77 results found
Shariatmadar S, Aleiferis P, Lindstedt R, 2022, Particle Size Distributions in Turbulent Premixed Ethylene Flames Crossing the Soot Inception Limit, Combustion and Flame, ISSN: 0010-2180
Aleiferis P, Shukla J, Brewer M, et al., 2021, Effect of Water Content in Ethanol on Spray Formation at Subcooled and Flash-Boiling Conditions, International Journal of Heat and Mass Transfer, Vol: 182, Pages: 1-18, ISSN: 0017-9310
Aleiferis P, Shukla J, Brewer M, et al., 2021, Spray Development of iso-Octane, Ethanol, Hydrous Ethanol and Water from a Multi-Hole Injector under Ultra Cold Fuel Temperature Conditions, Fuel, Vol: 303, Pages: 1-19, ISSN: 0016-2361
Aleiferis P, Papadopoulos N, 2021, Heat and Mass Transfer Effects in the Nozzle of a Fuel Injector from the Start of Needle Lift to after the End of Injection in the Presence of Fuel Dribble and Air Entrainment, International Journal of Heat and Mass Transfer, Vol: 165, Pages: 1-35, ISSN: 0017-9310
Bontitsopoulos S, Hamzehloo A, Aleiferis P, et al., 2020, Large Eddy Simulations of In-Nozzle Cavitation Phenomena for Cold Fuel Injection, ASME 2020 Power Conference, Publisher: The American Society of Mechanical Engineers
Bontitsopoulos S, Hamzehloo A, Aleiferis P, et al., 2020, Numerical Simulations of the Effect of Cold Fuel Temperature on In-Nozzle Flow and Cavitation Using a Model Injector Geometry, SAE Technical Papers, ISSN: 0148-7191
Large Eddy Simulations (LES) were performed using a 3D model of a step nozzle injector. The focus has been on modelling injections with pentane, chosen as a representative single component of the high-volatility components in gasoline. The influence of fuel temperature was investigated with comparisons primarily made between 20 deg C and -10 deg C. The test cases provided a description of the in-nozzle cavitating flow and the macroscopic near-nozzle spray jet structure across different cavitation regimes in order to shed light on engine cold-start effects, a phenomenon prevalent in a number of combustion applications, albeit not extensively studied. The results showed that the size and intensity of the cavitation features tend to become suppressed as the temperature of the fuel decreases. The 20 deg C cases (supercavitating regime) depicted a sporadic shedding of vapour nuclei from a continuous cavitation region that extended to the nozzle outlet surface. Collapse-induced wave dynamics in that region caused a transient entrainment of air from the discharge chamber towards the nozzle inlet. The extent of air entrainment appeared noticeably reduced at the coldest temperature of -10 deg C (incipient cavitation regime) due to the shorter length of the cavitation region, which impeded the backflow of air. Temporally averaged data showed that the near-nozzle jet appearance was also affected by the fuel temperature. The -10 deg C case produced a relatively symmetric jet, in contrast to the supercavitating cases that demonstrated an increased opening angle and a concave surface on the side of the step nozzle edge due to the intense cavitation and parallel air entrainment.
Smith JK, Roberts P, Kountouriotis A, et al., 2020, Thermodynamical Modelling of a Stratified Charge Spark Ignition Engine, International Journal of Engine Research, Vol: 21, Pages: 801-810, ISSN: 1468-0874
Combustion of a charge with spatially and temporally varying equivalence ratio in a spark ignition engine was modelled using the Leeds University Spark Ignition Engine quasi-dimensional thermodynamic code. New sub-models have been integrated into Leeds University Spark Ignition Engine that simulate the effect of burnt gas expansion and turbulent mixing on an initial equivalence ratio distribution. Realistic distribution functions were used to model the radially varying equivalence ratio. The new stratified fuel model was validated against experimental data, showing reasonable agreement for both the pressure trace and percentage heat released. Including the effect of turbulent mixing was found to be important to reproduce the trend in the differences between the stratified and homogeneous simulations.
