Combustion Engine Spectroscopy

Car engine emissions are responsible for large parts of air pollution in cities. The large range engine types and fuels produce numerous gaseous and particle-bound pollutants which makes research extremely complex and impactful.  We study the chemical mechanisms that lead to pollutant formation, assess abatement technology to reduce pollution, in collaboration with industry. Further, somehow pollutants are linked to incomplete combustion, which also reduces the engine efficiency. We tackle the fundamental chemical processes within a combustion engine, by means of optical and mass spectrometry, and with that we will advance knowledge for greener and more performing cars.
Car Exhaust Toxicity
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Is blue technology green enough yet? DeNOx technologies currently used for on-road diesel vehicles are not where they should be. This has become clear not only because of recent scan-dals but is evident when looking at long term trends of on-road emission data. Trends proved that gasoline vehicles followed the NOx emission limits which were lowered by 95% from 1990 to 2009. The opposite was found for diesel passenger cars and light duty vehicles. On road measurements indicate that NOx emissions, especially those of toxic and reactive NO2 have increased from 1990 until 2005 and are only slowly decreasing and one order of magnitude higher than those of comparable gasoline vehicles.

These findings indicate that deNOx technologies in real world operation are not efficient enough and have to be improved considerably. Current deNOx technologies emit toxic and environmentally relevant reactive nitrogen compounds like NO2, NH3, HNCO and N2O. These compounds contribute to the overall exhaust toxicity but are not limited by current vehicle legislation which lacks behind here.

Like for particle filters, Advanced Analytical Technologies and partners have established specific analytical procedures to assess the efficiency of deNOx technologies and to monitor secondary emissions like NO2, NH3, HNCO and N2O. Research is also expanding towards alternative exhaust treatment technologies such as Oxicat, DPF, GPF, SCR and combinations there-of.

In 2020, more than 50 million gasoline direct injection (GDI) vehicles may circulate on Euro-pean roads. The majority of these vehicles will not be equipped with particle filters and will release trillions of inhalable, persistent and toxic nanoparticles smaller than 100 nm. In the GASOMEP and related projects, we study several GDI vehicles under transient and steady driving conditions with varying converter technologies and fuels. With industrial partners, we study prototype gasoline particle filters (GPFs).

Our focus is on emissions of toxic and environmentally relevant pollutants. Particle characterization included size, number distribution and metal content. Emissions of carcinogenic compounds, especially the polycyclic aromatic hydrocarbons (PAH) and their nitrated forms are studied to assess the genotoxic potential of these exhausts and the effectiveness of filters on particles and carcinogenic compounds.

In upcoming research projects we’ll study how efficient in-series particle filters for GDI-vehicles are in comparison to stat-of the art diesel filter technology with proven filtration efficiencies of >98%.

Spark-induced Breakdown Spectroscopy of Engine-relevant Conditions

 

An experimental study of temporally and spatially resolved spark-induced breakdown spectroscopy (SIBS) of methane and hydrogen-enriched methane mixtures is carried out for premixed combustion in internal combustion engines. Experiments are conducted at quiescent conditions in a small constant volume chamber, varying pressure, stoichiometry and hydrogen admixture rates.

Spectral emissions of hydroxyl (OH) at 306 nm, NH at 336 nm, the cyanogen (CN) band at 388 nm and the nitrogen second positive system (N2) were spatially resolved on a time-integrated setup. OH emissions were found to be strongest between the electrodes, whereas CN emissions were more pronounced at the center and ground electrode. Metal emission lines were observed, partially interfering with the radicals of interest.

Energy dispersive X-ray spectroscopy showed nickel, copper and iron shares in the noble metal electrodes, confirming the origin of these metal emissions. Simultaneously to time-integrated spectra, temporally-resolved spectra at a frame rate of 100 kHz were recorded during the glow phase of the electrical discharge. Comparison of both spectra revealed a good agreement in terms of spectral characteristics and resolved species.

Temporally-resolved spectra highlighted the strong dependence on the electric discharge characteristics of the inductive coil ignition system in the early phase of ignition. Ratios of CN/OH and CN/NH were found to correlate with the fuel-air equivalence ratio, but shot to shot repeatability was up to a factor 3 larger than the dependence on the mixture composition. Moreover, these ratios changed with increasing pressure at ignition timing, and with the higher pressure metal emission lines became more pronounced.

Additionally, at pressures higher than 2 bar, the equilibrium position shifted to the disadvantage of the second positive system of nitrogen, suppressing this emission. Hydrogen admixture to methane of up to 50 vol% were found to not significantly alter the spectral signature between 300 and 400 nm, only marginally affecting the signal ratios of CN/OH and CN/NH.

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References

Muñoz, M., Haag, R., Zeyer, K., Mohn, J., Comte, P.,. Czerwinski, J., Heeb, N.V., (2018). Ef-fects of four prototype gasoline particle filters (GPFs) on nanoparticle and genotoxic PAH emissions of a gasoline direct injection (GDI) vehicle, Environmental Science & Technology, in press 2018.

 

Muñoz, M., Haag, R., Honegger, P., Zeyer, K., Mohn, J., Comte, P. Czerwinski, J., Heeb, N. V. (2018). Co-formation and co-release of genotoxic PAHs, alkyl-PAHs and soot nanoparti-cles from gasoline direct injection vehicles. Atmospheric Environment, 178, 242-254.

 

Heeb N.V. (2017). Der lange Weg zu sauberem Diesel, Nachrichten der Chemie, 65, 1079.

 

Munoz, M., Heeb, N.V., Haag, R., Honegger, P., Zeyer, K., Mohn, J., Comte, P., Czerwinski, J., (2016). Bioethanol blending reduces nanoparticle, PAH, and alkyl- and nitro-PAH emis-sions and the genotoxic potential of exhaust from a gasoline-direct injection flex-fuel vehicle, Environmental Science & Technology, 60, 11853-11861.

 

Heeb, N.V., Haag, R., Seiler, C., Schmid, P., Zennegg, M., Wichser, A., Ulrich, A., Honegger, P., Zeyer, K., Emmenegger, L., Zimmerli, Y., Czerwinski, J., Kasper, M., Mayer, A., (2012). Effects of a combined diesel particle filter-deNOx system (DPN) on reactive nitrogen compounds emissions: A parameter study, Environmental Science & Technology, 46, 13317-13325.

 

Kammermann, T., Kreutner, W., Trottmann, M., Merotto, L., Soltic, P., & Bleiner, D. (2018). Spark-induced breakdown spectroscopy of methane/air and hydrogen-enriched methane/air mixtures at engine relevant conditions. Spectrochimica Acta B: Atomic Spectroscopy, 148, 152-164.