Fuel Spray Combustion Research Articles

Large eddy simulation of ammonia-diesel dual fuel spray combustion: Effects of ambient condition on ignition characteristics

Large eddy simulation of ammonia-diesel dual fuel spray combustion: Effects of ambient condition on ignition characteristics

Study on the combustion characteristics and reaction mechanism of aluminum/alcohol-based nanofluid fuel

Enhancing the volumetric energy density of fuels is a crucial approach in the exploration of efficient energy sources. As a commonly used high-energy additive, Aluminum nanoparticles (Al NPs) holds broad application prospects. This study delves into the effects of Al NPs on the combustion characteristics of methanol and ethanol fuels through in-depth analysis of single droplet combustion and spray combustion experiments involving alcohol-based nanofluid fuels. The experiments revealed that adding Al NPs significantly enhances fuel combustion efficiency, shortening both the combustion life and ignition delay time. Spray combustion tests demonstrated that adding 2 wt% Al NPs increased the maximum and average flame propagation speeds of ethanol fuel spray by 48.93 % and 47.94 %, respectively, while the maximum explosion pressure rose from 0.66MPa to 0.83MPa, with a reduced time to reach peak explosion pressure by 106ms. Based on the SEM and XRD characterization results of the combustion residues and the analysis of flame morphology, a physical model of the alcohol-based nanofluid fuel spray combustion flame was established. Numerical simulations of the gas-phase kinetics model showed that the generation rates of radicals such as H, O, and OH were significantly increased with the addition of Al NPs, intensifying the combustion reaction. The findings provide a theoretical basis for future fuel design and combustion performance optimization.

Investigating the effect of fuel properties and environmental parameters on low-octane gasoline-like fuel spray combustion and emissions using machine learning-global sensitivity analysis method

The gasoline compression ignition mode is an advanced combustion mode that achieves high efficiency with low emissions. This study constructs a global sensitivity analysis (GSA) by coupling machine learning (ML) algorithms and conducts a comprehensive investigation into the statistical correlations between research octane number (RON), fuel sensitivity (S), three initial ambient parameters, and the spray combustion characteristics of gasoline-like fuels. Eighty sets of CFD numerical simulation data were used for training the machine learning model. Results show liquid length (LL) is most sensitive to changes in ambient pressure while ambient temperature significantly influences vapor penetration length (VPL). Regarding combustion behaviors, ignition delay (ID) and flame lift-off length (LOL) show the highest sensitivity to ambient temperature. The occurrence of distinct ignition points in the domain also advances from 1.75 ms to 0.42 ms as the ambient temperature rises from 1000K to 1200K. Additionally, the ambient temperature has higher-order interaction effects with ambient pressure on LOL. The production of NOx in the field is also more closely correlated with ambient temperature, with higher temperatures promoting its generation. Furthermore, ambient temperature exhibits a positive interaction effect with both ambient pressure and oxygen concentration on NOx emissions.

Toward Elimination of Soot Emissions from Jet Fuel Combustion.

Soot from jet fuel combustion in aircraft engines contributes to global warming through the formation of contrail cirrus clouds that make up to 56% of the total radiative forcing from aviation. Here, the elimination of such emissions is explored through N2 injection (containing 0-25 vol % O2) at the exhaust of enclosed spray combustion of jet fuel that nicely emulates aircraft soot emissions. It is shown that injecting N2 containing 5 vol % of O2 enhances the formation of polyaromatic hydrocarbons (PAHs) that adsorb on the surface of soot. This increases soot number density and volume fraction by 25 and 80%, respectively. However, further increasing the O2 concentration to 20 or 25 vol % enhances oxidation and nearly eliminates soot emissions from jet fuel spray combustion, reducing the soot number density and volume fraction by 87.3 or 95.4 and 98.3 or 99.6%, respectively. So, a judicious injection of air just after the aircraft engine exhaust can drastically reduce soot emissions and halve the radiative forcing due to aviation, as shown by soot mobility, X-ray diffraction, Raman spectroscopy, nitrogen adsorption, microscopy, and thermogravimetric analysis (for the organic to total carbon ratio) measurements.

