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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.

International audience; Among the technological solutions proposed to reduce air pollutants and greenhouse gas emissions, the so-called “downsizing” operating mode for internal combustion engines is considered one of the most promising. By boosting the intake air pressure, this operating mode achieves higher efficiency, thus reducing pollutant emissions. Modelling the combustion process in these drastic conditions (high pressure, high temperature and high dilution rate) remains challenging, however, as classical models of premixed turbulent combustion prove insufficiently robust. The present work presents, characterizes and validates a dedicated apparatus based on the innovative new one shot engine (NOSE) to investigate turbulent premixed flames under these drastic conditions. The great flexibility of NOSE can generate different internal flow aerodynamic conditions as well as temperature and pressure values, up to a turbulent intensity of 3.3 m/s at 21 bar and 585 K, so at a Ka number ~ 10, with a characteristic integral length of 2 mm. The first milestones of the present work focus on the aerodynamic characterization of NOSE with different ad-hoc studied configurations. The validation of the setup is supported by some examples of the combustion tests performed.

Combustion and emissions characteristics of a spark-ignition engine using direct injection of ethanol blended with ammonia and also pure ammonia were investigated in this study. The experiments were conducted using five different fuel compositions of ethanol/ammonia (C2H5OH/NH3): 100/0, 75/25, 50/50, 25/75, and 0/100. Two strategies of injection were conducted to reach homogenous or stratified conditions with three different intake pressures, 0.5, 1.0, and 1.5 bar corresponding to 2.8, 7.9, and 12 bar of IMEP. The performances and the pollutants emissions are compared as a function of fuel compositions at identical IMEP. High stability is observed for all blends and even for pure ammonia. However, operating conditions are more restrictive for pure ammonia: the injection must be executed during the intake phase to be in a fully premixed mode to guarantee engine stability. Delaying the injection time for pure ammonia is not possible and requires the split of injections with 50% of the ammonia amount injected during the intake. The thermal efficiency is improved by adding 25% of NH3 in ethanol but NOx emissions increase. The stratified strategy for blends improves the combustion durations and the addition of ammonia decreases the NOx emission compared to the homogeneous strategy. On the contrary, CO emissions roughly increase for blends. The presence of NH3 in the fuel composition clearly influences the change of formation of NOx and CO between both strategies.

International audience; The idea of using ammonia as a fuel is nothing new as its first wellknown use was accomplished in buses within a Belgian fleet during World War II. Although several studies performed during the mid-60's investigated the possibility to consider ammonia as fuel for internal combustion engines (mainly by means of CFR experiments or 0D modelling), ammonia-based combustion engine fueling methods were not ready to be marketed as the use of this toxic molecule still poses major challenges-not only because of its supply and associated safety issues, but also because of its physical characteristics compared to conventional fossil fuels. As a function of the target to supply ammonia either partially in standard engines to limit carbon footprint or to employ it mainly in dedicated engines to reach zero footprint, the technological challenges in dual or sole fuel injection, either in SI or CI engines, could vary if the molecule is used as a source for main power or for auxiliary power units (ie. to extend the range of battery vehicles). Its use would also be a function of the transportation type (medium duty or heavy duty engines for freight, construction, marine transportation, etc.), hence creating a complex scenario. In this chapter new results of advanced researches will be discussed in order to highlight the potential of this future green fuel in internal combustion engines.

International audience; As in most industrial cases, the expansion of premixed flames in Spark-Ignition (SI) engines is strongly affected by turbulence flow fields. However, as the flame radius and curvature are non-negligible during combustion development, the global stretch effect can drastically change the turbulent flame propagation speed. In this paper, spherical turbulent premixed flames were studied inside a constant-volume vessel for a wide range of air-isooctane mixtures, initial turbulent intensities and pressures by using simultaneously Mie scattering tomography and 2-View Schlieren imaging. The comparison between different radii enabled non-convected flames with a global spherical shape to be selected and the validity of a correction factor, first introduced by Bradley et al., was assessed. A set of turbulent flame speeds was obtained and the evolution as a function of the global stretch rate was analyzed. Various turbulent flame speed definitions were also evaluated on two different datasets.

International audience; Syngas is a promising low-carbon gaseous fuel for auxiliary electricity power generation through flexible compression ignition dual-fuel IC engines. But as syngas compositions are linked to the biomass source and the different production processes, this work has as first objective to provide fundamental data, I.e. laminar flame speed, for different syngas compositions in decane/syngas mixtures as a function of initial thermodynamic conditions, with decane as the reactive fuel surrogate. Then, some initial combustion performance results, in dual-fuel operation, are presented and analyzed as a function of diesel type fuel quantity in the main syngas charge. In future work, optical experiments will be done to contribute to the understanding of the combustion process.

Conventional combustion has been exploited for power generation purposes since ancient times. Considering all relevant analyses of primary energy consumption, it is obvious that worldwide it will still play a major role in heat generation and will only slowly be replaced in generation of electricity. Despite unpreceded breakthroughs, growing capacity and large success of environmentally more acceptable technologies in terms of global warming potential as well as their growing share in the primary energy consumption, relevant analyses do not predict a significant midterm decrease of combustion-generated energy (International Energy Agency, 2019). In this view, the main scientific focus should be the development of clean combustion approaches which are, emission wise, on par or even supersede currently available renewable energy technologies.

