Combustion Front Research Articles

Experimental Study of Oxygen-Rich in Situ Combustion for Heavy Oil Recovery

The in-situ combustion method is the commonly used method for heavy oil production with high recovery rate and low cost. However, the characteristics of the oil oxidation reaction during in-situ combustion are still not clearly understood so far. In this study, the thermal oxidation experiment was carried out for the in-situ combustion process based on the heavy oil from Du 66 block. The results show that: the fired oil zone can be divided into the combustion zone, the coking zone, the condensation zone, the movable oil zone, etc. When the combustion front is formed, the CO2 and CO contents rise to 10% and 20%, respectively. In the expansion phase of the combustion front, the oxygen utilization rate is 83.93%, and the H/C atomic ratio is 1.413, indicating that the high temperature oxidation reaction plays the leading role. Sustained gas injection with enough intensity can ensure that the combustion front moves forward continuously, and the combustion front can drive the crude oil forward in the form of snowballing due to the extremely high oil displacement efficiency. The pressure increases as the combustion front and the movable oil zone advance, but the movable oil zone begins to decrease as it advances to the production well. Through this study, it is concluded that effective combustion front and movement of combustion front are the foundation for the formation of movable oil zone. And the movable oil zone pressurization is an important mechanism for in-situ combustion. The findings of this study can help for better understanding of the in-situ combustion oxidation mechanism and can improve the production design for heavy oil reservoirs.

Моделирование волн давления при дефлаграционном горении облаков топливно- воздушных смесей

The paper examines the assumptions underlying a whole group of methods for estimating the parameters of shock waves (pressure waves) during the combustion of spherical fuel-air clouds - the so-called parametric formulas. The formulas allow to determine the parameters of pressure waves from the given energy release and combustion rate. To do this, a complete system of gas-dynamic equations is solved using high-precision numerical simulation. In this case, the combustion front is explicitly distinguished in the form of an infinitely thin discontinuity, on which the laws of conservation of mass, momentum, and energy are satisfied. The results of such a numerical calculation are compared with calculations using the corresponding parametric formulas. Clouds of a stoichiometric mixture hydrogen-air are considered. It is shown that the parametric formulas describe the expansion of clouds of hot products with a good degree of accuracy. Here, there is complete agreement with the direct numerical simulation. It is also shown that the parameters of pressure waves are satisfactorily described both in the calculation by parametric formulas and in direct numerical simulation. In this case, within the cloud, there is a greater increase in pressure than the parametric formulas predict. This is explained by the fact that the assumptions used in the formulas regarding the behavior of the flame front as an impenetrable piston do not fully reflect the physical processes: the combustion front is a semipermeable piston, and some of the mass of the initial mixture still penetrates through it. The third factor considered, which determines the achieved pressures, is the rarefaction wave that occurs in the air after the cloud burns out. This wave propagates in combination with the leading pressure front formed during combustion initiation. The extent of this complex remains practically constant, and its attenuation during spherical propagation is adequately described by the parametric formulas.

Simulation of energetic composite materials combustion

A numerical approach to simulate the evolution of the combustion surface of an energetic composite materials is described. Cubic spline interpolation is used to describe the dynamically changing shape of the combustion surface. The statement of the interpolation problem for the parametric description of the geometry and the problem of choosing the method for parameterizing the control points are given. The direct step-bystep method is used to calculate the combustion front. The normal velocity of the combustion surface is variable and is determined from the solution of an additional gas dynamics problem. The basic formulae for calculating the combustion rate of a solid propellant that consists of a particle-reinforced energetic composition are given. Examples of combustion simulation of a laboratory-scale structure for three values of the initial geometry parameters are presented.

Особенности формирования пламени пропано-воздушной смеси в узком канале

This paper presents a numerical study of the features of propane-air mixture flame propagation in a narrow cylindrical channel. The main purpose of the study is to determine the effect of the channel width on the combustion characteristics of a propane-air mixture with a composition close to stoichiometric. The problem is formulated using the methods of reactive gas dynamics. The solution method is based on the Van Leer method for determining flows on the faces of computational cells. The peculiarities of the combustion front formation and its propagation along the channel are revealed and analyzed. The formation of the curved flame front is shown to have a cyclical nature. The visible flame velocity is obtained as a function of the channel radius. The proposed physical and mathematical model can be used to determine the thermal conditions of operating cylindrical burners.

