Constant Volume Bomb Research Articles

Experimental and chemical kinetic study on effects of H2-DME fusion addition on laminar premixed flame speed and flame instability for ammonia composite combustion

Improvement of the laminar flame speed and stability for ammonia combustion by using H2 and DME has received significant attention. In this study, the characteristics of NH3/H2, NH3/DME and NH3/H2/DME were investigated in constant-volume bomb with high-speed schlieren technique and chemical kinetics. The results show that DME or H2 addition mainly acts as “start-up" or “acceleration" for ammonia laminar flame speed increasing, respectively. In NH3/H2/DME laminar flame, the increase of DME addition ratio not only increases the intensity but also advances the onset of self-acceleration. At ammonia substitution ratio of 10 %–70 %, the Markstein length of NH3/H2/DME flame are all significantly improved compared with pure ammonia flame. The H2-DME fusion-addition can mitigate the reduction of flame thickness and keep a relatively minor thermal expansion ratio. In NH3/H2/DME laminar flame, DME addition can increase the Lewis number greater than 1.0 at ammonia substitution ratio of 10 %–40 %, which significantly reduce the thermo-mass diffusion instability in comparison with H2 addition. Based on mixture design method and experimental validation, it was found that the flame speed at 473 K, 5 bar and φ = 1 for NH3/H2/DME blending ratios of 53.94 %/26.61 %/19.45 % are greater than those of NH3/H2 and NH3/DME with the same ammonia substitution ratios.

Numerical Simulation on Combustion Characteristics of Methane Air Premixed Flame Impacted by Hydrogen jet

Abstract Low-concentration coalbed methane is an efficient and clean unconventional natural gas with abundant reserves. It can greatly lessen the problem of energy scarcity when used to produce combustion power. Nevertheless, the engine finds it challenging to burn the CH4 directly due to its low and fluctuating concentration. This study suggests using a hydrogen jet to ignite low-concentration coalbed methane. The simulation method is used in this paper. To investigate the effects of various ignition injection strategies on the combustion characteristics of low concentration coalbed methane ignited by a hydrogen jet, a constant volume bomb model was developed. The results show that when the ignition and hydrogen injection interval is 2.0 ms, the cold jet of hydrogen does not burn immediately when it reaches the premixed flame, and there is a transition process from the premixed flame to the jet flame. The larger the interval between ignition and hydrogen injection, the more waste gas is produced after the premixed flame combustion, which has a certain inhibition effect on the formation of the jet flame. With the decrease in the interval between ignition and hydrogen injection, the combustion duration is obviously shortened. Therefore, the earlier hydrogen is involved in the ignition, the faster the combustion speed.

Study on Combustion Characteristics of Low Concentration Coalbed Methane Induced by Hydrogen Jet based on Excess Air Ratio

Low concentration coal bed gas used for power generation is a better treatment scheme at present, which solves the problem of environmental pollution caused by the direct emptying of coal bed gas. Coal bed methane is a methyl alkyl fuel, and slow combustion rate will cause abnormal combustion phenomena such as large combustion cycle changes. The initial ambient gas concentration has a great influence on the development and propagation of the flame. In this paper, a constant volume bomb model is established to change the excess air coefficient of methane air premix in the initial constant volume bomb, and the change law of combustion heat release is analyzed. The results show that when hydrogen participates in the combustion stage, the combustion rate increases with the increase of excess air coefficient. When hydrogen is burned out, the combustion rate decreases with the increase of excess air coefficient.

Demonstrating the significance of radiant energy exchange during metal dust combustion

Metal combustion is a process accompanied by strong light emission. Correspondingly, radiative loss can significantly affect the overall energy balance, and needs to be considered in the global numerical models describing metal dust combustion. In this work, we experimentally estimated the fraction of radiative loss during aluminum (Al) dust combustion by studying the heat release in a modified constant volume bomb calorimeter that enabled the additional measurement of pressure. The previously developed method of dispersing powder ensured nearly 100% combustion efficiency. The contribution of the combustion energy to heating the gas inside the calorimeter bomb was determined by analyzing the measured pressure traces and found to be measurably lower than 100%. The energy loss was attributed to radiant heat transfer from burning metal particles to the bomb wall. Aluminum powders with median size ranging from 4 μm to 100 μm were studied. The estimated fraction of radiative loss depended on the particle size. Radiative loss saturated at nearly 50% for larger particles and gradually reduced with the particle size decrease below 20 μm. We related the observed radiative loss to a recently introduced process that occurs during metal combustion, namely condense-luminescence. The results shown here have important implications for the role of radiant energy exchange in metal particle combustion and will transform future approaches to harnessing metal oxidation energy for a multitude of applications.