Price C, Hamzehloo A, Aleiferis P, et al., 2020, Numerical Modelling of Droplet Breakup for Flash-Boiling Fuel Spray Predictions, International Journal of Multiphase Flow, Vol: 125, ISSN: 0301-9322
Flash-boiling of fuel sprays can occur under injection of superheated fuel into ambient pressure that is lower than the saturation pressure of the fuel and can dramatically alter spray formation due to complex two-phase flow effects and rapid droplet evaporation phenomena. Such phenomena exist in-cylinder at low-load in-city driving conditions where strict engine emission regulations apply, hence the need for faithful flash-boiling fuel spray models by engine designers. To enhance the current modelling capability of superheated fuel sprays, with focus on near-nozzle plume expansion, a flash-boiling breakup modelling approach was developed to introduce the thermal breakup mechanism of droplets caused by nucleation and bubble growth. This model was particularly aimed at sprays where levels of superheat introduced noticeable radial expansion of the plumes upon discharge from the nozzle orifice. The model was able to simulate droplet shattering by introducing Lagrangian child parcels at breakup sites with additional radial velocity components instigated by rapid bubble growth and surface instabilities. Combination of the flash-boiling droplet breakup model with a flash-boiling effective nozzle model that was used as boundary condition for the spray plumes offered a more complete modelling approach, where both in-nozzle phase change effects and near-nozzle flashing through droplet shattering were incorporated into the Eulerian-Lagrangian two-phase computational framework. Sensitivity studies were carried out to investigate important parameters which are inherently difficult to measure experimentally and offered valuable insight into modelling superheated sprays. The model was able to capture important flash-boiling spray characteristics and quantitative validation was achieved through comparison to experimental data in the form of penetration lengths and droplet sizes with a good level of agreement.
Hamzehloo A, Aleiferis P, 2019, 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, Vol: 76, Pages: 309-334, ISSN: 0142-727X
A density-based solver with the classical fourth-order accurate Runge-Kutta temporal discretization scheme wasdeveloped and applied to study under-expanded jets issued through millimeter-size nozzles for applications in highpressuredirect-injection (DI) gaseous-fuelled propulsion systems. Both large eddy simulation (LES) and ReynoldsaveragedNavier-Stokes (RANS) turbulence modelling techniques were used to evaluate the performance of the newcode. The computational results were compared both quantitatively and qualitatively against available data from theliterature. After initial evaluation of the code, the computational framework was used in conjunction with RANSmodelling (k-ω SST) to investigate the effect of nozzle exit geometry on the characteristics of gaseous jets issued frommillimeter-size nozzles. Cylindrical nozzles with various length to diameter ratios, namely 5, 10 and 20, in addition toa diverging conical nozzle, were studied. This study is believed to be the first to provide a direct comparison betweenRANS and LES within the context of nozzle exit profiling for advanced high-pressure injection systems with theformation of under-expanded jets. It was found that reducing the length of the straight section of the nozzle by 50%resulted in a slightly higher level of under-expansion (~2.6% higher pressure at the nozzle exit) and ~1% higher massflow rate. It was also found that a nozzle with 50% shorter length resulted in ~6% longer jet penetration length. At aconstant nozzle pressure ratio (NPR), a lower nozzle length to diameter ratio resulted in a noticeably higher jetpenetration. It was found that with a diverging conical nozzle, a fairly higher penetration length could be achieved if anunder-expanded jet formed downstream of the nozzle exit compared to a jet issued from a straight nozzle with the sameNPR. This was attributed to the radial restriction of the flow and consequently formation of a relatively smallerreflected shock angle. With the conical
Smith JK, Ruprecht D, Kountouriotis A, et al., 2019, A Comparison of EGR Correction Factor Models Based on SI Engine Data, SAE International Journal of Engines, Vol: 12, Pages: 203-217, ISSN: 1946-3944
The article compares the accuracy of different exhaust gas recirculation (EGR) correction factor models under engine conditions. The effect of EGR on the laminar burning velocity of a EURO VI E10 specification gasoline (10% Ethanol content by volume) has been back calculated from engine pressure trace data, using the Leeds University Spark Ignition Engine Data Analysis (LUSIEDA) reverse thermodynamic code. The engine pressure data ranges from 5% to 25% EGR (by mass) with the running conditions, such as spark advance and pressure at intake valve closure, changed to maintain a constant engine load of 0.79 MPa gross mean effective pressure (GMEP). Based on the experimental data, a correlation is suggested on how the laminar burning velocity reduces with increasing EGR mass fraction. This correlation, together with existing models, was then implemented into the quasi-dimensional Leeds University Spark Ignition Engine (LUSIE) predictive engine code and resulting predictions are compared against measurements. It was found that the new correlation is in good agreement with experimental data for a diluent range of 5%-25%, providing the best fit for both engine loads investigated, whereas existing models tend to overpredict the reduction of burning velocity due to EGR.