Return of 4U 1730–22 after 49 yr Silence: The Peculiar Burst Properties of the 2021/2022 Outbursts Observed by Insight-HXMT

Staying in quiescence for 49 yr, 4U 1730–22 became active and had two outbursts in 2021 and 2022; 10 thermonuclear X-ray bursts were detected with Insight-HXMT. Among them, the faintest burst showed a double-peaked profile, placing the source as the seventh accreting neutron star (NS) exhibiting double-peaked type I X-ray bursts; the other bursts showed photospheric radius expansion (PRE). The properties of a double-peaked non-PRE burst indicate that it could be related to a stalled burning front. For the five bright PRE bursts, apart from the emission from the neutron star (NS) surface, we find the residuals both in the soft (<3 keV) and hard (>10 keV) X-ray bands. Time-resolved spectroscopy reveals that the excess can be attributed to an enhanced preburst/persistent emission or the Comptonization of the burst emission by the corona. We find, the burst emission shows a rise until the photosphere touches down to the NS surface rather than the theoretical predicted constant Eddington luminosity. The shortage of the burst emission in the early rising phase is beyond the occlusion by the disk. We speculate that the findings above are due to that the obscured part (not only the lower part) of the NS surface is exposed to the line of sight due to the evaporation of the obscured material by the burst emission, or the burst emission is anisotropic (ξ > 1) in the burst early phase. In addition, based on the fluxes of PRE bursts at their touchdown times, we derive a distance estimation as 9.0–12.4 kpc.

Combined Experimental and Numerical Investigation into Combustion Characteristics of Crude Oil under Different Permeability Ranges: Thermal EOR Implication

In situ combustion (ISC) has drawn much attention in the exploitation of heavy oil reservoirs because of its small surface footprint and high recovery efficiency relative to steam injection. As for now, the combustion characteristics of heavy crude oil under different permeability ranges have not been well-understood, particularly in low-permeability conditions. In this work, we systematically conducted the combustion tube (CT) experiments under permeabilities of roughly 650 and 480 mD. Following that, a reaction kinetics model that could simulate the CT results well was established. Finally, the corrected reservoir simulation approach was used to study the ISC characteristics of one heavy oil in the permeability range of 50–1000 mD. The combustion characteristics under different permeability ranges could be classified into four main types on the basis of the experimental studies and numerical predictions. (1) The consecutive combustion front failed to be formed from 50 to 180 mD. (2) The consecutive combustion front was formed and the coking zone appeared from 180 to 250 mD, which was accompanied by weak heat release and serious plugging effect of the oil bank and coking zone. (3) The stable combustion front was formed with obvious heat release from 250 to 500 mD, and there was a weak plugging effect of the oil bank and coking zone at the initial stage of combustion. (4) In the permeability range of 500–1000 mD, the stable combustion front featured with a peak temperature higher than 500 °C was formed with a negligible plugging effect of the oil bank and coking zone. For heavy oil reservoirs with permeabilities lower than 250 mD, much attention should be put on the variations into combustion front temperature and displacement pressure difference at the initial period of combustion. If the temperature continued to decrease and/or the displacement pressure difference continued to rise, some measures should be actively adjusted to increase heat release yielded by combustion, including the increase of the air injection rate and ignition temperature, the injection of catalysts, and so forth. This work could add new insights into the differences and connections of combustion characteristics of heavy oil under different permeability ranges, which should be of great significance for thermal enhanced oil recovery.