Experimental study on the intrinsic instabilities of spherically expanding CH4/H2/CO2/O2 flames

To study the instabilities of spherically expanding CH4/H2/CO2/O2 flames with an equivalence ratio of 0.80, isochoric combustion experiments were carried out in a 36 L constant volume bomb at an initial temperature (298±2 K) and atmospheric pressure (100 kPa). The crack length Lcrack, average cell area Scell, critical flame radius Rc and critical Peclet number Pec of CH4/H2/CO2/O2 flames were evaluated. The results show that the evolution of Lcrack at low hydrogen fractions is slightly affected by oxygen enrichment but significantly affected at high hydrogen fractions. Thermodiffusive instability dominates the evolution of Scell at low hydrogen fractions, but hydrodynamic instability dominates at high hydrogen fractions. At lower oxygen fractions, hydrogen addition results in more significant enhancement of the thermodiffusive and hydrodynamic instabilities. As the oxygen fraction increases, the maximum size of the thermodiffusive cells decreases, and the thermodiffusive instability weakens due to the increasing effective Lewis number, but the flame thickness decreases. This indicates that the weak thermodiffusive instability is amplified by the small flame thickness. With increasing oxygen fraction, the unstable region of the peninsula by the linear stability theory narrows in the Pe–n plane but broadens in the R–n plane. Therefore, the unstable peninsula in the R–n plane is consistent with the trend of crack growth observed in the experiments. Additionally, the experimental critical flame radius Rc,1 is closer to Rc calculated by the linear stability theory than Rc,2, where Rc,1 and Rc,2 represent the cross-cracking of the thermodiffusive cells and the onset of the hydrodynamic cells, respectively. Pecl exhibits a linear dependence on the Markstein number Ma. Moreover, a power law correlation of the experimental Rc with respect to oxygen enrichment and hydrogen addition is proposed.

A new reduced reaction mechanism of the surrogate fuel for RP-3 kerosene

By combining the reaction class-based global sensitivity analysis (RC-GSA) methodology, species sensitivity analysis (SSA) methodology, decoupling method and genetic algorithm (GA), a reduced reaction mechanism of the surrogate fuel (10% n-dodecane/14% n-decane/30% isohexadecane/36% methylcyclohexane/10% toluene, in mole fraction) for RP-3 kerosene was constructed. As an example, the detailed construction process of skeleton mechanism of methylcyclohexane (MCH) was presented, and the skeleton mechanism constructions of other components in the surrogate fuel were similar to that of MCH. First, the dominant reaction classes in the fuel-relevant mechanism of MCH were recognized by the RC-GSA, the representative species in each retained reaction classes were selected by the SSA, and the skeleton fuel-relevant mechanism of MCH was developed. Second, through combining the skeleton fuel-relevant mechanism of MCH with the reduced reaction mechanism of C0-C3 by the decoupling method, the initial skeleton mechanism of MCH was obtained. Third, based on the GA, the rate constants of fuel-relevant reactions in the initial skeleton mechanism of MCH were optimized to enhance the prediction performance. Finally, by coupling the skeleton reaction mechanisms of n-dodecane, n-decane, toluene, isohexadecane, MCH, and the reduced reaction mechanism of C0-C3, a reduced mechanism (containing 121 species and 469 reactions) of the surrogate fuel for RP-3 kerosene was formed. The predicted main species concentrations during the oxidation process in the jet-stirred reactor, the ignition delay times in the shock tube and laminar flame speeds in the constant volume bomb by this reduced mechanism are in good agreement with the corresponding experimental data of RP-3 kerosene.

