Constant Volume Combustion Chamber Research Articles

Experimental Investigation of Ammonia/Oxygen/Argon Combustion: The Role of Equivalence Ratio and Nozzle Shape in a Constant Volume Combustion Chamber with Sub-chamber

The global rise in carbon emissions presents a rising challenge for current and future generations. In the pursuit of zero carbon emissions, ammonia (NH3) has emerged as an attractive alternative energy source. Ammonia offers a carbon-free fuel option with a higher energy density than liquid hydrogen while maintaining ease of transport and storage. However, ammonia still has its drawbacks, such as a high autoignition temperature, slow burning velocity, and low heating value, that demand further investigation of its combustion characteristics. This experiment was done to study the effect of nozzle shape and equivalence ratio (ɸ) on the combustion of an ammonia/oxygen/argon mixture using a constant volume combustor equipped with a sub-chamber. The fuels were premixed for 10 minutes and conditioned to an initial pressure of 0.2 MPa and an initial mixture temperature of 423 K. The results show that the different nozzle shapes each have their advantages in terms of pressure and jet speed. Overall, the lean mixtures (ɸ0.6 and ɸ0.8) consistently performed better compared to the stoichiometric mixtures (ɸ1.0) in all categories investigated in this study. The round nozzle generates higher pressure, while the special shape nozzle enhances jet speed, highlighting trade-offs between the two.

Laminar burning characteristics of ammonia and hydrogen blends at elevated initial pressures up to 2.5 MPa

Ammonia is a highly promising alternative fuel, and blending it with hydrogen can mitigate its poor combustion performance. However, the combustion mechanism of ammonia-hydrogen mixtures requires further validation through measurements of laminar burning velocity, particularly under high-pressure conditions relevant to practical combustors. Experimental data at high initial pressures (>1.0 MPa) are notably scarce. In this study, experiments were conducted using an outwardly propagating spherical flame in a high-pressure, high-temperature, constant-volume combustion chamber to determine the laminar burning velocities of ammonia-hydrogen blends at elevated initial pressures. The effects of different equivalence ratios (0.6 ∼ 1.4), volumetric hydrogen ratios (0.1 ∼ 0.6), and initial pressures (0.1 ∼ 2.5 MPa) were evaluated. Chemical kinetics of ammonia and hydrogen combustion was investigated at high pressures. The experimental results were compared with the simulation results under a wide range of conditions using several existing mechanisms to evaluate their applicability. The results show that the laminar burning velocity increases first and then decreases as the equivalence ratio (ϕ) increases and reaches a maximum value around ϕ of 1.1. The laminar burning velocity increases non-linearly with the volumetric hydrogen ratio, with more pronounced acceleration at higher hydrogen ratios. In contrast, the laminar burning velocity decreases non-linearly with the increasing initial pressure, and this reduction becomes progressively slower as the initial pressure rises. The predictive performance of the mechanisms by Okafor et al. and Gotama et al. is relatively satisfactory under certain conditions, but further optimization based on experimental data is necessary. Additionally, reaction pathway analysis of ammonia-hydrogen combustion indicates that introducing hydrogen increases the concentration of active radicals such as OH, O, and H, thereby enhancing ammonia combustion. Sensitivity analysis of the laminar burning velocity identified the critical elementary reactions across varying pressures, providing strong support for optimizing ammonia-hydrogen chemical kinetics models and developing simulation models for practical combustion systems.

An experimental study on the influence of nozzle hole numbers and patterns of a passive pre-chamber spark ignition system

