Rapid Compression Expansion Machine Research Articles

Optical and thermodynamic investigation of jet-guided spark ignited hydrogen combustion

Hydrogen as an alternative fuel for engines is gaining interest to decarbonize the heavy-duty sector. Hydrogen combustion in engines conventionally relies on the Otto cycle and either port fuel or direct injection. This combustion concept usually results in poor power density and non-ideal efficiencies due to the lean premixed operation and low compression ratio required to avoid preignition and knocking. In this study, hydrogen is directly injected at high pressures into the combustion chamber and spark-ignited with two different ignition systems (inductive and nanosecond repetitively pulsed discharge) at the periphery of the jet, with fuel conversion taking place predominantly in jet-guided (diffusion) mode while injection remains active.A rapid compression expansion machine (RCEM) is used to investigate the jet-guided hydrogen combustion thermodynamically and optically by combining high-speed Schlieren and OH* chemiluminescence imaging, and spark-induced breakdown spectroscopy (SIBS).SIBS reveals low air to fuel ratios at ignition time and location, ranging from 2.8 up to pure air depending on the condition and significant variation among repetitions. Both OH* chemiluminescence and Schlieren images illustrate how air entrainment pushes the flame-plasma kernel from the ignition location at the periphery of the jet towards the fuel-richer core, resulting in fast combustion of the already premixed fuel. Subsequently, the combustion process becomes dominated by the mixing dynamics. Under conditions of low in-cylinder pressures, the Heat Release Rate (HRR) closely follows the injected mass flow rate multiplied by the lower heating value of hydrogen, i.e., the combustion is mixing controlled. However, as the cylinder pressure increases, the mixing and combustion rates fall below the injected mass flow until lower densities are reached again.The delay between the start of injection and ignition primarily impacts the premixed peak, but the in-cylinder pressure and ignition source also play significant roles. This distinctive combustion process shows essential similarities to compression ignition Diesel combustion. The process holds the potential to achieve high efficiency, as hydrogen can be burned using process parameters typical of Diesel combustion without facing the constraints of knock or preignition and a complete absence of soot.

Comparison of Tabulated and Complex Chemistry Approaches for Ammonia–Diesel Dual-Fuel Combustion Simulation

<div>Using ammonia as a carbon-free fuel is a promising way to reduce greenhouse gas emissions in the maritime sector. Due to the challenging fuel properties, like high autoignition temperature, high latent heat of vaporization, and low laminar flame speeds, a dual-fuel combustion process is the most promising way to use ammonia as a fuel in medium-speed engines.</div> <div>Currently, many experimental investigations regarding premixed and diffusive combustion are carried out. A numerical approach has been employed to simulate the complex dual-fuel combustion process to better understand the influences on the diffusive combustion of ammonia ignited by a diesel pilot. The simulation results are validated based on optical investigations conducted in a rapid compression–expansion machine (RCEM). The present work compares a tabulated chemistry simulation approach to complex chemistry-based simulations. The investigations evaluate the accuracy of both modeling approaches and point out the limitations and weaknesses of the tabulated chemistry approach. When using two fuels, the tabulated chemistry approach cannot reproduce misfiring events due to inherent model limitations. By adjusting the model parameters of the tabulated chemistry model, it is possible to reproduce experimental results accurately for a specific case. However, using the adjusted parameters for simulations with changed injection timing or interaction angle between the sprays shows that no predictive calculations are possible. The parameter set is only valid for a single operation point.</div> <div>Further simulations show that the complex chemistry approach can capture the complex interaction between both directly injected fuels for different operation points. It correctly predicts the ignition as well as heat release. Therefore, the approach allows predictive combustion simulations. Furthermore, it reproduces the occurrence of misfiring in cases of unsuitable interaction of both sprays and injection timing.</div>

Spectroscopic investigation of diesel-piloted ammonia spray combustion

This work investigates the flame emissions of diesel-piloted ammonia spray combustion under conditions relevant to internal combustion engines. Due to ammonia’s carbon-free structure, its flame emissions differ significantly from carbon-containing fuels. This work provides new insights into the combustion process by distinguishing pilot and main fuel combustion by analyzing spectrally resolved flame emission footprints between 275nm and 750nm in a rapid compression expansion machine (RCEM). Additional results based on Shadowgraphy (SG), OH*-chemiluminescence (CL), visible natural flame luminosity (NL) imaging, and heat release rate (HRR) analysis describe the combustion process in detail. OH*, NH*, NH2*, as well as broadband CL from NH2*, NO2*, and H2O* contribute to ammonia flame luminosity. The results show that the combustion process encompasses a pilot ignition phase, a flame transition phase, and an ammonia combustion phase, during which only ammonia-related flame emissions occur and the main share of heat is released. Background corrected OH*, NH*, and NH2* intensities reveal the evolution of individual contributions to the flame emissions. NH2*-CL is the main contributor to visible ammonia flame emissions under the conditions investigated. Therefore, visible flame emissions are a suitable indicator for the flame front during the ammonia combustion phase.

