Superior 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.
Abstract:The authors discuss in this paper the potential of two power plant concepts for distributed generation, based on the integration of a cogenerating micro gas turbine with a solar panel array. The first one relies on the adoption of a parabolic trough network with an intermediate thermal carrier, while the second one considers the direct heating of the working air in a solar tower system. The first solution also includes a bottoming organic Rankine cycle (ORC) plant, so that it is mainly addressed to the power output increase. The second one involves a relevant temperature increase of the air entering the combustor, so allowing a direct fuel energy saving, whose amount is strongly variable with both the solar irradiance and the eventual part-load operation. In addition, the latter solar-assisted scheme involves noticeable variations in the conditions for the combustion development. This suggested the authors to proceed with a detailed CFD analysis of the combustion, after a preliminary thermal cycle study for highlighting the main benefits from the solar integration of the power plant.
The authors discuss in this paper the potential of a micro gas turbine (MGT) combustor when operated under unconventional\ud conditions, in terms of variation in the fuel supplied. The authors' expertise in the field of micro-combustor has addressed, in\ud recent years, some topics of current interest, as the fuelling with gaseous and liquid biofuels and the NOx reduction through the\ud optimization of the combustor.While the previous authors' works were mainly referring to a tubular combustor of a 100kW MGT,\ud the present proposal deals with an annular, reverse flow combustor of a 30 kW MGT. In this case the particular location of both\ud the injectors and of the secondary and diluting holes allows the combustor process to develop under nearly RQL conditions. This\ud is of special interest when supplying the combustion chamber with low LHV fuels. In addition, recent authors' papers have\ud demonstrated that the integration of the MGT with a solar field leads the combustor to require a decreased fuel/air equivalence\ud ratio because of the higher air entry temperature. Under these aspects, the existence of a Rich region within the combustor may\ud be helpful for the early phases of the oxidation process. The pollutant formation rates should be effectively controlled by the\ud secondary (Quick-mix) and diluting (Lean) air flows.The authors' methodology relies on an advanced CFD approach that makes\ud use of a reaction scheme coupled with an accurate study of the turbulent interaction of the reacting species. Extended kinetic\ud mechanisms are also included in the combustion model. A preliminary set-up of the model will be based on the combustion\ud analysis with boundary conditions provided by thermodynamic analysis of the micro-turbine.\ud Several computational examples are discussed, namely:\ud - The analysis of the combustor response with reduced equivalence ratios or changes in the inlet air conditions;\ud -The comparison of combustion efficiency and pollutant production with different fuels
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