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Recent studies concluded that the use of ammonia in SI engines is possible thanks to an ignition booster or promoter. In this paper, the improvement of premixed ammonia/air combustion for internal combustion engines is studied as a function of performance and exhaust pollutants in a Spark-Assisted Compression Ignition single-cylinder engine, which supports a higher compression ratio (CR). For the first time, pure NH3 combustion was performed over a large range of engine operating conditions. The study concludes that neat ammonia can be used over a large operating range, here driven by the intake pressure, using a classical ignition device with a CR of 14–17 at 1000 rpm. The comparison with previous data obtained in a current single-cylinder SI engine clearly shows the potential of this engine mode, even for very low loads and various engine speeds (650, 1000, 2000 rpm), in spite of an initial aerodynamic that is not optimized to enhance flame-turbulence interaction. Kinetic simulations provide some explanations about exhaust emission behaviour, especially unburnt NH3, H2, NOx and N2O.

This work presents a study of a magnesium/air combustion process in the context of innovative zero carbon dioxide (CO2) energy carriers for reducing global warming effects. In order to analyze more deeply the confined combustion of magnesium under fluctuating overpressure conditions (0 to 24 hPa) and the generated gaseous by-products, magnesium/air flames have been realized in a combustion chamber with a conical bluff-body as flame holder and different contraction ratios diaphragms at the exit duct. Sieved magnesium samples with two size-fractions were tested: 20–50 µm and 50–70 µm. The gaseous emissions of nitrogen oxides (NOx) and dioxygen (O2) were analyzed with on-line infrared, ultraviolet and paramagnetic analyzers. A flame pulsating behavior was clearly observed from light emission intensity (monitored by a photodiode) and pressure fluctuations (monitored by a pressure sensor); the frequencies obtained ranged between 3 and 10 Hz. The frequency of the pulsation exhibited strong dependence on the geometric configuration of the chamber: a contraction diaphragm divided by two the frequency level of the fluctuations in the studied range of maximum overpressure. Such fluctuations may probably be the consequence of periodic perturbations of the recirculation zone behind the bluff-body. These periodic perturbations are themselves caused by strong periodic overpressure variations due to stiff contraction downstream responding to gas velocity fluctuations. This feed-back-loop mechanism was considered in this study. NOx emissions produced through the thermal pathway were analyzed for equivalence ratios ranging from 0.29 to 1. The representation of NOx versus equivalence ratio exhibited a parabolic shape with a maximum for an equivalence ratio of 0.4. Moreover, NOx emissions of this metal combustor have shown a similar order of magnitude than current internal combustion engines.

International audience; In order to tackle future challenges concerning zero greenhouse gases emissions, an innovative power generation system was designed and analyzed. It included a swirled-stabilized metal-air burner confined in a water-cooled combustion chamber, a secondary heat exchanger and a particle filtration system leading to a unique system of this kind. Magnesium particles in the range 50-70 µm were used as metal fuel. The effect of the swirl intensity was evaluated first on the flame position within the combustion chamber. As expected, the flame was stabilized closer to the burner head with the high swirl number than with the low one. To reach optimal heat to-mechanical conversion efficiency, an analysis of the heat recovery in the power generation system was performed. Experiments were conducted with a total chemical power ranging from 6 kW to 11 kW. Eighty percent of the power released by combustion were recovered in the power generation system and 50% in the combustion chamber. Ninety-eight percent of the magnesium oxide produced by combustion were trapped inside the system. Laser granulometry showed a number distribution for the metal oxide particles around 500 nm. Untrapped particles were measured by a Pegasor Particle Sensor (PPS), which was previously calibrated by comparison with measurements of the total suspended particles (TSP). Complementary TEM analysis confirmed that the metal oxide particles were aggregates of elementary submicron MgO cubic particles (10-1000 nm).

The objective of the present work was to experimentally investigate flow field instantaneous characteristics and their associated heat transfer for pulsating flows representative of engine exhaust flow operating conditions. The experimental apparatus consists of a stationary turbulent hot air flow, with a variable Reynolds number, excited through a pulsating mechanism and exchanging thermal energy with a water cooled steel pipe. Pulsation frequency ranges from 10 to 95 Hz. Simultaneous time-resolved measurements of velocity and temperature were achieved by mean of coupled hot-wire anemometry and micro-unsheathed thermocouples measurements to investigate the impact of the pulsation frequency on heat transfers. Flow pulsation was found to enhance heat transfers in the entire range of frequencies. Significant improvements were observed when the flow was excited with a frequency equal to a resonant mode of the system. With the increase in velocity-amplitude ratio, an increase in the convective heat transfer was observed, with a maximum enhancement corresponding to a factor three and higher, with respect to the relative Nusselt number. Combining experimental results with an analytical formulation, derived from the 1D energy balance equation for a turbulent pulsating flow, the velocity amplitude ratio was identified as the characteristic term representative of the predominant heat-transfer enhancement mechanism.