Ignition detection with the breakdown voltage measurement during nanosecond repetitively pulsed discharges

Nanosecond Repetitively Pulsed Discharge (NRPD) is a promising ignition concept for introducing diesel-like process parameters for hard-to-ignite renewable fuels in Spark Ignition (SI) engines. Knowing whether an ignition event initiated by a series of nanosecond electrical discharges was successful or not gives the possibility of using this information for closed-loop ignition control. This paper presents a methodology for detecting successful ignition under NRPD ignition.After a nanosecond discharge, the heat loss from the particles (plasma-gas) between the electrodes and the surrounding gas is different if a robust flame kernel is established. If a flame kernel is present, the heat losses are lower, resulting in a lower local density of the gas between the electrodes. The breakdown voltage value of a nanosecond pulse is proportional to the local density. A control pulse is applied after the main ignition sequence to detect successful ignition. Lower breakdown voltages of the control pulse are present if a robust early flame kernel is present. The control pulse is applied before the pressure rises due to the presence of fast combustion, allowing ignition to be detected during the inflammation phase, thus allowing the possibility to place additional ignition events, if necessary.This technique was experimentally analyzed in a Constant Volume ignition Cell (CVC) and in a Rapid Compression Expansion Machine (RCEM). In the CVC at the ignitability limit, lower breakdown voltages of the control pulse are mostly measured when no pressure rise is measured. In the RCEM, the heat release rate is analyzed with a two-zone thermodynamic model, and the early flame kernel formation is monitored with Schlieren imaging. Some overlap exists in the control pulses' breakdown voltages for the ignition and quenching experiments; nevertheless, the Schlieren videos outline that the overlapping cases have a similar flame kernel formation, and the difference arises thereafter.

An experimental study on the self-ignition and knocking characteristics for hydrogen-fueled homogeneous compression charge ignition engines

Self-ignition and knocking characteristics for hydrogen (H2)-fueled homogeneous compression charge ignition (HCCI) engines with no carbon emissions are experimentally studied using a rapid compression expansion machine (RCEM) for various compression ratio (ε) and fuel-equivalence ratio (ϕ) conditions without preheating intake air which is generally adopted to HCCI combustion but reduces engine efficiency. Results show that H2-air premixtures self-ignite at ϕ = 0.42 and ε = 22.0, while their theoretical self-ignition ε is 27.5, due to different boundary conditions. With increasing ε, the range of ϕ for stable operation with self-ignition and no knocking tends to increase, but it is limited, e.g., ϕ ≈ 0.1–0.2 at ε = 32.0. Depending on ϕ and ε when knocking occurs, various knocking peaks (bands) are observed in the frequency domain by the fast Fourier transform (FFT): the lowest knocking frequencies around 9–13 kHz, exhibiting a tendency of gradually increasing with increasing ϕ, and additional knocking peaks for enhanced ϕ. Compared with the narrow stable operation range in ϕ, the condition where the maximum indicated mean effective pressure (IMEP) is obtained includes moderate knocking and thus the actual operating range is significantly extended, e.g., up to 88% in ϕ at ε = 28.0.

Multi compression–expansion process for chemical energy conversion: Transformation of methane to unsaturated hydrocarbons and hydrogen