Experimental investigations of laminar and turbulent burning velocities of thermally cracked hydrocarbon fuels

A comprehensive understanding of the flame propagation characteristics of thermally cracked fuels is crucial for developing advanced scramjets using regenerative cooling techniques. In the present study, both the laminar and turbulent burning velocities of thermally cracked hydrocarbon fuels at typical pyrolysis temperatures were systematically measured using a newly developed, fan-stirred, constant-volume bomb. The results show that variations in fuel composition have no significant influence on the laminar burning velocities of pyrolysis gases and liquids. In addition, the promotional effects of pyrolysis gas on flame propagation of thermally cracked fuel depend on the gas-production rate and equivalence ratio. The normalized turbulent burning velocities of typical thermally cracked fuels can be well scaled using a power law with regard to the turbulent Reynolds number (ReT, f). The fitting exponents gradually increase with increasing equivalence ratio, indicating a stronger promotional effect by turbulence for fuel-rich flames. For premixed turbulent flames in the wrinkled/corrugated flamelet regimes, turbulence and preferential diffusion simultaneously affect the flame propagation process. The wrinkling effects of turbulence are weakened by thermal-diffusional stability when the combustible mixture has an effective Lewis number (Leeff) greater than one. By contrast, the wrinkling process is promoted by thermal-diffusional instability, and the flame propagation is simultaneously enhanced by turbulence and thermal-diffusional instability. A unified scaling law for normalized turbulent burning velocities of thermally cracked fuels is proposed based on ReT,f Leeff–0.6, which accounts for the impacts of preferential diffusion. The effective Lewis number corrected scaling law can be applied to thermally cracked fuels at different pyrolysis temperatures, with a maximum relative error not exceeding 15%.

Experimental and chemical kinetic study on the laminar flame characteristics of the blends of n-propanol and isooctane at elevated temperature and pressure

Laminar flame characteristics of n-propanol-isooctane blends were investigated at the initial temperature of 433 K, two pressures of 0.1 and 0.5 MPa, different equivalence ratios of 0.7–1.6 and various fuel blending ratios in a constant volume bomb. Laminar flame speeds and flame instability parameters were determined, and the effect of initial conditions were evaluated. It was found that laminar flame speeds of n-propanol decrease with the pressure increases, and the addition of n-propanol into isooctane results in the rise of laminar flame speed. To interpret the flame speed variation, the thermal and diffusion properties were discussed by determining the adiabatic flame temperature and Markstein length. However, the chemical kinetics is concluded as the dominant factor since the variation of adiabatic flame temperature and Markstein length exert different behaviors with laminar flame speed does. A high temperature chemical kinetic model was developed, and the model accuracy was validated with present data as well as several sets of data published previously. With this model, detailed sensitivity and reaction pathway analyses were carried out to aid the understanding of the inherent mechanism. It was found that the laminar flame speed is mainly sensitive to the small molecule reactions. The addition of n-propanol into isooctane induces limited effect on the reaction pathways of each fuel. Finally, the flame thickness and density ratio were presented with the hydrodynamic instability evaluated. Combining the schlieren pictures and the flame instability parameters, it was concluded that the thermal-diffusional mechanism dominates the flame instability variation with the addition of n-propanol.

Numerical simulation of the influence of high-pressure methane jet on the premixed ignition flame of constant volume bomb

