Constant Volume Combustion Bomb Research Articles

Study on the combustion characteristics of NH3 and the inhibition characteristics of R134a on NH3

NH3 has been considered as an alternative to hydrofluorocarbon (HFC) refrigerants due to its environmentally friendly properties, while it is flammable. Therefore, it is necessary to investigate the flammability of NH3 (R717) and find its matching flame retardant to broaden its application. In this paper, the combustion behaviors of R717 and the inhibition characteristics of flame retardant R134a on R717 were studied experimentally and theoretically. Firstly, the flame propagation pattern, flammability limit, laminar burning velocity, and Markstein length of pure R717 were measured by a constant volume combustion bomb from 300 K to 400 K. Then the flammability characteristics of R134a/R717 mixture were further tested. The results indicated that R134a had a distinct flame retardancy on the flammability limits of R717. Further, the flame retarding mechanism of R134a on R717 was analyzed by density functional theory (DFT) on the 6–311++G(d,p) level. The flame retarding effects of R134a were classified to physical and chemical mechanisms. The physical force mainly depended on the dilution effect of additional R134a. The chemical mechanism was contributed to the newly flame retarding reactions introduced by R134a, which reflected in the dehydrogenation of R717 and the consumption of OH and H active radicals by fluorine-contained radicals (CF3, CF2, and F).

Experimental and kinetic modeling study on laminar flame speeds and emission characteristics of oxy-ammonia premixed flames

The low flame speed and NOx emissions of ammonia are the key to affecting combustion temperature, stability, flame structure, and pollutant control, limiting its application in power generation devices. This study proposes oxy-ammonia combustion (oxygen content in oxidant = 100%, NH3/O2 combustion) as a novel method for significantly enhancing ammonia combustion. A method for measuring the laminar flame speed using the NH* distribution of the Bunsen burner flame is proposed, and the measured data is close to the constant volume combustion bomb. 21 kinetic models were collected and optimized after comparison with the experimental data of constant volume combustion bombs, and results show that Han et al.'s model has higher prediction accuracy for NH3/O2 flames. The preheating temperature was relevant to gas turbine combustors (298.15–500 K), and the equivalence ratio ranged from 0.7 to 1.6. At this extreme condition (oxygen content in oxidant = 100%), the results show that the maximum laminar flame speed reaches 1.25 m/s at ambient pressure and temperature, which is approximately 18 times that of NH3/air combustion, mainly due to the increased reaction rates of OH, H, O and NH2 radicals in the reaction zone (primary ammonia decomposition and H/O radical pool). The NO emission of NH3/O2 combustion at stoichiometric conditions is about 7216 ppmv@15%O2, 1.5 and 13 times that of NH3/air and CH4/air combustion, respectively. NO production and consumption may follow the N2O and NNH mechanism, and HNO is an important precursor for NO formation. Increasing the preheating temperature has less effect on the reaction pathway directions in the reaction network of nitrogen conversion but affects the path flux significantly.

Analysis of the combustion characteristics of ammonia/air ignited by turbulent jet ignition with assisted hydrogen injection in pre-chamber

Turbulent jet ignition (TJI) is an advanced ignition strategy that can improve the ignition and combustion characteristics of low-reactivity mixtures. The utilization of TJI system may be reliable to achieve the application of ammonia (NH3) internal combustion engines. Hydrogen (H2) is a potential auxiliary fuel for the pre-chamber, and the injection of a small amount of H2 in the pre-chamber is beneficial for promoting the ignition and combustion of NH3/air in the main chamber. In this study, the ignition and combustion characteristics of NH3/air adopting the active TJI with assisted H2 injection in pre-chamber were investigated, and the relevant experiments were conducted in the constant volume combustion bomb system. The results show that the H2 pre-chamber can improve the flammability of NH3/air, and properly increasing H2 injection is conducive to the rapid ignition of NH3/air in the main chamber. The turbulence introduced into the main chamber by the hot jet enhances the combustion process, and the generation of turbulence weakens the sensitivity of the combustion rate to the reactivity of the unburned mixture. The turbulence intensity can be increased by decreasing the pre-chamber orifice diameter, which increases the ignition delay but significantly shortens the combustion duration.

