| 51. |
- Ghanaati, Ali, 1979, et al.
(författare)
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A Comparative Study on Knock Occurrence for Different Fuel Octane Number
- 2018
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2018-September:September
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Tidskriftsartikel (refereegranskat)abstract
- Combustion with knock is an abnormal phenomenon which constrains the engine performance, thermal efficiency and longevity. The advance timing of the ignition system requires it to be updated with respect to fuel octane number variation. The production series engines are calibrated by the manufacturer to run with a special fuel octane number. In the experiment, the engine was operated at different speeds, loads, spark advance timings and consumed commercial gasoline with research octane numbers (RON) 95, 97 and 100. A 1-dimensional validated engine combustion model was run in the GT-Power software to simulate the engine conditions required to define the knock envelope at the same engine operation conditions as experiment. The knock intensity investigation due to spark advance sweep shows that combustion with noise was started after a specific advance ignition timing and the audible knock occur by increasing the advance timing. Therefore, the engine operation was divided into three regions; knock-free, light knock and heavy knock. The results for heavy-knock were well suited to audible knock detected by knock sensor. The simulation results from knock model divide the engine operation into two regions; normal combustion and knock region. The knock region was well suited to light-knock and heavy-knock which has been defined using experimental results. Next, an artificial neural network (ANN) model has been designed to classify the different RONs using engine rotational speed signal. The model classified different RONs accurately after starting point of noisy combustion (light-knock). This point defined from experimental results and was well suited with starting point of knock index increment from simulation results. The simulation tool ability to predict the knock envelope will reduce the experimental cost and time to generate the spark timing look-up table.
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| 52. |
- Golovitchev, Valeri, 1945, et al.
(författare)
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CFD COMBUSTION AND EMISSION FORMATION MODELING FOR A HSDI DIESEL ENGINE USING DETAILED CHEMISTRY
- 2006
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Ingår i: ASME 2006 Internal Combustion Engine Division Fall Technical Conference, ICEF 2006. ; , s. 349-358
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Konferensbidrag (refereegranskat)abstract
- In order to comply with current emissions regulations, a detailed analysis of the combustion and emission formation processes in the Diesel engines accounting for the effect of the main operating parameters is required. The present study is based both on 0D and 3D numerical simulations by compiling 0D chemical kinetics calculations for Diesel oil surrogate combustion and emission (soot, NOx) formation mechanisms to construct a φ-T (equivalence ratio - temperature) parametric map. In this map, the regions of emissions formation are depicted defining a possible optimal path between the regions by placing on the same map the engine operation conditions represented by the computational cells, whose parameters (equivalence ratio and temperature) are calculated by means of 3D engine modelling. Unlike previous approaches based on static parametric φ-T maps to analyze different combustion regimes and emission formations in Diesel engines, the present paper focuses on a construction of dynamic φ-T maps, in which the pressures and the elapsed times were taken in compliance with those calculated in the 3D engine simulations. The 0D chemical kinetics calculations have been performed by the SENKIN code of the Chemkin-2 library. In-cylinder conditions represented by computational cells with known φ and T are predicted using KIVA-3V code. When cells are plotted on the map, they identify the trajectories helping to navigate between the emissions regions by varying hardware and injection parameters. Sub-models of the KIVA-3V, rel. 2 code has been modified including spray atomization, droplet collision and evaporation, accounting for multi-component fuel vapor coupled with the improved versions of the chemistry/turbulence interaction model and new formulation of the combustion kinetics for the diesel oil surrogate (consisting in 70 species participating in 310 reactions). Simulations were performed for the HSDI 1.300 Fiat Diesel engine at optimized engine operating conditions and pilot injections. Finally, numerical results are compared with the experimental data on in-cylinder pressure, Rate of Heat Release, RoHR, and selected species distributions.
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| 53. |
- Grönstedt, Tomas, 1970, et al.