Considerable efforts have been invested in the automotive industry on electrified powertrains in order to reduce passenger cars’ dependence on fossil fuels. Powertrains electrification resulted in a wide range of mass-production hybrid vehicle models, ranging from micro-hybrid, to mild, full, and battery-extended hybrids such as plug-in and range-extender electric vehicles. Fuel savings of these powertrains strongly rely on the energy management strategy deployed on-board, as well as on the technology used to recover the waste heat energy. This paper investigates the fuel savings potential of a mild hybrid vehicle using an organic Rankine cycle for generating electricity from the engine-coolant circuit. The net mechanical power and electrical power generated from the organic Rankine cycle are determined based on experimental data recorded on a 1.2-L turbocharged engine. The coolant temperature is regulated at 85°C and 105°C depending on the engine load. The R-1234yf organic fluid is used and the Rankine operating pressure has been controlled to maximize the overall system efficiency under technological constraints. The dynamic programming control is used as a global optimal energy management strategy in order to define the best strategy for the engine operation and power-split between the electric and thermal paths of the powertrain. A sensitivity analysis is also performed to find the optimal size of the electric motor while taking into account the additional weight of the organic Rankine cycle system. Results show 2.4% of fuel economy improvement on The Worldwide Harmonized Light Vehicles Test Cycles.

In the global attempt to increase the powertrain overall efficiency of hybrid vehicles while reducing the battery size, engine waste heat recovery (WHR) systems are nowadays promising technologies. This is in particular interesting for series hybrid electric vehicles (SHEV), as the engine operates at a relative high load and under steady conditions. Therefore, the resulting high exhaust gas temperature presents the advantage of increased WHR efficiency. The Brayton cycle offers a relatively reduced weight compared to other WHR systems and presents a low complexity for integration in vehicles since it relies on an open system architecture with air as the working fluid, which consequently avoids the need for a condenser compared to the Rankine cycle. This paper investigates the potential of fuel consumption savings of a SHEV using the Brayton cycle as a WHR system from the internal combustion engine (ICE) exhaust gases. An exergy analysis is conducted on the simple Brayton cycle and several Brayton waste heat recovery (BWHR) systems were identified. A SHEV with ICE-BWHR systems is modeled, where the recovered engine waste heat is converted into electricity using an electric generator and stored in the vehicle battery. The energy consumption simulations is performed on the worldwide-harmonized light-vehicles test cycle (WLTC) while considering the additional weight of the BWHR systems. The intercooled Brayton cycle (IBC) architecture is identified as the most promising for automotive applications as it offers the most convenient compromise between high efficiency and low integration complexity. Results show that 5.5% and 7.0% improved fuel economy on plug-in and self-sustaining SHEV configurations respectively when compared to similar vehicle configurations with ICE auxiliary power units. In addition to the fuel economy improvements, the IBC-WHR system offers other intrinsic advantages such as low noise, low vibration, high durability which makes it a potential heat recovery system for integration in SHEV.

The objective of this paper is to provide new data about the possibility of using ammonia as a carbon-free fuel in a spark-ignition engine. A current GDI PSA engine (Compression Ratio 10.5:1) was chosen in order to update the results available in the literature mainly obtained in the CFR engine. Particular attention was paid to determine the lowest possible load limit when the engine is supplied with pure ammonia or a small amount of H2, depending on engine speed, in order to highlight the limitation during cold start conditions. It can be concluded that this engine can run stably in most of these operating conditions with less than 10% H2 (of the total fuel volume) added to NH3. Measurements of exhaust pollutants, and in particular NOx, have made it possible to evaluate the possibility of diluting the intake gases and its limitation during combustion with pure H2 under slightly supercharged conditions. In conclusion, the 10% dilution limit allows a reduction of up to 40% in NOx while guaranteeing stable operation.

