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

Coupling a single electron to a Bose-Einstein condensate

The coupling of electrons to matter is at the heart of our understanding of material properties such as electrical conductivity. One of the most intriguing effects is that electron-phonon coupling can lead to the formation of a Cooper pair out of two repelling electrons, the basis for BCS superconductivity. Here we study the interaction of a single localized electron with a Bose-Einstein condensate (BEC) and show that it can excite phonons and eventually set the whole condensate into a collective oscillation. We find that the coupling is surprisingly strong as compared to ionic impurities due to the more favorable mass ratio. The electron is held in place by a single charged ionic core forming a Rydberg bound state. This Rydberg electron is described by a wavefunction extending to a size comparable to the dimensions of the BEC, namely up to 8 micrometers. In such a state, corresponding to a principal quantum number of n=202, the Rydberg electron is interacting with several tens of thousands of condensed atoms contained within its orbit. We observe surprisingly long lifetimes and finite size effects due to the electron exploring the wings of the BEC. Based on our results we anticipate future experiments on electron wavefunction imaging, investigation of phonon mediated coupling of single electrons, and applications in quantum optics.Comment: 4 pages, 3 figures and supplementary informatio

In situ observation of chemistry in Rydberg molecules within a coherent solvent

We often infer the state of systems in nature indirectly, for example in high energy physics by recording the tracks particles leave behind in an ambient medium. We adapt this principle to energies 9 orders of magnitude smaller, to classify the final state of exotic molecules after internal conversion of their electronic state, through their interaction with an ambient quantum fluid, a Bose-Einstein condensate. The BEC is the ground-state of a million bosonic atoms near zero temperature, and a single embedded ultra-long range Rydberg molecule can coherently excite waves in this fluid, which carry tell-tale signatures of its dynamics. Bond lengths exceeding a micrometer allow us to observe the molecular fingerprint on the BEC in situ, via optical microscopy. Interpreting images in comparison with simulations shows that the molecular electronic state rapidly converts from the initially excited S- and D-orbitals to a much more complex molecular state (called "trilobite''), marked by a maximally localized electron. This internal conversion liberates energy, such that one expects final state particles to move rapidly through the medium, which is however ruled out by comparing experiment and simulations. The molecule thus must strongly decelerate in the medium, for which we propose a plausible mechanism. Our experiment demonstrates a coherent medium that facilitates and records an electronic state change of embedded exotic molecules in ultra-cold chemistry, with sufficient sensitivity to constrain velocities of final state particles.Comment: 11 pages and 11 figure