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

Assessment of air management strategies to improve the transient response of advanced gasoline engines operating under high EGR conditions

[EN] Advanced gasoline engines may lead the medium-term future of the passenger vehicle market, working in conventional and hybrid powertrains. Downsizing with turbocharging is the most extended way to improve fuel economy in gasoline engines. It is also proven that exhaust gas recirculation (EGR) reduces fuel consumption, but extracting the maximum benefit from EGR requires operating with high EGR rates. This fact can compromise the transient engine operation due to the greater turbocharger dependence. This research evaluates the EGR influence on the transient response of a turbocharged gasoline engine and, mainly, the potential of three air management strategies to accelerate the said response. Tip-in maneuvers at 1500 rpm (6-12 bar BMEP) were tested and simulated to this end. The three strategies are: reducing the EGR dilution by closing the EGR valve simultaneously with the throttle opening, using a pressurized air tank (PAT), and installing an electric supercharger at the compressor outlet in series. Engine tests show that the torque response time with EGR is 2-s slower than without EGR. 1D modeling results reveal that: the PAT connected to the intake manifold provides the fastest response, and the electric supercharger guarantees an excellent tradeoff between fuel consumption and torque response.Galindo, J.; Climent, H.; De La Morena, J.; González-Domínguez, D.; Guilain, S. (2023). Assessment of air management strategies to improve the transient response of advanced gasoline engines operating under high EGR conditions. Energy. 262. https://doi.org/10.1016/j.energy.2022.12558626

Cylinder-to-cylinder high-pressure exhaust gas recirculation dispersion effect on opacity and NOx emissions in a diesel automotive engine

[EN] The objective of the study is to determine the effect of the high-pressure exhaust gas recirculation dispersion in automotive diesel engines in NOx and smoke emissions in steady engine operation. The investigation quantifies the NOx and smoke emissions as a function of the dispersion of the high-pressure exhaust gas recirculation among cylinders. The experiments are performed on a test bench with a 1.6-L automotive diesel engine. In order to track the high-pressure exhaust gas recirculation dispersion in the intake pipes, a valves system to measure CO2, that is, exhaust gas recirculation rate, was installed pipe to pipe. In addition, a valves device to measure NOx emissions cylinder to cylinder in the exhaust was installed. Moreover, a smoke meter device was installed downstream the turbine, to measure the effect of the high-pressure exhaust gas recirculation dispersion on smoke emissions. Five different engine speeds were studied with different torque levels; thus, the engine map was widely studied, from 1250 to 3000 r/min and between 6 and 20 bar of brake mean effective pressure. The exhaust gas recirculation rate varies between 4% and 25% depending on the operating point. The methodology focused on experimental tools combining traditional measuring devices with a specific valves system, which offers accurate information about species concentration in both the intake and the exhaust manifolds. The study was performed at constant raw NOx emissions to observe the effect of the exhaust gas recirculation dispersion in the opacity and fuel consumption. The study concludes that when the exhaust gas recirculation dispersion is low, the opacity presents reduced values in all operating points. However, above a certain level of exhaust gas recirculation dispersion, the opacity increases dramatically with different slopes depending on the engine running condition. This study allows quantifying the exhaust gas recirculation dispersion threshold. In addition, the exhaust gas recirculation dispersion could contribute to increase the fuel consumption up to 3.5%.Macian Martinez, V.; Luján, JM.; Climent, H.; Miguel-García, J.; Guilain, S.; Boubennec, R. (2021). Cylinder-to-cylinder high-pressure exhaust gas recirculation dispersion effect on opacity and NOx emissions in a diesel automotive engine. International Journal of Engine Research. 22(4):1154-1165. https://doi.org/10.1177/1468087419895401S1154116522

Surge detection on an automotive turbocharger during transient phases

International audienceThe surge limit on automotive turbocharger needs to be avoided to prevent operations with pressure and mass flow oscillations. Mild surge is accompanied by noise which is disturbing. Deep surge can cause significant loss of engine power and severe drivability issues. It is necessary to know the stationary limit in order to match a turbocharger with an engine, ensuring enough surge margin. However, this choice does not guarantee surge free operation during transient functioning. In this paper, the surge onset of a compressor while closing a downstream valve is studied. Various tests have been carried out varying the closing time, the position of the initial operating point and the volume of the circuit. The inlet and outlet signals of physical parameters are analyzed with spectral and temporal methods in order to define the instant of the surge occurrenc

Surge detection on an automotive turbocharger during transient phases

International audienceThe surge limit on automotive turbocharger needs to be avoided to prevent operations with pressure and mass flow oscillations. Mild surge is accompanied by noise which is disturbing. Deep surge can cause significant loss of engine power and severe drivability issues. It is necessary to know the stationary limit in order to match a turbocharger with an engine, ensuring enough surge margin. However, this choice does not guarantee surge free operation during transient functioning. In this paper, the surge onset of a compressor while closing a downstream valve is studied. Various tests have been carried out varying the closing time, the position of the initial operating point and the volume of the circuit. The inlet and outlet signals of physical parameters are analyzed with spectral and temporal methods in order to define the instant of the surge occurrenc