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
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.
Roberts P, Kountouriotis A, Okroj P, et al., 2018, Effects of Valve Deactivation on Thermal Efficiency in a Direct-Injection Spark-Ignition Engine under Dilute Conditions, SAE Technical Paper Series, Vol: 2018, ISSN: 0148-7191
Reported in the current paper is a study into the cycle efficiency effects of utilising a complex valvetrain mechanism in order to generate variable in-cylinder charge motion and therefore alter the dilution tolerance of a Direct Injection Spark Ignition (DISI) engine.A Jaguar Land Rover Single Cylinder Research Engine (SCRE) was operated at a number of engine speeds and loads with the dilution fraction varied accordingly (excess air (lean), external Exhaust Gas Residuals (EGR) or some combination of both). For each engine speed, load and dilution fraction, the engine was operated with either both intake valves fully open - Dual Valve Actuation (DVA) - or one valve completely closed - Single Valve Actuation (SVA) mode.The engine was operated in DVA and SVA modes with EGR fractions up to 20% with the excess air dilution (Lambda) increased (to approximately 1.8) until combustion stability was duly compromised. At 1500 Revolutions Per Minute (RPM), 3.6 bar and 7.9 bar Gross Mean effective Pressure (GMEP), the dilution tolerance of the engine was significantly increased for a given combustion stability limit utilising SVA. This resulted in fuel consumption reductions of up to 3.8% and 3.1% respectively for these two engine speed and load conditions as a result of being able to operate the engine with more thermodynamically attractive mixtures when adopting SVA. At 2000RPM, 9.8 bar GMEP, the dilution tolerance was only marginally increased which resulted in a fuel consumption reduction of 1.3% when adopting SVA over DVA (for the same reasons outlined above).Increased dilution tolerance in all cases was achieved as a result of significant enhancement in charge motion when adopting SVA. By enhancing the in-cylinder charge motion (confirmed using Computational Fluid Dynamics (CFD)), ignition to 10% Mass Fraction Burned (MFB) and 10-90% MFB durations for equivalent levels of dilution were significantly shorter when adopting SVA. This therefore allowed greater dilution tolera
Aleiferis PG, Behringer MK, Malcolm JS, 2017, Integral Length Scales and Time Scales of Turbulence in an Optical Spark-Ignition Engine, Flow, Turbulence and Combustion, Vol: 98, Pages: 523-577, ISSN: 1573-1987
Price C, Hamzehloo A, Aleiferis P, et al., 2016, An Approach to Modelling Flash-Boiling Fuel Sprays for Direct-Injection Spark-Ignition Engines, Atomization and Sprays, Vol: 26, Pages: 1197-1239, ISSN: 1936-2684
Aleiferis PG, Behringer MK, OudeNijeweme D, et al., 2016, Insights into Stoichiometric and Lean Combustion Phenomena of Gasoline–Butanol, Gasoline–Ethanol, iso-Octane–Butanol and iso-Octane–Ethanol Blends in an Optical SI Engine, Combustion Science and Technology, Vol: 189, Pages: 1013-1060, ISSN: 1563-521X
Introduction of novel fuels, such as mixtures of ethanol or butanol with hydrocarbons, requires new fundamental understanding of in-cylinder combustion properties in modern direct-injection spark-ignition engines since those can be quite sensitive to fuel properties. Gasoline and its blends with 25% ethanol and butanol at 25% and 16% per volume (the latter equivalent to 10% ethanol blending ratio in terms of oxygen content) were studied in comparison to gasoline, ethanol, and butanol combustion. The same alcohol blending ratios were also employed with iso-octane as the base component for direct comparison. Testing was performed at 1500 RPM with 0.5 bar intake plenum pressure using 20°C or 80°C engine coolant temperature. Thermodynamic parameters were derived using in-cylinder pressure analysis for stoichiometric (ϕ = 1.0) and lean (ϕ = 0.83) fueling over a range of spark advances. Additionally, high speed color and greyscale chemiluminescence imaging was conducted at gasoline’s maximum break torque spark timing, calculating flame growth speeds, flame roundness, and centroid motion. Laminar burning velocity data from the literature and in-cylinder flow measurements from the same engine were used for interpretation. Overall, the analysis showed small differences between gasoline and the blends in general, but showed changes for the pure alcohols with typically much faster flame progression for ethanol and issues with the combustion stability of butanol at low engine temperatures. Alcohol blending, particularly with iso-octane, showed some benefits at lean conditions.