Open Access; International audience; Faced with the problem of reducing greenhouse gas emissions and transitioning toward a greater use of renewable energies, ammonia, as an energy carrier, is increasingly seen as a potential 'green' fuel for transportation, in particular marine applications. However, its combustion characteristics (high minimum ignition energy and auto-ignition temperature, low combustion speed in comparison to usual hydrocarbon fuels) are drawbacks that have so far limited its use. Due to the evolution of different pollutant standards for road transportation, Spark-Ignition engines and thus the combustion process itself have been subjected to many changes over the last 20 years (e.g., gasoline direct injection, downsizing). The objective of this article is to discuss the potential of ammonia as a fuel for spark-ignition engines thanks to the studies carried out so far and to point out directions for future work.

Laminar flame speeds of ammonia with oxygen-enriched air (oxygen content varying from 21 to 30 vol.%) and ammonia-hydrogen-air mixtures (fuel hydrogen content varying from 0 to 30 vol.%) at elevated pressure (1-10 bar) and temperature (298-473 K) were determined experimentally using a constant volume combustion chamber. Moreover, ammonia laminar flame speeds with helium as an inert were measured for the first time. Using these experimental data along with published ones, we have developed a newly compiled kinetic model for the prediction of the oxidation of ammonia and ammonia-hydrogen blends in freely propagating and burner stabilized premixed flames, as well as in shock tubes, rapid compression machines and a jet-stirred reactor. The reaction mechanism also considers the formation of nitrogen oxides, as well as the reduction of nitrogen oxides depending on the conditions of the surrounding gas phase. The experimental results from the present work and the literature are interpreted with the help of the kinetic model derived here. The experiments show that increasing the initial temperature, fuel hydrogen content, or oxidizer oxygen content causes the laminar flame speed to increase, while it decreases when increasing the initial pressure. The proposed kinetic model predicts the same trends than experiments and a good agreement is found with measurements for a wide range of conditions. The model suggests that under rich conditions the N 2 H 2 formation path is favored compared to stoichiometric condition. The most important reactions under rich conditions are: NH 2 + NH = N 2 H 2 + H, NH 2 + NH 2 = N 2 H 2 + H 2 , N 2 H 2 + H = NNH + H 2 and N 2 H 2 + M = NNH + H + M. These reactions were also found to be among the most sensitive reactions for predicting the laminar flame speed for all the cases investigated.

International audience; Ammonia is increasingly recognized as a potential emission-lean and sustainable energy carrier. Producing fossil-free ammonia from variable renewable energy sources (VRES) through water electrolysis may soon become economically viable. Ammonia is a comparatively cheap and safe medium for hydrogen transport and storage, allowing to cope with the variability of the renewable energy supply in time and space and facilitating the penetration of VRES in the energy systems. Moreover, ammonia features promising properties as a fuel, allowing retrieving stored energy by means of direct combustion or fuel cell use to satisfy heat and power demand during VRES production lows. In particular, its high octane rating makes it suitable for use in spark-ignition (SI) engines, which may be a low-cost, low-complexity, high-reliability solution for local heat and power generation. Power-to-Ammonia-to-Power and Heat (P2A2P+H) could thus be an interesting bridging concept in new energy systems. However, such technologies present a low maturity level and their economic performance is highly uncertain and hard to quantify, thus slowing down their implementation. Therefore, the present work proposes a cost assessment of a grid-assisted P2A2P+H system based on a wind farm, an ammonia production and storage plant and a SI engine generator providing power and heat to a residential district. The optimal system designs are investigated by means of a multi-objective optimization method based on a genetic algorithm. Results show that such systems may be commercially competitive if the grid prices increase, and allow a local energy system to be highly self-sufficient, thus preventing risks of shutdowns associated with increasing shares of VRES. Seasonal storage appears particularly relevant and the ammonia system provides non-negligible amounts of heat to the consumers.

International audience; Ammonia combustion appears as a meaningful way to retrieve stored amounts of excess variable renewable energy, and the spark-ignition (SI) engine has been proposed as a practical conversion system. The present work aims at elucidating the combustion characteristics of ammonia blends in engine-relevant turbulent conditions. To that end, laminar and turbulent flame experiments were conducted in a constant-volume vessel at engine-relevant conditions of 445 K and 0.54 MPa to assess the combustion behavior of ammonia/hydrogen/air, ammonia/methane/air and methane/hydrogen/air mixtures observed in an all-metal single-cylinder SI engine. Results show that the respective accelerating or decelerating effects of hydrogen or methane enrichment observed in the SI engine could not be sufficiently explained by the measured laminar burning velocities of the mixtures. Since the latter are very low, the studied combustion regimes are at the boundary between the thin and broken reaction zones regimes, and thus strongly influenced by flame-turbulence interactions. The quantification of the flame response to turbulence shows much higher effects for ammonia blends, than for methane-based fuels. The aforementioned opposite effects of ammonia enrichment with hydrogen or methane are observed on the turbulent burning velocity during the turbulent flame experiments and correlated to the thermochemical properties of the reactants and the flame sensitivity to stretch. The latter may explain an unexpected bending effect on the turbulent-to-laminar velocity ratio when increasing the hydrogen fraction in the ammonia/hydrogen blend. Nevertheless, a very good correlation of the turbulent velocity was found with the Karlovitz and Damköhler numbers, that suggests that ammonia combustion in SI engines may be described following the usual turbulent combustion models. This encourages further investigations on ammonia combustion for the optimization of practical systems, by means of dedicated experiments and numerical simulations.