(författare)
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Design Considerations of Low Bypass Ratio Mixed Flow Turbofan Engines with Large Power Extraction
- 2022
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Ingår i: Fluids. - : MDPI AG. - 2311-5521. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of extracting large amounts of electrical power from turbofan engines is becoming increasingly desirable from an aircraft perspective. The power consumption of a future fighter aircraft is expected to be much higher than today's fighter aircraft. Previous work in this area has concentrated on the study of power extraction for high bypass ratio engines. This motivates a thorough investigation of the potential and limitations with regards to performance of a low bypass ratio mixed flow turbofan engine. A low bypass ratio mixed flow turbofan engine was modeled, and key parts of a fighter mission were simulated. The investigation shows how power extraction from the high-pressure turbine affects performance of a military engine in different parts of a mission within the flight envelope. An important conclusion from the analysis is that large amounts of power can be extracted from the turbofan engine at high power settings without causing too much penalty on thrust and specific fuel consumption, if specific operating conditions are fulfilled. If the engine is operating (i) at, or near its maximum overall pressure ratio but (ii) further away from its maximum turbine inlet temperature limit, the detrimental effect of power extraction on engine thrust and thrust specific fuel consumption will be limited. On the other hand, if the engine is already operating at its maximum turbine inlet temperature, power extraction from the high-pressure shaft will result in a considerable thrust reduction. The results presented will support the analysis and interpretation of fighter mission optimization and cycle design for future fighter engines aimed for large power extraction. The results are also important with regards to aircraft design, or more specifically, in deciding on the best energy source for power consumers of the aircraft.
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| 54. |
- Heyne, Stefan, 1979, et al.
(författare)
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Numerical simulations of a prechamber autoignition engine operating on natural gas
- 2009
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Ingår i: ECOS 2009 - 22nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. ; , s. 1969-1978
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Konferensbidrag (refereegranskat)abstract
- Small to medium scale cogeneration engines are a common means of power production in remote areas. Reducing emissions of this type of power generation equipment-while maintaining high efficiencies-is an effective way of reducing greenhouse gas emissions both on a local and global level. At out laboratory extensive research has been conducted on the conversion of conventional Diesel cogeneration engines to operation on natural gas and biogas. By equipping the engines with a prechamber, Swiss emission limits could be kept without exhaust gas treatment while keeping high efficiencies. Recent research has focused on further improving the prechamber concept by converting the spark ignited prechamber to a prechamber operating in autoignition mode. In the framework of this research, a numerical simulation of a prechamber autoignition gas engine has been performed based on an experimental test case. With a simplified finite-rate/eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. However the predefined empiric constant of the eddy-dissipation model had to be increased by a factor of 10. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with the simulation model. The influence of burnt gases inside the prechamber was assessed simulating the mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the combustion duration. The simulation showed that the new and cylindrical geometry envisaged did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is in fact not sufficient to properly ignite the main chamber. The model can be used to further guide design modifications of the prechamber engine to improve performance.
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| 55. |
- Hlaing, Ponnya, et al.
(författare)
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Effects of volume and nozzle area in narrow-throat spark-ignited pre-chamber combustion engines
- 2022
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 313
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Tidskriftsartikel (refereegranskat)abstract
- The pre-chamber combustion concept (PCC) concept shows promises for lean combustion to achieve improved combustion stability and engine efficiency. The KAUST narrow-throat pre-chamber design, which can readily fit into the diesel injector pocket of a heavy-duty engine, has demonstrated an increased lean limit extension compared to conventional pre-chamber designs without a distinct throat. This study examines the effect of pre-chamber volume and nozzle opening area on the PCC concept by employing five different pre-chambers with fixed throat diameter. The engine was fueled with methane, and the combustion characteristics of each pre-chamber were assessed at different operating conditions. A 1-D GT-Power pre-chamber engine model was utilized to estimate the temperature and mixture composition inside the pre-chamber and main chamber. A multi-chamber heat release analysis method was applied to determine the response of the main chamber heat release process with different pre-chamber geometries. Engine-out emissions were also measured to compare the emission performance between the different pre-chambers. It was found that an increased pre-chamber volume promoted earlier ignition in the main chamber, and the throat area was a critical limiting factor in determining the engine performance for the pre-chambers with different nozzle opening areas at a given pre-chamber volume.
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| 56. |
- Husberg, Tobias, 1975, et al.