Study on the Synergistic Suppression Effect and Mechanism of N2/Ultrafine Water Mist on Liquefied Petroleum Gas Explosion.

Liquefied petroleum gas (LPG) is widely used for its cleanliness and high efficiency in industry and city life. In order to improve the suppression effect on LPG explosion, a constant volume combustion bomb was used to investigate the synergistic influence of N2/ultrafine water mist on the explosion and combustion characteristics of 6% premixed LPG/air gas. The results showed that (1) the effect of a single ultrafine water mist on suppressing LPG explosion is unstable. When the concentration of ultrafine water mist is low, the flame acceleration in the initial stage of explosion is promoted, and when the ultrafine water mist with a mass fraction of 420 g/m3 is introduced, the maximum pressure rise rate increases. (2) The combination of N2/ultrafine water mist has a synergistic effect on LPG explosion. Compared to the individual suppression effects, the combination of N2/ultrafine water mist showed more effective suppression on the explosion pressure, flame propagation, and flame instability of LPG explosion. (3) Through the mechanism analysis, it is found that the combined action of N2/ ultrafine water mist can better reduce the mole fraction and ROP peak of active free radicals such as H, O, and OH by inhibiting the main reaction of generating H, O, and OH radicals during the explosion of LPG, resulting in the reduction of flame free radicals in the explosion system, thus effectively inhibiting the chain reaction of ignition and explosion of LPG. This research can provide guidance for a better understanding and implementation of gas-liquid two-phase suppression technology for LPG explosion.

Experimental study on the combustion of NH3/H2/air based on the passive turbulent jet ignition

The mixture of ammonia (NH3) and hydrogen (H2) is the potential alternative fuel for internal combustion engines (ICEs). The turbulent jet ignition (TJI) system can provide high ignition energy and turbulent disturbance to promote the combustion of the mixture for NH3/H2 ICEs. Therefore, the combustion characteristics of NH3/H2/air under passive TJI conditions were experimentally studied in the present study. The experiment was conducted in a constant volume combustion bomb, and the effect of fuel composition and equivalence ratio was investigated. The experimental results show that compared to spark ignition, the combustion of NH3/H2 can be effectively improved by using TJI, especially under high NH3 fraction conditions. The addition of H2 has a significant positive effect on the ignition and combustion performance. With the addition of H2, the ignition delay and combustion duration decrease evidently. And the H2 addition is beneficial for improving the ignition mechanism and achieving flame ignition. In addition, poor ignition performance may occur under rich conditions due to the fluid-dynamic quenching of the jet. However, the high flame propagation rate on the rich side still leads to lower combustion duration. Moreover, increasing the orifices number appropriately can enhance the ignition and combustion performance. The jet strength is weakened by the increased total orifice area and the ignition of NH3/H2 can be improved.

Experimental study on high pressure injection characteristics of gas fuel based on turbulent constant volume combustion bomb

In the face of strict carbon regulations, the internal combustion engine industry is turning to carbon-neutral and low-emission fuels. The experimental study of the high-pressure direct jet characteristics of gaseous fuels is still limited to the study of the high-pressure direct jet characteristics in stationary and non-uniform turbulent environments. The effect of isotropic turbulence on the high-pressure direct jet characteristics of gaseous fuels has not been thoroughly investigated. This paper investigates the high-pressure direct injection characteristics of gaseous fuels in an isotropic turbulent environment. Based on the experimental platform of turbulent constant volume combustion bomb, the effects of laminar flow environment and turbulence intensity on the high-pressure injection characteristics of gaseous fuels in turbulent environment are investigated in this paper. The results show that the turbulent environment has accelerated the axial development of high-pressure gaseous fuel injection compared to the laminar environment. The greater the velocity of the jet front, the greater the penetration distance. Under the turbulence intensity of 2.25 m/s, the penetration distance was 94.2 mm at 2.5 ms with a jet pressure of 6 MPa, which was 12.3% larger than that in the laminar flow environment (83.9 mm). Turbulence increases the radial development of the high-pressure gaseous fuel jet, facilitates radial diffusion and mixing at the jet boundary, accelerates the continuous merging and fragmentation process of the vortices at the jet boundary, enhances the entrainment of the surrounding medium gases, and contributes to the mixing of fuel and air in the jet. The stronger the turbulence intensity, the larger the near-field cone angle and far-field cone angle, and the larger the excess air coefficient. The stronger the turbulence intensity, the more the jet volume will be. This paper reveals the mechanism of background turbulence on jet development. The study is of great academic significance to enrich and deepen the theory of gaseous fuel jets.