Because of stringent emissions regulations, internal combustion engines using natural gas have become an important direction for the low-carbon development of the internal combustion engine industry. The combustion process of the internal combustion engines using natural gas involves the interaction between the gas jet and the flame. In this study, the process of a methane jet impinging on a methane premixed ignition flame inside a constant volume bomb was simulated by CONVERGE software, and the changes in combustion and flow within the jet impinging flame flow field were investigated. A k-value was defined by the ratio of jet velocity to laminar combustion velocity, and k is found to be inversely proportional to the maximum value of the rate of change of flame surface area A, and k is proportional to the peak value of the rate of change of turbulent kinetic energy. It was also found that the jet intensifies the initial premixed flame under three k-value operating conditions, and the OH-based change rate within the flow field increases abruptly by a factor of 4–9 after the jet is added. The process of jet impingement on the flame is divided into three stages according to the mutual position of the jet and the premixed flame surface, and the evolution of the flame structure and the combustion behavior in the flow field under different stages are analyzed in the article. It was found that the initial premixed flame induced by the jet became unstable in the second stage and a stable turbulent combustion flame was formed in the third stage. Analysis of the parameter changes at three points on the axial direction of the jet nozzle revealed that the jet disturbance at the near-nozzle end was too large to form stable combustion. Meanwhile, at the far-nozzle end, the jet disturbance formed a vortex volume suitable for combustion, and turbulent combustion was produced by the heat-induced by the flame moving toward the unburned area and the vortex volume disturbance.

Laminar Burning Speed of Aviation Kerosene at Low Pressures

Aero-engine combustors may experience extreme low pressures in the case of an in-flight shutdown, which makes the study of aviation kerosene flame propagation characteristics at low pressures important. The present work examined flame propagation during the combustion of aviation kerosene over the pressure range from 25 to 100 kPa using a constant-volume bomb apparatus. The laminar burning speeds at different initial pressures, temperatures and equivalence ratios were measured and compared. In addition, numerical simulations were used to examine the reaction sensitivity of the laminar burning speed at low pressure. In trials at the lean flammability limit, the data indicated that it was more difficult to ignite the fuel under a lower pressure condition of 25 kPa and a lower temperature condition of 420 K. The experimental results of laminar burning speed were fitted to an equation providing the laminar burning speeds expected at different pressures (25–100 kPa), temperatures (400–480 K) and equivalence ratios (0.8–1.5). The temperature index (α=1.76) and pressure index (β=−0.15) of the fitting equation were obtained. Both hydrodynamic and diffusional thermal flame instabilities were found to be suppressed at low pressures. The negative effects of two specific reactions on laminar burning speed were greatly reduced at these same low pressures of 25 kPa.

Experimental Study on Entrainment Characteristics of High-Pressure Methane Free Jet.

Entrainment occurs during the high-pressure gas jet process, which is crucial for a natural gas direct injection engine. This study presents an experimental investigation on the high-pressure methane jet from one single-hole injector and proposes a method to obtain the entrainment mass flow rate based on kinetic energy conservation. The entrainment is related to three variables, i.e., spring plate moving distance Δx, gas jet mass at the nozzle outlet mn, and gas jet velocity u1. A spring-set test rig is built to measure the spring plate moving distance Δx, and the schlieren method is adopted to test the gas jet velocity u1 based on a constant-volume bomb (CVB) optical test rig; finally, the weight method is used to obtain the methane gas jet mass at the nozzle outlet mn. This combined measuring method is verified to be valid in the near field to the nozzle. The results show that the methane jet mass flow rate gradually increases along the jet direction and has a two-zone entrainment process. Zone I: near field (Lr < 10), the methane jet mass flow rate linearly increases up to the maximum; in the nozzle exit field (Lr < 1), it is conserved, and no entrainment occurs. Zone II: far field (Lr ≥ 10), the jet mass flow rate maintains the maximum, and the entrainment becomes saturated with a saturation value larger than the initial value at the nozzle outlet. The entrainment rate experiences three stages, linearly increasing in stage I and early stage II but not in late stage II and stage III. The methane injection pressure causes great effects on the mass flow rate and entrainment. As the injection pressure increases, the methane jet mass flow rate increases linearly, but the entrainment rate decreases.