Due to its strong impact on health, particulate matter is increasingly regulated by government emission standards for vehicles. As one of the sources of particulate matter is the soot produced by internal combustion engines, it remains a challenge to improve advanced combustion modes to reduce it. There is still, however, some lack of understanding about the formation and oxidation processes of soot, especially in “realistic” conditions, such as for example at high temperature and pressure conditions with or without the presence of exhaust gases. The objective of this study is to investigate soot formation in the case ofn-Dodecane spray flames at conventional Diesel engine conditions generated in the New One Shot Engine by using diffused back-illumination extinction with different CO2and water vapour contents. It was found that CO2addition reduces the soot mass fraction if its volumetric concentration in ambient mixtures is at least 4.5% while 1% of water is sufficient to significantly reduce the soot mass fraction. The impact of the ambient mixture obtained in ECN spray A pre-burn vessels was also investigated to assess the accuracy against soot measurements available in the literature.

As bio-butanol would be one promising alternative fuel to mitigate the energy crisis and reduce the environmental impact of the automotive sector, its potential as blend in gasoline has been widely evaluated especially for conventional Spark Ignition engines. But recent studies prove that Gasoline Compression Ignition operating mode could be a future interesting advanced combustion mode to reach higher efficiency and lower pollutant emissions than conventional SI engines. The objective of this paper is to underline the effect of butanol blend in gasoline in injections conditions needed in GCI by set experimental study in a High Pressure/ High Temperature chamber. Therefore, first data about sprays and combustion characteristics as a function of the butanol content in a gasoline surrogate (PRF80) at injection conditions of GCI, i.e. high pressure (6 MPa) and high-temperature (900 K) conditions but with injection pressure of 40 MPa are given and he results discussed thanks to kinetics simulation of ignition delays.

Thermodiffusive and hydrodynamic instabilities cause a departure from laminar combustion and, as such, are responsible for flame self-acceleration behavior. Due to the presence of hydrogen, syngas is a fuel prone to instabilities and is frequently diluted with CO2 or co-fired with CH4. This paper, thus presents an experimental study on how syngas mixed with CO2 and/or CH4 influence the onset of both kinds of instability. First, the results show that the laminar flame thickness is the controlling parameter in determining the critical radius at which cellularity appeared when CH4 is added to syngas. Moreover, higher levels of CO2 dilution translated into a constant critical radius, illustrating that the thermodiffusive mechanism is counterbalanced by the hydrodynamic one. To help differentiate between both kinds of instability, it is suggested herein to use the coefficient of self-acceleration or the ratio of the flame speed at the critical flame radius on the laminar flame speed. Finally, a correlation predicting the onset of cellularity is proposed based on the equation format proposed by Jomaas et al. (2007), derived from the stability analysis of a spherically expending flame. The correlation expresses the critical Peclet as a function of hydrodynamic and thermodiffusive instabilities and was successfully validated against experimental data from this study and the literature.

International audience; Syngas (for synthetic gas) is a well known gaseous biofuel, also known as producer gas or wood gas. It is composed mainly of N2, CO2, CO, H2 and CH4, with varying shares depending on the gasification process and biomass source. When syngas is used in Internal Combustion engines for stationary electricity generation, the operation modes have to be adapted. The problem is that, for the moment, the combustion parameters of complex syngas compositions are not fully covered by the literature. In this study, the laminar flame speeds and Markstein lengths are measured for three syngas compositions. These compositions were chosen to represent typical production of three types of gasifiers (Updraft, Downdraft and Fluidized Bed). Measurements were made at varying initial temperatures (298–423 K), pressures (1–5 bar) and equivalence ratios (0.6–1.4). The method used was the outwardly propagating spherical method. Higher H2 and CO contents on the Updraft and Downdraft compositions produced flame speeds two times higher than the Fluidbed composition. Results were compared to the data from the only two previous studies but no quantitative agreement was found. The results obtained from kinetic modeling with four kinetic mechanisms provide a global agreement specially those from the CRECK mechanism that only deviated from the experimental results by 5–10%

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.

International audience; The successful implementation of innovative fuels relies on many factors and requires a precise description of thecombustion characteristics. In practice, traditional indicators, such as octane or cetane numbers, are used. Obtaining thesenumbers however requires a specific setup. Moreover, they are not sufficient to predict the combustion timing for innovativeconcepts, such as homogeneous charge compression ignition (HCCI). Evaluating and reporting the characteristics of new fuels istherefore challenging. Using a regular diesel engine converted to HCCI operation, we developed a screening methodology toeasily characterize and present key features of new fuels. This paper describes the methodology and then applies it to new fuelsproduced from biomass: valeric biofuels. The methodology presented in this study intends to bridge the work on fundamentalchemical kinetics with conventional engine experiments.

The present study introduces new laminar burning velocity data for ammonia/hydrogen/air mixtures measured by means of the outwardly propagating spherical flame method at atmospheric pressure, for previously unseen unburned gas temperatures ranging from 298 to 473 K, hydrogen fractions ranging from 0 vol% to 60 vol% in the fuel and equivalence ratios in the range [0.8–1.4]. Results show increasing velocities with increasing hydrogen fraction and temperature, with maximum values obtained for rich mixtures near stoichiometry. The new experimental dataset is compared to dedicated laminar burning velocity correlations from the literature and to simulations using detailed kinetic mechanisms. The ammonia/air correlation presents a good agreement with measurements over the whole range of experimental conditions. The ammonia/hydrogen/air correlation captures the effect of the initial temperature satisfactorily for equivalence ratios below 1.3 and hydrogen fractions below 50 vol% in the fuel, but discrepancies are observed in other conditions. The effect of hydrogen addition is reproduced satisfactorily for hydrogen fractions between 20 and 40 vol% in the fuel, but discrepancies are observed for rich mixtures below 20 vol% hydrogen and for all mixtures containing 50 vol% hydrogen and more. An optimization of both correlations is proposed thanks to the experimental data obtained, but only with partial improvement of the ammonia/hydrogen/air correlation. State-of-the-art detailed kinetic reaction mechanisms yield values in close agreement with the present experiments. They could thus be used along with additional experimental data from different techniques to develop more accurate correlations for time-effective laminar burning velocity estimates of NH3/H2/air mixtures.