Aleiferis PG, Behringer MK, 2016, Modulation of Integral Length Scales of Turbulence in an Optical SI Engine by Direct Injection of Gasoline, iso-Octane, Ethanol and Butanol Fuels, Fuel, Vol: 189, Pages: 238-259, ISSN: 1873-7153
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
Hamzehloo A, Aleiferis PG, 2016, Gas Dynamics and Flow Characteristics of 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: 1879-3487
The current study used large eddy simulations to investigate the sonic and mixing characteristics of turbulent under-expanded hydrogen and methane jets with various nozzle pressure ratios issued into various ambient pressures including elevated conditions relevant to applications in direct injection gaseous-fuelled internal combustion engines. Due to the relatively low density of most gaseous fuels such as hydrogen and methane, DI requires high injection pressures to achieve suitable mass flow rates for fast in-cylinder fuel delivery and rapid fuel-air mixing. Such pressures typically form an under-expanded fuel jet past the nozzle exit. Test cases of hydrogen injection with nozzle pressure ratio (NPR) of 10 issued into quiescent air with pressure P∞ ≈ 1, 5 and 10 bar were simulated. Direct comparison between hydrogen and methane jets with NPR = 8.5 and P∞ ≈ 1 was also made. The effect of ambient pressure on features of transient development of the near-nozzle shock structure and tip vortices (vortex ring) was investigated. It was observed that at constant NPR, higher ambient pressure resulted in slightly faster formation of the Mach reflection and shorter Mach disk settlement time. Different mechanisms were observed between hydrogen and methane with regards to transient formation of their initial tip vortex rings. It was found that the initial transient tip vortices of hydrogen jets may also contribute to the flow instabilities at the boundary of the intercepting shock and, unlike for methane, promote fuel-air mixing before the Mach reflection. It was also shown that the near-nozzle shock structure was only affected by NPR regardless of the ambient pressure. Furthermore, no flow recirculation zone was found just downstream of the Mach disk, a finding comparable to all previous experimental investigations. Also, it was observed that a locally richer mixture was created for jets with higher NPR or with higher ambient pressure at constant NPR.
Aleiferis PG, Behringer MK, 2015, Flame front analysis of ethanol, butanol, iso-octane and gasoline in a spark-ignition engine using laser tomography and integral length scale measurements, Combustion and Flame, Vol: 162, Pages: 4533-4552, ISSN: 0010-2180
Direct-injection spark-ignition engines have become popular due to their flexibility in injection strategies and higher efficiency; however, the high-pressure in-cylinder injection process can alter the airflow field by momentum exchange, with different effects for fuels of diverse properties. The current paper presents results from optical studies of stoichiometric combustion of ethanol, butanol, iso-octane and gasoline in a direct-injection spark-ignition engine run at 1500 RPM with 0.5 bar intake plenum pressure and early intake stroke fuel injection for homogeneous mixture preparation. The analysis initially involved particle image velocimetry measurements of the flow field at ignition timing with and without fuelling for comparison. Flame chemiluminescence imaging was used to characterise the global flame behaviour and double-pulsed Laser-sheet flame tomography by Mie scattering to quantify the local topology of the flame front. The flow measurements with fuel injection showed integral length scales of the same order to those of air only on the tumble plane, but larger regions with scales up to 9 mm on the horizontal plane. Averaged length scales over both measurement planes were between 4 and 6 mm, with ethanol exhibiting the largest and butanol the smallest. In non-dimensional form, the integral length scales were up to 20% of the clearance height and 5–12% of the cylinder bore. Flame tomography showed that at radii between 8 and 12 mm, ethanol was burning the fastest, followed by butanol, iso-octane and gasoline. The associated turbulent burning velocities were 4.6–6.5 times greater than the laminar burning velocities and about 13–20% lower than those obtained by flame chemiluminescence imaging. Flame roundness was 10–15% on the tomography plane, with largest values for ethanol, followed by butanol, gasoline and iso-octane; chemiluminescence imaging showed larger roundness (18–25%), albeit with the same order amongst fuels. The
