Pollutant formation

Air quality is becoming more and more a concern in cities and around industrial regions. The formation and transport of pollutant is of primary importance and is inherently connected to the combustion processes. In that context, BURN is active in developing reduced approaches for NO modelling in (non-conventional) combustion processes, as well as experimental monitoring of the emissions from biomass stoves and boilers and real-driving-emissions from light-duty vehicles.

Reduced model development

The conversion of conventional and unconventional fuels is mainly accomplished through combustion. However, combustion inevitably produces greenhouse gases and pollutant species such as nitrogen oxides. Conventional techniques used to reduce these emissions are often post-combustion treatments and they may include CO2 storage, flue gases clean up by catalytic and non-catalytic conversions. Alternatively, one can act directly on the process to limit pollutant emissions at the source while maximizing combustion efficiency. New processes are currently using this strategy, including MILD combustion.
Other open issues in NO_MILDMILD regime concerns how to deal with turbulence-chemistry interactions and pollutant formation. Indeed, in MILD combustion, the lower temperatures and the absence of large fluctuations inhibit thermal NOx formation. Therefore, NOx formation is controlled by other formation routes such as N2O- and NNH-intermediate.
BURN is active in the development of reduced NO models for CFD applications, including non-conventional formation routes beside the conventional ones.

Our work on reduced NO  models for CFD applications can be found here:
[1] Galletti, C., Ferrarotti, M., Parente, A., & Tognotti, L. (2015). Reduced NO formation models for CFD simulations of MILD combustion. International Journal of Hydrogen Energy,  40, 4884–4897.  link
[2] Li, P. P., Wang, F. F., Mi, J. J., Mei, Z. Z., Zhang, J. J., Dally, B. B., & Parente, A. (2014). Mechanisms of NO formation in MILD combustion of CH4/H2 fuel blends. International Journal of Hydrogen Energy, 39(33), 19187-19203. link
[3] Parente, A., Galetti, C., & Tognotti, L. (2011). A simplified approach for predicting NO formation in MILD combustion of CH4-H2 mixtures. Proceedings of the Combustion Institute, 33, 3343-3350.  link

 

Particulate Matter (PM) from biomass combustion

The European Union has set a target to produce at least 20 % of energy from renewable sources by 2020. A significant fraction will be generated by the combustion of biomass fuels. For the purpose of residential heating, this is done in small scale combustion appliances such as open fireplaces, wood stoves, pellet stoves and boilers, wood log boilers and wood chip boilers. Different forms of biomass fuels are used in these appliances such as: wood logs, wood pellets, agro-pellets, saw dust, wood chips, forest residues, straw etc.

The combustion of biomass in small scale heating appliances is however a common source of both particulate matter (PM) and gaseous emissions such as polycyclic aromatic hydrocarbons (PAH), volatile organic compounds (VOC), carbon monoxide, carbon dioxide, nitrogen oxides and sulphur oxides. In comparison to liquid and gaseous fuels, the emissions of particulate matter from biomass are high and there is growing concern about particle emissions from biomass combustion. The majority of the particles is less than 1 μm in diameter and emitted directly to the ambient air from the combustion devices. A number of studies have shown that increased particle concentrations in the ambient air correlate with adverse health effects in the exposed population. 

To investigate the emissions of PM from small biomass combustion appliances, such as stoves and boilers, BURN has set-up a lab facility to measure the performance of such systems under laboratory conditions. This test-bench is equipped with a particle sampling setup. The setup consists of an Electrical Low Pressure Impactor Plus (ELPI+) from Dekati with a two stage dilution system with a porous tube diluter and an ejector diluter. The ELPI+ is an instrument that measures particle concentrations and size distributions in real time with a sample rate of 10 Hz in 14 size classes, ranging from 7 nm to 14 μm.  

We have experience with real time measurements of PM from the combustion of alternative biomass fuels such as for instance pellets made from: apple pomace (Malus domestica), reed canary grass (Phalaris arundinacea), pectin waste from citrus shells (Citrus reticulata), sunflower husk (Helianthus annuus), peat, wheat straw pellets (Triticum aestivum) and of course different kinds of wood pellets.

[1] Verma, V. K., Bram, S., Delattin, F., Laha, P., Vandendael, I., Hubin A. & De Ruyck, J. (2012).  Agro-pellets for domestic heating boilers: Standard laboratory and real life performance. Applied Energy, 90(1), 17-23.  link

Particle matter in real-driving conditions

PNDue to the environmental context, pollutant emissions standards are becoming more and more strict. Car manufacturers developed then new technologies to meet standards such as catalytic converter or particulate filter. For Spark-Ignition (SI) vehicles, car manufacturers developed intensively the use of gasoline direct injection (GDI) system in order to reduce both consumption and pollutant emissions. However it is well known that the use of direct injection system can promote particle formation due to the mixing process which, in some cases, is not efficient enough. If this process has been widely investigated in diesel engine, the subject is still quite recent for SI engine. In Europe, standards on particulate matter (PM) emissions for SI engine only appeared with EURO5 in 2009. With EURO6, the standard on PM for SI is becoming as strict as for diesel engine and even stricter regarding the mass of PM. Moreover the development of the new WLTC (World-harmonized Light vehicle Test Cycle) represents an important challenge for car manufacturers. PM emissions by SI engines start then to be an issue for the industry but also for the impact on human health due to the size of the particle as for the diesel.

We are using the Electrical Low Pressure Impactor (ELPI+) manufactured by Dekati Ltd to measure PM emissions in real-driving conditions. This device is able to give the size distribution of the particles in the 0.007 μm to 14 μm range with 14 different classes at a rate of 10 Hz. It has already been successfully implemented in car engine studies. We specifically focus on the emissions of ultrafine particles from direct injection spark ignition engines in real-life conditions.