Combustion performance and flame front morphology of producer gas from a biomass gasification-based cookstove

The present work investigates the last phase of the biomass gasification-based cookstove, which is the combustion process of biomass producer gas (BGP). A constant volume combustion bomb and kinetic simulation are used to characterize the behavior of the biomass producer gas and its pollutant emissions under a conventional premixed combustion process. The BGP combustion processes of two types of biomasses available in Colombia (Pinus Patula and Cordia Alliodora) are studied under certain conditions of pressure, temperature, and equivalence ratio. To characterize the combustible mixture of gases obtained after biomass gasification, a combustion chamber with cylindrical geometry equipped with a Schlieren optical diagnostic system to visualize the combustion process, and a piezoelectric pressure transducer to register the instantaneous pressure are used. By visualizing the flame front, the flame propagation speed at which the flame propagates through the combustion chamber and the morphology of the flame are studied. Instantaneous pressure is the input of a two-zone diagnostic model through which variables, such as burning velocity, temperature, mass burned fraction, etc., are obtained to characterize the combustion process of the mentioned gasification gases. Experimental results are compared and complemented with kinetic modeling results obtained with the Cantera package using the Gri-Mech 3.0 and Aramko 1.3 kinetic mechanisms, in terms of laminar burning velocity and NO, NO2, CO, and CO2 exhaust emissions. Results show that Cordia Alliodora presents higher burning velocities than Pinus Patula BP. However, lower CO2 emissions are obtained during the Cordia Alliodora combustion, and NOx emissions are not influenced by the type of biomass considered.

Study on spray characteristics of biodiesel alternative fuels for in-cylinder environment of diesel engine

This paper presents an experimental study of spray characterization of MD-NH (a blend of methyl decanoate and n-heptane in a molar ratio of 1:1 to characterize biodiesel) in an in-cylinder environment of diesel engines to provide a reference for the experimental study of engines in advanced combustion mode. Based on the Peng-Robinson state equation, the thermodynamic model of real fluid was established, and the influence law of ambient temperature and pressure on the diffusion characteristics of fuel flow was analyzed. Based on the constant volume combustion bomb experiments, the variations of spray penetration distance, spray cone angle, spray projection area, spray air entrainment mass, and spray fragmentation forms in different critical environment conditions were studied. The results show that the transport properties of the fuel change abruptly within the critical point neighborhood of the fuel. As the ambient temperature increases, near the critical temperature, the thermal conductivity of biodiesel decreases and then increases; density and kinematic viscosity decrease at an accelerated rate; and surface tension increases to a maximum and then disappears sharply. The diffusion coefficient decreases sharply when the ambient pressure reaches the critical pressure. The spray characteristics of biodiesel in sub/supercritical conditions were different. Compared with the subcritical environment, the biodiesel spray penetration distance decreases, the spray cone angle increases, the spray projection area decreases, and the air entrainment mass increases in the supercritical atmosphere, which induces a gas-liquid interface mixing layer and promotes the mixing of biodiesel with the atmosphere gas. The experimental data in this paper fill the gap in the study of biodiesel spray characteristics in supercritical environments and provide a basis for high-fidelity numerical simulation of the spray model.

