In-Cylinder Heat Transfer Model Proposal Compatible with 1D Simulations in Uniflow Scavenged Engines

[EN] Advanced two-stroke engines are considered as powertrains for range extenders in hybrid electric vehicles due to size, simplicity, cost, and power density advantages. In-cylinder heat transfer is a phenomenon that affects the temperature of burnt gases and fresh air in an internal combustion engine. Compared to four-stroke units, this influence is more critical in two-stroke engines during the scavenging process since the gases velocity field inside the cylinder evolves rapidly in space and time. This study proposes a new convective heat transfer coefficient model beyond those based on Reynolds number calculation with the mean piston velocity. The model uses semi-empirical equations with non-dimensional numbers since it has to be integrated within the frame of a physical engine model, where thermo- and fluid dynamic properties of the gases inside the engine are solved using 0D or 1D approaches. In this particular application, the temperature deviation led to a poor prediction of trapped mass in the cylinder. The proposed convective heat transfer coefficient is calculated using a pseudo-velocity of the gases inside the cylinder based on the mass flow rates in the intake and exhaust ports during scavenging. The experimental results validate the 1D engine physical model, which is then used as initial conditions for CFD simulations. These CFD results are used to deduce the necessary conclusions for enhanced temperature predictability during scavenging, where deviations of less than 2% can be observed and an impact of up to 12% on the in-cylinder trapped mass can be seen.Climent, H.; Tiseira, A.; Gómez-Soriano, J.; Darbhamalla, A. (2023). In-Cylinder Heat Transfer Model Proposal Compatible with 1D Simulations in Uniflow Scavenged Engines. Applied Sciences. 13(6). https://doi.org/10.3390/app1306399613

Assessment of Variable Geometry Orifice Compressor Technology Impact in a New Generation of Compression Ignition Powertrains at Low-End and Transient Operation

[EN] Surge is a phenomenon that limits the operating range of the compressor at low engine speeds and high boost pressure in turbocharged powertrains. This article assesses two prototype turbochargers of variable geometry orifice (VGO) which compensate for the limitation of the boost pressure at low engine speeds. The VGO prototypes modify the inlet compressor section, extending the compressor characteristic map into lower mass flows (surge limit region). The VGO turbochargers analyzed are also both equipped with variable geometry turbine (VGT) technology. The experiments focus on low-end torque operation ranges in steady and transient engine running conditions. The experimental results are used to validate a 1D physical model. From the modelling perspective, a comprehensive study of the VGO-VGT prototypes is assessed. Results reveal the benefits of VGO technology in terms of attaining higher boost pressure, improved compressor efficiency, and overall engine performance at low engine speeds.This research work has been supported by Grant PDC2021-120821-I00 funded by the Spanish Ministerio de Ciencia e Innovacion-Agencia Estatal de Investigacion (MCIN/AEI/10.13039/501100011033), and by the European Union NextGenerationEU/PRTR.Serrano, J.; Climent, H.; Gómez-Vilanova, A.; Darbhamalla, A.; Guilain, S. (2022). Assessment of Variable Geometry Orifice Compressor Technology Impact in a New Generation of Compression Ignition Powertrains at Low-End and Transient Operation. Applied Sciences. 12(24):1-19. https://doi.org/10.3390/app122412869119122

