Study of the cycle-to-cycle variations of an internal combustion engine fuelled with natural gas/hydrogen blends from the diagnosis of combustion pressure

Producción CientíficaSe presenta una metodología para el estudio de la influencia de la adicción de hidrógeno (de 0 a 100% en sustitución del gas natural en mezclas de gas natural/aire en la dispersión cíclica de la combustión de un motor de encendido provocado. Se utiliza un algoritmo genético que optimiza un modelo de diagnóstico de la combustión a partir de la presión medida experimentalmente en la cámara de combustión de forma que se optimizan entradas al modelo de diágnóstico como son el ángulo de la presión máxima y el offset de presión, la relación de compresión volumétrica, el índice de la transferencia de calor a las paredes, etc. Se observa que la adición de hidrógeno aumenta mucho la velocidad de combustión a partir de un valor del 60%.Ministerio de economía y competitividad de Españ

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

Prediction of the flame kernel growth rate in spark ignition engine fueled with natural gas, hydrogen and mixtures

Producción CientíficaThe knowledge of combustion duration is a key tool in the development of engines, specially nowadays for engines adapted to new fuels with low C/H ratio such as natural gas and hydrogen. This work is aimed to develop a correlation that predicts the duration of the first phase of combustion until the process becomes turbulent in a SI engine. The flame kernel radius when this transition occurs, , is the study variable. To determine this variable from the experimental pressure records, a flame kernel growth predictive model is used. The predictive model is adjusted to the experimental data, determining the most appropriate value. The pressure records of 500 consecutive cycles of 48 test points have been processed. The averaged values of of each test point have been correlated with the characteristic parameters of the process: turbulence and properties of the fuel–air mixtures. Finally, and integral length scale ratio is correlated with Damköhler number. A wide range of operating conditions have been studied, reaching the novel conclusion that it is possible to analyze the kernel growth phenomenon from a spatial point of view rather than from a temporal point of view, as had been studied in many previous works. The developed correlation can be used in combustion predictive modeling to support SI engine design. Other practical conclusion from the work, that can be used in SI engine development, is that decreasing the integral length scale reduces the time of the first phase of combustion.Ministerio de Ciencia e Innovación (PID2019-106957RB-C22). “Analysis and characterization of dual fuel combustion for the reduction of CO2 emissions in the transport sector

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