Effect of Turbulence and Diffusional–Thermal Instability on Hydrogen‐Rich Syngas Turbulent Premixed Flame

As a kind of fuel with low‐carbon emissions, hydrogen‐rich syngas has a large resource potential and is a promising alternative energy resource. A series of experiments in a constant volume combustion bomb are carried out to investigate the effects of turbulence and diffusional–thermal (DT) instability on a hydrogen‐rich syngas turbulent premixed flame. The flow field in the constant volume combustion bomb is calibrated, and the turbulent flow field's homogeneity and isotropy were investigated. The effects of different speeds of fan (1366–4273 rpm), hydrogen fractions (55%–95%), pressures (1.0–3.0 bar), and equivalence ratios (0.6–1.0) on the hydrogen‐rich syngas turbulent premixed flame are studied. According to the analyses, the flow field in the experimental device exhibits good homogeneous and isotropic characteristics. With the increase of turbulence intensity, equivalence ratio, hydrogen fraction, or pressure, the turbulent flame propagation speed increases gradually. As the hydrogen fraction increases or the equivalence ratio decreases, the effective Lewis number decreases, and the effect of DT instability on the flame increases. The research in this article is crucial for the clean and efficient utilization of hydrogen‐rich syngas and the design of related burners.

Experimental and simulation study on the combustion characteristics of ammonia/n-dodecane mixtures

Laminar burning velocity is a crucial characterization parameter in fuel combustion progress. Investigating the combustion properties is significant to improve combustion efficiency. This paper employs a constant volume combustion bomb and high-speed ripple shadow camera technology to explore the influence of equivalence ratios (0.8–1.4) and ammonia energy shares (0%–40%) on the laminar burning velocity of n-dodecane/ammonia mixture at an ambient temperature of 400 K and a pressure of 1 bar. The results illuminated that the unstretched laminar burning velocity of n-dodecane increased from 46 cm/s at ϕ = 0.8 to 61 cm/s at ϕ = 1 and then decreased to 32 cm/s at ϕ = 1.4. When the ammonia energy ratio reaches 40%, the maximum laminar burning velocity experiences a reduction of 44% because the blended ammonia inhibited the formation of H and O radicals based on kinetic analysis in the fast reaction zone. With the increase of ammonia ratio, the Markstein length of mixed burned gas gradually increases. Particularly under a 1.4 equivalent ratio condition, the Markstein length increases from 0.2 mm to 0.8 mm, indicating that ammonia components significantly enhance flame stability. To gain a deeper understanding of the influence mechanisms of laminar burning velocity, a simplified Yao-Otomo (Y-O) model with 92 species and 355 reactions is proposed, coupling the mechanisms of n-dodecane and ammonia. The Y-O model has demonstrated a predictive trend that is consistent with more detailed WUT-NH3 model (176 species and 2839 reactions), and the Y-O model reduces the amount of computation to save calculation time, which has a higher engineering applicability. The turbulent kinetic energy (TKE) induced by premixed fuel in engine cylinders is estimated through comprehensively analyzing the laminar burning velocity and flame thickness characteristics. The findings indicate a 45% reduction in the peak value of TKE as the ammonia energy ratio increases.

Energy attenuation behavior on propane–air premixed combustion on account of nonmetallic spherical spacers in confined space with two perforated plates

AbstractEnergy attenuation behavior on propane premixed combustion on account of nonmetallic spherical spacers (NSSs) was investigated in a constant volume combustion bomb with two accelerative perforated plates. The flame evolution process is captured by a photography device with schlieren. Energy attenuation effects of NSSs were explored on flame propagation, overpressures, and pressure oscillation. Normal combustion accomplished with flame acceleration, jet autoignition, deflagration, and weak detonation is observed, respectively. NSSs show a good energy attenuation effect on propane normal combustion, jet autoignition, and deflagration evolution behavior, however, during the evolution of weak detonation, the attenuation effect is relatively weak. The mean velocities difference, as well as explosion overpressure decay rate caused by NSSs, decreases from (45.70 m/s and 26.48%) to (2.70 m/s and 18.15%) when the initial pressure increases from 0.1 to 0.5 MPa, namely, attenuation effect of NSSs on propane explosion decreases with increasing initial pressure.