Spray Behavior, Combustion, and Emission Characteristics of Jet Propellant-5 and Biodiesel Fuels with Multiple Split Injection Strategies

This study focuses on an analysis of the spray behavior, combustion, and emission characteristics of jet propellant-5 (JP-5) and biodiesel fuels with single-injection timing and multiple split injection strategies in a common rail direct injection (CRDI) single-cylinder diesel engine system. The analysis includes visualization of the spray and combustion. Multiple split injection strategies (e.g., double, triple, quadruple, and quintuple) were considered by equally distributing the fuel injection amount within the single-injection. Injection of biodiesel has a delayed start (0.2 ms) as well as shorter spray tip penetration compared with JP-5. As the fuel injection timing was approached to the top dead center (TDC), the engine performance and combustion efficiency improved. Retarding the injection timing contributed to an increase in carbon dioxide (CO2) (JP-5: max. 2.6% up, BD100: max. 1.5% up) and a decrease in carbon monoxide (CO) (JP-5: max. 93% down, BD100: max. 91% down) and nitrogen oxides (NOx) (JP-5: max. 83% down, BD100: max. 82% down). In comparison with JP-5, biodiesel showed disadvantages from the point of its combustion and emission characteristics for all injection timings. The quadruple-injection strategy, in which fuel injection was performed four times, showed excellent combustion, engine performance, and combustion efficiency. The CO2 emissions were highest with the quadruple-injection strategy (JP-5: 6.6%, BD100: 5.8%). The CO emissions of biodiesel decreased as the pulses of split injection extended, and a significant reduction of 83.8% was observed. NOx increased as the number of split injections increased (JP-5: max. 37% up, BD100: max. 52% up). JP-5 was a longer ignition delay than that of biodiesel from combustion flame visualization results. The final combustion in the multiple-injection strategy showed a typical diffusion combustion pattern.

Comparative Study on Spray Auto-Ignition of Di-n-Butyl Ether and Diesel Blends at Engine-Like Conditions

Abstract Di-n-butyl ether (DBE), a promising lignocellulosic biofuel, has been suggested as a potential alternative fuel for compression ignition engines. In this study, the spray auto-ignition characteristics of diesel/DBE blends were experimentally measured on a constant volume combustion chamber. Time-resolved pressure traces and heat release rates in fuel spray combustion were measured at changed fuel blending fractions, ambient temperatures, and oxygen concentrations. Further, ignition delay and combustion delay that evaluates fuel spray ignition tendency were derived and compared for different test blends. Experimental results indicated that fuel spray ignition tendency is promoted with DBE addition, evidenced by the advanced pressure rise and heat release processes, and the shortened ignition and combustion delays. Peak heat release rates are fuel-dependent at high ambient oxygen concentrations since the relative fractions of the premixed and diffusive burns alter with changed DBE addition. However, as the oxygen concentration drops to 11%, fuel effects on the peak heat release rates become less noticeable. Reduced ambient oxygen concentration effectively extends fuel ignition and combustion delays, and typical two-stage pressure rises and heat releases are observed for all test blends, as the oxygen concentration drops to 11%.

Rate of heat release characteristics of supercritical sprays of dieseline blend in constant volume combustion chamber

In present experimental study, combustion characteristics of homogeneous supercritical (SC) fuel spray injection system are analyzed in cylindrical constant volume combustion chamber (CVCC) at experimental conditions similar to diesel engine-like operating conditions. A comparative study is also performed between SC fuel spray and normal diesel spray combustion under similar conditions. Combustion characteristics of SC fuel sprays includes rate of heat release (ROHR) and peak pressure (PP). Operating parameters include hot surface temperature range (673 ​K–723 ​K), pre-firing cylinder air pressure range (20 ​bar–40 ​bar) and injection pressure (IP) range of 100 ​bar–300 ​bar. Piezoresistive pressure transducer is employed for indicating and recording combustion processes. Diesel fuel and dieseline blend (50% gasoline and 50% diesel by v/v) are used for normal diesel spray and SC spray combustion respectively. It is found that ROHR in SC fuel spray combustion is smaller than in normal diesel spray combustion at all operating conditions. In SC fuel spray combustion, ROHR increases with increase in IP but decreases with increase in HST and CP due to homogeneous and hot air combustion nature of SC fuel sprays. Percentage reduction in ROHR of SC fuel spray combustion as compared to ROHR in normal diesel spray combustion is found to be nearly 34% at normal operating conditions of diesel engine. PP reached during SC spray combustion is noted to be less than PP reached during normal diesel spray combustion in all cases and is responsible for reduced NOx formation in SC spray combustion.