International audience; Nowadays, one of the main challenge in the automotive sector concerns the increase of Internal Combustion Engine efficiency. Present and future stringent standards call for reduction of fuel consumption and cut of pollutant emissions. In this respect, one technical solution is the downsizing of the engines that consists in increasing the intake pressure and temperature, through a turbocharger, while reducing the displacement. To avoid abnormal combustion occurrences, the use of high dilution rates is required. It is evident that due to these drastic constraints, high pressure and high dilution, the propagation and the stability of the premixed turbulent flame are strongly affected. Beyond this case, the laminar flamelet regime concept remains the base for the models used in industrial applications. Therefore, the knowledge of laminar burning speed is still crucial and an open research topic. As this parameter is dependent of fuel, its investigation is fundamental in order to evaluate potential suitable surrogates or/and alternative fuels. The present study aims to validate the TRF-E (a Toluene Reference Fuel blended with 5%vol ethanol) as suitable surrogate of a commercial gasoline and to gather a wide laminar burning velocities database for the TRF-E. For that, the laminar flame propagation inside a spherical stainless steel vessel was observed via a Double-View Schlieren technique. The temperature was set at 373, 423 and 473 K, while pressure and dilution were, respectively, 0.1, 0.2, 0.3 and 0.5 MPa and 0, 10 and 20%, for equivalence ratio range from 0.8 to 1.3. Thanks to this large laminar burning velocity database, it was possible to determine coefficients from the mathematical correlation proposed by Metghalchi and Keck (1982) with high precision by solving a global optimization problem. Reference conditions were fixed at 473 K, 0.1 MPa and 0% of dilution. In this case, the laminar burning velocity difference between TRF-E and gasoline is less than 4%. But the decrease of temperature and the increase of pressure or dilution affect the laminar burning velocity of these two fuels in a different way. Anyway, this gap is limited to 10–15% in the worst cases, confirming that TRF-E may be considered as a suitable surrogate of the investigated gasoline.

International audience; The mitigation of climate change implies the increasing use of variable renewable energy sources. Energy storage and transport solutions will contribute to ensure the stability, reliability and flexibility of the energy systems. Ammonia is a well-known chemical of formula NH3 and, amongst other electrofuels, a promising energy carrier and carbon-free combustible fuel. There-fore, it is of significant interest to study ammonia combustion systems. The present investiga-tion focusses on premixed ammonia/hydrogen/air combustion to assess stability ranges, perfor-mance and pollutant emissions by means of a systematic parametric study, in the purpose of optimization in the case of a current spark-ignition engine. Gaseous ammonia blends with a wide range of hydrogen fuel fractions and equivalence ratio were tested at two different loads. Results show a power output and indicated efficiency benefit of low H2 enrichment for slightly rich and slightly lean mixtures, respectively. Hydrogen is therefore mainly an ignition promoter, rather than a global combustion promoter assumedly due to high thermal losses. A small amount of H2, along with supercharged operation greatly improves the performances of the engine and its stability, thus rendering NH3 a very suitable fuel for SI-engines in case of in-situ H2 gener-ation. Hydrogen also mitigates unburned NH3 emissions, yet not sufficiently but those could be combined with the evenly elevated NOx emissions in dedicated selective catalytic reduction systems.

Sometimes forest fires have unpredictable and dangerous behaviors for human lives. One of these behaviors leads to accelerating forest fires, characterized by an augmentation of the rate of spread and of the energy released by the fire. The phenomenon mechanisms are not well understood but a thermochemical approach supports that volatile organic compounds coming from heated vegetation and smoke may create a flammable atmosphere near the fire front; according to the literature, α-pinene (C10H16) and benzene (C6H6) were found to be the main compounds. Therefore, we studied α-pinene/benzene/air mixtures by varying the initial temperature from 75°C to 180°C, equivalence ratio from 0.7 to 1.4, and fuel proportion. We focused on two combustion characteristics: laminar burning speeds and Markstein lengths. We observed a maximal laminar burning speed shifted from 1.1 equivalence ratio, when mixtures are rich in α-pinene, to 1.2, when mixtures are rich in benzene. With the increase of benzene percentage, l...

With the different kinds of fuel now available, modern spark ignition engines have to be adapted, owing not only to the difference between the characteristic heat of combustion of the different fuels, but also to the response of the flame to stretch. As the burning rate is a function of the laminar burning speed which is a function of the flame stretch, this parameter has to be taken into account by combustion models. In this study, a zero-dimensional combustion model, based on the Flame Surface Density equation, is enhanced with a model for the stretched laminar burning speed. Numerical results are compared with the experimental results of three lean air-fuel mixtures with isooctane, propane and methane as fuels, that have similar unstretched laminar burning speeds but different Lewis numbers. Laminar burning speed, flame radius, burnt mass fraction, and turbulent flame wrinkling are compared with experimental results. The simulation trends are similar to those of experimental results. Methane and propane (Lewis number 0.99 and 1.80 respectively) show similar wrinkling rates, while isooctane (Lewis number 2.90) has a lower wrinkling rate. The observed difference between computed burnt mass fraction with stretched and unstretched flame speed models reveals that the impact of stretch and Lewis number needs to be taken into account and that a stretched laminar burning speed must be used for modeling, especially for mixtures with a Lewis number much greater than unity.