Экспериментальные и расчетно-аналитические исследования совместимости горючих веществ друг с другом и с окислителями

The danger of chemical reactions in the interaction of incompatible substances manifests itself in an increase in temperature and pressure, ignition, and finally, these reactions can be accompanied by an explosion. By the method of a constant volume bomb, the processes of interaction of mutually reacting substances are studied, as which mixtures of combustible substances (sodium, magnesium, sulfur, and an organic liquid — glycerin) with a changing mass of the oxidizer (ammonium nitrate, ammonium perchlorate, potassium permanganate, potassium bichromate) and in a mixture of these substances of stoichiometric composition are studied: a combustible component and an oxidizer. Analysis of the dependences of the coefficient of participation of a substance in an explosion on the coefficient of excess of an oxidizer of various interacting substances indicates that these dependences can be of two types: with an extremum and in the form of a direct dependence. Continuous increase in the coefficient of participation in the explosion with an increase in the coefficient of excess of the oxidizer indicates the ability to decompose and participate in the explosion of the oxidizer itself. This type of dependence established experimentally for the powders of combustible sulfur and magnesium with oxidizing agents-ammonium nitrate and ammonium perchlorate, shows that both combustible and decomposition products of a flammable oxidizing substance participate in the explosion. Other mixtures (magnesium, glycerin mixed with potassium permanganate, potassium bichromate) have an extremum, and the oxidizer does not participate in the pressure increase when the oxidizer content in the mixture increases. Calculation confirms the possibility of determining chemical compatibility (incompatibility) of substances using the standard Gibbs energy. Based on the example of the experimentally established incompatibility of mixtures of magnesium and sulfur with ammonium nitrate, the calculation also shows that these substances are incompatible with each other. In the absence of experimental data on the compatibility of substances, the input data for calculating the Gibbs energy, the information on the compatibility (incompatibility) of substances can be borrowed from tables 15–17 of GOST 12.1.004. Hazardous and especially hazardous substances indicated under numbers 3 and 4 in these tables are incompatible.

Effect of equivalence ratio on spark ignition combustion of an air-assisted direct injection heavy-fuel two-stroke engine

In the small aviation field, the research of direct injection (DI) heavy-fuel two-stroke engines has attracted much attention. The safety and unity of aviation heavy-fuel (i.e., aviation kerosene and diesel) is better than those of gasoline, which is more suitable for small aviation engines. In this paper, the influence of air-assisted injection on the formation and combustion of aviation kerosene direct injection mixture is studied on an aviation heavy-fuel direct injection spark ignition (DISI) two-stroke engine. Firstly, the spray simulation model of three-dimensional air-assisted injector was established by Computational Fluid Dynamics (CFD) software. And the effectiveness of the spray model was verified by comparing the simulation results with the experimental data of constant volume bomb spray. The combustion system CFD model of the two-stroke engine was further established to study the heavy-fuel spark ignition combustion at different ignition timings and equivalence ratios. The results show that when the ignition advance angle is 30°CA BTDC, higher combustion pressure and faster flame propagation speed can be achieved without knock. Aviation kerosene is less prone to knock than diesel and can achieve better combustion performance under the condition of rich mixture.

Development of diesel surrogates for reproducing the effect of fuel properties on engine combustion and emissions using an optimized decoupling physical–chemical surrogate (DPCS) model

An optimized decoupling physical–chemical surrogate (DPCS) model was carried out to formulate different diesel surrogates effectively. In the optimized DPCS model, the physical candidates of ten components and the chemical candidates of four components are coupled by the rule of hydrocarbon type to match the physical–chemical properties of diesel fuel. The composition of the physical components is determined using genetic algorithm (GA), and then the coupling rule is applied to derive the composition of the chemical components. To validate the robustness of the optimized DPCS model, the prediction results are compared with the experimental results containing vapor penetration distance in a constant volume bomb (CVB) and the combustion and emission characteristics in a convention diesel combustion (CDC) engine utilizing different diesel fuels. The results show that the predictions of the diesel surrogates formulated by the optimized DPCS model accurately fit the experimental results, and the impacts of diesel fuel properties on the spray and combustion behaviors can be well reproduced. Besides, the factors that dominate the spray and combustion features of different diesel fuels are identified.

