1,720,969 research outputs found
Innovative combustion analysis of a micro-gas turbine burner supplied with hydrogen-natural gas mixtures
No full textThe author discusses in this paper the potential of a micro gas turbine (MGT) combustor when operated under unconventional fuel supplied. The combustor of C30 gas turbine is a reverse flow annular combustor. The CFD analysis of the reacting flow is performed with the 3D ANSYS-FLUENT solver. Specific computational experiments refer to the use of hydrogen - natural gas mixtures in order to define the optimal conditions for pilot and main injections in terms of combustion stability and NOx production. The author's methodology relies on an advanced CFD approach that compares different schemes like eddy dissipation concept, together with the flamelet-PDF based approach coupled with an accurate study of the turbulent chemistry interaction. Extended kinetic mechanisms are also included in the combustion model. Some test cases are examined to make a comparison of combustion stability and efficiency and pollutant production with high hydrogen / natural gas ratios
Comparison between hydrogen and syngas fuels in an integrated micro gas turbine/solar field with storage
No full textIn recent years, the use of alternative fuels in thermal engine power plants has gained more and more attention, becoming of paramount importance to overcome the use of fuels from fossil sources and to reduce polluting emissions. The present work deals with the analysis of the response to two different gas fuels—i.e., hydrogen and a syngas from agriculture product—of a 30 kW micro gas turbine integrated with a solar field. The solar field included a thermal storage system to partially cover loading requests during night hours, reducing fuel demand. Additionally, a Heat Recovery Unit was included in the plant considered and the whole plant was simulated by Thermoflex® code. Thermodynamics analysis was performed on hour-to-hour basis, for a given day as well as for 12 months; subsequently, an evaluation of cogeneration efficiency as well as energy saving was made. The results are compared against plant performance achieved with conventional natural gas fueling. After analyzing the performance of the plant through a thermodynamic analysis, the study was complemented with CFD simulations of the combustor, to evaluate the combustion development and pollutant emissions formation, particularly of NOx, with the two fuels considered using Ansys-Fluent code, and a comparison was made
Ignition and combustion modelling in a dual fuel diesel engine
No full textA numerical simulation of a single cylinder research diesel engine fuelled by natural gas and diesel oil in dual fuel mode was conducted to test the reaction mechanism presented by Li and Williams in Ref. [1] for methane ignition. The mechanism made of only 9 reactions can represent a good compromise between reduction of computational time and accuracy of results. Simulations reproduce test cases previously carried out experimentally and numerically with a simpler kinetic mechanism at three different premixed ratios (10%, 15% and 22%). Finally, a last case characterized by a supply of methane consistent with the typical load levels for this kind of engines (80%), was investigated only numerically. All the simulations were performed with the KIVA-3V solver on a geometry which includes open valve periods, intake and exhaust ducts. Through a comparison between experimental and numerical results, a calibration of the model has been performed and a quite good fitting of the models has been achieved
Numerical Analysis of Dual Fuel Combustion in a Medium Speed Marine Engine Supplied with Methane/Hydrogen Blends
No full textCompression ignition engines will still be predominant in the naval sector: their high
efficiency, high torque, and heavy weight perfectly suit the demands and architecture of ships.
Nevertheless, recent emission legislations impose limitations to the pollutant emissions levels in this
sector as well. In addition to post-treatment systems, it is necessary to reduce some pollutant species,
and, therefore, the study of combustion strategies and new fuels can represent valid paths for limiting
environmental harmful emissions such as CO2. The use of methane in dual fuel mode has already
been implemented on existent vessels, but the progressive decarbonization will lead to the utilization
of carbon-neutral or carbon-free fuels such as, in the last case, hydrogen. Thanks to its high reactivity
nature, it can be helpful in the reduction of exhaust CH4. On the contrary, together with the high
temperatures achieved by its oxidation, hydrogen could cause uncontrolled ignition of the premixed
charge and high emissions of NOx. As a matter of fact, a source of ignition is still necessary to have
better control on the whole combustion development. To this end, an optimal and specific injection
strategy can help to overcome all the before-mentioned issues. In this study, three-dimensional
numerical simulations have been performed with the ANSYS Forte® software (version 19.2) in an
8.8 L dual fuel engine cylinder supplied with methane, hydrogen, or hydrogen–methane blends with
reference to experimental tests from the literature. A new kinetic mechanism has been used for the
description of diesel fuel surrogate oxidation with a set of reactions specifically addressed for the low
temperatures together with the GRIMECH 3.0 for CH4 and H2. This kinetics scheme allowed for the
adequate reproduction of the ignition timing for the various mixtures used. Preliminary calculations
with a one-dimensional commercial code were performed to retrieve the initial conditions of CFD
calculations in the cylinder. The used approach demonstrated to be quite a reliable tool to predict