The Reitz and Diwakar and the KHRT atomization models are widely used for high-pressure diesel-fuel spray. The constants in both models must be calibrated to correctly predict the injection process based on the nozzle geometry, injection conditions, and fuel. Calibration can be significantly time-consuming given the four constants in both models. This paper suggests a strategy to assess the impact of models’ constants on spray tip penetration and mean droplet-diameter predictions on a reference case, with an injection pressure of 700 bar, to characterize the influence of the atomization model’s calibration. The assessment used a design of experiment method (DOE), which demonstrated the important interaction between constants on the results. Obtained calibrations were used for comparing the models’ performances qualitatively and quantitatively by accounting for spray and air-entrainment characteristics. Both models gave similar results, but the KHRT model yielded a better spray shape. Finally, based on DOE results, a method is proposed to modify the model’s constants for higher pressures (900 and 1300 bar).

International audience; In a context of decreasing pollutant emissions, the transport sector has to tackle improvements to the engine concept as well as fuel diversification. The use of these different fuels often has an impact on the combustion performance itself. In the case of Spark Ignition (SI) engines, efficiency is a function of the combustion speed, i.e. the speed at which the fresh air–fuel mixture is consumed by the flame front. Every expanding flame is subject to flame curvature and strain rate, which both contribute to flame stretch. As each air–fuel mixture responds differently to flame stretch, this paper focuses on understanding the impact of flame stretch on fuel performances in SI engines. Different air–fuel mixtures (different fuels or equivalence ratios) with similar unstretched laminar burning speeds and thermodynamic properties but different responses to stretch were selected. The mixtures were studied in a turbulent spherical vessel and in an optical engine using Mie-Scattering tomography. The combustion phasing was also investigated in both optical and all-metal single cylinder engines. Results show that flame stretch sensitivity properties such as Markstein length and Lewis number, determined in laminar combustion conditions, are relevant parameters that need to be taken into consideration to predict the global performance of fuels, either experimentally or for modeling simulation.

Ameliorant les connaissances sur les phenomenes mis en jeu lors de la combustion, des technologies optiques apportent les donnees indispensables pour valider les modeles necessaires au developpement des moteurs propres. Ainsi, la LII (ou incandescence induite par laser), appliquee aux moteurs Diesel, permet de detecter et caracteriser les particules de suies generees lors de la combustion, afin d’en reduire les emissions.

International audience; 8 The mitigation of climate change implies the increasing use of variable renewable energy sources. Energy 9 storage and transport solutions will contribute to ensure the stability, reliability and flexibility of the energy 10 systems in that context. Ammonia is a well-known chemical of formula NH3 and, amongst other electrofuels, 11 a promising energy carrier and carbon-free combustible fuel. In the present experimental study, engine per-12 formance, combustion characteristics and pollutant emissions of a recent spark ignition engine fueled with 13 premixed ammonia/hydrogen/air mixtures were assessed. Gaseous ammonia blends in a wide range of hydro-14 gen fuel fractions and equivalence ratios were tested at two different engine loads. Results show performances 15 comparable with conventional fuel operation when the appropriate promotion strategies are used. Specifically, 16 blending up to 20% hydrogen in the fuel by volume improves the cyclic stability and avoids misfires, while 17 granting the best work output and indicated efficiencies near stoichiometry. Higher hydrogen fractions result 18 in depleted efficiency, attributed to higher wall heat losses. The combustion duration is directly correlated to 19 the LBV of the mixtures, thus being accelerated by hydrogen blending. The accelerating effect of hydrogen is 20 particularly remarkable during the initial stage of the combustion. Hydrogen appears therefore mainly as an 21 ignition promoter. Increasing the engine load improves the furnished work and allows to extend the operating 22 boundaries in terms of mixture composition. 23

Laminar natural gas flames are investigated at engine-relevant thermochemical conditions where the ignition delay time τ is short due to very high ambient temperatures and pressures. At these conditions, it is not possible to measure or calculate well-defined values for the laminar flame speed sl, laminar flame thickness δl, and laminar flame time scale τ l = δ l / s l due to the explosive thermochemical state. Here, the corresponding reference values, sR, δR, and τ R = δ R / s R , that account for the effects of autoignition, are numerically estimated to investigate the enhancement of flame propagation, and the competition with autoignition that arises under nominally autoignitive conditions (characterised here by the number τ/τR). Large values of τ/τR indicate that autoignition is unimportant, values near or below unity indicate that flame propagation is not possible, and intermediate values indicate that a combination of both flame propagation and autoignition may be important, depending upon factors such as device geometry, turbulence, stratification, et cetera. The reference quantities are presented for a wide range of temperatures, equivalence ratios, pressures, and hydrogen concentrations, which includes conditions relevant to stationary gas turbine reheat burners and boosted spark ignition engines. It is demonstrated that the transition from flame propagation to autoignition is only dependent on residence time, when the results are non-dimensionalised by the reference values. The temporal evolution of the reference values are also reported for a modelled boosted SI engine. It is shown that the nominally autoignitive conditions enhance flame propagation, which may be an ameliorating factor for the onset of engine knock. The calculations are performed using a recently-developed, detailed 177 species mechanism for C0–C3 chemistry that is derived from theoretical chemistry and is suitable for a wide range of thermochemical conditions as it is not tuned or optimised for a particular operating condition.

