept under control. NOx levels will be measured in the IMFT experimental rigs and computed in the digital twins using complex chemistry descriptions available in AVBP, the code of CERFACS used in SCIROCCO. They will be incorporated in the cost functions used to make decisions on the configurations choice. Experiments will be installed at IMFT and all simulations (which will be Direct Numerical Simulations (DNS) for these small low Reynolds number flames) will be run by IMFT and CERFACS. A typical configuration (a flame stabilized behind a cylinder) for WP1 is displayed in Fig. 5 with 4 possible locations for H2 injection.

Streamlines and flame position (red line) for a methane / air laminar flame configuration of IMFT with 4 possible hypothetical locations for H2 injection. The flame is stabilized behind the blue cylinder (the ‘flame holder’). Positions 1 to 4 indicate places where H2 injectors could be located. For position 4, an example of ’intrinsically stable’ design using an adjustable impedance system for the H2 line is displayed.

The first location (marked 1) corresponds to the stagnation point upstream of the cylinder, the second one (marked 2) would propel H2 in the boundary layer of the cylinder and then into its wake where the flame is stabilized. The third position (marked 3) would change the flame behavior when it reaches the wall of the chamber: this maybe an interesting zone for injection because flame / wall interaction in these flames is a source of instabilities and pollution. The last location (marked 4) corresponds to a case where H2 would be injected upstream of the flame holder and would have a finite, tunable time to mix with methane before reaching the flame. All these zones are ‘sensitive’ regions where pure H2  injection will have a drastic effect on the flame. The figure also displays an example of simple passive control system to adjust the impedance of the hydrogen line which would be useful to control combustion instabilities. Of course, other locations of injection and other possibilities (such as using multiple simultaneous injection) will also be considered if needed. These various systems of H2 injection will be used to study two classes of problems: the control of combustion instabilities and the extension of the operability domain.

 

WP2: Turbulent swirled two-phase flames controlled by H2 injection. 

The second class of flames studied in SCIROCCO is more complex (Juste 2006, Poinsot 2017) and corresponds to technologies used in furnaces or in gas turbines for propulsion and power generation. In these systems, fuel is injected as a liquid and the flow is ‘swirled’: a strong rotation is added on the mean flow to create more compact, two-phase, turbulent flamesof much higher power than in WP1. 

As an example, the figure below shows a swirled injector (similar to the future SCIROCCO injector) and indicates where hydrogen could be introduced. In these complex-geometry injectors, it is not easy to modify the design in order to introduce H2. Fortunately, most of them already include multiple lines to inject fuel because this has been required to develop low NOX, lean burn systems in a long series of European and industrial programs since the 90s. We will focus on systems using low NOx, ‘multipoint’ injections where fuel is injected both at the center of the swirler (near the central plug of the swirler) and at its outer periphery using additional small holes. Therefore, for SCIROCCO, the first two places tested to add hydrogen injection devices will be:

 An example of possible H2 injection locations on a modern swirled injector (Jaegle et al 2011). Left: geometry of multipoint injector.  Right: instantaneous velocity field (AVBP result). The two possible locations for hydrogen injection are the central plug (on the swirler axis) and the multipoint holes.

These zones can be easily modified to allow hydrogen injection in many modern swirlers so that it will be possible to extend SCIROCCO results to real injectors. 

 

WP3: Flames stabilized on porous burners. 

An elegant solution to burn fossil fuels and H2 is to use a porous burner where a flame is stabilized on or in a porous medium.

These configurations raise all kinds of fundamental problems which will be addressed in SCIROCCO using experiments, simulations but also purely analytical theoretical approaches. As an example a first test of flames stabilized on a porous burner is displayed below.

 

 

REFERENCES

Published on  September 12th, 2019