(författare)
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Analysis of advanced multiple injection strategies in a heavy-duty diesel engine using optical measurements and CFD-simulations
- 2008
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
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Tidskriftsartikel (refereegranskat)abstract
- In order to meet future emissions legislation for Diesel engines and reduce their CO 2 emissions it is necessary to improve diesel combustion by reducing the emissions it generates, while maintaining high efficiency and low fuel consumption. Advanced injection strategies offer possible ways to improve the trade-offs between NOx, PM and fuel consumption. In particular, use of high EGR levels ( > 40%) together with multiple injection strategies provides possibilities to reduce both engine-out NOx and soot emissions. Comparisons of optical engine measurements with CFD simulations enable detailed analysis of such combustion concepts. Thus, CFD simulations are important aids to understanding combustion phenomena, but the models used need to be able to model cases with advanced injection strategies. Thus, in the study presented here, engine tests were performed with settings selected to simplify CFD simulation, with long dwell times between the injections and only injection changes between engine settings in test cases presented in this paper. The key to reducing both soot and NOx emissions by applying pilot injections is that the pilot injected fuel should not ignite before sufficient mixing/lean-out has occurred. Hence, substantial heat releases prior to the main injection must be prevented. Thus, high EGR levels are needed to increase the bulk gas mass and reduce the temperature so that there is sufficient time for the pilot injections to mix and become locally lean before ignition. Copyright © 2008 SAE International.
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| 57. |
- Jia, Zhiqin, 1983, et al.
(författare)
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A Hybrid Approach Using Design of Experiment and Artificial Neural Network in a Camless Heavy-Duty Engine
- 2022
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Ingår i: Journal of Energy Resources Technology, Transactions of the ASME. - : ASME International. - 1528-8994 .- 0195-0738. ; 144:12
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Tidskriftsartikel (refereegranskat)abstract
- Increasingly stricter emission regulations and fleet CO2 targets drive the engine development toward clean combustion and high efficiency. To achieve this goal, planning and conducting experiments in a time- and cost-effective way play a vital role in finding the optimal combinations of all selectable parameters. This study investigated the effects of five engine parameters on two engine-out responses in a camless variable valve actuation (VVA) heavy-duty engine. Five engine parameters were intake valve lift (IVL), inlet valve closing (IVC), injection pressure, start of injection (SOI), and exhaust gas recirculation (EGR). Initially, a design of experiment (DoE) model was generated to predict both engine-out responses: brake-specific fuel consumption (BSFC) and BSNOx emissions. Due to a poor fit of the BSFC regression model from DoE analysis, an artificial neural network (ANN) model was developed to predict BSFC instead. A d-optimal design with five engine parameters at five levels was used to design the experiment. Extra test points together with d-optimal design points were utilized to train the ANN model. The well-trained ANN model for BSFC and DoE model for BSNOx were combined with a genetic algorithm (GA) to generate the Pareto-optimal front. The results proved the concept of using a hybrid statistical approach (DoE + ANN) with GA as an effective tool to generate a range of compromise design solutions. By extracting designs along the Pareto-optimal front, the impact of engine parameters on the system can be explained.
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| 58. |
- Jia, Zhiqin, 1983, et al.
(författare)
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Experimental investigation into the combustion characteristics of a methanol-Diesel heavy duty engine operated in RCCI mode
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 226, s. 745-753
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Tidskriftsartikel (refereegranskat)abstract
- This study examines combustion in a dual-fuel methanol-Diesel heavy duty engine using three different methanol injection configurations: port injection into the intake manifold; direct injection during the intake stroke (DI_E) and direct injection during the compression stroke (DI_L). The latter two methanol direct injection configurations were used in the attempt to reduce HC and CO emissions, which were considerably high in the port-injected high-octane fuel RCCI combustion. Engine experiments were performed using a double Diesel injection strategy with two pilot Diesel injections (PI1 and PI2) and a constant engine speed of 1500 rpm. The effects of three parameters – the PI1 and PI2 injection timings, and the PI2/PI1 duration ratio – were investigated at 5 bar IMEP for the three methanol injection configurations. The onset of unstable combustion and excessive combustion phasing advancement imposed lower or upper limits on the sweeps over the studied parameters. The DI_L configuration achieved lower net indicated thermal efficiencies than the other two methanol injection configurations. The influences of the methanol injection pressure and methanol substitution percentage (MSP) were also investigated for the DI_L configuration at 5 bar IMEP, revealing that the combustion process was relatively insensitive to the methanol injection pressure but was adversely affected by increasing the MSP. Finally, the port and DI_L configurations were tested at various loads. Neither configuration offered any advantage over pure Diesel combustion in terms of net indicated thermal efficiency nor emissions of HC and CO, but both offered lower greenhouse gas emissions at all load points. However, only the methanol port injection configuration achieved ultra-low NO x and soot emissions at 12 bar IMEP.