Mathematical models for estimate of the ecological consequences of the impact of the pyrogenic factor on forest ecosystems

There is a need for the development of simple analytical mathematical models of the burning of large forest areas, necessary for the assessment of the ecological consequences of the impact of the pyrogenic factor. Purpose. Develop mathematical models describing the spread of large-scale forest fires aimed at estimate the ecological consequences of the impact of the pyrogenic factor. Methods. Analytical review of research on the problem, theoretical and computational, mathematical modeling. Results. The results of the main parameters analysis of large forest areas combustion are presented. These include the area covered by the fire, the duration of the fire, the burnout time, the specific mass of combustible materials, the energy and power of combustion, the specific calorific value, the intensity of combustion, the movement speed of the combustion front, the influx of combustible materials, etc. Simple analytical mathematical models of large forest areas combustion have been established. These include the following models: a model with a constant growth rate of the fire area, a two-dimensional model, a model with sectorial movement of the combustion front, a model with a linear growth of the length of the combustion front, a model with a quadratic growth of the change rate of the fire area, and a generalized model. A new fire intensity classification has been proposed, containing 1–7 points from extremely low to extreme intensity. The maximum area covered by the fire (10–100 thousand km2), combustion energy (1–10 EJ) and combustion power (0.1–1 PW) have been estimated. Conclusions. Simple analytical mathematical models of the combustion process of large forest surface areas, which are necessary for quantitative assessment of the ecological consequences of fires, have been developed.

Deflagration Waves Out of Hot Spots

It is widely accepted that shock initiation and detonation of heterogeneous explosives come about by a two-step process known as ignition and growth. In the first step a shock, sweeping through an explosive cell (control volume), creates hot spots that become ignition sites. In the second step deflagration waves (or burn waves) propagate out of those hot spots and transform the reactant in the cell into reaction products. The macroscopic (or average) reaction rate of the reactant in the cell depends on the speed of those deflagration waves and on the average distance between neighboring hot spots. Here we simulate the propagation of deflagration waves out of hot spots on the mesoscale in axial symmetry using a 2D hydrocode, to which we add heat conduction and bulk reaction. The propagation speed of the deflagration waves may depend on both pressure and temperature. It depends on pressure for quasistatic loading near ambient temperature, and on temperature at high temperature levels resulting from shock loading. From the simulation we obtain deflagration (or burn) fronts emanating out of the hot spots. For intermediate shock levels the emanating fronts propagate as deflagration waves to consume the explosive between hot spots. For higher shock levels the deflagration waves interact with the sweeping shock to become detonation waves on the mesoscale. From the simulation results we extract average deflagration wave speeds.

Pore-scale study of coke formation and combustion in porous media using lattice Boltzmann method

In-situ combustion (ISC) has long been recognized as a promising technique for heavy oil recovery. However, ISC includes multiple physicochemical processes, which are still poorly understood and difficult to predict and control. This study establishes a lattice Boltzmann (LB) model to simulate the two important aspects of ISC at the pore scale: coke formation and combustion. The LB model includes thermal expansion effects and solves the reactive air-coke interface without iterations. Moreover, this model improves upon previous models by considering both coke formation and two-step coke combustion, as well as the growth of solid geometry. Results show that the LB model correctly captures coke combustion properties. Meanwhile, the newly introduced coke formation and two-step combustion yield important findings. As heat released from combustion transfers downstream, oil cracking and coke formation ahead of the combustion front are successfully tracked. The generated coke fuels the upstream combustion, making the system self-sustained. During coke formation and combustion, four coke transition states are identified. In addition, a parametric study demonstrates that the large inlet oxygen content and driving force are desirable, while too high a driving force should be avoided as it causes high burning temperature. Furthermore, it suggests that the inlet air temperature should be set appropriately. On one hand, a high temperature may promote coke formation and retard the front propagation. On the other hand, a low temperature may slow down the combustion of coke 2, even though it is high enough to ensure the ignition of coke 1. The decelerated coke 2 combustion may further cause the insufficient heat release and the failed coke formation, thus inducing the early termination of combustion. Such effects of the inlet temperature indicate the necessity of considering coke formation and two-step coke combustion. These results help to improve the understanding and facilitate the development of ISC.

