Nanoscale characterisation of soot particulates from gasoline direct injection engines

Understanding the intricacies of particulate emissions from internal combustion engines is important due to their harmful impact on human health and the environment, as well as their contribution to engine wear and performance. Particulate emissions were historically associated with diesel engines which are predominantly using direct-injection systems. Thus, diesel soot is widely covered in the literature. However, the increasing market share of vehicles with gasoline direct-injection (GDI) engines over recent years raises the question of how GDI soot compares to diesel soot and if existing knowledge can be applied. The aim of this work was to close this gap in knowledge between GDI and diesel engine soot. Fringe analysis was assessed as a tool for quantifying graphitic nanostructures from transmission electron microscopy (TEM) images. A considerable influence of the processing parameters on the produced metrics was demonstrated, and optimised parameters were proposed. Moreover, the importance of the TEM focus point and the role of image quality was outlined. Subsequent thermogravimetric analysis of soot-in-oil samples suggested that the soot deposition rate into the lubricating oil is similar for GDI engines compared to diesel engines, even though their exhaust particulate emissions are generally considered to be one order of magnitude lower. Direct comparison of GDI and diesel engine soot samples and a carbon black identified primary particles with similar core-shell nanostructures in TEM images. However, for the GDI samples, also particles with surrounding amorphous layer were observed along with entirely amorphous particulates and traces of wear and oil chemistry. Fringe analysis revealed that fringes of GDI soot were distinctly shorter compared to the other soot types. This finding was confirmed by Raman spectroscopy, indicating that GDI soot is more disordered. Electrical mobility measurements of particulate emissions were acquired for a GDI engine with a differential mobility spectrometer (DMS). As additional processing is required to compare the detailed particle size distributions to the regulatory solid particle number (SPN), different methods were assessed. While lognormal function fitting can be sufficient for SPN23 measurements, modelling of counting efficiencies by applying digital filtering functions is required for measurements below 23 nm. A new function was designed to match the proposed counting efficiencies for SPN10 of upcoming regulations. Measurements with the DMS combined with a catalytic stripper showed an increase of up to 11.2% using this new function compared to the closest previous sub-23 nm function. However, the results are highly dependent on the shape of the particle size distribution. For a matrix of test conditions, the shift from SPN23 to SPN10 was observed to result in increases of 27% to 390%. Furthermore, soot particulates were sampled from the exhaust gas on TEM grids for three operating conditions. Core-shell primary particles were observed for all conditions. In addition, some particles at 1500 rpm fast-idle exhibited a surrounding amorphous layer. For 1500 rpm with 40 Nm brake torque, crystalline features within agglomerates and entirely amorphous/crystalline particulates could be found. Fringe analysis of the graphitic primary particle nanostructures did not find significant differences between the operating conditions; however, longer fringes than for the soot-in-oil samples were identified. An additional feature observed in all samples were separate sub-10 nm particulates of non-volatile nature. The average diameter of these particulates was below the lower detection size limit of the DMS

Nanoscale characterisation of soot particulates from gasoline direct injection engines

Understanding the intricacies of particulate emissions from internal combustion engines is important due to their harmful impact on human health and the environment, as well as their contribution to engine wear and performance. Particulate emissions were historically associated with diesel engines which are predominantly using direct-injection systems. Thus, diesel soot is widely covered in the literature. However, the increasing market share of vehicles with gasoline direct-injection (GDI) engines over recent years raises the question of how GDI soot compares to diesel soot and if existing knowledge can be applied. The aim of this work was to close this gap in knowledge between GDI and diesel engine soot. Fringe analysis was assessed as a tool for quantifying graphitic nanostructures from transmission electron microscopy (TEM) images. A considerable influence of the processing parameters on the produced metrics was demonstrated, and optimised parameters were proposed. Moreover, the importance of the TEM focus point and the role of image quality was outlined. Subsequent thermogravimetric analysis of soot-in-oil samples suggested that the soot deposition rate into the lubricating oil is similar for GDI engines compared to diesel engines, even though their exhaust particulate emissions are generally considered to be one order of magnitude lower. Direct comparison of GDI and diesel engine soot samples and a carbon black identified primary particles with similar core-shell nanostructures in TEM images. However, for the GDI samples, also particles with surrounding amorphous layer were observed along with entirely amorphous particulates and traces of wear and oil chemistry. Fringe analysis revealed that fringes of GDI soot were distinctly shorter compared to the other soot types. This finding was confirmed by Raman spectroscopy, indicating that GDI soot is more disordered. Electrical mobility measurements of particulate emissions were acquired for a GDI engine with a differential mobility spectrometer (DMS). As additional processing is required to compare the detailed particle size distributions to the regulatory solid particle number (SPN), different methods were assessed. While lognormal function fitting can be sufficient for SPN23 measurements, modelling of counting efficiencies by applying digital filtering functions is required for measurements below 23 nm. A new function was designed to match the proposed counting efficiencies for SPN10 of upcoming regulations. Measurements with the DMS combined with a catalytic stripper showed an increase of up to 11.2% using this new function compared to the closest previous sub-23 nm function. However, the results are highly dependent on the shape of the particle size distribution. For a matrix of test conditions, the shift from SPN23 to SPN10 was observed to result in increases of 27% to 390%. Furthermore, soot particulates were sampled from the exhaust gas on TEM grids for three operating conditions. Core-shell primary particles were observed for all conditions. In addition, some particles at 1500 rpm fast-idle exhibited a surrounding amorphous layer. For 1500 rpm with 40 Nm brake torque, crystalline features within agglomerates and entirely amorphous/crystalline particulates could be found. Fringe analysis of the graphitic primary particle nanostructures did not find significant differences between the operating conditions; however, longer fringes than for the soot-in-oil samples were identified. An additional feature observed in all samples were separate sub-10 nm particulates of non-volatile nature. The average diameter of these particulates was below the lower detection size limit of the DMS