With the global energy system moving towards renewable energies, there is an increasing demand for flexible conversion processes which can cope with the temporally and locally fluctuating nature of energy supply and energy demand. Promising candidate processes are based on coupled chemical/energy conversion. In this work, the pyrolytic conversion of methane to valuable high-energy content substances like hydrogen and unsaturated hydrocarbons by the compression/expansion process of a piston engine is investigated. In particular, the potential of running this conversion in a multi-compression–expansion (MCE) mode where a gas sample is subject to multiple compression–expansion strokes, is assessed. The methane conversion and target species yields of this multi-compression mode relative to a single compression–expansion mode are assessed. Experimental studies with a rapid compression–expansion machine are used for this. The experiments are complemented by numerical simulations, which help to interpret the experimental findings. We found that both conversion and target species yields can be increased significantly by the multi-compression–expansion processes relative to a single compression–expansion. For instance, at typical engine operation conditions, ten compression–expansion cycles increase the methane conversion by a factor of three to four (from approx. 15 % to 68 %), the hydrogen yield by a factor of five, and the unsaturated hydrocarbon yields by a factor of three, compared to a single compression–expansion process. The results encourage considering a new role for piston-engines as work-to-chemical energy converters, in addition to their conventional heat-engine (chemical energy to work) operation.

A thermodynamic model of a rapid compression expansion machine applied for the estimation of the flame speed of air/hydrogen mixtures

This work presents a thermodynamic inverse model to extract the main flame propagation characteristics of an ultra-lean air/hydrogen mixture burning in a rapid compression/expansion machine (RCEM). Differently from combustion vessels, RCEMs allow fundamental combustion studies under thermodynamic conditions of temperature and pressure relevant to internal combustion engine (ICE) operations.The presented thermodynamic model takes into account all the main phenomena occurring in an RCEM, such as the wall heat transfer, and mass, species, and energy exchange with the crevice volumes. Moreover, combining the inverse model with a simplified geometrical description of the flame front, the flame propagation velocities are derived from experimental data of pressure and piston position.The model is applied to investigate the combustion process of a hydrogen/air mixture with λ between 2.1 and 2.6 and thermodynamic states relevant to ICE operations (initial pressure and temperature of around 30 bar and 720 K, respectively). The methodology is validated against direct measurements of flame front velocities realized by optical access in the combustion chamber. The model and measurements underline that the flame speed related to the unburned gas progressively decreases as λ increases, passing from 4.4 m/s at λ = 2.1 down to 2.5 m/s at λ = 2.6. The model/experiment RMSE on the absolute flame velocity is of 0.6 m/s over twelve test points, supporting the consistency of the presented thermodynamic model.

Optical evaluation of orifice orientation and number effects on active pre-chamber spark ignition combustion

Pre-chamber spark ignition combustion has shown several advantages for its implementation in engines, mainly related to its capability to achieve stable operation at lean or diluted mixtures and increased combustion speed. However, such systems have two challenges compared to traditional spark-ignition combustion: on the one hand, the stratification of the combustion process implies the usage of advanced tools for the analysis and optimization of the combustion system; on the other hand, the ignition process and overall combustion development is very sensitive to variations in the pre-chamber geometry. Previous works have explored particularly the effects of the pre-chamber volume compared to the engine displacement, the relationship between this volume and the total flow area of the nozzle connecting it to the rest of the cylinder, as well as the number and distribution of the nozzle orifices. In this work, the effect of the orientation of such orifices is explored on an optically-accessible rapid compression-expansion machine. Two main configurations are used: straight nozzle, where the axes of all the orifices intersect in a single point approximately in the center of the pre-chamber volume; and tilted nozzle, where the axes of two opposed orifices are displaced 1.5 mm, inducing a swirling motion both in the pre-chamber during the compression process and in the main chamber once ejection starts. Additionally, a sensitivity to the number of orifices is performed for the tilted nozzle layout. The results show that the induced swirling motion has little effect on the pre-chamber combustion development and initial ejection velocity, but it has a positive impact on the subsequent flame propagation and combustion efficiency, especially for ultra-lean conditions.

Characterization of ammonia spray combustion and mixture formation under high-pressure, direct injection conditions

Ammonia has the potential to replace fossil fuels in internal combustion engines (ICEs). However, ammonia is characterized by unfavorable combustion characteristics and a propensity to form pollutants during combustion. The pilot-ignited high pressure, direct-injection of ammonia is promising regarding its prospective performance with ammonia as fuel. In this work, optical investigations (Mie-scattering (MS), shadowgraphy (SG), OH* chemiluminescence (CL)) and heat release rate (HRR) analysis are complemented by 1-D spray modeling to provide fundamental insight into distinctive features of ammonia spray combustion and mixture formation under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). CL measurements reveal that ammonia spray flames do not stabilize after ignition by a diesel pilot injection. Instead, the lift-off length gradually increases until the end of injection and beyond. To aid in the interpretation of the lift-off behavior, a 1-D, mixing-limited spray model is validated by experimental results for ammonia spray penetration and stationary liquid length (LL) under non-reactive conditions. Modeling results reveal that ammonia sprays are marked by low temperatures close to the nozzle exit, followed by a rapid decrease in mean equivalence ratios well below 1. Based on a mechanism that suggests flame stabilization by product re-entrainment and subsequent auto-ignition, the inhibition of flame stabilization in ammonia sprays is explained by high mixing requirements with combustion products to undergo auto-ignition. Implications of the lack of a self-stabilized flame on combustion characteristics are discussed and diesel post-injections, fuel pre-heating and reduction of the natural lift-off length are suggested as measures to avoid extensive pollutant formation in regions upstream of the lift-off length after the end of ammonia injection.