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| 59. |
- Jonsson, Isak, 1990
(författare)
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Experimental aero- and thermal investigation for a next generation engine exit module.
- 2019
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Ingår i: Linköping Electronic Conference Proceedings. - 1650-3686 .- 1650-3740. - 9789175190068 ; 162
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Beyond 2020, new efforts are required to improve the engine efficiency and fuel burn to meet the Advisory Council for Aeronautics Research in Europe (ACARE) goals for the year 2035 and 2050. The year 2050 targets aim for a 75% reduction in CO2 emissions, a 90% reduction in NOx emissions and a 65% reduction of the perceived noise relative to engine and aircraft performance of year 2000. It is commonly agreed that the geared turbofan engines have the potential to make a significant step towards the above targets. These engines will have a higher overall pressure ratio which will result in increased operating temperatures. They also have higher by-pass ratios, i.e., larger fan with relatively smaller engine cores, which has consequently a wider operating envelope for the LPT. For the turbine rear structures (TRS) this development implies that designs are needed that: can withstand higher temperatures and temperature variations, and furthermore, can operate under more severe LPT off-design conditions. GKN Aerospace in Trollhättan, with a dominating market position on the TRS for commercial aeroengines, is addressing these challenges in this program. A unique facility for experimental testing of TRS at engine-realistic flow conditions is currently available at Chalmers' Laboratory of Thermal and Fluids Science and will be used for testing of novel TRS designs for future more efficient aero-engines. The unique design of the facility includes an open test section which permits investigation of the complete TRS assemblies consisting of a TRS and a core exhaust nozzle. The facility is equipped with a 1.5 stage shrouded low-pressure turbine (LPT) providing realistic inflow to the tested TRS. The main objective at Chalmers is to gain an understanding of the flow mechanism affecting the performance of the LPT-OGV and to validate designs that take advantage of the acquired knowledge. One expected outcome of the project is the most comprehensive aerothermal validation database for TRS designs. For this new measurement methods have been developed and implemented. At the time of writing hotwire and PIV are used to investigate boundary layer development and IR thermography for steady-state heat transfer but further extensive testing is planned within the project. The most up to date results from the test campaign will accompany the already published scientific work in this presentation.
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| 60. |
- Jonsson, Isak, 1990, et al.
(författare)
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Feasibility Study of a Radical Vane-Integrated Heat Exchanger for Turbofan Engine Applications
- 2020
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Ingår i: Proceedings of the ASME Turbo Expo. ; 7C-2020
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Konferensbidrag (refereegranskat)abstract
- The density of liquid hydrogen (LH2), at the normal boiling point, is two times higher than that of highly compressed hydrogen. This makes LH2 the prime candidate for hydrogen storage in aviation. However, LH2 is stored at cryogenic temperatures that require adequate insulation, as well as the integration of heat exchangers to warm up the hydrogen on its way to the combustion chamber. Ideally, the required heat exchangers are strategically placed in the engine core to produce optimum heat management, thus improving the engine efficiency, increase its durability as well as to reduce emissions. Moreover, the combination of hydrogen high specific heat with cryogenic temperatures results in formidable cooling capacity, that can be explored by more compact HEX solutions. The present work numerically investigates a novel concept of a compact compressor vane-integrated heat exchanger, for application in cryogenically fuelled gas turbine engines. The baseline engine used for establishing the HEX requirements is a large geared turbofan, operating on liquid hydrogen. The HEX aero-thermal performance is first estimated using zero-dimensional models and Chalmers in-house gas turbine performance tool GESTPAN. After, the conceptual design of an outlet guide vane-HEX is developed and integrated into a three-stage low-pressure compressor. The baseline compressor geometry is a lightly loaded high-speed booster with a design pressure ratio of 2.8. The multi-stage compressor with the integrated HEX is evaluated using steady-state computational fluid dynamics. Results allow to estimate the heat exchanger performance in terms of total pressure loss, heat transfer effectiveness, and the potential enhanced radial flow turning capability. Further, the impact of the new developed OGV-HEX on the compressor characteristics is also reported and discussed.
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