Analysis of the Internal Thermofluid-Dynamics in a Uniflow Scavenged Engine

[ES] El transporte terrestre es uno de los principales contribuyentes a las emisiones y tiene un impacto en los cambios climáticos y los peligros para la salud. Para abordar estos problemas, la industria automotriz se está movien- do hacia la movilidad sostenible, donde se están evaluando nuevas tecnologías como vehículos híbridos y vehículos eléctricos. Sin embargo, dado la falta de competencia en alternativas libres de combustibles fósiles para la producción de electricidad, se está abordando la dependencia de motores de combustión interna (ICEs) para ser utilizados como extensores de autonomía y producción de electricidad. Estos extensores de autonomía son generalmente motores de dos tiempos. Debido a su diseño y rango de operación, estos ICE pueden ser compactos, tener una gran reducción de tamaño y producir menos emisiones. Por lo tanto, es esencial comprender el rendimiento de estos nuevos conceptos de ICE, mostrar beneficios potenciales y ayudar en mejoras adicionales. Con el objetivo anterior en este trabajo de tesis, se evalúa un concepto de motor de dos tiempos de barrido uniflow. Se obtienen datos experimentales de una celda de prueba de motor utilizando dos disposiciones de escape, tres velocidades de motor y dos condiciones de carga. Se desarrolla y valida un modelo gasodinámico 1D con respecto a todos los puntos probados. Se mo- dela una réplica en 3D del motor y se utiliza en una simulación CFD en 3D. Los resultados del modelo 1D validados fluidodinámicamente se utilizan como condiciones iniciales y de contorno para evaluar las métricas térmicas y de barrido de este motor en particular. Al comparar los resultados 1D y CFD, se observó que la temperatura y el cortocircuito de aire no se capturaron bien utilizando modelos de transferencia de calor y barrido de última generación durante el proceso de barrido. Esto llevó a la propuesta de un nuevo modelo de transferencia de calor y una curva sintética de barrido. La transferencia de calor en el cilindro es un fenómeno que afecta la tem- peratura de los gases quemados y el aire fresco en un motor de combustión interna. En comparación con las unidades de cuatro tiempos, esta influencia es más crítica en los motores de dos tiempos durante el proceso de barrido, ya que el campo de velocidad del gas dentro del cilindro evoluciona rápidamente en el espacio y el tiempo. Este estudio propone un nuevo modelo de coeficiente de transferencia de calor convectivo más allá de aquellos basados en el cálculo del número de Reynolds con la velocidad media del pistón. El modelo utiliza ecuaciones semiempíricas con números adimensionales ya que debe integrarse en el marco de un modelo físico de motor, donde las propiedades termo y fluidodinámicas de los gases dentro del motor se resuelven mediante enfoques 0D o 1D. En esta aplicación particular, la desviación de temperatura llevó a una predicción deficiente de la masa atrapada en el cilindro. El coeficiente propuesto se calcula utilizando una pseudo-velocidad de los gases dentro del cilindro basada en las tasas de flujo de masa en los puertos de admisión y escape durante el barrido. El barrido en un motor de dos tiempos presenta un proceso complejo, dis- tinto del ciclo de cuatro tiempos, ya que los procesos de admisión y escape ocurren simultáneamente durante una parte significativa del período de inter- cambio de gases. Debido a esta naturaleza superpuesta y a la duración más corta del intercambio de gases en comparación con un motor de cuatro tiempos, modelar con precisión la dinámica de gas dentro del cilindro se vuelve crucial. Este proceso de modelado tiene como objetivo garantizar la retención efectiva de la carga fresca suministrada y la extracción eficiente de los gases residuales del ciclo de motor anterior durante la fase de intercambio de ga- ses. Este modelado es particularmente crucial en motores avanzados de dos tiempos para obtener estimaciones confiables de la composición de la mezcla atrapada y predecir con precisi.[CA] El transport terrestre és un dels principals contribuents a les emissions i té un impacte en els canvis climàtics i els riscos per a la salut. Per abordar aquests problemes, la indústria automobilística es mou cap a la mobilitat sos- tenible, on s'estan avaluant noves tecnologies com ara vehicles híbrids i vehicles elèctrics. No obstant això, donada la manca de competència en alternatives lliures de combustibles fòssils per a la producció d'electricitat, s'està abordant la dependència dels motors de combustió interna (ICEs) per ser utilitzats com a extensors d'autonomia i producció d'electricitat. Aquests extensors d'auto- nomia són normalment motors de dos temps. A causa del seu disseny i rang operatiu, aquests ICEs poden ser compactes, força reduïts de mida, i emetre menys. Per tant, és essencial entendre les actuacions d'aquests nous conceptes de ICE, mostrar els beneficis potencials, i ajudar en millores addicionals. Amb l'objectiu anterior en aquest treball de tesi, es valora un concepte de motor de dos temps de flux uniflow. S'obtenen dades experimentals d'una cel·la de prova de motor utilitzant dues disposicions d'escapament, tres velo- citats de motor i dues condicions de càrrega. Es desenvolupa i valida un model gasodinàmic 1D amb tots els punts provats. Es modela una rèplica en 3D del motor i s'utilitza en una simulació CFD en 3D. Els resultats del model 1D va- lidats fluidodinàmicament s'utilitzen com a condicions inicials i de contorn per avaluar les mètriques tèrmiques i de flux de gas d'aquest motor en particular. En comparar els resultats 1D i CFD, es va observar que la temperatura i el tall-circuit d'aire no es van capturar bé utilitzant models de transferència de calor i flux de gas de última generació durant el procés de flux. Això va portar a la proposta