The Influence of Reservoir Clay Composition on Heavy Oil In Situ Combustion

Thermally enhanced oil recovery methods, such as in situ combustion and steam injection, are generating considerable interest in terms of improving oil reserve exploitation and satisfying oil demand and economic growth. However, the early breakthrough of the in situ combustion front and the significant amount of heat loss associated with steam injection for deeper reservoir applications are the main challenges that require urgent solutions. Further data collection related to the effects of a reservoir’s physical and chemical properties, temperature, and pressure on in situ combustion front propagation and steam injection heat transfer inefficiency would be needed to achieve better reservoir oil recovery. Most studies have focused on the application of catalytic systems and the investigation of minerals’ effects on combustion front stabilization; however, the effect of clay interlayers’ minerals on the performance of in situ combustion is still poorly understood. This paper takes a new look at the role played by the interlayers’ minerals in stabilizing the combustion front using X-ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC) combined with nuclear magnetic resonance (NMR), and combustion tube experiments. The studied samples’ compositions were analyzed by XRD, TG/DSC, and NMR techniques. Meanwhile, the effects of interlayers’ minerals on oil production were screened by combustion tube experiments. The data obtained from this study suggest that clay dispersion within a reservoir would improve oil recovery via in situ combustion, and our study led us to obtain an 80.5% recovery factor. However, the experiments of models with clay interlayers showed less recovery factors, and the model with interlayers led to a 0% recovery factor in the presence of air injection. Meanwhile, the same model in hydrothermal and air injection conditions led to a 13.9% recovery factor. This was due to the hydrothermal effect improving permeability and pore enlargement, which allowed the transfer of heat and matter. Moreover, our study found that clay minerals exhibit excellent catalytic effects on the formation of fuel deposition and the coke oxidation process. This effect was reflected in the significant role played by clay minerals in decreasing the number of heteroatoms by breaking down the C-S, C-N, and C-O bonds and by stimulating the processes of hydrocarbon polymerization during the in situ combustion. Our results add to a growing body of literature related to in situ combustion challenges and underline the importance of a reservoir’s physical parameters in the successful application of in situ combustion.

Experimental study on the in-situ combustion retorting of domanik oil shale

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology.

Field performance and numerical simulation study on the toe to heel air injection (THAI) process in a heavy oil reservoir with bottom water

Extra-heavy oil and bitumen (EHOB) comprise 30 percent of the remaining recoverable fossil fuel resources on Earth. This means EHOB could play an important role in a secure transition towards net zero emissions (NZE) by 2050. Technological developments, such as toe to heel air injection (THAI), have been shown to efficiently recover heavy oil with reduced environmental footprint. The Kerrobert project was the first to utilise the THAI technology in presence of bottom water (BW) in the reservoir. The project demonstrated a good performance (with average oil rate of 10 m3/day per well) compared to the conventional ISC operations in a BW situation. Lessons taken from the Kerrobert operational experience can assist the forthcoming THAI operations explicitly in the presence of BW. Dynamic field data for one of the best performing THAI pilot well pairs (K2), were analysed in this work. It was found that the K2 pilot must have experienced interference from K5, which is the closest neighbouring THAI well pair to the K2. Previously developed THAI models have not been validated against actual field data. A new field-scale THAI model in the presence of BW was constructed and, for the first time, validated against the field data from the Kerrobert project in this work. In addition, the quasi-staggered line drive well arrangement, as used for the K2 pilot, was studied. The daily and cumulative oil production rates were predicted well (the final agreement with field data was within 3 percent). The history matched model was then used to investigate the effect of the variation in air injection rates on THAI performance in presence of BW. Major developed zones during the propagation of the combustion front were numerically examined. It was demonstrated that extra air ingress from the neighbouring THAI well pair has caused a reduction in oxygen utilisation throughout the process. As a result, the simulated temperature profile declined with the increasing combustion time. The oxygen profile around the horizontal producer (HP) well was studied via the new history-matched model. An inversely proportional relationship was detected between the coke concentration and the oxygen profile around the HP well. It was found that the size of the steam zone, ahead of the combustion front, differs with variation in air injection rates. It was observed that some of the mobilised oil sank into the BW, leaving a significant amount of oil trapped in the reservoir. To prevent such an event, the location of the HP well was altered as a potential strategy to optimise the THAI efficiency. Consequently, the oxygen utilisation was improved by 13%, resulting in 73% higher cumulative oil production in comparison with the history-matched model.