Tracer-Based High-Speed Laser-Induced Fluorescence Measurements Of Temperature And Fuel Concentration Fields In A Rapid Compression Expansion Machine

Tracer planar laser-induced fluorescence (PLIF) using 1-methylnaphthalene (1-MN) is applied to study temperature and fuel courses during compression in a rapid compression expansion machine (RCEM). A burst mode Nd:YAG-laser at 266 nm is utilized for excitation of tracer fluorescence at a repetition rate of 7.5 kHz. A high-speed intensified CMOS camera equipped with an image doubler is applied for 2-color LIF (2c-LIF). The measurements were conducted in nitrogen atmosphere for which a calibration curve is presented that was generated in a flow cell. The temperature and fuel concentration fields are very homogeneous at early points in time during compression, however, inhomogeneities in terms of millimeter-sized hot and cold gas regions can be found especially near top dead center (TDC). These inhomogeneities were also visible in the fuel partial density field and are due to the distinct heat transfer between the hot gas and the cool walls, and probably also because of roll-up vortices induced by the piston movement. Especially at TDC the minimal gas temperature is about 300 K lower than the peak temperature near the cylinder head. These temperature differences are much larger than in piston engines and in other RCEMs reported in the literature at comparable conditions. This is because of the special design of the present layout of the machine. A relatively large difference to the adiabatic temperature can be overserved particularly at TDC. About 70 K lower temperatures were measured, which can be explained by these temperature inhomogeneities in the cylinder.

Ignition and combustion characteristics of diesel piloted ammonia injections

Ammonia is considered a potential carbon-free alternative to fossil fuels. However, its unfavorable combustion characteristics and propensity to form fuel NOx pose a challenge for its use as fuel for internal combustion engines. The high-pressure dual fuel (HPDF) direct-injection of ammonia could offer the potential to reduce ammonia slip and decrease NOx formation. The feasibility of this combustion process has not yet been shown experimentally in literature. This work examines the ignition and combustion characteristics of diesel piloted liquid ammonia sprays under engine-relevant conditions in a rapid-compression-expansion-machine (RCEM). By examining heat release rates (HRRs) under a variety of spatial and temporal spray interaction configurations, charge conditions as well as different diesel pilot amounts and injection durations, the fundamental prerequisites for successful combustion of liquid ammonia sprays are revealed. Strong interaction of the two fuels is found necessary to properly ignite ammonia. Misfiring due to deterioration of the pilot mixture formation can be avoided by injecting diesel first. A strong correlation between main ignition delay and burnout rate suggests a significant influence of wall quenching effects. An investigation of less reactive charge conditions suggests poor suitability of the combustion process for low-load engine operation. While reliable ammonia ignition was achieved for diesel pilot amounts as small as 3.2% of the total injected LHV, ignition is increasingly delayed for smaller pilot amounts. For an operating point, which showed favorable ignition behavior and high conversion rates, pilot fuel amount and injection duration are found to have a major influence on the combustion process.

An experimental study on the backfire occurrence and combustion stabilization of high-efficiency hydrogen-fueled free-piston linear power systems

A scavenging method suitable for high-efficiency hydrogen (H2)-fueled two-stroke free-piston linear power systems as a next-generation alternative engine is experimentally studied, investigating the driving and backfire suppression characteristics of various scavenging methods by using a rapid compression expansion machine. A simple structured loop-scavenging method which was expected to be unfavorable for suppressing backfire in H2-fueled power systems is more advantageous than the valve-driven scavenging methods when the system performance is evaluated together. For the loop-scavenging method, no backfire is observed at the fuel-equivalence ratio φ ≤ 0.6 when the ignition timing IGT is set for the maximum pressure (MPT) and the backfire limit can be extended to φ = 0.8 if IGT is advanced than MPT, showing the maximum indicated thermal efficiency of 48%. The performance test using a single-type H2-fueled free-piston linear power system adopting the loop-scavenging successfully demonstrates stable continuous operation with no backfire at φ ≤ 0.8.