Experimental Research of High-Pressure Methane Pulse Jet and Premixed Ignition Combustion Performance of a Direct Injection Injector

Natural gas (NG) direct injection (DI) technology benefits the engine with high efficiency and clean emissions, and the high-pressure gas fuel injection process causes crucial effects on the combustion. This study presents an optical experimental investigation on the high-pressure methane single-hole direct injection and premixed ignition combustion based on a visualization cuboid constant volume bomb (CVB) test rig. The experimental results show that the methane jet process is divided into two stages. The methane gas jet travels at a faster speed during the unstable stage I than that during the stable stage II. The injection pressure causes more influence on both the jet penetration distance and the jet cone area during stage II. The methane jet premixed flame is a stable flame with a nearly spherical shape, and its equivalent radius linearly increases. The methane jet premixed flame area also increases while the flame stretch rate declines. The methane jet premixed flame velocity rises as both the standing time and equivalent ratio increase. The methane jet premixed flame is a partial premixed flame, and the peak of the methane jet premixed flame occurs at greater equivalence ratio ϕ, i.e., ϕ &gt; 2. As the injection pressure rises, the jet premixed flame equivalent radius increases, and the flame velocity linearly increases. The higher the methane injection pressure, the faster the jet premixed flame velocity.

Экспериментальные исследования воспламенения нитрата аммония при взаимодействии с порошками магния и серы

Выполнены экспериментальные исследования взрывоопасности взаимореагирующих веществ: нитрата аммония (аммиачной селитры), который является сильным окислителем, относится к пожароопасным соединениям, в смеси с магнием и серой. Исследования свидетельствуют о взрывоопасности металлов и серы при их взаимодействии с пожароопасным веществом - окислителем (нитратом аммония). Эти особенности аммиачной селитры должны учитываться в процессе ее обращения (производство, хранение, транспортирование, применение, утилизация), при предотвращении и тушении пожаров. Ammonium nitrate (ammonia nitrate) is widely used in industry and in agriculture. The use of ammonium nitrate as a fertilizer gives this strong oxidizer a reputation of harmless agricultural chemical. At the same time, many cases of fires and explosions were registered during the storage, transportation and processing of saltpeter. Saltpeter decomposes with the release of highly toxic nitrogen oxides, which actively maintain combustion, and in case of fire also with release of oxygen. The analysis of statistical data on fires and explosions during the circulation of ammonium nitrate indicates serious problems in ensuring fire and explosion safety of buildings and structures in particular facilities of its storage. Clean and dry saltpeter explodes at normal temperature only in the presence of large volumes of the substance under the influence of a strong initiator, for example, a detonator. However, in the presence of some substances of both organic and inorganic origin the decomposition temperature of saltpeter decreases and this process of chemical spontaneous combustion can lead to an explosion. There are conducted experimental investigations by the method of constant volume bomb to determine the excess explosion pressure (ΔР) at interaction of ammonium nitrate with magnesium and sulfur powders and to compare these data with the calculated data of the excess explosion pressure (ΔР). It is established that the explosion pressure increases continuously with an increase in the concentration of the oxidant for mutually reactive substances consisting of combustible chemical element (magnesium, sulfur) and ammonium nitrate. This feature of the explosion of metals with an oxidizer - ammonium nitrate is a consequence of metal oxidation as well as the direct influence of decomposition products of the oxidizer in explosion. The growth of the overpressure of the explosion is also determined in the experiments when changing the volume of the reaction vessel (bomb camera) At the same specific weight of the mixture of mutually reactive substances (magnesium - ammonium nitrate) the explosion pressure increases with the volume of the bomb (the camera). The performed studies show that the contact of ammonium nitrate (ammonia nitrate) with foreign inclusions (additives) and, in particular, with metals and sulfur can lead to an explosion.

Study on pressure oscillation characteristics in a constant volume bomb

The pressure oscillation characteristics of a promising gasoline additive Di-isopropyl Ether (DIPE) were studied. The experiments were operated in a constant volume bomb (CVB) under different initial pressure (1, 3, 5 bar) and equivalence ratio (0.8–1.6). The experimental data acquisition system includes pressure, sound pressure and vibration detection system and Schlieren system. The experimental results show that the pressure oscillation intensity first increases and then decreases with increasing of the equivalence ratio, and the overall oscillation intensity increases with initial pressure. The sound pressure, vibration intensity and gray-scale brightness extracted from flame processing photos all have the same tendency. N2 is replaced by He and CO2 dilution gas with different blending ratios to investigate the change of oscillation. The effects of several factors’ behavior were studied. When Markstein length is low, the pressure oscillations become much easier to occur. The increase of Zeldovich number can decrease the intensity of oscillations. It is induced that the combustion instability is the main reason for pressure oscillations in constant volume bomb.