d'un nou model de transferència de calor i una corba sintètica de flux. La transferència de calor al cilindre és un fenomen que afecta la tempera- tura dels gasos cremats i l'aire fresc en un motor de combustió interna. En comparació amb les unitats de quatre temps, aquesta influència és més crítica en els motors de dos temps durant el procés de flux, ja que el camp de velocitat del gas dins del cilindre evoluciona ràpidament en l'espai i el temps. Aquest estudi proposa un nou model de coeficient de transferència de calor convectiu més enllà dels basats en el càlcul del número de Reynolds amb la velocitat mitjana del pistó. El model utilitza equacions semiempíriques amb nombres no-dimensionals ja que ha de ser integrat dins del marc d'un model físic de motor, on les propietats termo i fluidodinàmiques dels gasos dins del motores resolen mitjançant enfocaments 0D o 1D. En aquesta aplicació particular, la desviació de temperatura va portar a una predicció deficient de la massa atrapada al cilindre. El coeficient de transferència de calor convectiu proposat es calcula utilitzant una pseudo-velocitat dels gasos dins del cilindre basada en les taxes de flux de massa en els ports d'entrada i d'escapament durant el flux. El flux en un motor de dos temps presenta un procés complex, diferent del cicle de quatre temps, ja que els processos d'admissió i d'escapament ocorren simultàniament durant una part significativa del període d'intercanvi de ga- sos. A causa d'aquesta naturalesa superposada i de la durada més curta de l'intercanvi de gasos en comparació amb un motor de quatre temps, modelar amb precisió la dinàmica del gas dins del cilindre es torna crucial. Aquest procés de modelatge té com a objectiu assegurar la retenció efectiva de la càr- rega fresca lliurada i l'extracció eficient dels gasos residuals del cicle de motor anterior durant la fase d'intercanvi de gasos. Aquest modelatge és particular- ment crucial en motors avançats de dos temps per obtenir estimacions fiables de la composició de la mescla atrapada i predir amb precisió el rendiment del motor.[EN] Transportation on land is one of the major contributors to emissions and has an impact on climatic changes and health hazards. To address these is- sues, the automotive industry is moving toward sustainable mobility, where new technologies such as hybrid vehicles and electric vehicles are being assessed. However, given the lack of competence in fossil fuel-free alternatives for electricity production, dependence on internal combustion engines (ICEs) to be used as range extenders and electricity production is being addressed. These range extenders are usually two-stroke engines. Due to their design and operating range, these ICEs can be compact, be heavily downsized, and have fewer emissions. Hence it is essential to understand the performances of these new ICE concepts, showcase potential benefits, and aid in further improvements. Aiming towards the above objective in this thesis work a two-stroke uniflow scavenged engine concept is assessed. Experimental data from an engine test cell using two exhaust layouts, three engine speeds, and two load conditions is obtained. A 1D gas dynamic model is developed and validated against all tested points. A 3D replica of the engine is modeled and used in 3D CFD simulation. Fluid dynamically validated 1D model results are used as initial and boundary conditions to assess the thermal and scavenging metrics of this particular engine. On comparing 1D and CFD results, it was observed that temperature and short-circuiting of air were not well captured using state-of- the-art heat transfer and scavenging models during the scavenging process. This led to the proposal of a new heat transfer model and a synthetic scavenging curve. In-cylinder heat transfer is a phenomenon that affects the temperature of burnt gases and fresh air in an internal combustion engine. Compared to the four-stroke units, this influence is more critical in two-stroke engines during the scavenging process since gas velocity filed inside the cylinder evolves rapidly in space and time. This study proposes a new convective heat transfer coefficient model beyond those based on Reynolds number calculation with the piston mean velocity. The model uses semi-empirical equations with non-dimensional numbers since it has to be integrated within the frame of a physical engine model, where thermo and fluid dynamic properties of the gases inside the engine are solved using 0D or 1D approaches. In this particular application, the temperature deviation led to a poor prediction of trapped mass in the cylinder. The proposed convective heat transfer coefficient is calculated using a pseudo-velocity of the gases inside the cylinder based on the mass flow rates in the intake and exhaust ports during scavenging. Scavenging in a two-stroke engine presents a complex process, distinct from the four-stroke cycle, as the intake and exhaust processes occur simultaneously for a significant portion of the gas exchange period. Due to this overlapping nature and shorter gas exchange duration compared to a four-stroke engine, accurately modeling the in-cylinder gas dynamics becomes crucial. This modeling process aims to ensure the effective retention of the fresh charge delivered and the efficient extraction of residual gases from the previous engine cycle during the gas exchange phase. Such modeling is particularly crucial in advanced two-stroke engines to obtain reliable estimations of the trapped mixture composition and predict engine performance accurately.I would like to thank Universitat Politècnica de València for their support with FPI grant with reference FPI-2020-S2-21414Darbhamalla, A. (2024). Analysis of the Internal Thermofluid-Dynamics in a Uniflow Scavenged Engine [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/20464