the performance of a marine engine working under dual fuel mode with hydrogen-based blends at
medium load. As a result, the system modelling shows that using hydrogen as fuel in the engine can
achieve the same performance as diesel/natural gas, but when hydrogen totally replaces methane,
CO2 is decreased up to 54% at the expense of the increase of about 76% of NOx emissions
CFD Study of Dual Fuel Combustion in a Research Diesel Engine Fueled by Hydrogen
No full textSuperior fuel economy, higher torque and durability have led to the diesel engine being widely used in a variety of fields of application, such as road transport, agricultural vehicles, earth moving machines and marine propulsion, as well as fixed installations for electrical power generation. However, diesel engines are plagued by high emissions of nitrogen oxides (NOx), particulate matter (PM) and carbon dioxide when conventional fuel is used. One possible solution is to use low-carbon gaseous fuel alongside diesel fuel by operating in a dual-fuel (DF) configuration, as this system provides a low implementation cost alternative for the improvement of combustion efficiency in the conventional diesel engine. An initial step in this direction involved the replacement of diesel fuel with natural gas. However, the consequent high levels of unburned hydrocarbons produced due to non-optimized engines led to a shift to carbon-free fuels, such as hydrogen. Hydrogen can be injected into the intake manifold, where it premixes with air, then the addition of a small
amount of diesel fuel, auto-igniting easily, provides multiple ignition sources for the gas. To evaluate the efficiency and pollutant emissions in dual-fuel diesel-hydrogen combustion, a numerical CFD analysis was conducted and validated with the aid of experimental measurements on a research engine acquired at the test bench. The process of ignition of diesel fuel and flame propagation through a premixed air-hydrogen charge was represented the Autoignition-Induced Flame Propagation model included ANSYS-Forte software. Because of the inefficient operating conditions associated with the combustion, the methodology was significantly improved by evaluating the laminar flame speed as a function of pressure, temperature and equivalence ratio using Chemkin-Pro software. A numerical comparison was carried out among full hydrogen, full methane and different hydrogen-methane mixtures with the same energy input in each case. The use of full hydrogen was characterized by enhanced combustion, higher thermal efficiency and lower carbon emissions. However, the higher temperatures that occurred for hydrogen combustion led to higher NOx emissions
Solar-assisted micro gas turbine with humid air or steam-injected option
No full textIn the present work a low environmental impact, innovative, hybrid plant for the field of distributed energy is
presented. The plant is obtained from the integration of a 30 kW micro gas turbine with a solar field and a
bottoming ORC system. The plant is supplied with hydrogen fuel and is provided with steam injection to mitigate
NO
x formation. Furthermore, the cogeneration arrangement of the plant allows for flexibility in the choice between the production of electrical and thermal energy.
A thermodynamic analysis of the plant was conducted and various organic fluids for the bottom ORC plant are
tested. The feasibility of a single-stage Radial-Inflow Turbine (RIT) as expander for the ORC cycle is verified for
various working fluids, with a two-step approach: a preliminary screening is carried out based on kinematic
considerations; subsequently, a proper turbine preliminary design is developed for most interesting working
fluids.
Moreover, the combustion process resulting from the introduction of hydrogen fuel is studied by means of 3D
CFD calculations and the effectiveness of the steam injection is verified. Finally, the off-design performance of the
plant is investigated by means of a thermodynamic analysis.
Results show that the novel plant achieves significant improvements in terms of power output and efficiency
and fuel saving is achieved over several months thanks to the solar field and the ORC plant. The ORC working
fluid is found to play a crucial role over plant performance and particularly over the feasibility of a single stage
RIT, making working fluids with larger molecular weight preferable. Finally, CFD calculations proved the steam
injection to be effective for NOx production reduction
Hydrogen/Diesel Combustion Analysis in a Single Cylinder Research Engine
No full textThe application of an alternative fuel such as hydrogen to internal combustion engines is proving to be an effective and flexible solution for reducing fuel consumption and polluting emissions from engines. An easy to use and immediate application solution is the dual fuel (DF) technology. It has the potential to offer significant improvements in carbon dioxide emissions from light compression ignition engines. The dual fuel concept (natural gas / diesel or hydrogen / diesel) represents a possible solution to reduce emissions from diesel engines by using low-carbon or carbon-free gaseous fuels as an alternative fuel. Moreover, DF combustion is a possible retrofit solution to current diesel engines by installing a PFI injector in the intake manifold while diesel is injected directly into the cylinder to ignite the premixed mixture. In the present study, dual fuel operation has been investigated in a single cylinder research engine. The engine run at two engine speeds (1500 and 2000 rpm), and hydrogen has been injected in the intake manifold in front of the entrance of the tumble intake port. The aim of the study is to compare the DF hydrogen combustion with the DF methane combustion. Premixed ratio up to 92 and 83 has been realized with methane and hydrogen, respectively. In-cylinder combustion pressures and pollutant emissions have been analysed. Finally, cycle resolved optical diagnostics have been applied to detect visible and infrared images from the combustion chamber
