Influence of Environmental Changes Due to Altitude on Performance, Fuel Consumption and Emissions of a Naturally Aspirated Diesel Engine

[EN] The present study shows the effects of environmental conditions (atmospheric temperature, pressure and relative humidity) due to altitude changes on performance, fuel consumption and emissions in a naturally aspirated diesel engine. Due to changes in altitude, the atmospheric conditions are altered, mainly the air density, associated to hydrostatic pressure, temperature profile and humidity and relative nitrogen/oxygen ratio, thus modifying the engine intake conditions. The study considers changes in altitude from sea level to 2500 m above sea level, which are representative of the orographic conditions in Ecuador. As a main part of this research, a parametric study of variation of atmospheric temperature, pressure and relative humidity is carried out in AVL BOOST (TM), showing the effects on mean effective pressure, fuel consumption and specific pollutant emissions (CO2, NOx, CO and soot). The study considers effects at regional level (change from an altitude to another) and local level (changes in the atmospheric conditions due to local anticyclone or storm, temperature and humidity). The quantitative effects are expressed in the form of sensitivity coefficients, e.g., relative change in an engine output variable due to the change in atmospheric pressure, temperature or humidity. In addition, several global correlations have been obtained to provide analytical expressions to summarize all results obtained, showing the separate effect of pressure and temperature on each engine performance variable.Ceballos, JJ.; Melgar, A.; Tinaut-Fluixá, FV. (2021). Influence of Environmental Changes Due to Altitude on Performance, Fuel Consumption and Emissions of a Naturally Aspirated Diesel Engine. Energies. 14(17):1-41. https://doi.org/10.3390/en14175346141141

A correlation for turbulent combustion speed accounting for instabilities and expansion speed in a hydrogen-natural gas spark ignition engine

[EN] An analysis of the turbulent premixed combustion speed in an internal combustion engine using natural gas, hydrogen and intermediate mixtures as fuels is carried out, with different air-fuel ratios and engine speeds. The combustion speed has been calculated by means of a two-zone diagnosis thermodynamic model combined with a geometric model using a spherical flame front hypothesis. 48 operating condi- tions have been analyzed. At each test point, the pressure record of 200 cycles has been processed to calculate the cycle averaged turbulent combustion speed for each flame front radius. An expression of turbulent combustion speed has been established as a function of two parameters: the ratio between turbulence intensity and laminar combustion speed and the second parameter, the ratio between the in- tegral spatial scale and the thickness of the laminar flame front increased by instabilities. The conclusion of this initial study is that the position of the flame front has a great influence on the expression to calculate the combustion speed. A unified correlation for all positions of the flame front has been ob- tained by adding one correction term based on the expansion speed as a turbulence source. This unified correlation is thus valid for all experimental conditions of fuel types, air¿fuel ratios, engine speeds, and flame front positions. The correlation can be used in quasi-dimensional predictive models to determine the heat released in an ICE.The authors of this work would like to thank the Spanish Ministry of Science and Innovation for the financial support of this research through the ENE 2012-34830 (with FEDER funds) and the Regional Government of Castile and Leon for funding the Excellence Research Group GR203Gimenez, B.; Melgar, A.; Horrillo, A.; Tinaut-Fluixá, FV. (2021). A correlation for turbulent combustion speed accounting for instabilities and expansion speed in a hydrogen-natural gas spark ignition engine. Combustion and Flame. 223:15-27. https://doi.org/10.1016/j.combustflame.2020.09.026S152722

Experimental study of premixed gasoline surrogates burning velocities in a spherical combustion bomb at engine like conditions

Producción CientíficaIn this work are presented experimental values of the burning velocity of iso-octane/air, n-heptane/air and n-heptane/toluene/air mixtures, gasoline surrogates valid over a range of pressures and temperatures similar to those obtained in internal combustion engines. The present work is based on a method to determine the burning velocities of liquid fuels in a spherical constant volume combustion bomb, in which the initial conditions of pressure, temperature and fuel/air equivalence ratios can be accurately established. A two-zone thermodynamic diagnostic model was used to analyze the combustion pressure trace and calculate thermodynamic variables that cannot be directly measured: the burning velocity and mass burning rate. This experimental facility has been used and validated before for the determination of the burning velocity of gaseous fuels and it is validated in this work for liquid fuels. The values obtained for the burning velocity are expressed as power laws of the pressure, temperature and equivalence ratio. Iso-octane, n-heptane and mixtures of n-heptane/toluene have been used as surrogates, with toluene accounting for the aromatic part of the fuel. Initially, the method is validated for liquid fuels by determining the burning velocity of iso-octane and then comparing the results with those corresponding in the literature. Following, the burning velocity of n-heptane and a blend of 50% n-heptane and 50% toluene are determined. Results of the burning velocities of iso-octane have been obtained for pressures between 0.1 and 0.5 MPa and temperatures between 360 and 450 K, for n-heptane 0.1–1.2 MPa and 370–650 K, and for the mixture of 50% n-heptane/50% toluene 0.2–1.0 MPa and 360–700 K. The power law correlations obtained with the results for the three different fuels show a positive dependence with the initial temperature and the equivalence ratio, and an inverse dependence with the initial pressure. Finally, the comparison of the burning velocity results of iso-octane and n-heptane with those obtained in the literature show a good agreement, validating the method used. Analytical expressions of burning velocity as power laws of pressure and unburned temperature are presented for each fuel and equivalence ratio.Ministerio de Ciencia e Innovación (PID2019-106957RB-C22

