Experimental Investigation of ultra-high fuel injection pressure spray for GDI engines

Gasoline Direct Injection Engines (GDI) for passenger cars currently use fuel injection systems operating at pressures of up to 350 bar. Injection pressures have increased over time, and there is evidence that particulate emissions could be reduced by raising them further, up to 500 bar. However, it is not clear whether further beneficial effects would be achieved by using higher injection pressures exceeding 600 bar. This thesis presents experimental studies on sprays and combustion conducted to assess the benefits and downsides of substantially increased fuel injection system pressures (between 200 and 1500 bar) in GDI engines. Experiments on spray characteristics and spray-air interaction revealed that raising the injection pressure from 200 to 600 bar significantly improved spray atomization. This pressure effect on atomization became less significant when the injection pressure was over 800 bar. High pressure sprays also evolved much faster than low pressure ones, but the spray tip penetration at the end of injection did not vary greatly with the injection pressure. High pressure sprays induced more air flow because of their high velocity and good atomization, which increased the likelihood and strength of spray-air interactions. These results indicate that high injection pressures result in better mixture formation because they accelerate evaporation and induce stronger air flow. However, spray impingement caused by high spray velocities and penetration may cause problems during engine operation

Ultra-High Pressure Spray for Gasoline Direct Injection Engines

There is an increasingly urgent need for vehicle manufacturers to reduce emissions from passenger vehicles to protect the environment and comply with increasingly stringent emissions standards such as Euro 6d, which came into force in January 2021, and Euro 7, which will probably come into force around 2025. Current emissions standards limit passenger vehicles\u27 particulate number emissions to at most 6*10^{11} [#/km], making it necessary to find ways of reducing the engine-out particulate emissions of gasoline direct injection engines to meet this requirement. A promising way of doing this is to use fuel injection pressures above 200 bar, which was the most commonly used injection pressure until recently. This thesis presents a comprehensive experimental evaluation of the potential for reducing particulate number emissions from GDI engines by using high fuel injection pressures.Basic spray characteristics such as spray tip penetration, droplet size, and spray-induced air motion were investigated in a constant-volume spray chamber. Spray tip penetration was determined by post-processing images captured with a high speed video camera, while droplet size was measured by Phase Doppler Interferometry and the motion of air around the spray was captured by means of Particle Image Velocimetry using tracer particles and a CCD camera. In addition, the behavior of combusting sprays inside a cylinder was studied using a single cylinder optical engine with a high speed video camera, and the effects of the fuel injection pressure on combustion characteristics and emissions were investigated using a single cylinder metal engine.Increasing the injection pressure increased the spray velocity and therefore increased spray tip penetration. However, raising the injection pressure from 200 bar to 1500 bar also reduced the droplet size by over 50% because high injection pressures enhance droplet atomization. The high spray velocities and small droplet diameters seen with an injection pressure of 1500 bar increased air entrainment into the spray: the mass of air entrained at 1500 bar injection pressure was 40% higher than at 200 bar. In addition, air entrainment occurred in a shorter time frame at higher injection pressures, which improved fuel-air mixing in the cylinder. Engine tests revealed that the use of high injection pressures reduced PN emissions by up to 50% at standard SOI timings, and by a factor of 1000 when using advanced SOI timings under hot-steady conditions. Interestingly, the most significant effects on spray characteristics were seen when raising the injection pressure from 200 bar to 600 bar, and only relatively minor changes in spray behavior were seen when raising the injection pressure further. However, beneficial effects on emissions continued to be observed even when increasing the injection pressure to above 1000 bar

Large-Eddy Simulation Study of Ultra-High Fuel Injection Pressure on Gasoline Sprays

The development of gasoline spray at ultra-high injection pressures was analyzed using Large-Eddy simulation (LES). Two different nozzle hole geometries, divergent and convergent shape, were considered to inject the fuel at injection pressures ranging from 200 to 1500 bar inside a constant volume spray chamber maintained at atmospheric conditions. The discrete droplet phase was treated using a Lagrangian formulation together with the standard spray sub-models. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on the spray development. The calibrated model was then used to investigate the impact of ultra-high injection pressures on mean droplet size and droplet size distribution. In addition, the spray-induced large-scale eddies and entrainment rate were evaluated at different ultra-high injection pressures. Overall, simulation results showed a good agreement with available measurement data. At ultra-high injection pressures mean droplet sizes were significantly reduced and comprised very high velocities. Integral length scales of spray-induced turbulence and air entrainment rate into the spray were larger at higher injection pressure compared to lower ones