Laboratory experiments of in situ combustion in core samples with simulated fractures

In situ combustion is one of the oldest enhanced oil recovery methods usually applied to heavy oil fields to improve recovery. In this process, air or oxygen-enriched gas is injected into a reservoir, burning some of the oil in place and generating heat and combustion gases. A considerable fraction of heavy oil resources resides in naturally fractured systems. There is no reported successful application of in situ combustion in a field with fractured systems in the literature to date. There is a limited number of studies regarding the subject in the literature. Thus, fundamental understanding of the process in fractured systems is limited.In this study, laboratory experiments of in situ combustion in core samples with the presence of fractures were conducted. A total of 12 combustion tube experiments were conducted with 12° API heavy oil from the Bati Raman field in Turkey. These experiments differ in their configuration of fractures and oxygen concentration in the injected gas. Based on our experimental observations three distinct behaviors were observed regarding front propagation through fractured systems. The first type is strictly diffusion-limited, the second type is characterized by a thick combustion front and the last is homogenous behavior. These observations could provide a fundamental basis for possible field applications of in situ combustion in fractured systems.

Self-propagating high-temperature synthesis of heterophase materials in the Zr–Mo–Si–B system. Kinetics and mechanisms of combustion and structure formation

The paper focuses on the study of the combustion kinetics and mechanisms of elemental mixtures in the Zr–Mo–Si–B system, as well as the analysis of phase and structural transformation stages in the combustion wave. A thermodynamic analysis of potential chemical reactions occurring in the combustion wave was carried out. The reaction of ZrB2 formation is preferred in the range of 298–2500 K. Above 2200 K, the formation of MoB becomes more thermodynamically advantageous as compared to MoSi2. Phase stability estimates of combustion products showed that ZrB2, MoSi2 and MoB phases are in equilibrium. Experimental dependences Тc(Т0) and Uc(Т0) are linear, which implies an unchanged combustion mechanism at T0 = 298÷800 K. Preheating leads to an increase in Uc. Similarly, an increase in the proportion of Zr and B in the mixture has a similar effect, i.e. an increase in heat emission and Tc. With a minimum content of Zr and B, the interaction between Mo and Si with the formation of MoSi2 by the reaction diffusion mechanism is decisive. As the proportion of Zr and B increases, the rise of T0 to 750 K does not affect the Tc. Eeff values (50–196 kJ/mol) confirm the significant influence of liquid-phase processes on the combustion kinetics. The mechanism of structure formation was studied. A Si–Zr–Mo melt is formed in the combustion front. The primary grains of ZrB2 and MoB crystallize from this melt as it is saturated with boron. At the same time, the melt spreads over the surface of Zr and Mo particles. This leads to the formation of ZrSix, MoSix films. Core-shell structures are formed behind the combustion front, which disappear as they move towards the post-combustion zone. The phase composition of products is formed in the combustion front in less than 0.25 s.

A Novel Approach in Understanding the Role of Water in Oxidation and Upgrading Reactions during In-Situ Combustion Oil Recovery, Part B: Interpretations

Summary To understand the role of connate water as a source of hydrogen in oxidation and upgrading of bituminous oil at high temperature, heavy water (D2O) and O-18 enriched water (H2O18) were used as connate water in two different in-situ combustion experiments using a conical tube. Aside from a fundamental understanding of the role of such reactions in in-situ combustion, the results could also potentially help in optimizing in-situ hydrogen generation and upgrading of heavy and bituminous oil. The conical tube had previously been used for understanding the impact of air flux in sustaining the combustion front (please see Alamatsaz et al. 2011Alamatsaz et al. 2012,2). Significant upgrading was observed in these tests with a produced API gravity of 35 °API compared to the original bitumen gravity of 9 °API. The produced fluids (gases and water) were analyzed with a mass spectrometer to demonstrate the effectiveness of using D2O and H2O18 as tracers in bitumen upgrading reactions and specifically to determine whether the H2O18 would be more effective than D2O in understanding the role of connate water. It was found that heavy water exchanges too readily with hydrogen atoms in the bitumen when the two are mixed. As a result, it could not be reliably used as an indicator for identifying the role of water. The run with O-18 enriched water, however, provided a better indication of water participation in the oxidation reactions. The results obtained from the mass spectrometry analysis of evolved gases and water samples collected in the second test showed that water does split during the reaction and O atoms of indigenous water molecules do combine with C atoms (from the hydrocarbon) to form CO2. These findings open the path for mechanistic considerations around the processes taking place during in-situ combustion and in-situ upgrading reactions.