A CASE STUDY REGARDING THE IN-CYLINDER AIR MOTION CHARACTERISTICS IN A MOTORED GASOLINE ENGINE: CFD VS. PIV

International audienceFuel economy is a prime objective in order to meet regulatory and customer demands. Given this context, engine manufacturers are forced to introduce complex systems such as variable valve actuation (VVA). One of the simplest form of a VVA system is what is usually called as variable valve timing (VVT). What’s important in these particular cases is in what way the internal aerodynamics and gas exchange phenomena interacts. To study internal aerodynamics, 2 methods are used: an experimental one, employing PIV (particle image velocimetry) technique (for instance) and a numerical one, employing 3D CFD simulation.In the present study, the internal aerodynamics of a motored VVT gasoline engine is examined by using the 2 methods presented above. The purpose is to see the correlation degree between the experimental results obtained on a transparent single cylinder engine through PIV technique and the ones obtained from a three dimensional CFD (computational fluid dynamics) simulation through RANS (Reynolds-Averaged Navier Stokes) approach. The paper describes the methodology used to perform the CFD simulation, the experimentation and the PIV - CFD comparison; it also discusses about the limitation of the CFD simulation and about the difficulties of such a study.Keywords: internal aerodynamics, tumble, CFD, PIV

On combustion instability induced by water condensation in a low-pressure exhaust gas recirculation system for spark-ignition engines

[EN] Water condensation in low-pressure exhaust gas recirculation systems is a concern because of a potential impact on components durability, but its implication into the operation of modern spark-ignition engines has not been investigated in detail. In this work, such aspects are evaluated by tests in a turbocharged multi-cylinder engine installed in a climatic test bench. First, a previously developed and validated zero-dimensional model is used to identify conditions where condensation is produced inside the water charge-air cooler, so that the compressor durability and operation is not affected. Then, different engine points are tested with a constant 25% of recirculated rate. Results show that combustion instability can increase up to 6% (absolute) due to droplets accumulation and release inside the water charge-air cooler, confirmed by an endoscope at the WCAC outlet. The evaporation of these droplets during the intake stroke causes charge overleaning in specific cycles, affecting combustion and inducing occasional misfires. Consequently, the fuel consumption and unburned hydrocarbons can be increased up to 4% and 30%, respectively, compared to the results achieved without condensation. The low speed and load condition was clearly the most affected by the sudden dilution given the lower in-cylinder temperatures. The combustion model shows that condensation formation and eventual overleaning phenomenon is increased if low or zero-carbon fuels such as natural gas, methanol, hydrogen or ammonia are used. Results showed an increased temperature for condensation compared to a traditional gasoline, around 10 degrees C for methane and methanol and 20 degrees C for hydrogen and ammonia.This research work has been supported by Grant PDC2021-120821-I00 funded by MCIN/AEI/10.13039/501100011033 and by European Union NextGenerationEI/PRTR. The authors would like to thank Mr. Vicente Esteve for his collaboration during the experimental campaign.Galindo, J.; Navarro, R.; De La Morena, J.; Pitarch-Berná, R.; Guilain, S. (2022). On combustion instability induced by water condensation in a low-pressure exhaust gas recirculation system for spark-ignition engines. Energy. 261:1-11. https://doi.org/10.1016/j.energy.2022.12512211126

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

Investigation of the Aerodynamic Performance of the Miller Cycle from Transparent Engine Experiments and CFD Simulations

This paper assesses the effect of the Miller cycle upon the internal aerodynamics of a motored transparent spark ignition engine via CFD simulation and particle image velocimetry. Since the transparent Miller engine does not allow for measurements in the roof of the combustion chamber, the extraction of information regarding the aerodynamic phenomena occurring here is based on CFD simulation, i.e., the results of the CFD simulation are used to allow for the extrapolation of the experimental data; thus, they are used to complete the picture regarding the aerodynamic phenomena occurring inside the whole cylinder. The results indicate that implementing the early intake valve closing strategy to obtain the Miller cycle has a negative impact on the mean kinetic energy, turbulent kinetic energy, and fluctuating velocity toward the end of the compression stroke, thus affecting, the combustion process. This supports the need to intensify the internal aerodynamics when applying the Miller cycle such that the turbulence degradation is not too big and, consequently, to still gain efficiency in the Miller cycle

Compressor Surge Mitigation in Turbocharged Spark-Ignition Engines without an Anti-Surge Control System during Load-Decrease Operation

[EN] Automotive manufacturers are showing an increasing preference for hybrid powertrains based on advanced gasoline engines. The most extended solution to improve fuel economy in these engines consists in downsizing with direct injection, while turbocharging is required to compensate the consequent power loss. However, turbocharging is associated with different issues, such as compressor surge. It can appear during fast throttle closings (tip-outs), when the engine air flow is abruptly reduced. A usual strategy to manage this kind of maneuver is the installation of an anti-surge valve (ASV) that connects the compressor inlet and outlet when approaching the surge limit. In pursuit of cost reduction, the removal of the ASV system was assessed in this research. To this end, tip-outs without ASV were tested in a turbocharged gasoline engine equipped with a low-pressure EGR loop, and two strategies were analyzed: throttle closure optimization and reduction of the compressor inlet pressure through the intake flap (located upstream of the compressor to increase the EGR rate). The instantaneous compressor outlet pressure and its time derivative were used for surge detection. Experimental tip-outs without ASV revealed that applying a certain intake flap closing combined with an optimized throttle actuation led to a fast torque decrease, similar to that observed for the reference case with ASV, without compressor instabilities.Galindo, J.; Climent, H.; De La Morena, J.; González-Domínguez, D.; Guilain, S.; Besançon, T. (2022). Compressor Surge Mitigation in Turbocharged Spark-Ignition Engines without an Anti-Surge Control System during Load-Decrease Operation. Applied Sciences. 12(3):1-15. https://doi.org/10.3390/app1203175111512