Quantifying soot nanostructures: Importance of image processing parameters for lattice fringe analysis

Fringe analysis is a commonly used method to quantify soot nanostructures. However, the settings of the involved filters and their impact on the results are rarely addressed. In this study, the influence of the three filter parameters as well as two aspects of the image acquisition was assessed experimentally. For the analysis, a carbon black as well as one diesel engine and one gasoline direct injection (GDI) engine soot sample were used. Gaussian low-pass filter standard deviations larger 1.5 yielded only minor differences in fringe metrics. Standard deviations between 2.0 and 3.0 enabled realistic representation of fringes. A linear correlation was found between the white top-hat transformation disk size and all fringe analysis metrics. For realistic nanostructure representation, disk sizes of 5 px and 7 px are most suitable. Threshold values as calculated by Otsu's method generally yielded the best nanostructure representation. Any deviation distorted the extracted fringes and noticeably reduced their total number. Thus, consistent use of Otsu thresholds without alterations is advised. Deviating from the neutral electron microscope focus point by under- and over-focusing resulted in distinctive drops in both fringe lengths and Otsu thresholds. Consistent focusing with the help of fast Fourier transformations of the respective particles is vital for reliable results. The effect of reduced noise levels by repeated averaged images was found to be minor beyond the model of the camera used. The region of interest size correlated linearly with the number of extracted fringes, however, it did not affect the fringe metrics. For statistically reliable analysis, a minimum of 4000 fringes is suggested. The GDI sample exhibited the shortest fringes and the highest tortuosity. For diesel soot and carbon black, similar fringe lengths could be observed. The highest tortuosity was found for GDI soot, followed by diesel soot and carbon black

Comparative nanostructure analysis of gasoline turbocharged direct injection and diesel soot-in-oil with carbon black

Two gasoline turbocharged direct injection (GTDI) and two diesel soot-in-oil samples were compared with one flame-generated soot sample. High resolution transmission electron microscopy imaging was employed for the initial qualitative assessment of the soot morphology. Carbon black and diesel soot both exhibit core-shell structures, comprising an amorphous core surrounded by graphene layers; only diesel soot has particles with multiple cores. In addition to such particles, GTDI soot also exhibits entirely amorphous structures, of which some contain crystalline particles only a few nanometers in diameter. Subsequent quantification of the nanostructure by fringe analysis indicates differences between the samples in terms of length, tortuosity, and separation of the graphitic fringes. The shortest fringes are exhibited by the GTDI samples, whilst the diesel soot and carbon black fringes are 9.7% and 15.1% longer, respectively. Fringe tortuosity is similar across the internal combustion engine samples, but lower for the carbon black sample. In contrast, fringe separation varies continuously among the samples. Raman spectroscopy further confirms the observed differences. The GTDI soot samples contain the highest fraction of amorphous carbon and defective graphitic structures, followed by diesel soot and carbon black respectively. The AD1:AG ratios correlate linearly with both the fringe length and fringe separation

Reconnection rates and X line motion at the magnetopause : Global 2D-3V hybrid-Vlasov simulation results

