CFD-based methodology for the characterization of the combustion process of a passive pre-chamber gasoline engine

Pre-chamber (PC) ignition systems, enabling Turbulent Jet Ignition (TJI) combustion, represent a promising technology to extend the lean limit of Spark Ignition Internal Combustion Engines. Indeed, the higher ignition energy provided by the turbulent jets contributes to the limitation of combustion duration and variability even in diluted conditions. However, a detailed analysis of the combustion process is needed to maximize the performance of the system. More specifically, the interaction between the chemical and the turbulent scales are key factors in assessing the probabilities of main chamber (MC) ignition, determining the ignition pattern, and characterizing the combustion process. For this reason, the development of reliable numerical models is a crucial factor to pave the way toward a deeper understanding of details concerning TJI combustion. In the present work, a 3D-CFD numerical model was validated against experimental data at 4000 rpm, in stoichiometric and lean (i.e., λ = 1.2) conditions in a single-cylinder gasoline engine equipped with a passive pre-chamber. In both operations, the evolution of the turbulent combustion regimes over the whole combustion process was investigated, highlighting analogies and differences between the selected operative conditions. Additionally, a methodology to characterize the MC ignition and combustion process, able to describe the different phases of the interaction between PC and MC, and assess the thermal, turbulent, and chemical effects of the turbulent jets is presented

Ordered Arrays of Size-Selected Oxide Nanoparticles

A bottom-up approach to produce a long-range ordered superlattice of monodisperse and isomorphic metal-oxide nanoparticles (NP) supported onto an oxide substrate is demonstrated. The synthetic strategy consists of self-assembling metallic NP on an ultrathin nanopatterned aluminum oxide template followed by a morphology-conserving oxidation process, and is exemplified in the case of Ni, but is generally applicable to a wide range of metallic systems. Both fully oxidized and core-shell metal-metal-oxide particles are synthesized, up to 3-4 nm in diameter, and characterized via spectroscopic and theoretical tools. This opens up a new avenue for probing unit and ensemble effects on the properties of oxide materials in the nanoscale regime

A promyelocytic leukemia protein-thrombospondin 2 axis and the risk of relapse in neuroblastoma

Purpose. Neuroblastoma is a childhood malignancy originating from the sympathetic nervous system with a complex biology, prone to metastasize and relapse. High-risk, metastatic cases are explained in part by amplification or mutation of oncogenes such as MYCN and ALK and loss of tumour suppressor genes in chromosome band 1p. However, it is fundamental to identify other pathways responsible for the large portion of neuroblastomas with no obvious molecular alterations. Experimental design. Neuroblastoma cell lines were used for assessment of tumour growth in vivo and in vitro. Protein expression in tissues and cells was assessed using immunofluorescence and immunohistochemistry. The association of PML expression with neuroblastoma outcome and relapse was calculated using log-rank and Mann-Whitney tests, respectively. Gene expression was assessed using chip microarrays. Results: PML is detected in the developing and adult sympathetic nervous system, whereas it is not expressed or low in metastatic neuroblastoma tumours. Reduced PML expression in patients with low-risk cancers - i.e. localized and negative for the MYCN protooncogene - is strongly associated with tumour recurrence. PML-I, but not PML-IV, isoform suppresses angiogenesis via upregulation of thrombospondin-2 (TSP-2), a key inhibitor of angiogenesis. Finally, PML-I and TSP-2 expression inversely correlates with tumour angiogenesis and recurrence in localized neuroblastomas. Dvorkina et al. A promyelocytic leukaemia protein-thrombospondin 2 axis and the risk of relapse in neuroblastoma 3 Conclusions: Our work reveals a novel PML-I-TSP2 axis for regulation of angiogenesis and cancer relapse, which could be used to identify patients with low-risk, localized tumours that might benefit from chemotherapy

Optical diagnostics in a spark ignition engine for two-wheel vehicles

Different optical techniques were applied to describe the thermal and chemical processes that occur in a SI small engine from the ported fuel injection and in-cylinder mixture formation to the combustion process and the exhaust emission. In PFI SI engines, the atomized fuel is sprayed towards the intake valves, where it may evaporate, puddle or rebound. Furthermore, a portion of the fuel may flow directly into the cylinder or impinge upon the port walls. These phenomena occur in varying degrees and depend upon the engine design, injector location and engine operation. Potentially the fuel can enter the cylinder in a poorly atomized state, leading to an increased unburned hydrocarbon emissions. This is particularly true during cold operation, when evaporation is low. In the small-motorcycle and scooter engines the fuel injection occurs in smaller intake manifold than light-duty vehicle engines, increasing the criticism of the fuel-wall interaction. The experimental investigations were performed in a single cylinder engine constituted by an elongated optically accessible piston and equipped with the head and injection system of a reference 4-stroke engine for small vehicles. High spatial resolution imaging was used to characterize the fuel injection phase. The cycle resolved visualization was performed to follow the flame propagation from the intake spark ignition to the exhaust phase. Natural emission spectroscopy measurements were applied in the ultraviolet-visible wavelength range to identify the chemical species that are markers of the combustion process and to follow the formation of pollutants

Progettazione per un motore GDI a carica stratificata reso otticamente accessibile

In this work the changes necessary to make optically accessible a commercial spark ignition and direct injection engine (GDI), operating in stratified charge condition, have been designed trying to keep as much as possible its operational characteristics. To this aim it was decided to design two optical accesses which would interfere as little as possible with the combustion chamber, that is a key condition in the formation of stratified charge, creating an "optical" 4-cylinder engine, versus the classic single-cylinder, so as to leave unchanged the thermo-fluid dynamics configuration of the real engine and so its emissions and fuel consumption. A first optical access has been achieved in the piston head and a second by inserting an endoscopic fiber probe in the header. Both combinations allow a complete analysis of the injection and combustion in an engine whose features are nearly similar to the standard one

Effect of the fuel injection pressure on the combustion process in a PFI boosted spark-ignition engine

In this paper, low-cost solutions were proposed to reduce the fuel consumption in a boosted port fuel injection spark ignition (PFI SI) engine, taking into account the engine performances and the pollutants emission. To this purpose, the optical characterization of the fuel injection and of the combustion process was carried out in a PFI SI engine. The experiments were performed on a partially transparent single-cylinder SI engine, equipped with a four-valve head and an external boost device. The intake manifold was optically accessible through three holes that allowed the introduction of an endoscope and of optical fibres. The standard injection condition planned by the engine manufacturer was investigated; it consisted in the fuel injection at 3.5 bar when the intake valves were closed. Moreover, the fuel injection with open intake valves was tested; 3.5 and 6.5 bar fuel pressures were studied for open and closed valves conditions. Optical techniques based on 2D-digital imaging were used to follow the fuel injection spray in the intake manifold and the flame propagation in the combustion chamber. The results of in-cylinder optical investigations were correlated with the engine performances and with the exhaust emissions