Optical experiment study on Ammonia/Methanol mixture combustion performance induced by methanol jet ignition in a constant volume combustion bomb

Ammonia as an alternative fuel has shown great potential in reducing carbon dioxide emissions. However, the issues of high ignition temperature and unstable combustion of ammonia limit its extensive application. As an ignition energy enhanced method, the ignition chamber (pre-chamber) seems to be an effective solution to improve the combustion performance and extend the ammonia lean flammability limit. In this study, the methanol was provided as relatively high activity fuel to improve the mixture activity in the ignition chamber and main chamber. The mixture activity control method was introduced to accelerate ammonia premixed combustion. The visualization experiment compounded with shadow method was applied to investigate. Results showed that the methanol fueled ignition chamber as jet ignition model reduced the combustion duration by almost half compared to spark ignition method. The methanol jet flame propagation formatted multiple zones of ignition and combustion in the main chamber. The ammonia combustion speed shifted from being determined by laminar flame propagation speed to being determined by jet velocity. The methanol jet velocity is related to the methanol energy substitution ratio and nozzle diameter of the ignition chamber. A 2 % methanol energy substitution ratio is optimized for the lean condition of Φ = 0.8 compared to 1 % methanol energy substitution ratio achieve for the condition Φ = 1.0 in the main chamber. When 50 % methanol (energy) was added in the main chamber, the activity thermo-atmosphere improvement induced the combustion duration to decrease by 43.8 % and 51.9 % at equivalent ratios of 1.0 and 0.8, respectively, compared to pure ammonia. The small nozzle diameter of ignition chamber can improve the jet velocity, however it caused the methanol combustion flame quenching leading to unstable combustion phenomenon. A 3 mm nozzle diameter achieved a short combustion duration compared to 4.5 mm and 6 mm nozzle diameter.

An investigation on the laminar flame propagation and auto-ignition characteristics of a coal-derived rocket kerosene-Part I: Experimental study

The energy structure of coal-rich and oil-poor in China, makes the conversion of coal to liquid fuels an attractive option to reduce petroleum dependence. In this study, the combustion characteristics of a newly developed coal-derived rocket kerosene were investigated to provide fundamental parameters for evaluating the feasibility and compatibility of the new fuel in potential applications. The laminar flame propagation properties of the fuel were studied at pressures of 1, 2 and 5 bar over a temperature range of 423–483 K for equivalence ratio of 0.7–1.8 in a constant volume combustion bomb, and the auto-ignition characteristics of the target fuel were then experimentally studied in a heated shock tube. Flame propagation process was studied based on the recorded flame morphology firstly. The unsteady transition from spark assisted ignition kernel propagation to normal flame was analyzed and was found to become less conspicuous in flames with stronger reaction intensity (higher initial pressure or temperature) and smaller Lewis number (higher equivalence ratio). The Markstein length was extracted by extrapolating the flame trajectories and used to investigate the flame instability. The results shows that the increase of pressure, equivalence ratio enhance the flame instability, but the impact of initial temperature shows no prominent pattern. The laminar burning velocity and ignition delay times were reported over a wide range to strengthen the understanding of combustion characteristics of the new fuel. A kinetic model was proposed to simulate the combustion chemistry of the fuel and kinetic analysis was performed to identify the key reactions driving the flame propagation and auto-ignition. The present study is hoped to provide insights into the evaluation of fuel application in the future and database support for further combustion reaction kinetic mechanism development.