Papadopoulos N, Aleiferis P, 2015, Numerical Modelling of the In-Nozzle Flow of a Diesel Injector with Moving Needle during and after the End of a Full Injection Event, SAE International Journal of Engines, Vol: 8, Pages: 2285-2302, ISSN: 1946-3944
The design of a Diesel injector is a key factor in achieving higher engine efficiency. The injector's fuel atomisation characteristics are also critical for minimising toxic emissions such as unburnt Hydrocarbons (HC). However, when developing injection systems, the small dimensions of the nozzle render optical experimental investigations very challenging under realistic engine conditions. Therefore, Computational Fluid Dynamics (CFD) can be used instead. For the present work, transient, Volume Of Fluid (VOF), multiphase simulations of the flow inside and immediately downstream of a real-size multi-hole nozzle were performed, during and after the injection event with a small air chamber coupled to the injector downstream of the nozzle exit. A Reynolds Averaged Navier-Stokes (RANS) approach was used to account for turbulence. Grid dependency studies were performed with 200k-1.5M cells. Both k-ε and k-ω SST models were considered in the validation process, with the k-ω SST found to predict better the injector's flow rate. The cavitation models of Schnerr-Sauer and the Zwart-Gerber-Belamri were employed for validation against optical data of cavitation in a simplified nozzle geometry obtained from the literature. The Schnerr-Sauer model was in better agreement with the experiments, hence this model was subsequently employed for the real injector simulations. The motion of the injector needle was modeled by a dynamic grid methodology. An injection pressure of 400 bar was applied at the inlet of the injector. Two outlet pressures were examined, 60 bar and 1 bar. The results showed that the flow was far from steady-state during the injection event and that hysteresis existed between the needle opening and closing phases. This indicated the importance of transient simulations, contrary to widely-used steady state simulations at fixed needle lifts. The two outlet pressures resulted in very different final states of the flow-field in the nozzle. Specifica
Butcher AJ, Aleiferis PG, Richardson D, 2015, Characterisation of Spray Development from Spark-Eroded and Laser-Drilled Multihole Injectors in an Optical DISI Engine and in a Quiescent Injection Chamber, SAE Technical Paper Series, Vol: 2015, ISSN: 0148-7191
This paper addresses the need for fundamental understanding of the mechanisms of fuel spray formation and mixture preparation in direct injection spark ignition (DISI) engines. Fuel injection systems for DISI engines undergo rapid developments in their design and performance, therefore, their spray breakup mechanisms in the physical conditions encountered in DISI engines over a range of operating conditions and injection strategies require continuous attention. In this context, there are sparse data in the literature on spray formation differences between conventionally drilled injectors by spark erosion and latest Laser-drilled injector nozzles. A comparison was first carried out between the holes of spark-eroded and Laser-drilled injectors of same nominal type by analysing their in-nozzle geometry and surface roughness under an electron microscope. Then the differences in their spray characteristics under quiescent conditions, as well as in a motoring optical engine, are discussed on the basis of high-speed imaging experiments and image processing methods. Specifically, the spray development mechanism was quantified by spray tip penetration and cone angle data under a range of representative low-load and high-low engine operating conditions (0.5 bar and 1.0 bar absolute, respectively), as well as at low and high injector body temperatures (20 °C and 90 °C) to represent cold and warm engine-head conditions. Droplet sizing was also performed with the two injectors using Phase Doppler Anemometry in a quiescent chamber.