Assessment of Two Novel Turbocharging Systems to Improve Performance in Future Combustion Engines

[ES] Este trabajo estará dedicado a la evaluación de dos estrategias novedosas en el sistema de turbosobrealimentación de un motor de combustión interna. En particular, se evaluarán dos motores diferentes: un motor diesel para turismos y un motor de camión. Los objetivos son los siguientes: 1. En el motor de camión, se probará un sistema de doble turbosobrealimentación para proporcionar tasas de EGR muy altas mediante un código de simulación de motor 1D. La válvula EGR será reemplazada por una segunda turbina (por lo tanto, se incluirá un segundo turbogrupo en el motor) y el consumo de combustible se evaluará en condición de plena carga en condiciones estacionarias. 2. En el vehículo de pasajeros, se estudiará las prestaciones de un compresor de geometría variable en estado estacionario y condiciones transitorias de funcionamiento del motor utilizando simulaciones por ordenador con un enfoque 1D, junto con una campaña experimental en un banco de ensayos de motores.[EN] This work will be devoted to the evaluation of two novel strategies in the turbocharging system of an internal combustion engine. In particular, two different engines will be assessed: a passenger car Diesel engine and a heavy-duty engine. The objectives are the following: 1. In the heavy-duty engine, a twin turbocharging system to provide very high EGR rates will be tested by means of a 1D engine simulation code. The EGR valve will be replaced by a second turbine (hence, a second turbocharger will be included in the engine) and the fuel economy will be assessed in steady state full load condition. 2. In the passenger vehicle, a performance analysis of a Variable Inlet Compressor in steady state and transient engine running conditions will be studied by using computer simulations in the frame of a 1D approach, together with an experimental campaign in an engine test bench.Darbhamalla, A. (2021). Assessment of Two Novel Turbocharging Systems to Improve Performance in Future Combustion Engines. Universitat Politècnica de València. http://hdl.handle.net/10251/174966TFG

Energy recovery potential by replacing the exhaust gases recirculation valve with an additional turbocharger in a heavy-duty engine

[EN] A simulation-based assessment of different twin-turbocharging configurations allowing energy recovery from the exhaust gas recirculation flow is performed in a heavy-duty engine from the basis of a single-stage turbocharging architecture. This baseline configuration consists of a single stage turbocharged engine with a low-pressure exhaust gas recirculation system. Experimental data from the baseline engine tests are used to calibrate the model. The novelty of this study is to evaluate the energy recovery potential from the low-pressure exhaust gas recirculation flow by replacing its control valve with a turbine so that the flow energy is not lost due to the expansion across the valve. This additional turbine is coupled to a compressor placed in the intake line so that the turbocharging system is converted into a twin-turbocharging architecture. Different twin-turbocharging con-figurations are tested to attain maximum exhaust gas recirculation rates at 1100, 1500, and 2200 rpm engine speeds with boost pressures ranging from 1.8 to 2.6 bar. Fuel consumption calculations have been performed at constant exhaust gas recirculation rates for all three speeds as well as 1500 rpm partial load operation to attain 11.5 bar of brake mean effective pressure. The results in 8 engine running conditions show that twin-turbocharging with the compressors in series configuration with the exhaust gas recirculation turbine dis-charging after the first stage benefits, in average, from increasing about 5% maximum exhaust gas recirculation rates and saves up to 7% in fuel economy compared to the single-stage turbocharging layout.This research work has been supported by Grant PDC2021-120821- I00 funded by the Spanish Ministerio de Ciencia e Innovacion - Agencia Estatal de Investigacion (MCIN/AEI/10.13039/501100011033) , and by the European Union NextGenerationEU/PRTR.Serrano, J.; Climent, H.; Piqueras, P.; Darbhamalla, A. (2022). Energy recovery potential by replacing the exhaust gases recirculation valve with an additional turbocharger in a heavy-duty engine. Energy Conversion and Management. 271:1-11. https://doi.org/10.1016/j.enconman.2022.11630711127

Assessment of Variable Geometry Orifice Compressor Technology Impact in a New Generation of Compression Ignition Powertrains at Low-End and Transient Operation

Surge is a phenomenon that limits the operating range of the compressor at low engine speeds and high boost pressure in turbocharged powertrains. This article assesses two prototype turbochargers of variable geometry orifice (VGO) which compensate for the limitation of the boost pressure at low engine speeds. The VGO prototypes modify the inlet compressor section, extending the compressor characteristic map into lower mass flows (surge limit region). The VGO turbochargers analyzed are also both equipped with variable geometry turbine (VGT) technology. The experiments focus on low-end torque operation ranges in steady and transient engine running conditions. The experimental results are used to validate a 1D physical model. From the modelling perspective, a comprehensive study of the VGO-VGT prototypes is assessed. Results reveal the benefits of VGO technology in terms of attaining higher boost pressure, improved compressor efficiency, and overall engine performance at low engine speeds