Modelling internal combustion engines with dynamic staggered mesh refinement

Modelling internal combustion engines (ICEs) with multidimensional computational fluid dynamics (CFD) is challenging due to the fuel spray, combustion chemistry and moving piston involved. To accurately simulate ICEs as well as to maintain acceptable computational cost, dynamic mesh refinement techniques could be applied. Although modelling ICEs with staggered mesh is ubiquitous in the engine combustion community, the dynamic refinement of staggered mesh in the context of multidimensional engine simulations is not reported in the literatures due to the numerical difficulties in the momentum solution at the gird fine-coarse interface and to deal with moving boundaries. To address these difficulties, we propose a dynamic refinement scheme to cell-by-cell refine the staggered mesh on-the-fly based on the fuel evaporation and thermochemical state in the multidimensional dynamic staggered mesh and it is able to handle the complexity caused by the moving boundaries in engine simulations and momentum solution at the fine-coarse interface in the dynamic mesh. This mesh refinement scheme is then implemented in the widely-used ICEs simulation codes for engine simulations with fuel sprays. A wide variety of computational examples including shock wave, compression, constant volume fuel spray, constant volume fuel spray combustion are first employed to test the scheme and finally, compression ignition combustion engine simulations are conducted with the proposed methodology.

The Possibility of Active Attitude Control for Fuel Spray

Abstract The internal combustion engine (ICE) is an attractive power source for automobiles, with its superior storability, transportability, and suppliability of liquid fuel with high energy density. Compact ICEs with high performance and a low environmental load are greatly needed. In the future, smart active control of combustion by means of fuel spray injection must be considered as a breakthrough technology to address serious issues related to conventional ICEs, such as emissions. A designed fuel injection rate and spray pattern during the injection period have been technically developed, and combustion can be partially controlled in the conventional ICE. However, spatial fuel distribution is not progressing as desired in the field of combustion; thus, new and effective active control technologies for fuel spray are very necessary for the smart control of combustion. Cavitation, flash boiling, spray-to-spray interaction, spray-to-wall interaction, and air flow have potential as a basis for active attitude control of fuel spray. This article uses evidence from the literature to discuss the possibility of active spray attitude control for future fuel spray combustion technology in a smart compact ICE.

Singular perturbed vector field method applied to combustion in diesel engine: Continuous case with thermal runaway

• The singular perturbed vector filed is a new method (SPVF) for extracting and exposing the hierarchy of a given ODE system. • We apply the SPVF to the problem of thermal explosion of polydisperse fuel spray combustion . • We describe the droplets size using probability density function. • We take into account the thermal radiation effects on the droplets evaporation. In this study, we employ the well-known method of a singularly perturbed vector field (SPVF) and its application to the thermal runaway of diesel spray combustion. Given a system of governing equations, consisting of hidden multi-scale variables, the SPVF method transfers and decomposes such a system into fast and slow singularly perturbed subsystems. The resulting subsystem enables us to better understand the complex system and simplify the calculations. Powerful analytical, numerical, and asymptotic methods (e.g., the method of slow invariant manifolds and the homotopy analysis method) can subsequently be applied to each subsystem. In this paper, we compare the results obtained by the methods of slow invariant manifolds and SPVF, as applied to the spray (polydisperse) droplets combustion model.