Price C, Hamzehloo A, Aleiferis PG, et al., 2015, Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays, SAE Technical Paper Series, ISSN: 0148-7191
Aleiferis P, Charalambides A, Hardalupas Y, et al., 2015, Schlieren-based temperature measurement inside the cylinder of an optical spark ignition and homogeneous charge compression ignition engine, Applied Optics, Vol: 54, Pages: 4566-4579, ISSN: 1559-128X
Aleiferis PG, van Romunde ZR, Larson G, et al., 2015, On the Effect of Ambient Turbulence and Thermodynamic Conditions on Fuel Spray Development for Direct-Injection Spark-Ignition Engines, Flow, Turbulence and Combustion, Vol: 95, Pages: 29-60, ISSN: 1573-1987
High-pressure multi-hole injectors for direct-injection spark-ignition engines offer certain flexibility in spray directionality by selecting the number and angle of the nozzle’s holes to suit the design of a particular combustion chamber. However, the spray’s pattern can change significantly for injector-body temperatures representative of real engine operation at low-load conditions with injection strategies in the early intake stroke. This is due to rapid phase change effects from flash boiling of the high-volatility components of gasoline. This work presents results from an optical investigation into the effects of injector-body temperature and back pressure on the pattern of spray formation, especially when coupled to different levels of ambient turbulence. Specifically, gasoline and iso-octane fuels were tested in the range of 20–120 °C injector-body temperatures and for ambient pressures of 0.5–5.0 bar. Additionally, the ambient turbulence was varied in the range 0–4 m/s to observe its effect on flash-boiling and non-flash-boiling sprays. Results from a combination of high-speed shadowgraphy and simultaneous Schlieren and Mie scattering optical techniques are presented in terms of imaged spray areas and plume penetration. Calculations of the Stokes number are also discussed with respect to turbulence and fuel properties. The results demonstrate a marginal effect of the degree of turbulence intensity on non-flash-boiling sprays that maintained their nominal plume directionality throughout the injection event. However, a significant effect on the spray’s penetration and mixing at conditions of fuel flash-boiling was observed with increasing levels of turbulence intensity; the collapsed pattern of the spray’s formation exhibited much faster dispersion and mixing.
Aleiferis PG, Behringer MK, OudeNijeweme D, et al., 2015, Spray Imaging and Droplet Sizing of Spark-Eroded and Laser-Drilled Injectors with Gasoline-Butanol and Gasoline-Ethanol Blends, International Conference on Fuel Systems for IC Engines, Pages: 179-198
Charalambides AG, Hardalupas Y, Soulopoulos N, et al., 2015, Using Infrared Laser Absorption to Measure Hydrocarbon Concentration in a Lean-Burn, Stratified-Charge, Spark-Ignition Engine, Combustion Science and Technology, Vol: 187, Pages: 679-696, ISSN: 1563-521X
The operating range of lean-burn spark-ignition (SI) engines is limited by the cycle-to-cycle variability of the fuel concentration at or near the spark plug at ignition timing. An experimental investigation was undertaken to measure the temporal and spatial distribution of hydrocarbon (HC) concentration in a spark-ignition engine, using the infrared (IR) laser absorption at 3392 nm. The purposes were to establish whether there is a correlation between time-resolved HC measurements for a range of global air-to-fuel (A/F) ratios (A/F = 15.5–23) with the strength of the firing stroke and to establish how this varies with fuel port-injection strategies against either open (injection timing 30° crank angle (CA) after intake top dead center) or closed-valves (injection timing 180°CA after intake top dead center), respectively resulting in stratified and near-homogeneous charge distributions. The results showed that IR line-of-sight (LOS) averaged A/F ratio measurements yielded a good agreement with the global A/F ratio readings obtained by the linear air-to-fuel (LAF) zirconia-based sensor. Furthermore, the cyclic variability of the measurements of the fuel concentration increased with increasing A/F ratio. At A/F = 23, closed-valve injection strategy resulted in small spatial stratification of the fuel charge with an ensemble-averaged correlation coefficient of fluctuations of the IR LOS A/F ratios with fluctuations of peak in-cylinder pressure of 0.37. For open-valve injection strategy, which resulted in axial fuel mixture charge-stratification but no radial charge-stratification, a maximum correlation coefficient of the IR LOS A/F ratios with fluctuations of peak pressure of 0.34 was measured (at the measurement location closest to the spark). This correlation was reduced to 0.17 at locations furthest from the spark plug. Finally, results showed that at A/F = 23, fuel stratification can be used to control lean-burn SI combustion, while at A/F = 15.5, no