Computational study of the Premixed Charge Compression Ignition combustion in a Rapid Compression Expansion Machine: Impact of multiple injection strategy on mixing, ignition and combustion processes

Combustion processes operating under the low-temperature (LTC) are a promising alternative for internal combustion engines, achieving high efficiency and low emissions within the legislative framework. Under this field of study, the concept of Premixed Charge Compression Ignition (PCCI) was introduced to control the combustion phase by varying the injection strategy. The present research, based on the aforementioned combustion strategy, employs Computational Fluid Dynamics (CFD) to study the mixing, ignition and initial combustion processes in a Rapid Compression and Expansion Machine (RCEM). The operating conditions of the PCCI strategy are achieved through the split injection technique, which separate the injection into several shots. In this case, the injection strategy consists of a long base injection and two very short, consecutive post injections delivered when the piston is close to the top dead center. Three different operating conditions have been considered which differ mainly in the duration and the starting time of the first injection. Large Eddy Simulations (LES) are selected to account for the effects of turbulence. Results are validated against experimental data, showing good agreement between both approaches. The effect of the first injection on the second one in multiple injection strategy is appreciated as the penetration of the subsequent fuel sprays is faster. Differences in the local mixture field and ignition dynamics are observed as a function of varying operating conditions. The ignition process is highly influenced by the operating strategies affecting the distribution of the mixture and thus the location of the low temperature oxidation. In the current computational study, in addition to the evaporating fuel scalar, the corresponding source term due to evaporation has also been provided to three passive transported scalars, namely three mixture fractions, one for each injection event. This allows for discerning the fuel stemming from each one of the pulses in the overall distribution, thus offering new insights into the effect of the injection strategy.

Development of Thermodynamic Model of a Rapid Compression Expansion Machine Applied for the Estimation of the Flame Front Speed of Air/Hydrogen Mixtures

Development of Thermodynamic Model of a Rapid Compression Expansion Machine Applied for the Estimation of the Flame Front Speed of Air/Hydrogen Mixtures

Herriott cell enhanced SMF-coupled multi-scalar combustion diagnostics in a rapid compression expansion machine by supercontinuum laser absorption spectroscopy

A novel supercontinuum laser absorption spectroscopy (SCLAS) approach combining a planar external Herriott multi-pass cell (HMPC) with fully single-mode fiber (SMF) coupling is presented for broadband multi-scalar combustion measurements in a rapid compression expansion machine (RCEM). For the HMPC, 1-dimensional refractive index gradients occurring in the RCEM combustion chamber are analyzed via ray-tracing with respect to axial and vertical beam steering. The impact of beam steering on the SCLAS signal is compared with the ray-tracing analysis and high-speed flame luminosity images. SCLAS based measurements are presented during compression, auto-ignition and combustion in the RCEM for n-heptane/methane mixtures at varied AFR (air-fuel ratio) and n-heptane/EGR (exhaust gas recirculation) mixtures at temperatures exceeding 1800 K and pressures up to 80 bar. Simultaneous temperature and mole fraction courses of H2O, CH4, and CO2 are inferred from NIR (near-infrared) broadband absorbance spectra detected by a Czerny Turner spectrometer (CTS) in a spectral range of 1374 nm to 1669 nm. The multi-pass approach with SMF coupling, which avoids multi-mode fiber induced noise, allows for high-speed multi-species SCLAS measurements with low standard deviations; for temperature this amounts to about 5 K and partially below at a temporal resolution of 25 µs.