Skeletal mechanism development for a 3-component jet fuel surrogate using semi-global sub-mechanism construction and mechanism reduction

A skeletal mechanism with 110 species and 352 reactions is developed from a detailed mechanism that includes 369 species and 2691 reactions for a 3-component jet fuel surrogate which is composed of methylcyclohexane (MCH), n-dodecane and m-xylene. Firstly, the semi-global sub-mechanisms of MCH and n-dodecane are constructed to substitute the corresponding portions in detailed mechanism, the construction is guided by main reaction pathways and involves isomer lumping, parallel reaction lumping and reaction product substituting, the rate parameters of key reactions are tuned via genetic algorithm (GA) to fit ignition delays. Secondly, the aromatics and base sub-mechanisms are reduced by DRGEP and iterative sensitivity analysis (ISA). ISA calculates the sensitivity parameter for every objective and only removes the one with the lowest value in every iteration. This approach could remove redundant species and reactions effectively. The skeletal mechanism is validated against ignition delays in shock tube, laminar flame speeds and species concentration profiles in shock tube and plug flow reactor over a wide range of conditions. Furthermore, the skeletal mechanism is employed to simulate 3D jet fuel spray combustion and ignition delay times are validated against experimental data.

The potential of on- and off-resonant formaldehyde imaging combined with bootstrapping in diesel sprays

Formaldehyde (CH2O) is an important intermediate in spray combustion of diesel-like fuels. Experimentally, its spatial distribution is often assessed by means of planar Laser-Induced Fluorescence (PLIF), using a frequency-tripled Nd:YAG laser for excitation and spectrally-filtered fluorescence detection. Especially in soot-laden spray flames, however, considerable spectral interference cannot be avoided, which renders interpretation of the fluorescence distribution challenging. We introduce a more selective strategy, involving dye laser excitation and background subtraction by means of off-resonant excitation in combination with a bootstrap evaluation of sets of individual events. The latter extracts persistent features out of non-simultaneously recorded snapshots of stochastic events, thereby mitigating possible interpretation issues related to the turbulent nature of the process under study. Following this approach, recurrent patterns can be distinguished from random high-intensity events (allegedly due to turbulent fluctuations). We demonstrate our method on the Engine Combustion Network (ECN) “Spray A”-benchmark, with 15 vol-% and 21 vol-% ambient oxygen; we also present spatially well-delimited CH2O fluorescence distributions, and compare these to simultaneously recorded OH* chemiluminescence intensities.

Modeling Nonequilibrium Combustion Chemistry Using Constrained Equilibrium Flamelet Model for Kerosene Spray Flame

Numerical simulation employing different models is popularly used to predict spray combustion of liquid fuels. In the present work, we have compared the effects of three different combustion models, viz., eddy dissipation model, laminar flamelet model with detailed chemical reaction mechanism, and constrained equilibrium flamelet model, on the temperature, soot, and NOx distributions in an axisymmetric combustor burning kerosene spray. Experiments have also been performed in a combustor of the same geometry to validate some predictions from the models. The constraint condition for the equilibrium flamelet model has been adopted by suitably accounting the effects of scalar dissipation rate on the prediction of scalar variables in a laminar flamelet and by considering the mixture fraction and scalar dissipation rate distributions in the combustor under test. It is found that the results predicted by the two flamelet models agree closely between them and also with the experiments. On the other hand, the eddy dissipation model predicts a much higher flame temperature, soot, and NOx concentrations in the combustor. The results suggest the importance of chemistry in the prediction of the turbulent spray flame. It also suggests that with a proper choice of the constraint condition, the equilibrium flamelet model can address the nonequilibrium chemistry in the flame due to the high value of scalar dissipation rate.