Aleiferis PG, Ashrafi-Nik M, Ladommatos N, et al., 2014, A Study of Droplet Collision Modelling for Spray Formation and Mixing with a Two-Row Group-Hole Injection Nozzle for Diesel Engines, Atomization and Sprays, Vol: 24, Pages: 1089-1135, ISSN: 1936-2684
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
Burning hydrogen in conventional internal combustion (IC) engines is associated with zero carbon-based tailpipe exhaust emissions. In order to obtain high volumetric efficiency and eliminate abnormal combustion modes such as preignition and backfire, in-cylinder direct injection (DI) of hydrogen is considered preferable for a future generation of hydrogen IC engines. However, hydrogen's low density requires high injection pressures for fast hydrogen penetration and sufficient in-cylinder mixing. Such pressures lead to chocked flow conditions during the injection process which result in the formation of turbulent under-expanded hydrogen jets. In this context, fundamental understanding of the under-expansion process and turbulent mixing just after the nozzle exit is necessary for the successful design of an efficient hydrogen injection system and associated injection strategies. The current study used large eddy simulation (LES) to investigate the characteristics of hydrogen under-expanded jets with different nozzle pressure ratios (NPR), namely 8.5, 10, 30 and 70. A test case of methane injection with NPR = 8.5 was also simulated for direct comparison with the hydrogen jetting under the same NPR. The near-nozzle shock structure, the geometry of the Mach disk and reflected shock angle, as well as the turbulent shear layer were all captured in very good agreement with data available in the literature. Direct comparison between hydrogen and methane fuelling showed that the ratio of the specific heats had a noticeable effect on the near-nozzle shock structure and dimensions of the Mach disk. It was observed that with methane, mixing did not occur before the Mach disk, whereas with hydrogen high levels of momentum exchange and mixing appeared at the boundary of the intercepting shock. This was believed to be the effect of the high turbulence fluctuations at the nozzle exit of the hydrogen jet which triggered Gortler vortices. Generally, the primary mixing was observed to
Serras-Pereira J, Aleiferis PG, Richardson D, 2014, An Experimental Database on the Effects of Single- and Split-Injection Strategies on Spray formation and Spark Discharge in an Optical Direct-Injection Spark-Ignition Engine Fuelled with Gasoline, iso-Octane and Alcohols, International Journal of Engine Research, Vol: 16, Pages: 851-896, ISSN: 1468-0874
This article presents results from a comprehensive optical study of a direct-injection spark-ignition research engine running on gasoline, iso-octane, ethanol, n-butanol and E10 fuels injected from a multi-hole central vertically positioned injector. The analysis was based on images of spray development, spark discharge and combustion to understand the effects of early and late injection strategies on in-cylinder phenomena. Specifically, `single'-injection strategies from early to late intake stroke as well as multiple `split' injection events with triple pulses in the early intake stroke or double pulses in the intake stroke and late compression stroke were investigated. The engine was run at 1500 r/min at part- and full-load conditions (0.5 and 1.0 bar inlet plenum pressure, respectively). Engine coolant temperatures of 20°C–90°C were employed to understand how fuel volatility was related to the phenomena observed. The sprays were imaged over a series of cycles primarily by laser sheet illumination on one vertical and two horizontal planes to identify three-dimensional aspects of the spray's development and its interactions with the incoming flow, valves, piston and liner. There was a clear fuel-impingement trade-off between early and late injection timings. The spark discharge was also imaged with all injection strategies and clear differences were observed. Selective combustion imaging provided insights into the flame's growth and motion with early and double early–late split injection strategies. The double earlylate injection strategy demonstrated the potential for control of the mixture formation and flow field over the early flame development stage of combustion.
Behringer M, Aleiferis P, OudeNijeweme D, et al., 2014, Spray Formation from Spark-Eroded and Laser-Drilled Injectors for DISI Engines with Gasoline and Alcohol Fuels, SAE International Journal of Fuels and Lubricants, Vol: 7, Pages: 803-822, ISSN: 1946-3952
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