This paper presents the spray and combustion characterization of Acetone-Butanol-Ethanol mixture and alcohol fuels, blended with n-Dodecane at different volume ratio, as 20% Acetone-Butanol-Ethanol (ABE20), 20% Butanol (Bu20), 40% Butanol (Bu40), 20% Ethanol (Eth20), as well as 20% Butanol/20% Ethanol (Bu20Eth20) to evaluate the impact of the physical and chemical characteristics, especially fuel oxygen contents. The experiments were carried out in “New One Shot Engine” at high-pressure and high-temperature conditions, established as Spray A condition, defined by Engine Combustion Network (ECN): 60 bar ambient pressure, 22.8 kg/m 3 ambient density and various ambient temperatures (800, 850, and 900 K). The liquid and vapor spray parameters were characterized by diffused-back illumination and Schlieren techniques in non-reactive condition (in pure nitrogen). In reactive conditions (with 15% oxygen), the lift-off length and absolute ignition delay were measured by OH ∗ chemiluminescence. First, as expected because of slight difference in fuel density, mass flow rates, vapor spray penetration, and spray angle are almost similar. But, due to the highest volatility, the liquid length of ABE20 is shorter compared to pure n-Dodecane and other blends. Also its ignition delay and lift-off length are shorter than those of alcohol blends due to difference in expected cetane number and latent heat of vaporization. The increase of butanol quantity or the addition of ethanol in blends increase the liquid length due to the cooling effect from the latent heat of vaporization, while the lift-off length and ignition delay increase with oxygen contents. Finally, ABE20 seems to be a good candidate for diesel-blended fuel due to the similar behavior as n-Dodecane itself.

Fuels for Advanced Combustion Engine (FACE)-C gasoline/air and toluene primary reference fuel (TPRF) (51.6 vol% iso-octane, 21.5 vol% n-heptane and 26.9 vol% toluene)/air mixtures corresponding to the same Research Octane numbers (RON) of 85 were characterized in terms of determining their burning rates in a fan stirred turbulent vessel and filmed using a high-speed dual Schlieren imaging technique. Also, a Mie scattering planar laser tomography was employed to characterize the variations of flame morphology induced by the simultaneous existences of different turbulent length scales and the susceptibility to develop cellular structures at elevated pressures (through the Darrieus-Landau instability). Measurements were performed in a well-controlled environment of initial pressures 0.1, 0.5 and 1.0 MPa at a fixed initial temperature of 358 K at a range of measured turbulence intensities from 0.5 to 2.0 m/s. The enhancement of turbulent burning velocity ST as a function of turbulence intensity was evaluated. The absence of bending regime was accounted for based on the size of the vessel and limited range of turbulent intensities investigated in the present work. All the present data were empirically correlated by power-law correlation derived for a different flame-type configuration to test its sensitivity to the geometry and type of the burner investigated.

Reactivity-controlled compression ignition (RCCI) is a dual-fuel variant of low-temperature combustion that uses in-cylinder fuel stratification to control the rate of reactions occurring during combustion. Using fuels of varying reactivity (autoignition propensity), gradients of reactivity can be established within the charge, allowing for control over combustion phasing and duration for high efficiency while achieving low NOx and soot emissions. In practice, this is typically accomplished by premixing a low-reactivity fuel, such as gasoline, with early port or direct injection, and by direct injecting a high-reactivity fuel, such as diesel, at an intermediate timing before top dead center. Both the relative quantity and the timing of the injection(s) of high-reactivity fuel can be used to tailor the combustion process and thereby the efficiency and emissions under RCCI. While many combinations of high- and low-reactivity fuels have been successfully demonstrated to enable RCCI, there is a lack of fundamental understanding of what properties, chemical or physical, are most important or desirable for extending operation to both lower and higher loads and reducing emissions of unreacted fuel and CO. This is partly due to the fact that important variables such as temperature, equivalence ratio, and reactivity change simultaneously in both a local and a global sense with changes in the injection of the high-reactivity fuel. This study uses primary reference fuels iso-octane and n-heptane, which have similar physical properties but much different autoignition properties, to create both external and in-cylinder fuel blends that allow for the effects of reactivity stratification to be isolated and quantified. This study is part of a collaborative effort with researchers at Sandia National Laboratories who are investigating the same fuels and conditions of interest in an optical engine. This collaboration aims to improve our fundamental understanding of what fuel properties are required to further develop advanced combustion modes.

International audience

International audience; As in most of industrial cases, in Spark-Ignition (SI) engines, the expansion of premixed flames is strongly affected by turbulence flow fields. However, as the flame radius and curvature are non-negligible during the combustion development, global stretch effect can drastically change the turbulent flame propagation speed. In this paper, spherical turbulent premixed flames are studied inside a constant-volume vessel for a wide range of air-isooctane mixture and initial turbulence by using simultaneously Mie scattering tomography and 2-views Schlieren techniques. With the 2-views Schlieren diagnostic, the flame volume can be reconstructed and a more 'real' flame radius can be determined. The comparison between this radius, which is more usually determined by only 1-view Schlieren, and the one obtained by tomography was possible, and enabled to select non-conveyed flames with a global spherical shape. In the first part, the values of the correction factor for Schlieren images, first introduced by Bradley et al. in 2003, is discussed as function of the turbulent intensity and initial pressure. In the second part, the effect of turbulent intensity and initial pressure for isooctane/air mixtures on flame propagation speed evolution is evaluated as function of the stretch rate.