Oxy-combustion of Low-Volatility Liquid Fuel with High Water Content

Following our previous studies of swirl-stabilized spray combustion of fuels that have a high water content, in this work, we investigate low-volatility fuels, specifically glycerol. Results show that, to obtain a self-sustained flame, the concentration of glycerol in water is much higher than that of ethanol (a high-volatility fuel) in water. However, even for glycerol concentrations as high as 60 wt %, the self-sustained flame is lifted from the nozzle and not attached, as in the ethanol case. The calculated stoichiometric adiabatic flame temperature (Tad) for 60 wt % glycerol is 2602 °C, whereas for 15 wt % ethanol (which is a very stable flame), it is only 673 °C. The two systems differ in that ethanol is more volatile than water, whereas glycerol is less. Thus, in the former case, the fuel is preferentially vaporized, whereas in the latter case, water is preferentially vaporized. Thus, flame stabilization is particularly challenging for fuels where the volatility is less than that of water when the water content of the spray is high. To assist flame stability for glycerol–water solutions, tert-butanol and ethanol were added in low concentrations. Experimental results revealed that stable attached flames can be obtained for 30 wt % glycerol in water when 8.3 wt % tert-butanol (B8.3/G30) or 10 wt % ethanol (E10/G30) is added under oxy-fired conditions. Both tert-butanol and ethanol have been shown to be particularly volatile in water when present at low concentrations because of their high vapor pressures and very high activity coefficients. The flame stability for B8.3/G30 and E10/G30 was characterized under 100 and 85% swirl flow conditions. Temperature measurements were conducted for four stable flames, and temperature contours were generated. For the stable flames, a hot zone exists in the near burner region, because of the preferential vaporization of the high-volatility fuel component, which provides heat to robustly vaporize the fuel and stabilize the flame.

Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber

This work investigates the spray combustion of Jet-A fuel in an optical constant-volume combustion chamber under different ambient initial conditions. Ambient temperature was varied at 800K, 1000K, and 1200K and five different ambient O2 concentrations were used, spanning 10–21%. These ambient conditions can be used to mimic practical diesel engine working conditions under different fuel injection timings and exhaust gas recirculation (EGR) levels. Both transient and quasi-steady state analyses were conducted. The transient analysis focused on the flame development from the beginning to the end of the combustion process, illustrating how the flame structure evolves with time. The quasi-steady state analysis concentrated on the stable flame structure and compared the flame emissions in terms of spatially integrated intensity, flame effective area, and intensity per pixel. The transient analysis was based on measurements using high-speed imaging of both OH∗ chemiluminescence and broadband natural luminosity (NL). For the quasi-steady state analysis, three flame narrow-band emissions (OH∗ at 310nm, Band A at 430nm and Band B at 470nm) were captured using an ICCD camera. Based on the current Jet-A data and diesel data obtained from previous experiments, a comparison between Jet-A and diesel was made in terms of flame development during the transient state and spatially integrated intensity, flame effective area, and intensity per pixel during the quasi-steady state. For the transient results, Jet-A shares a similar flame development trend to diesel, but featuring a narrower region of NL and a wider region of OH∗ with the increase of ambient temperature and O2 concentration. The soot cloud is oxidized more quickly for Jet-A than diesel at the end of combustion, evident by comparing the area of NL, especially under high O2 concentration. The quasi-steady state results suggest that soot is oxidized effectively under high O2 concentration conditions by the wider region of OH∗ in the downstream locations where only OH∗ emission is observed. The intensity of OH∗ is higher for Jet-A than diesel under low O2 concentration but lower under high O2 concentration. The intensity of NL is higher for Jet-A for all the conditions investigated. However, the intensities of Band A and Band B are lower for Jet-A for all these conditions. Based on the imaging of multiple-band flame emissions, the spray flame structures were further analyzed for the two fuels under both low temperature and conventional combustion modes. Conceptual flame structures were proposed to complement the previous conceptual models for spray combustion under different combustion modes.

The Influence of Hydrogen Addition to Diesel Fuel Spray Combustion for Different Atomization Conditions

The negative effects of hydrocarbon fuels are widely highlighted by increasing global warming and declining quality of human health. Therefore, it is important to reduce the level of emissions from liquid hydrocarbon combustion. Hydrogen addition to the combustion chamber is one of the proven methods to improve emssions level. In this research, an experiment was conducted on diesel fuel spray combustion with hydrogen addition. The effect of additional hydrogen was observed on CO, CO2, NO and THC exhaust gas emissions. A small hydrogen fraction (0~3 vol %) was added to the rich premixed spray combustion. The results show that increasing the hydrogen fraction reduced the emission indexes of CO and THC, and increased the emission index of CO2. Increasing the hydrogen fraction caused an increase in the emission index of NO, but the actual physical amount was insignificant. Increasing the atomizing air flow rate reduced the CO and THC emission indexes, but increased the CO2 and NO emission indexes.