Combustion characteristics of hydrogen in a noble gas compression ignition engine

Hydrogen eliminates carbon emissions from compression ignition (CI) engines, while noble gases eliminate nitrogen oxide (NOx) emissions by replacing nitrogen. Noble gases can increase the in-cylinder temperature during the compression stroke due to their high specific heat ratio. This paper aims to find the optimum parameters for hydrogen combustion in an argon–oxygen atmosphere and to study hydrogen combustion in all noble gases, providing hydrogen combustion data with suitable engine parameters to predict hydrogen ignitability under different conditions. Simulations are performed with Converge CFD software based on the Yanmar NF19SK direct injection CI (DICI) engine parameters. The results are validated with the experimental results of hydrogen combustion in an argon–oxygen atmosphere with a rapid compression expansion machine (RCEM), and modifications of the hydrogen injection timing and initial temperature are proposed. Hydrogen ignition in an argon atmosphere is dependent on a minimum initial temperature of 340 K, but the combustion is slightly unstable. Helium and neon are found to be suitable for hydrogen combustion in low compression ratio (CR) engines. However, krypton and xenon require temperature modification and a high CR for stable ignition. Detailed parameter recommendations are needed to improve hydrogen ignitability in conventional diesel engines with the least engine modification.

A Study on Diesel Spray Flame by Time-Resolved PIV with Chemiluminescence of OH*

<div class="section abstract"><div class="htmlview paragraph">To clarify the relationship between the local heat release and the velocity distribution inside the diesel spray flame, simultaneous optical diagnostics of OH* chemiluminescence and particle image velocimetry (PIV) have been applied to the diesel spray flame under the elevated in-cylinder pressure and temperature conditions formed in a rapid compression expansion machine (RCEM). The cranking speed of the RCEM was 900 rpm, and the in-cylinder pressure and temperature were 8 MPa and 800 K at the start of injection, respectively. The amount of fuel was 10.2 mg. The injection pressure was 120, 90, and 60 MPa. To minimize the disturbance of luminous flame on optical diagnostics, a solvent, with comparable combustion characteristics to diesel fuel was used as fuel. The oxygen concentration was set to 15%. Results clearly show that PIV can successfully analyze the velocity distribution in diesel spray flames. The local velocity fluctuation inside the diesel spray flame represents the peak value slightly inside of the high-temperature region. In addition, the intensity of local velocity fluctuation increases as the injection pressure increases.</div></div>

Combustion analysis of a stratified pre-chamber ignition system by means of a zero-dimensional turbulence and flame speed model

In the current work, the combustion process inside a stratified pre-chamber ignition system is analyzed. The pre-chamber is installed on a Rapid Compression-Expansion Machine (RCEM) and runs at different combinations of fuel-air equivalence ratio in the main chamber as well as in the pre-chamber, which is controlled by a fuel injection during the compression stroke. In order to analyze the results in detail, a zero-dimensional model for the pre-chamber is proposed. First, a K-k-ϵ model is developed and calibrated according to three-dimensional simulations in motoring conditions performed in a Computational Fluid Dynamic solver (Converge). Then, a thermodynamic model including the mass exchange between both chambers as wells as the heat transfer losses to the walls is used to compute the instantaneous heat release rate in the pre-chamber. Both pieces of information are combined to evaluate the effective flame propagation speed, and also to decouple the effects in terms of laminar flame speed, turbulence-flame interaction and gas velocity due to expansion effects in the burned products. The flame speed values obtained are consistent when the equivalence ratio in the pre-chamber is maintained, regardless the conditions in the main chamber, while a significant deterioration is seen once lean operation appears in the pre-chamber. Finally, the flame speed is compared to an average propagation speed estimated from broadband chemiluminescence visualization tests, showing good consistency with the model predictions.

The Assessment of Autoignition of Modified Jet Fuels

The condition of the natural environment, including breathable air, indicates that actions are to be taken related to the reduction of exhaust emissions from transport. One of the sectors of transport is aviation. The reduction of emissions is tightly related to the types of fuels in this sector of transport. In the paper, the authors propose the application of a new generation of jet fuels. A full exploration of the physicochemical properties of these fuels requires research under actual engine operation. The conducted research pertains to the autoignition of modified jet fuels in terms of the thermodynamic indicators and optical analyses of the early phase of flame development. The investigations were conducted using a Rapid Compression Expansion Machine with a simultaneous recording of images using a high-speed camera. Owing to this technique, the authors could assess the thermodynamic properties and analyze the early flame development processes. The investigations enabled the assessment of fuel properties indicating an increased delay of the autoignition process compared to the reference fuel (diesel fuel). The performed analyses have confirmed a huge role of modern fuels (including HEFA in particular) in contemporary aviation–significant delay of autoignition at a simultaneous significant formation of autoignition spots and high intensification of combustion.

Study on promotion of lean combustion by oxygen enrichment using a rapid compression expansion machine

Study on promotion of lean combustion by oxygen enrichment using a rapid compression expansion machine