Surrogate models of thermally cracked hydrocarbon fuels at typical pyrolysis temperatures

Construction of surrogate fuel model for thermally cracked fuel holds fundamental importance to its combustion characteristics. In the present study, series of thermal cracking experiments of hydrocarbon fuel were carried out at supercritical pressure. Thermally cracked fuels at three typical pyrolysis temperatures, which covered the low, middle, and high levels of thermal cracking, were selected and analyzed. A formulation method to construct surrogate models for thermally cracked fuels was developed, in which the pyrolysis gas and liquid were considered separately, and then combined by a key parameter of gas-production rate. Laminar burning velocities of the target fuels and their corresponding surrogate models were measured using a constant-volume bomb, and then compared to validate the fidelity of surrogate models. Results show that the pyrolysis gas can be well substituted by a mixture of hydrogen, methane, ethylene, ethane, and propylene. Surrogate models of pyrolysis liquids contain eight large hydrocarbons, taking into account the variations of hydrocarbon classes and carbon number distribution. By changing mole fractions of candidate species, the proposed surrogate models of pyrolysis liquids reasonably match all target properties, including the averaged molecular weight (MW), hydrogen-to-carbon ratio (H/C), lower heating value (LHV), derived cetane number (DCN) and density. Surrogate models of thermally cracked fuels combine those of both pyrolysis gases and liquids, and can accurately predict the laminar burning velocities. With thirteen candidate components and the formulating strategy, the current method is capable of constructing a surrogate model for thermally cracked fuel with a fuel-conversion rate up to 73%.

Analysis of the Ignition Behavior Based on Similarity Factor Method

The chemical kinetics mechanism is an important factor to accurately predict the combustion characteristics of constant-volume bomb (CVB). In this study, an n-heptane oxidation mechanism constructed by Wang et al. is introduced to study the correlation of the ignition behaviors with the mechanism constructed by Chang et al. The effects of the similarity factor method in the analysis of ignition behaviors of fuel in CVB were repeatedly verified by changing the important spraying parameters: injection pressure and hole diameter. Through further verification, it was found that the combustion process was controlled at approximately 850 K and stoichiometric ratio mixture of fuel/air in CVB, which corresponds to the negative temperature coefficient region at stoichiometric ratio mixture in shock tube (ST). The mechanism verified by the experiment under the condition in ST can reflect the chemical ignition in CVB. In addition, the similarity factor method was less dependent on the chemical reaction mechanism and boundary conditions.

Drive Control Experimental Studies on the Injection Characteristics of a Self-Pressurized Injector

As a miniaturized direct-injection (DI) solution, a self-pressurized injector is of great significance for small aviation piston engines, such as the spark-ignited two-stroke heavy-fuel engines. Accurate control of the timing and amount of injections is an important application prerequisite. In this paper, a high-speed camera is employed to study the spray characteristics, injection delay and fuel injection duration under three drive modes in a constant-volume bomb environment. The results show that the 8-A constant-current drive mode ensures the minimum injection dead zone and linearity of the flow characteristic curve, and the spray characteristics are close to those under a peak current of 10 A and holding current of the 8-A drive mode, which indicates that the drive circuit can be simplified. Ambient pressure increase leads to an increased injection delay and shortened injection duration. Therefore, it is recommended to apply the 10-A constant-current drive mode to reduce the impact of the ambient pressure. The double-injection characteristics of the self-pressurized injector are also studied, and the results demonstrate that when the interval time is reduced to 2 ms, the spray characteristics of the secondary injection are affected, and when the interval time is reduced to 0.2 ms, the spray characteristics of the primary injection are also affected. To ensure consistency of the spray characteristics, the minimum spray interval should be longer than 3 ms.