ÈN] Abstract The intermediate fermentation mixture of butanol production, Acetone, Butanol and Ethanol (ABE), is increasingly considered as a new alternative fuel in CI engines due to its physical and chemical properties, which are similar to those of butanol, and its advantages of no additional cost or energy consumption due to butanol separation. In a previous study, the High-Pressure and High-Temperature (HPHT) chamber, called ‘New One Shot Engine” (NOSE), was used to investigate macroscopic spray-combustion parameters by validating Spray-A conditions of the Engine Combustion Network. The present study concerns the spray-combustion characteristics of the ABE mixture (volume ratio 3:6:1), blended with n-dodecane at a volumetric ratio of 20% (ABE20), compared to n-dodecane as reference fuel. The macroscopic spray and combustion parameters were investigated, for non-reactive conditions, in pure Nitrogen and for reactive conditions, in 15% oxygen, at ambient pressure (60 bar), ambient density (22.8 kg/m3 ) and different ambient temperatures (800 K, 850 K and 900 K). The liquid and vapor spray penetrations were investigated by the Diffused Back Illumination (DBI) and Schlieren techniques in non-reactive conditions. In reactive conditions, the lift-off length was measured by OH* chemiluminescence images at 310 nm. The Schlieren technique was also used to verify the choice of detection criterion. The ignition delay results of the two fuels were compared. It was found that the behavior of the two fuels as a function of temperature was similar even if the liquid length of ABE20 was shorter than that of n-dodecane at all ambient temperatures. On the other hand, no real difference in vapor spray penetration between the two fuels was observed. The vaporization properties and the lower autoignition ability of ABE20 led to longer ignition delays and lift-off length., The authors acknowledge the National Research Agency (contract ANR-14-CE22-0015-01) for financial support to the ECN-France project and Region Centre Val de Loire (CPER 2007-2013 Energies du Futur) and FEDER for financial support to build the experimental set-up. We also thank G.Bruneaux and M.Bardi from IFPen for interesting discussions that helped us to refine the analysis.

The comparison of butanol/isooctane blends with an ethanol/isooctane blend was characterized with respect to laminar combustion, by using the spherical expanding flame methodology, in a constant volume vessel. This paper presents the results obtained for blends with alcohol concentrations of 0%, 25%, 50%, 75% and 100% (in volume) and an equivalence ratio ranging from 0.7 to 1.4, at different initial pressures (0.1, 0.3, 0.5 and 1.0 MPa) and an initial temperature of 423 K. The addition of alcohol to isooctane increases the laminar burning velocity, but increasing the initial pressure limits this increase. From burned gas Markstein length estimates, the flame of ethanol/isooctane and air mixture seems to be less sensitive to the total stretch rate and thermo-diffusive instabilities. From experimental data, a correlation with laminar burning velocity is suggested as a function of initial pressure, equivalence ratio and alcohol concentration.

International audience; In the present study, experiments were carried out in a single-cylinder downsized SI engine with different rates of oxygen (15% to 27% by volume in the total mixture of intake gases except fuel) and equivalence ratios (from 0.45 to 1). Therefore, the oxygen volume fraction is due to oxygen enrichment or nitrogen dilution. The study of the impact of controlling the oxygen concentration on the combustion characteristics and emissions was performed at 1 400 rpm, at several loads (Indicated Mean Effective Pressure (IMEP) from 400 to 1 000 kPa). For each operation point, the spark advance and the intake pressure were adjusted simultaneously in order to maintain the load and obtain a minimum value of the indicated Specific Fuel Consumption (SFC). The effect of the oxygen concentration on the engine combustion characteristics was simulated by using the commercial software AMESim, with the combustion model developed by IFP Energies nouvelles, and an adapted algorithm was used to avoid residual gas calibration. By implementing a correlation for the laminar burning velocity, the in-cylinder pressures were perfectly predicted with a maximum pressure relative error of less than 2% for almost all the operating points. The classification of engine combustion according to the Peters-Borghi diagram, gives a deeper insight into the interaction between turbulence and the flame front.; Dans cette étude, des expériences sur monocylindre essence suralimenté ont été réalisées avec comme variable le taux d'oxygène (15 % à 27 % en volume dans le mélange total de gaz d'admission à l'exception du carburant) admis et la richesse (0,45 à 1). La fraction volumique d'oxygène représente en fait soit un enrichissement en oxygène de l'admission moteur ou de l'azote de dilution. L'étude de l'impact du contrôle de la concentration d'oxygène sur les caractéristiques de combustion et les émissions a été effectuée à 1 400 tr/mn, pour plusieurs charges, de 400 à 1 000 kPa. Pour chaque point de fonctionnement, l'avance à l'allumage et la pression d'admission ont été ajustées simultanément afin d'obtenir la charge maximale et la valeur minimale de consommation spécifique indiquée de carburant. L'effet de la concentration en oxygène dans la combustion du moteur a été simulé à partir du logiciel AMESim, avec le modèle de combustion développé par l'IFP Energies nouvelles, et un algorithme adapté a été utilisé pour éviter l'étalonnage de gaz résiduels. À partir d'une corrélation pour la vitesse de combustion laminaire, les valeurs de pression cylindre ont été prédites avec une erreur relative inférieure à 2 %, pour tous les points de fonctionnement. Le classement de la combustion selon le diagramme de Peters-Borghi a permis d'avoir une idée plus précise de l'interaction entre la turbulence et le front de flamme dans ces conditions.