Optical Diagnostics to Study Hydrogen/Diesel Combustion with EGR in a Single Cylinder Research Engine
No full textIn order to reduce fuel consumption and polluting emissions from engines, alternative fuels such as hydrogen could play an important role towards carbon neutrality. Moreover,
dual-fuel (DF) technology has the potential to offer significant
improvements in carbon dioxide emissions for transportation
and energy sectors. The dual fuel concept (natural gas/diesel
or hydrogen/diesel) represents a possible solution to reduce
emissions from diesel engines by using low-carbon or carbonfree gaseous fuels as an alternative fuel. Moreover, DF combustion is a possible retrofit solution to current diesel engines by
installing a PFI injector in the intake manifold while diesel is
injected directly into the cylinder to ignite the
premixed mixture. In the present study, dual fuel operation has been investigated in a single cylinder research engine. The engine run
at two engine speeds (1500 and 2000 rpm), and hydrogen has
been injected in the intake manifold in front of the entrance
of the tumble intake port. The aim of the study is to compare
the DF hydrogen combustion with the DF methane combustion with the use of exhaust gas recirculation gases. Premixed
ratio up to 92% and 83% has been realized with methane and
hydrogen, respectively. In-cylinder combustion pressures and
pollutant emissions have been analyzed. Finally, cycle resolved
optical diagnostics have been applied to detect visible and
infrared images from the combustion chamber. IR intensities
have been recorded and compared with the rate of heat release
curves showing a good agreement. This information is of
interest for CFD analysis of ultra-lean hydrogen combustion
CFD Analysis of Different Methane/Hydrogen Blends in a CI Engine Operating in Dual Fuel Mode
No full textNowadays, the stricter regulations in terms of emissions
have limited the use of diesel engines on urban roads.
On the contrary, for marine and off-road applications
the diesel engine still represents the most feasible solution for
work production. In the last decades, dual fuel operation with
methane supply has been widely investigated. Starting from
previous studies on a research engine, where diesel-methane
dual fuel combustion has been deepened both experimentally
and numerically with the aid of a CFD code, the authors
implemented and tested a kinetic mechanism. It is obtained
from the combination of the well-established GRIMECH 3.0
and a detailed scheme for a diesel surrogate oxidation.
Moreover, the Autoignition-Induced Flame Propagation
model, included in the ANSYS Forte® software, is applied
because it can be considered the most appropriate model to
describe dual fuel combustion. However, the higher emissions
of unburned hydrocarbons have pushed researchers to move
towards a more eco-friendly gaseous fuel such as hydrogen.
Since the former scheme is capable to deal with H2 oxidation
as well, in this work an increasing substitution of methane
with H2 is analyzed for a critical engine operating condition
at 1500 rpm with a low load level and poor equivalence ratio;
in particular, three percentages of hydrogen substitution are
simulated, 20, 50 and 80%. The results of this activity have
shown that the contribution of H2 an increased peak pressure
and a better combustion efficiency, confirming the reduction
of CO2 and unburned hydrocarbon emissions
Combined CFD - Experimental Analysis of the In-Cylinder Combustion Phenomena in a Dual Fuel Optical Compression Ignition Engine
No full textMethane supply in diesel engines operating in dual fuel mode has demonstrated to be effective for the reduction of particulate matter and nitric oxides emissions from this type of engine. In particular, methane is injected into the intake manifold to form a premixed charge with air, while a reduced amount of diesel oil is still directly injected to ignite the mixture inside the cylinder. As a matter of fact, the liquid fuel burns following the usual diffusive combustion, so activating the gaseous fuel oxidation in a premixed flame. Clearly, the whole combustion process appears to be more complex to be described in a CFD simulation, mainly because it is not always possible to select in the 3-dimensional codes a different combustion model for each fuel and, also, because other issues arise from the interaction of the two fuels. In this work, the Autoignition-Induced Flame Propagation model, which is included in the ANSYS Forte® tool, is applied since it represents the most appropriate model to describe the dual fuel combustion. Indeed, this model uses the G-equation to track the position and the propagation of the premixed turbulent flame, but the flame activation source is represented by the autoignition kinetics reaction scheme for the n-dodecane. The results discussed in this paper refer to experimental tests carried out on an optically accessible research engine whose real geometry and mesh were reproduced with the K3PREPW tool. Through the use of a system of sensors and optical diagnostic, the combined numerical - experimental study allows a deeper investigation of phenomena that take place in real dual fuel operations characterized by different engine speeds, 1500 and 2000 rpm, load levels, 2 and 5 bar of BMEP, injection timing and a premixed ratio between 86 and 89%
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