Characterization of cycle-to-cycle variations in a natural gas spark ignition engine

Producción CientíficaSe presenta un estudio de la influencia del dosado o relación combustible/aire y del régimen de giro de un motor de combustión interna alternativo sobre la dispersión cíclica del motor de encendido provocado funcionando con mezclas de aire y gas natural. Para ello se utilizan dos parámetros comúnmente utilizados y uno nuevo basado en la masa quemada y en la tasa de masa quemada. Para esto se utiliza un modelo de diagnóstico de la combustión a partir de la presión medida en la cámara de combustión, de forma que se determina la fracción de masa quemada. Posteriormente se utiliza un modelo de algoritmos genéticos de forma que se optimizan los principales parámetros del modelo de diagnóstico de forma objetiva y con exactitud, como son la posición angular y offset de la presión medida, la relación de compresión volumétrica y los coeficientes de transmisión de calor por las paredes. Se concluye que la dispersión cíclica es altamente dependiente del régimen de giro y muy poco del dosado.Ministerio de Ciencia, Innovación y Universidades (grant ENE2012-34830

Characterization of the combustion process and cycle-to-cycle variations in a spark ignition engine fuelled with natural gas/hydrogen mixtures.

Producción CientíficaSe presenta un estudio de la influencia del dosado o relación combustible/aire y del régimen de giro de un motor de combustión interna alternativo sobre la combustión y la dispersión cíclica del motor de encendido provocado funcionando con mezclas de aire, gas natural e hidrógeno. Para ello se utilizan dos parámetros comúnmente utilizados y uno nuevo basado en la masa quemada y en la tasa de masa quemada. Para esto se utiliza un modelo de diagnóstico de la combustión a partir de la presión medida en la cámara de combustión, de forma que se determina la fracción de masa quemada. Posteriormente se utiliza un modelo de algoritmos genéticos de forma que se optimizan los principales parámetros del modelo de diagnóstico de forma objetiva y con exactitud, como son la posición angular y offset de la presión medida, la relación de compresión volumétrica y los coeficientes de transmisión de calor por las paredes. Se concluye que la dispersión cíclica es altamente dependiente del régimen de giro y muy poco del dosado

Combustion and Flame Front Morphology Characterization of H2–CO Syngas Blends in Constant Volume Combustion Bombs

Producción CientíficaThe need to develop new, alternative, and bio-origin fuels for use in internal combustion engines has motivated the realization of this research, which aims to characterize the combustion process synthesis gas, represented by H2–CO blends, which are its main constituents. Syngas can be considered a biofuel because it is a mixture of carbon monoxide, hydrogen, and other hydrocarbons, and it is formed by partial combustion of biomass. Experimental tests have been developed in two constant volume combustion bombs with spherical and cylindrical geometries to analyze the combustion process and the influence of the blend composition on the burning velocity. In the first one, the pressure registered during the combustion has been used to obtain the mass burning rate, temperatures, and burning velocities. The cylindrical bomb has two optical accesses through which the combustion process can be visualized and recorded with the Schlieren technique, and it has been used to characterize the morphology of the flame, the evolution of the flame front, or the laminar burning velocities, among other parameters of interest in the combustion process. For initial conditions of 0.1 MPa and 300 K, blends with different compositions and equivalence ratios have been studied. The introduction of hydrogen enhances combustion velocity and pressure, introducing also instabilities visible on flame front images, similar effects to those produced by increasing the equivalence ratio. Regarding the morphology of the flames, note that the tend to wrinkle and the cellularity increases as the hydrogen content of the mixture increases and the equivalence ratio decreases. The dependence of the numerical values of burning velocity has been expressed as a correlation on pressure and temperature. Finally, comparing the results of the burning velocities obtained in the spherical bomb and in the cylindrical bomb with those of different authors of the bibliography has checked the consistency and validity of them. Results of syngas blends are essential for the validation, optimization, and development of kinetic models for combustion development.Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (grant PID2019-106957RB-C22

Study and characterization of the instabilities generated in expanding spherical flames of hydrogen/methane/air mixtures

Producción CientíficaIn the present work an analysis of the origin and nature of intrinsic instabilities in combustion processes with different hydrogen/methane mixtures is developed. These expanding spherical flame front experiments have been developed in a cylindrical constant volume combustion bomb, which allows recording the process through Schlieren photography method. The stability study in combustion processes has a great importance to assure their security and control, since the understanding of flame instabilities is necessary for improving the internal combustion engines performance. To carry out this mentioned study, a review of the concepts and parameters used in spherical flame front instabilities research is first proposed, as well as a physical explanation of each concept and the relations among them. Additionally, a methodology that aims to determine the influence of the fuel mixtures in the origin and development of the flame front instabilities is suggested. Moreover, the intrinsic effects of the combustion process, such as the thermal-diffusive and the hydrodynamic effect, are separately studied, including their individual contributions to the growth rate of instabilities which allows to determine combustion nature and to obtain the instability peninsula of each fuel mixture. Finally, this methodology includes a qualitative study of the cellularity phenomenon (when the instabilities develop all over the flame front), considering the parameters which influence on this phenomenon.Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (grant PID2019-106957RB-C2