We present results from a first study of the local reconnection rate and reconnection site motion in a 2D-3V global magnetospheric self-consistent hybrid-Vlasov simulation with due southward interplanetary magnetic field. We observe magnetic reconnection at multiple locations at the dayside magnetopause and the existence of magnetic islands, which are the 2-D representations of flux transfer events. The reconnection locations (the X lines) propagate over significant distances along the magnetopause, and reconnection does not reach a steady state. We calculate the reconnection rate at the location of the X lines and find a good correlation with an analytical model of local 2-D asymmetric reconnection. We find that despite the solar wind conditions being constant, the reconnection rate and location of the X lines are highly variable. These variations are caused by magnetosheath fluctuations, the effects of neighboring X lines, and the motion of passing magnetic islands.Peer reviewe

Soot in the Lubricating Oil: An Overlooked Concern for the Gasoline Direct Injection Engine?

Formation of soot is a known phenomenon for diesel engines, however, only recently emerged for gasoline engines with the introduction of direct injection systems. Soot-in-oil samples from a three-cylinder turbo-charged gasoline direct injection (GDI) engine have been analysed. The samples were collected from the oil sump after periods of use in predominantly urban driving conditions with start-stop mode activated. Thermogravimetric analysis (TGA) was performed to measure the soot content in the drained oils. Soot deposition rates were similar to previously reported rates for diesel engines, i.e. 1 wt% per 15,000 km, thus indicating a similar importance. Morphology was assessed by transmission electron microscopy (TEM). Images showed fractal agglomerates comprising multiple primary particles with characteristic core-shell nanostructure. Furthermore, large amorphous structures were observed. Primary particle sizes ranged from 12 to 55 nm, with a mean diameter of 30 nm and mode at 31 nm. Particle agglomerates were measured by nanoparticle tracking analysis (NTA). The agglomerates were found to range between 42 and 475 nm, with a mean size of 132 nm and mode at 100 nm. The distribution was shifted towards larger sizes with a minor concentration of very large agglomerates observed around 382 nm. While deposition rate and agglomerate morphology were similar to diesel engines, distinctive amorphous carbon and smaller particles were observed. Hence, existing knowledge for diesel applications might not be directly transferrable

Investigating the Effect of Volatiles on Sub-23 nm Particle Number Measurements for a Downsized GDI Engine with a Catalytic Stripper and Digital Filtering

Recent efforts of both researchers and regulators regarding particulate emissions have focused on the contribution and presence of sub-23 nm particulates. Despite being previously excluded from emissions legislation with the particle measurement programme (PMP), the latest regulatory proposals suggest lowering the cut-off sizes for counting efficiencies and the use of catalytic strippers to include solid particles in this size range. This work investigated particulate emissions of a 1.0 L gasoline direct injection (GDI) engine using a differential mobility spectrometer (DMS) in combination with a catalytic stripper. Direct comparison of measurements taken with and without the catalytic stripper reveals that the catalytic stripper noticeably reduced variability in sub-23 nm particle concentration measurements. A significant portion of particles in this size regime remained (58–92%), suggesting a non-volatile nature for these particles. Digital filtering functions for imposing defined counting efficiencies were assessed with datasets acquired with the catalytic stripper; i.e., particle size distributions (PSDs) with removed volatiles. An updated filtering function for counting efficiency thresholds of d65 = 10 nm and d90 = 15 nm showed an increase in particulate numbers between 1.5% and up to 11.2%, compared to the closest previous digital filtering function. However, this increase is highly dependent on the underlying PSD. For a matrix of operating conditions (1250 to 2250 rpm and fast-idle to 40 Nm brake torque), the highest emissions occurred at fast-idle 1250 rpm with 1.93 × 108 #/cm3 using the updated filtering function and catalytic stripper. This setup showed an increase in particulate number of +27% to +390% over the test matrix when compared to DMS measurements without the catalytic stripper and applied counting efficiency thresholds of d50 = 23 nm and d90 = 41

Ultra-Fast Adaptive Digital Polarization Control in a Realtime Coherent Polarization-Multiplexed QPSK Receiver

Pfau T, Wördehoff C, Peveling R, et al. Ultra-Fast Adaptive Digital Polarization Control in a Realtime Coherent Polarization-Multiplexed QPSK Receiver. In: Proceedings of OFC/NFOEC 2008. 2008.A digital polarization control system integrated in a 2.8 Gbit/s realtime polarization-multiplexed coherent QPSK system compensates for endless polarization changes having a maximum gradient of 3.5 krad/s (12 krad/s) with 1 dB (3.9 dB) loss in receiver sensitivity