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Upcoming regulations for vehicle exhaust emission demand substantial reduction of particle emission in diesel exhaust. To achieve these emission levels, the car manufacturing industry is developing new combustion concepts and exhaust after-treatment techniques such as the use of catalysts and particle filters. Many of the state-of-the-art analytical instruments do not meet the required detection limits, in combination with a high temporal resolution necessary for engine optimization. This paper reports a new detection system and the first results of its application to on-line diesel exhaust soot measurements on a engine test bench (MAN diesel engine facility Nürnberg, Germany). The instrument is based on differential photoacoustic (PA) spectroscopy of black carbon aerosol. It contains two identical PA cells, one for the measurement of the aerosol particles and one which analyses the particle-free gas. Thus, a potential cross-sensitivity to gaseous absorbers in the exhaust gas can be excluded. The PA cells were characterized in a laboratory set-up, with water vapor as reference gas and artificial soot generated by a spark discharge generator. The detection limit was found to be 2 microg m(-3) BC (for diesel soot) with a sampling rate of 3 Hz. The temporal response of the system was found to be in the order of 1 s. After full characterization of the cells, the system was transferred into a mobile 19"-rack. Characterization of the mobile sensor system under real-world conditions was performed during several measurement campaigns at an engine test bench for heavy-duty diesel engines. Results for the limit of detection, the time resolution, accuracy, repeatability, and robustness of the sensor system are very promising with regards to a routine application of the system in engine development.

Polyoxymethylene dimethyl ethers (OME) are promising candidates as substitutes for fossil diesel fuel. A regenerative electricity-based production, using captured airborne carbon dioxide (CO2) and hydrogen (H2) from water electrolysis as reactants, provides a valuable contribution to the energy transition in mobile applications. Besides the possibility of carbon-neutral production, OME offer the advantage of a sootless combustion, which resolves the trade-off between soot and nitrogen oxides (NOx) emissions, and supports the efforts of air pollution control. While the emission behaviour of OME-powered diesel engines in raw exhaust has been studied extensively, interactions between this exhaust and components of the after-treatment system are mainly unknown. This study contains investigations conducted using a urea dosing variation (alpha titration) on a heavy-duty engine in combination with a system for selective catalytic reduction (SCR). These investigations showed a lower NOx reduction efficiency in OME operation in partial load operation compared with the one in fossil diesel operation. This can be attributed, among other reasons, to lower exhaust temperatures in OME operation. However, the high tolerance of OME to exhaust gas recirculation (EGR) compensates for this disadvantage because of the reduction of the raw NOx emission level. The difference in SCR efficiency disappeared at a high load operation point. Additionally, the alpha titration revealed, that urea dosing decreases formaldehyde emission in the SCR system. A pre-conditioned WHSC and WHTC cycle demonstrated the potential of an OME engine with after-treatment in the form of a twin-dosing SCR system for ultra-low emissions. For the specific evaluation of the emissions during these test cycles, this study contains the detailed calculation of the required factors – so-called ‘ u-values’– for OME exhaust according to the technical standard UN/ECE R49.

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The still-remaining high amounts of pentachlorophenol (PCP), used as wood preservative, in buildings and in waste wood are a potential risk for humans and the environment. To ensure a fast and selective measurement of PCP, a screening tool was developed, which is not only sensitive, but, unlike conventional methods, it requires no added chemicals, is simple, cost-effective, mobile, and capable of on-site operation. The instrument combines light-induced thermodesorption sampling followed by an external cavity diode laser based photoacoustic detector. Measurements on wood samples proved that the system can determine PCP to as low as a concentration of 10 microg/cm2 within minutes without destruction of the sample. The system was calibrated with reference to the concentration of PCP impregnated on the wood surface. It is demonstrated that measurements are not influenced by moisture content of the wood samples.