International audience; The turbulent combustion of three different lean fuel–air mixtures has been investigated in a spherical vessel running at different turbulent intensities. Those mixtures were selected to present almost the same unstretched laminar flame speed but various Markstein lengths and Lewis numbers which are relevant parameters to describe flame-stretch interactions. Mie-scattering tomography has been used to measure a global flame stretch and an equivalent flame propagation speed. Results prove that mixtures have same ranking in terms of flame stretch sensitivity as in laminar regime and show the importance of taking into account this parameter in modeling and to evaluate fuel performance in terms of burning speed in Spark-Ignition engine. Flame wrinkling and curvature measurement were also carried out and the wrinkling effect on the flame propagation has been identified.

Further improving the environmental performances of Internal Combustion Engines (ICE) increasingly requires moving beyond traditional multidimensional simulation tools based on a cycle averaged approach (Reynolds-Averaged Navier–Stokes, RANS), and to reliably predict and control individual engine cycles under realistic operating conditions. Large-Eddy Simulation (LES) offers this unique potential by predicting spatially filtered flow realizations, thus opening up new perspectives for extending the scope of application of Computational Fluid Dynamics (CFD) for ICE. Since its 1 edition in 2008, the LES4ICE conference provides a forum for exchange concerning research and development of LES and related experimental techniques for their application to ICE flows. It brings together researchers and engineers working in the field of piston engine combustion to debate the state of the art in LES applied to ICE and examine advanced experimental techniques capable of supporting and validating its development. The present special issue proposes an extract from the contributions to the 2014 edition of LES4ICE, following a selection by the conference’s Scientific Committee. The selected four articles provide a view on some recent advances in the domain of LES and related experimental techniques, and on their application to ICE flows. The study of Cyclic Combustion Variability (CCV) in Spark-Ignition Engines (SIE) has become a prominent topic for LES research in the past decade. It has been demonstrated how combining advanced optical diagnostics and state-of-the-art LES can allow identifying the causes of CCV, and that the acquired understanding could efficiently be capitalized in the form of reduced models for 1D CFD simulations of complete engine systems. This on-going research opened exciting perspectives for the application of LES to other yet poorly understood and mastered non-cyclic phenomena in SIE, as in particular the link between CCV and engine knock. A longstanding issue when studying the causes of CCV in SI engines is the relative importance of the variability of large-scale coherent structures, and of small scale turbulent fluctuations. A method aiming at addressing this question was proposed by S. Buhl, F. Hartmann and C. Hasse, in their contribution “Identification of Large-Scale Structure Fluctuations in IC Engines using POD-Based Conditional Averaging” [1]. They propose a method combining POD and conditional averaging, and discuss its application to the analysis of the origins of CCV for two different LES datasets. Oil & Gas Science and Technology – Rev. IFP Energies nouvelles (2016) 71, E1 C. Angelberger and C. Mounaim-Rousselle, published by IFP Energies nouvelles, 2016 DOI: 10.2516/ogst/2015048 IFP Energies nouvelles International Conference Rencontres Scientifiques d'IFP Energies nouvelles

Experimental tests were carried out on a single-cylinder port-fuel injection SI engine to quantify the potential of butanol/isooctane blends (with an alcohol concentration of 0%vol, 25%vol, 50%vol, 75%vol and 100%vol) to reduce regulated pollutants (CO, CO2, Nox and THC), and non-regulated pollutants (methane, acetylene, ethylene, benzene, acetaldehyde and formaldehyde), without deteriorating the engine performance. A comparison with results obtained for ethanol/isooctane blends is given. It was observed that the addition of alcohol results in an increase of the fuel consumption of about 30% with butanol and 60% with ethanol, but only a slight increase (about 2%) in CO2 emissions. A strong decrease in HC and Nox emissions was obtained for both alcohols. For the non-regulated pollutants, the addition of ethanol induces a reduction of up to 100% in ethylene emissions, whereas with butanol, a strong increase is observed. The addition of butanol induces a greater decrease, of up to 100%, in methane emissions than ethanol. For benzene emissions, a strong reduction is observed for both alcohols. Moreover, the addition of alcohol engenders a reduction in acetylene emissions and an increase in formaldehyde emissions, but at different levels for both alcohols. Finally, no effects or trends were distinguishable for acetaldehyde and CO emissions.

Ameliorant les connaissances sur les phenomenes mis en jeu lors de la combustion, de nouvelles technologies optiques apportent les donnees indispensables pour valider les modeles necessaires au developpement des moteurs propres. Ainsi, la LII (ou incandescence induite par plan laser), appliquee aux moteurs Diesel, permet de detecter et caracteriser les particules de suies generees lors de la combustion, afin d’en reduire les emissions.

The potential of butanol as an additive in iso-octane used as gasoline fuel was characterized with respect to laminar combustion, and compared with ethanol. New sets of data of laminar burning velocity are provided by using the spherical expanding flame methodology, in a constant volume vessel. This paper presents the first results obtained for pure fuels (iso-octane, ethanol and butanol) at an initial pressure of 0.1 MPa and a temperature of 400 K, and for an equivalence range from 0.8 to 1.4. New data of laminar burning velocity for three fuel blends containing up to 75% alcohol by liquid volume are also provided. From these new experimental data, a correlation to estimate the laminar burning velocity of any butanol or ethanol blend iso-octane-air mixture is proposed.