Propagation of Non-Adiabatic Heterogeneous Solid Combustion Waves with Effect to Internal Microstructure and Heat Release

ABSTRACT Propagation of combustion front with effect to the external heat loss is studied by the two-dimensional discrete periodic and disorder systems. Discrete periodic systems are modeled by the regular arrangement of burnt and unburnt point heat sources characterized by the identical rate of heat release and different heat loss parameter. Discrete disorder systems, namely, S1, S2 and S3 are considered with the concatenation of regular burnt and unburnt point heat sources distributed by different shaping parameter of beta distribution function. The unburnt point heat sources in a discrete disorder system are characterized by the different heat loss parameter and incorporation of two categories of distributions for the rate of heat release namely (i) gamma (a = 20) and (ii) gamma (a = 2). The oscillations in ignition time delay, with the manifestation of bifurcation pattern, have been detected for discrete periodic systems. In a discrete disorder system, the external heat loss plays a crucial role in developing the fingering instabilities and determining the early onset of unstable combustion, quenching and combustion limit. Degree of randomness in the distribution of heat release for the disorder system affects the duration of combustion, burn rate without affecting the combustion limit. Computed values of burn rate and combustion limit from the discrete combustion model have been compared with the available data from experiment.

Burner stabilized flames: Towards reliable experiments and modelling of transient combustion

In this work the diffusive–thermal pulsations of the burner stabilized methane-air flames are investigated experimentally, by analysing the OH∗ chemiluminescence signal, and numerically within the model with various detailed reaction mechanisms. The employment of the nitrogen co-flow configuration to isolate the flame from the surrounding air allows us to obtain the experimental data of high fidelity such that the difference between the numerical data calculated with different reaction mechanisms is greater then the experimental uncertainty, demonstrating that the proposed technique can be used to verify the reaction mechanisms. Sensitivity analyses are carried out and it is shown that the steady and pulsating regimes of combustion has different although partly overlapping subsets of most important elementary reactions, especially for the case of relaxational oscillations in which the combustion front exhibits stages close to quenching and re-ignition. The suggested configuration can thus be used to access “transient combustion” and to gain an additional information to verify mechanisms.

A Novel Approach in Understanding the Role of Water in Oxidation and Upgrading Reactions during In-Situ Combustion Oil Recovery, Part A: Experimental Observations

Summary To understand the role of connate water as a source of hydrogen in oxidation and upgrading of bituminous oil at high temperature, heavy water (D2O) and O-18 enriched water (H2O18) were used as connate water in two different in-situ combustion experiments using a conical tube. Aside from fundamental understanding of the role of such reactions in in-situ combustion, the results could also potentially help in optimizing in-situ hydrogen generation and upgrading of heavy and bituminous oil. The conical tube had previously been used for understanding the impact of air flux (AF) in sustaining the combustion front (Alamatsaz et al. 2011). Significant upgrading was observed in these tests with a produced API gravity of 35 ° compared to the original bitumen gravity of 9 °API. This paper (Part A) deals with the experimental results including a comparison between conical tube and a combustion tube (CT) results. A subsequent paper (Part B) will discuss the upgrading aspects and the mass spectrometry results.

Theoretical Study of the Formation of Inhomogeneous Structures at the Combustion Front Based on the Reduced Model

Theoretical Study of the Formation of Inhomogeneous Structures at the Combustion Front Based on the Reduced Model

A “riding” combustion mode in CuO/Al reactive multilayer nano-foils

Reactive multilayer nano-foils possess high heat release and combustion temperature, which makes them very attractive for advanced applications, such as materials joining materials, tuning ignition and actuation, energy microsources, and others. The combustion mechanism of CuO/Al foils has not been adequately described yet. In this work, we report experimental evidence of an amazing combustion mode in CuO/Al reactive multilayer nano-foils. A set of droplets of molten combustion products forms behind the reaction front and “rides” this front under the action of surface tension. When the combustion front arrives at the edge of substrate and stops, the droplets start to fly-by inertia along-track direction of the combustion propagation. Thus, the combustion front can throw hot micro-droplets toward a predetermined target to perform some specific action, e.g., distance ignition, actuating pulse, or energy transfer.