The Role of Porous Media in Homogenization of High Pressure Diesel Fuel Spray Combustion

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper, we investigate a novel approach to the development of a homogenous charge-like environment through the use of porous media. The primary purpose of the media is to enhance the spread as well as the evaporation process of the high pressure fuel spray to achieve charge homogenization. In this paper, we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure and temperature plays in further enhancing this process.

Soot temperature and KL factor for biodiesel and diesel spray combustion in a constant volume combustion chamber

This paper presents measurements of the soot temperature and KL factor for biodiesel and diesel combustion in a constant volume chamber using a two-color technique. This technique uses a high-speed camera coupled with two narrowband filters (550nm and 650nm, 10nm FWHM). After calibration, statistical analysis shows that the uncertainty of the two-color temperature is less than 5%, while it is about 50% for the KL factor. This technique is then applied to the spray combustion of biodiesel and diesel fuels under an ambient oxygen concentration of 21% and ambient temperatures of 800, 1000 and 1200K. The heat release result shows higher energy utilization efficiency for biodiesel compared to diesel under all conditions; meanwhile, diesel shows a higher pressure increase due to its higher heating value. Biodiesel yields a lower temperature inside the flame area, a longer soot lift-off length, and a smaller soot area compared to diesel. Both the KL factor and the total soot with biodiesel are lower than with diesel throughout the entire combustion process, and this difference becomes larger as the ambient temperature decreases. Biodiesel shows approximately 50–100K lower temperatures than diesel at the quasi-steady stage for 1000 and 1200K ambient temperature, while diesel shows a lower temperature than biodiesel at 800K ambient. This result may raise the question of how important the flame temperature is in explaining the higher NOx emissions often observed during biodiesel combustion. Other factors may also play an important role in controlling NOx emissions. Both biodiesel and diesel temperature measurements show a monotonic dependence on the ambient temperature. However, the ambient temperature appears to have a more significant effect on the soot formation and oxidation in diesel combustion, while biodiesel combustion soot characteristics shows relative insensitivity to the ambient temperature.

High-Speed Flow and Combustion Visualization to Study the Effects of Charge Motion Control on Fuel Spray Development and Combustion Inside a Direct-Injection Spark-Ignition Engine

High-Speed Flow and Combustion Visualization to Study the Effects of Charge Motion Control on Fuel Spray Development and Combustion Inside a Direct-Injection Spark-Ignition Engine

Numerical simulation of emulsified fuel spray combustion with puffing and micro-explosion

The purpose of this study was to develop numerical simulation of spray combustion of emulsified fuel with considering puffing and micro-explosion. First, a mathematical model for puffing was proposed. In the proposed puffing model, the rate of mass change of a droplet during puffing was expressed by the evaporation rate of dispersed water and the mass change rate due to fine droplets spouted from the droplet surface. The mass change rate due to fine droplets was related to the evaporation rate of the dispersed water and each liquid content. This model had only one experimental parameter. The essential feature of this model was that it was simple to apply to numerical simulation of spray combustion. First, the validity of the proposed puffing model was investigated with the experimental results for a single droplet. The calculated results for a single droplet with the experimental parameter varying from 5.0 to 10 were in good agreement with the experimental results. Moreover, numerical simulation of spray combustion of emulsified fuel was carried out. The occurrence of puffing and micro-explosion was determined by the inner droplet temperature. When micro-explosion occurred, a droplet changed to vapor rapidly. When the proposed puffing model was used in numerical simulation of spray combustion, the experimental parameter in the puffing model was determined for each droplet by random numbers within the range 5.0–10. The calculated results of spray combustion of emulsified fuel without considering puffing or micro-explosions were different from the experimental results even where combustion reactions were almost terminated. Meanwhile, the calculated results when considering puffing and micro-explosions were in good agreement with experimental results at the same location.