10 results found
Price C, Hamzehloo A, Aleiferis P, et al., 2018, Numerical modelling of fuel spray formation and collapse from multi-hole injectors under flash-boiling conditions, Fuel, Vol: 221, Pages: 518-541, ISSN: 0016-2361
© 2018 Elsevier Ltd Flash-boiling of fuel sprays can occur when the fuel enters a metastable superheated state, which is common in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or hot fuel temperatures. The effect of flash-boiling on the resultant spray formation can be both detrimental and advantageous to engine operation, hence numerical modelling capability is essential in future engine optimisation and design. A recently-developed new model by the current authors that can be applied as zero-dimensional boundary condition for multi-hole flash-boiling fuel spray predictions was investigated over a wide range of injection systems, focusing on the model's ability to quantify in-nozzle phase change effects and automatically predict important global spray characteristics such as spray collapse, droplet recirculation and plume merging within a Lagrangian particle tracking framework. Mesh-type sensitivity was highlighted using a uniform Cartesian and a non-uniform polyhedral mesh. The model was also normalised through a dimensionless parameter for a wide range of single component fuels. The model was validated both qualitatively and, where possible, quantitatively against experimental data. The model's ability to deal with a wide range of injection configurations and operating conditions was confirmed and a number of limitations are highlighted and discussed with respect to future work.
Hamzehloo A, Aleiferis PG, 2016, Gas dynamics and flow characteristics of highly turbulent under-expanded hydrogen and methane jets under various nozzle pressure ratios and ambient pressures, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 41, Pages: 6544-6566, ISSN: 0360-3199
Hamzehloo A, Aleiferis PG, 2016, Numerical modelling of transient under-expanded jets under different ambient thermodynamic conditions with adaptive mesh refinement, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 61, Pages: 711-729, ISSN: 0142-727X
Price C, Hamzehloo A, Aleiferis P, et al., 2016, AN APPROACH TO MODELING FLASH-BOILING FUEL SPRAYS FOR DIRECT-INJECTION SPARK-IGNITION ENGINES, Atomization and Sprays, Vol: 26, Pages: 1197-1239, ISSN: 1044-5110
Price C, Hamzehloo A, Aleiferis P, et al., 2015, Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays, SAE Technical Papers, Vol: 2015
Copyright © 2015 SAE International. Flash-boiling of sprays may occur when a superheated liquid is discharged into an ambient environment with lower pressure than its saturation pressure. Such conditions normally exist in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or high fuel temperatures. The addition of novel high volatile additives/fuels may also promote flash-boiling. Fuel flashing plays a significant role in mixture formation by promoting faster breakup and higher fuel evaporation rates compared to non-flashing conditions. Therefore, fundamental understanding of the characteristics of flashing sprays is necessary for the development of more efficient mixture formation. The present computational work focuses on modelling flash-boiling of n-Pentane and iso-Octane sprays using a Lagrangian particle tracking technique. First an evaporation model for superheated droplets is implemented within the computational framework of STAR-CD, along with a full set of temperature dependent fuel properties. Then the computational tool is used to model the injection of flashing sprays through a six-hole asymmetric injector. The computational results are validated against optical experimental data obtained previously with the same injector by high-speed imaging techniques. The effects of ambient pressure (0.5 and 1.0 bar) and fuel temperature (20-180° C) on the non-flashing and flashing characteristics are examined. Effects of initial droplet size and break-up sub-models are also investigated. The computational methodology is able to reproduce important physical characteristics of flash-boiling sprays like the onset and extent of spray collapse. Based on the current observations, further improvements to the mathematical methodology used for the flash-boiling model are proposed.
Hamzehloo A, Aleiferis P, 2014, Numerical Modelling of Mixture Formation and Combustion in DISI Hydrogen Engines with Various Injection Strategies, SAE Technical Papers, Vol: 2014-October
Copyright © 2014 SAE International. International obligations to reduce carbon dioxide emissions and requirements to strengthen security of fuel supply, indicate a need to diversify towards the use of cleaner and more sustainable fuels. Hydrogen has been recommended as an encouraging gaseous fuel for future road transportation since with reasonable modifications it can be burned in conventional internal combustion engines without producing carbon-based tailpipe emissions. Direct injection of hydrogen into the combustion chamber can be more preferable than port fuel injection since it offers advantages of higher volumetric efficiency and can eliminate abnormal combustion phenomena such as backfiring. The current work applied a fully implicit computational methodology along with the Reynolds-Averaged Navier-Stokes (RANS) approach to study the mixture formation and combustion in a direct-injection spark-ignition engine with hydrogen fuelling. Hydrogen was issued into the combustion chamber by a six-hole side-mounted injector. The effects of two injection strategies, namely single and double-pulse injections per cycle, were examined whilst maintaining an equivalence ratio of 0.5 at part-load conditions of 0.5 bar intake pressure at 1,000 RPM. The combustion process was also computed using a 'partially-premixed homogeneous reactor' approach in conjunction with a detailed chemical kinetics combustion solver. The results were discussed in relation to previously published work on in-cylinder experiments of hydrogen engines.
Hamzehloo A, Aleiferis PG, 2014, Large eddy simulation of highly turbulent under-expanded hydrogen and methane jets for gaseous-fuelled internal combustion engines, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 39, Pages: 21275-21296, ISSN: 0360-3199
Hamzehloo A, Aleiferis PG, 2014, Large Eddy Simulation of Near-Nozzle Shock Structure and Mixing Characteristics of Hydrogen Jets for Direct-Injection Spark-Ignition Engines, 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2014)
Hamzehloo A, Aleiferis P, 2013, Computational study of hydrogen direct injection for internal combustion engines, SAE Technical Papers, Vol: 11
Hydrogen has been largely proposed as a possible fuel for internal combustion engines. The main advantage of burning hydrogen is the absence of carbon-based tailpipe emissions. Hydrogen's wide flammability also offers the advantage of very lean combustion and higher engine efficiency than conventional carbon-based fuels. In order to avoid abnormal combustion modes like pre-ignition and backfiring, as well as air displacement from hydrogen's large injected volume per cycle, direct injection of hydrogen after intake valve closure is the preferred mixture preparation method for hydrogen engines. The current work focused on computational studies of hydrogen injection and mixture formation for direct-injection spark-ignition engines. Hydrogen conditions at the injector's nozzle exit are typically sonic. Initially the characteristics of under-expanded sonic hydrogen jets were investigated in a quiescent environment using both Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) techniques. Various injection conditions were studied, including a reference case from the literature. Different nozzle geometries were investigated, including a straight nozzle with fixed cross section and a stepped nozzle design. LES captured details of the expansion shocks better than RANS and demonstrated several aspects of hydrogen's injection and mixing. In-cylinder simulations were also performed with a side 6-hole injector using 70 and 100 bar injection pressure. Injection timing was set to just after inlet valve closure with duration of 6 s and 8 s, leading to global air-to-fuel equivalence ratios φ typically in the region of 0.2-0.4. The engine intake air pressure was set to 1.5 bar absolute to mimic boosted operation. It was observed that hydrogen jet wall impingement was always prominent. Comparison with non-fuelled engine conditions demonstrated the degree of momentum exchange between in-cylinder hydrogen injection and air motion. LES highlighted details of hydrog
Hamzehloo A, Aleiferis P, LES and RANS Modelling of Under-Expanded Jets with Application to Gaseous Fuel Direct Injection for Advanced Propulsion Systems, International Journal of Heat and Fluid Flow, ISSN: 0142-727X
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