Gas turbine systems are among potential energy converters to substitute the internal combustion engine in future series hybrid electric vehicle. Fuel consumption of these powertrains strongly relies on the energy converter efficiency, the energy management strategy deployed on-board as well as on the transient operation during start-up phase. This paper presents a dynamic modeling and the fuel consumption calculation of an intercooled regenerative reheat gas turbine system used as an auxiliary power unit on a series hybrid electric vehicle. A vehicle model is developed and an optimization method is proposed to optimize the powertrain operation. It consists of using the dynamic programing as an energy management strategy in order to minimize the fuel consumption and the number of switching On/Off of the power unit. Fuel consumption simulations are performed on the worldwide-harmonized light vehicles test cycle while considering the electric and the thermal comfort vehicle energetic needs. Then, a gas turbine dynamic model is developed, where turbomachinery and heat exchanger components are modeled by taking into account their dynamic inertias. The efficiency, the power, and the fuel consumption are calculated during transient operations. Based on the optimization results of switching ON and OFF the system, the fuel consumption dynamic simulation results are considered instead of the dynamic programming results. A constant power start-up strategy and a constant fuel strategy were investigated. Results show an increase in fuel consumption between 2.4% and 3.8% with the first start-up scenario and between 5.7% and 6.4% with the second scenario, compared with static model.

Significant research efforts are considered in the automotive industry on the use of low carbon alternative fuels in order to reduce carbon emissions of future vehicles, some of which are only compatible with external combustion machines. These machines are only suitable for electrified powertrains relying on electric propulsion, particularly in range extenders, where the energy converter operates steadily at a constant power at its optimal efficiency. The fuel consumption of these powertrains strongly relies on the performance of the energy converter in terms of efficiency, as well as on the deployed energy management strategy. This paper investigates the potential of fuel savings of a Extended Range hybrid Electric Vehicle (EREV) using a Thermoacoustic Engine (TAE) system as energy converter substitute to the conventional Internal Combustion Engine (ICE). An exergo-technological explicit analysis is conducted to identify the different TAE-system thermodynamic configurations. The Regenerative Reheat two-stage thermoacoustic engine is selected among numerous identified thermodynamic configurations, offering high efficiency and net specific work compared to other configurations. An EREV model is developed and the presented RRe-n2-TAE configuration is integrated. Fuel consumption simulations are performed on the Worldwide-harmonized Light Vehicles Test Cycle (WLTC). Results are compared to the reference ICE-APU. Results show more than 20% of fuel savings with the RRe-n2-TAE as Auxiliary Power Unit (APU) compared to the basic TAE configuration and comparable fuel consumption with the ICE. Consequently, the studied RRe-n2-TEG-APU presents a potential for the implementation in EREVs with zero carbon alternative fuels.

International audience

International audience

International audience; In a context of growing concerns over climate change, aluminum has the potential to serve as a dense energy carrier in order to replace fossil fuels and reduce greenhouse gases emissions. Indeed, its combustion in air may provide carbon-free energy for applications in which a high-energy storage capacity is required. However, attempts of designing a metal-fueled combustor will conflict with a relatively large dispersion of the burning velocity values reported in the literature, even when similar powders are used. This uncertainty is partially due to the range of experimental conditions and techniques used on those previous studies. In the present work, an experimental Bunsen-type aluminum-air burner is introduced. It is shown that the setup is capable of generating stable dust suspensions under well-controlled conditions. The stabilized aluminum-air flames are studied using emission spectroscopy, Particle Image Velocimetry, laser sheet tomography, and direct visualization of the AlO(g) emissions. The measured burning velocities are then compared to previous results obtained for similar powders as a function of dust concentration. A reasonable agreement is obtained, and it is shown that metal flame tomography can yield a more precise indicator of the flame front position than AlO(g) emissions, helping to reduce the data scatter regarding dust-air burning velocities.

International audience; Les problèmes tels que le changement climatique et le réchauffement planétaire sont liées à la consommation des carburants fossiles. Malgré des systèmes de conversion d'énergie propre déjà existants, notre incapacité actuelle à stocker massivement cette énergie est le principal obstacle au développement de ces solutions alternatives aux combustibles fossiles. Pour répondre à ce défi, une solution consiste à développer un nouveau vecteur énergétique basé sur des poudres métalliques. En effet, la combustion métallique est fortement exothermique et les oxydes formés par cette réaction peuvent être recyclés par des procédés alimentés avec de l'énergie renouvelable. Ce vecteur énergétique fonctionnerait ainsi en boucle fermée et sans générer de gaz à effet de serre sur l'ensemble de son cycle. En revanche, les propriétés fondamentales et les structures de ces flammes hétérogènes métalliques sont encore méconnues, avec des écarts constatés dans la littérature. Dans ce contexte, un brûleur de type Bunsen capable de stabiliser une flamme Aluminium/Air a été développé et permet ainsi la caractérisation de ces flammes à l'aide de différents diagnostiques optiques. Les estimations de la vitesse et de la température de flamme obtenues démontrent la possibilité d'exploiter le potentiel énergétique des poudres d'aluminium, constituant ainsi une alternative crédible aux combustibles fossiles grâce à ses propriétés de combustion et sa grande disponibilité sur terre.