Laminar burning characteristics of ammonia and n-butanol blend fuels

Blending n-butanol with ammonia has been shown to effectively improve the combustion performance of ammonia and enable carbon–neutral combustion systems. This study investigated the laminar burning speed and Markstein length of n-butanol/ammonia/air mixtures at various equivalence ratios (0.8–1.4) using the spherical flame method with the nonlinear extrapolation model (NQ) in a cylindrical constant-volume combustion bomb. The initial temperatures varied from 393 K to 453 K, and the initial pressures ranged from 0.1 MPa to 0.6 MPa, with ammonia fractions ranging from 50% to 80%. Results illustrate that the unstretched laminar propagating speed and laminar burning speed have a negative correlation with the ammonia fraction and initial pressure, but are positively correlated with the initial temperature, with peak values occurring at aroundϕ = 1.0 orϕ = 1.1 under all initial conditions. Adiabatic flame temperature is negatively related to the ammonia fraction and positively correlated with the initial temperature, but varies minimally with increasing initial pressure. Hydrodynamic instability is negatively related to the ammonia fraction and initial temperature but positively correlated with the initial pressure. When xNH3=80%, the Markstein length Lb and Markstein number Ma firstly decrease and then slightly increase as the equivalence ratios increase. The results of Lb and Ma indicate that the ammonia addition plays a primary role in the flame instability of ammonia/n-butanol blends at both ϕ≤0.9 and ϕ≥1.3, while the effect of n-butanol matters more at ϕ=1.0-1.2 under xNH3=80%. Both Rcr and Pecr increase with increasing ammonia fractions under Tin = 423 K, Pin = 0.6 MPa andϕ = 1.4. The findings indicate that the burning flux has a negative correlation with the ammonia fraction, whereas it is positively related to the initial pressure and initial temperature, with peak values occurring at around ϕ=1.0 under all tested conditions.

Experimental and kinetic modeling study on propane enhancing the laminar flame speeds of ammonia

The laminar flame speeds of ammonia/propane in air were investigated in a constant volume combustion bomb at 1–5 atm, over 298–453 K, at the equivalence ratios of 0.7–1.6, with the propane in fuel varying from 0 to 90 vol%. The measured data were provided for the validity of the proposed M-NUIG model. The comparison showed that M-NUIG model could successfully predict the measured data of propane, ammonia and mixtures under wide conditions. The results showed that the addition of 20% propane can enhance the LBV of ammonia by a factor of 3 at 1 atm, 298 K. Based on kinetic analysis, NH2 is mainly consumed by the oxidation of N-contained species in NH3/air flame, and it is completely consumed through reacting with O, OH, H and HO2 in NH3/C3H8/air flame. As for the NH3/C3H8 interactions, NH can react with CH3, forming CH2NH which completely converts to HCN. HNO also reacts with CH3 to generate NO. Thus, the CN interactions are crucial to the formation of harmful emissions. Moreover, with 50% propane addition, the peak concentrations of OH and H radicals are much higher than in NH3/air flame which is the main reason for the higher LBV.

Experimental and kinetic modeling study on the oxidation and laminar combustion characteristics of natural gas

The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO2 and H2O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions.

Study of fuel spray characteristics using a high-pressure common rail diesel injection system by the method of Schlieren

The supercritical atmosphere created by the increase in temperature and pressure in the diesel engine cylinder is the key factor that causes changes in the fuel atomization process. In this study, the differences in spray morphology of n-heptane under different ambient temperature and pressure conditions were investigated using a constant volume combustion bomb combined with the Schlieren method. Based on the Peng-Robinson equation of state (PR equation), several transport characteristics models are constructed to predict the transport characteristics of n-heptane under different operating conditions. During the experiment, the injection pressure and fuel temperature were kept constant (80 MPa, 300 K), the ambient pressure was varied from 2 to 5 MPa, and the fuel temperature was changed from 400 to 800 K, spanning from subcritical to supercritical state. Three different spray regions have been identified based on the fuel temperature and spray geometry: liquid phase region, gas-liquid interface mixing layer, gas phase region. The results show that in a subcritical environment (400 K, 2 MPa), the fuel injection and atomization process is dominated by evaporation. The degree of heat exchange between the fuel and the medium gas is very low, while a small amount of phase change occurs. When the fuel is in low (600 K, 3 MPa) and medium supercritical (600 K, 4 MPa) ambient atmosphere, turbulence becomes the dominant factor in the fuel atomization process. The mixing layer at the gas-liquid interface at the edge of the liquid jet increases significantly. When the fuel is in a high supercritical (700 K, 4 MPa; 800 K, 5 MPa) atmosphere, the jet takes on a shape similar to that of a gas jet, and the mixing layer at the gas-liquid interface becomes the main part of the spray projection area.

