Decarbonization of the automotive industry is one of the major challenges in the transportation sector, according to the recently proposed climate neutrality policies, e.g., the EU 'Fit for 55' package. Hydrogen as a carbon-free energy career is a promising alternative fuel to reduce greenhouse gas emissions. The main objective of the present study is to investigate non-reactive hydrogen jet impingement on a piston bowl profile at different injection angles and under the effect of various pressure ratios (PR), where PR is the relative ratio of injection pressure (IP) to chamber pressure (CP). This study helps to gain further insight into the mixture formation in a heavy-duty hydrogen engine, which is critical in predicting combustion efficiency. In the experimental campaign, a typical high-speed z-type Schlieren method is applied for visualizing the jet from the lateral windows of a constant volume chamber, and two custom codes are developed for postprocessing the results. In particular, the jet's major characteristics i.e., penetration, width, and cross-sectional area are calculated at different PRs (25, 10, 5, and 2.5). The results show that higher pressure ratios lead to faster penetration and larger cross-sectional areas of the hydrogen jet. In addition, the jet-piston interaction at different angles as well as the flow around the piston towards the liner and back to the main cylinder volume are studied considering the optimization of mixture formation in the cylinder. By changing the injection angle (10°, 15°, and 20°), jet-piston impingement occurs near the edges, which results in greater hydrogen concentration around those areas, adversely affecting mixture formation. The measurements are further used to validate a numerical model for hydrogen injection and mixing in a similar jet-piston geometry, applying an unsteady Reynoldsaveraged Navier-Stokes simulation approach in the commercial software Star-CCM+.
<div class="section abstract"><div class="htmlview paragraph">The current transportation fuels have been one of the biggest contributors towards climate change and greenhouse gas emissions. The use of carbon-free fuels has constantly been endorsed through legislations in order to limit the global greenhouse gas emissions. In this regard, ammonia is seen as a potential alternative fuel, because of its carbon-free nature, higher octane number and as hydrogen carrier. Furthermore, many leading maritime companies are doing enormous research and planning projects to utilize ammonia as their future carbon-free fuel by 2050. Flash boiling phenomenon can significantly improve combustion by enhancing the spray breakup process and ammonia possessing low boiling point, has a considerable potential for flash boiling. However, present literature is missing abundant research data on superheated ammonia sprays. Therefore, this research work aims to optically investigate the behavior of ammonia sprays under different conditions of fuel temperatures for varying chamber pressures. This work probes overall ammonia spray geometry at engine relevant conditions and compare the results with gasoline sprays. A multi-hole solenoid gasoline injector is used to inject fuels into a constant volume spray chamber and fuel sprays are investigated using optical z-type schlieren imaging technique. Higher fuel temperatures are achieved by installing a heater coil on the injector tip with a sleeve in between to avoid possible heat transfer losses. The experimental results show significant effect of superheating on ammonia and gasoline sprays. The liquid and vapor phase are clearly characterized upon flash boiling, resulting in decreased spray tip penetration and areas compared to ambient fuel temperature conditions. The results also show differences between the overall spray geometries of both fuels, and that ammonia sprays are more sensitive to chamber pressure as compared to gasoline.</div></div>
<div class="section abstract"><div class="htmlview paragraph">Hydrogen (H<sub>2</sub>), a potential carbon-neutral fuel, has attracted considerable attention in the automotive industry for transition toward zero-emission. Since the H<sub>2</sub> jet dynamics play a significant role in the fuel/air mixing process of direct injection spark ignition (DISI) engines, the current study focuses on experimental and numerical investigation of a low-pressure H<sub>2</sub> jet to assess its mixing behavior. In the experimental campaign, high-speed z-type schlieren imaging is applied in a constant volume chamber and H<sub>2</sub> jet characteristics (penetration and cross-sectional area) are calculated by MATLAB and Python-based image post-processing. In addition, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach is used in the commercial software Star-CCM+ for numerical simulations. The H<sub>2</sub> jet dynamics is investigated under the effect of nozzle geometry (single-hole, double-hole, and multiple-hole (5-hole)), which constitutes the novelty of the present research, and pressure ratio (PR = injection pressure (P<sub>i</sub>) / chamber pressure (P<sub>ch</sub>)). The results show that the H<sub>2</sub> jet from the single-hole nozzle possesses the fastest penetration and smallest cross-sectional area. On the contrary, the H<sub>2</sub> jet from the double-hole nozzle possesses the slowest penetration and largest cross-sectional area. The H<sub>2</sub> jet from the multiple-hole nozzle shows characteristics between those of the single-hole and double-hole. Overall, since higher pressure ratio and larger jet cross-sectional area lead to higher uniformity of the fuel/air mixture, high-pressure injection with the double-hole nozzle seems more advantageous to attain efficient mixing.</div></div>
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