Prolonged maturation of prefrontal white matter in chimpanzees

Delayed maturation in the prefrontal cortex, a brain region associated with complex cognitive processing, has been proposed to be specific to humans. However, we found, using a longitudinal design, that prefrontal white matter volume in chimpanzees increased gradually with age, and the increase appears to continue beyond the onset of puberty, as in humans. This provides the first evidence for a prolonged period of prefrontal connection elaboration in great apes

Versatile strategy using vaccinia virus-capping enzyme to synthesize functional 5′ cap-modified mRNAs

様々な5'キャップ構造をもつ機能的なmRNAの汎用的な合成方法 酵素を用いて簡便かつ効率的に. 京都大学プレスリリース. 2023-02-03.Development of a versatile method to synthesize functional mRNAs with diverse 5' cap structures. 京都大学プレスリリース. 2023-02-03.The potential of synthetic mRNA as a genetic carrier has increased its application in scientific fields. Because the 5′ cap regulates the stability and translational activity of mRNAs, there are concerted efforts to search for and synthesize chemically-modified 5′ caps that improve the functionality of mRNA. Here, we report an easy and efficient method to synthesize functional mRNAs by modifying multiple 5′ cap analogs using a vaccinia virus-capping enzyme. We show that this enzyme can introduce a variety of GTP analogs to the 5′ end of RNA to generate 5′ cap-modified mRNAs that exhibit different translation levels. Notably, some of these modified mRNAs improve translation efficiency and can be conjugated to chemical structures, further increasing their functionality. Our versatile method to generate 5′ cap-modified mRNAs will provide useful tools for RNA therapeutics and biological research

Imaging of gasoline-like sprays with planar laser-induced exciplex fluorescence using a stereoscopic imaging system

The role of the fuel injection systems in direct injected gasoline engines is to achieve a suitable fuel vapor distribution, homogeneous or with some degree of stratification, while avoiding unwanted effects such as wall wetting. Planar laser-induced exciplex fluorescence (PLIEF) is a method suitable for the characterization of such sprays since it enables separate imaging of both vapor and liquid phase of fuel simultaneously. In this study a hollow-cone spray generated with an outwards-opening piezo-actuated injector is investigated, with the injector mounted in a constant volume, constant pressure spray chamber with quartz windows, providing a controlled steady test environment. N-hexane is used as surrogate fuel of gasoline, together with exciplex-forming fluorescence tracers - fluorobenzene and diethylmethylamine. Fluorescence excitation is carried out with a parallel laser sheet from the fourth harmonic light of a Nd:YAG-laser (266 nm) running at 10 Hz. Exciplex fluorescence images from liquid phase and monomer fluorescence spray images from vapor phase can be acquired by a single UV-sensitive CMOS camera equipped with a stereoscope having filters selectively transmitting monomer fluorescence at 295 nm and exciplex fluorescence at 355 nm. Since the fluorescence is strongly quenched by oxygen, most of the experiments were carried out in a nitrogen atmosphere. Images were recorded during the injection and at various time steps after the end of the injection, and typical spray development for this type of injector was observed, i.e. the fuel forms an expanding cone, the sheet breaks up to form a vortex structure and the vortices continue to expand after the end of the injection. Fuel vapor is firstly observed at the same locations as the liquid drops, and is then accumulated into the center of the vortices. In addition, penetration of liquid phase and vapor phase are found to be very similar. Various injection pressures have been tested, which shows that increasing the fuel pressure from 10 to 20 MPa results in a larger vortex structure. The fuel evaporation can be followed by studying the evolution of the monomer and exciplex fluorescence as a function of time. At room temperature the vaporization is found to be very slow, but above 40\ub0C there is a noticeable presence of vapor at the end of the injection, and at higher temperatures, the vaporization goes even faster