Simulation study of fuel spray dynamics in a constant volume combustion chamber

ABSTRACT The OpenFOAM computational fluid dynamics code was used to investigate the performance characteristics of spray jet in a constant volume combustion bomb. The total duration of fuel spray was approximately second, and the total mass of fuel sprayed was kilogram. The results show that there was a positive and somewhat positive qualitative correlation between the profiles of the number of parcels and the mass flow rate of the injected fuel at between second. Furthermore, at between the number of parcels experienced a sharp rise while the injected mass flow rate was decreasing, see Figure 6. The results of the present study show that the spray droplet sizes vary from to which were found to be reasonably representative of measurement data that are usually observed at the top dead centre position of internal combustion engine test bed experiments. Furthermore, the results of the study show the contour plots of pressure and temperature. The pressure rise varies from the initial value of 50 bar to 75 bar at the end of combustion while the temperature rose from to its final value of . The specific details of the results from this study are summarised in the conclusion section.

Study of water and hydrogen addition on the pyrolysis and combustion characteristics of isooctane

Water injection and hydrogen combustion technologies have gained widespread attention in recent years. Combining H2O and H2 injection could bring more desirable combustion based on the needs of different engine conditions. To fully explore what effects the simultaneous injection of H2O and H2 would have on the combustion process of isooctane, three different subtests were performed in this study: investigation on chemical reaction mechanism, the laminar flame speed measurements and real engine tests. Firstly, H2O and H2 were added to the JSR (Jet Stirred Reactor) reactor to analyze the synergistic effect of H2O and H2 on the pyrolysis process of isooctane. The experimental results showed that the addition of H2O and H2 leads to an increase of OH and H radicals, which increases the concentrations of C1-C3 species and decreases the concentrations of C4 species. To further investigate the effect of H2O and H2 on the radical reaction of isooctane combustion process, this study then measured the laminar flame speed of IC8H18/H2/O2/H2O gas mixture by using constant volume combustion bomb, and found that water injection would reduce the laminar flame speed, and H2 would increase the laminar flame speed accordingly. Sensitivity analysis showed that it was more sensitive to reactions R1, R97 and R12, and was more sensitive to H2O than to H2. Finally, real engine tests were performed on a modified 1.5L gasoline equipped with port H2O and H2 injection systems at 1300 rpm with 30% throttle opening. The results showed that the use of H2O and H2 permitted the manipulation of engine combustion speed. Specifically, H2O injection led to a decrease in the peak cylinder pressure; and the addition of H2 increased the cylinder pressure again·H2O injection resulted in increased ignition delay and slower flame spread, slowing the engine's burn rate when needed. Using H2 addition led to a short ignition delay and accelerated combustion velocity, which counteracted the negative impacts of H2O injection and elevated the engine combustion speed to optimize efficiency. In summary, this paper revealed the complementary coordination between H2O and H2 through experimental and simulation studies. It will provide theoretical guidance for the development of H2O injection with H2 technology for gasoline engines.

An experimental study on the laminar burning velocities of RP-3 kerosene and its surrogate fuel at elevated pressures and temperatures

This work develops a new surrogate fuel for RP-3 kerosene. Based on five optimizing targets (molecular weight, hydrogen/carbon ratio, cetane number, lower heating value and threshold sooting index) to emulate the chemical and physical properties of RP-3 kerosene, the surrogate fuel was determined to contain 22% n-dodecane, 15% iso-cetane, 48% decalin and 15% 1,2,4-trimethylbenzene. The laminar burning velocities of RP-3 kerosene and its surrogate fuel were investigated at the unburnt temperature of 413, 443, 473, 503 K, pressure of 1, 2, 5 bar and equivalence ratio of 0.6 ∼ 1.6 in a constant volume combustion bomb. The results show that the laminar burning velocities of the surrogate fuel were in good agreement with that of RP-3 kerosene. Meanwhile, a kinetic model was adopted, which well predicted the laminar burning velocities of RP-3 kerosene and the surrogate fuel. Finally, the flame propagation process and flame instability of RP-3 kerosene under elevated temperatures and pressures conditions were analyzed. It was found that the surrogate fuel was slightly different from RP-3 kerosene in terms of the combustion instability under fuel-rich conditions.