Pre-chamber spark ignition system enhances the combustion stability and efficiency of lean burn engines. Pre-chamber spark ignition system performance directly relies on the characteristics of the turbulent flame jet, which are governed by the pre-chamber geometrical parameters and nozzle hole configurations. Based on the existing literatures, limited research on nozzle hole numbers and patterns is noted with passive pre-chamber, and thus, the impact of these nozzle hole configurations on the combustion and flame development characteristics for hydrogen-methane-air mixtures is investigated in a constant volume combustion chamber. In the current study, single-layer nozzle hole configurations with three, four, six, and eight nozzle holes and double-layer nozzle hole configurations with six and eight nozzle holes are designed and tested in an optically accessible combustion chamber under various equivalence ratio conditions. The results indicated that the combustion characteristics deteriorated with an increase in nozzle holes, except with the single-layer four nozzle hole configuration. Compared to the single-layer eight nozzle hole configuration, the ignition delay and combustion duration for hydrogen-methane-air mixtures with single-layer four nozzle hole configuration was reduced by 31.9% and 30.7% under lean conditions. A reduction in flame jet penetration length, area and velocity and increased adjacent flame jet interaction was noticed for the single-layer configuration with more nozzle holes, and thus, a different nozzle hole pattern was studied in the current study. The double-layer configurations with more nozzle holes showed better combustion and flame development characteristics than single-layer configurations due to their unique flame structure, uniform and faster flame jet distribution, and reduced adjacent flame jet interaction. The ignition delay and combustion duration for hydrogen-methane-air mixtures with the double layer eight nozzle hole configuration were reduced by 30.5% and 40.7% compared to the single-layer eight nozzle hole configuration.

Influence of Blending Ratio on Spray Characteristics of Gasoline–Hydrogenated Catalytic Biodiesel Blended Fuel

Blending gasoline with hydrogenated catalytic biodiesel has the potential to improve combustion problems of gasoline direct-injection compression combustion, and the spray characteristics of the blending fuel can directly affect the combustion effect. In order to understand the spray characteristics of a gasoline–hydrocatalyzed catalytic biodiesel mixture, a numerical spray model of constant volume combustion chamber was established, and the accuracy of the model was verified by experimental data in the literature. Based on this model, the spray penetration, sauter mean diameter, spray velocity field and concentration field of gasoline–hydrocatalyzed catalytic biodiesel at different blending ratios were studied. The results show that under the conditions of 850 K ambient temperature, 5 MPa ambient pressure, and 80 MPa injection pressure, as the proportion of hydrogenated catalytic biodiesel in the blending fuel increases, the spray penetration increases, the sauter mean diameter decreases slightly, and the area of high velocity and high concentration at the spray center increases. The results of this study will contribute to the development of blended fuels for superior combustion performance and reduced pollutant emissions at appropriate blending ratios.

An optical study on the spray and combustion characteristics of coal-derived naphtha/diesel blends in a constant volume combustion chamber

ABSTRACT Coal-derived naphtha (CDN) is well suited as an additive for diesel to achieve soot reduction in diesel engines; however, there is no study so far to qualitatively reveal the mechanisms through the spray and combustion processes. In this paper, the spray and combustion characteristics of CDN/diesel blends with 10%, 20%, 30% and 40% CDN in volume were studied under various injection pressures in a constant volume combustion chamber. In addition, gasoline/diesel blend with 20% gasoline in volume was also studied for comparison. Results show that, compared with pure diesel, CDN/diesel blends have the improved fuel spray evaporation, the notably reduced peak integrated natural flame luminosity and soot formation. The blend with 40% CDN shows the greatest soot formation reduction of 39.7% under 100 MPa injection pressure. When the volume fraction of gasoline and CDN are both 20% in blends, there is little difference in spray characteristics, but CDN/diesel blend exhibits a greater advantage in soot formation reduction. Under the test conditions, increasing the injection pressure may improve fuel-air mixing to some extent, but its effect on reducing soot formation is not significant, especially at higher CDN proportions.

Experimental study on the effects of n-butanol and n-propanol on the spray and combustion characteristics of diesel/biodiesel blends in a constant volume combustion chamber

The depletion of fossil fuel resources and the escalating environmental impact of greenhouse gas emissions have intensified the global exploration of renewable and sustainable energy sources. Biodiesel produced from vegetable oils and animal fats has become a promising alternative to conventional diesel fuel due to its renewability and lower carbon emission. This study investigates the differences in spray, combustion and flame characteristics between soybean-based biodiesel blended with propanol and butanol at various ratios. The results indicate that the liquid spray penetration length of biodiesel mixed with propanol and butanol exceeds that of soybean-based biodiesel. And the increase of spray penetration is accompanied by a longer flame lift-off length, which indicates the improvement of spray characteristics. Regarding combustion, alcohol-fuel blends exhibit a reduction in peak combustion pressure but an increase in peak apparent heat release rate. Additionally, these fuels show a shorter ignition delay and combustion duration. The peak natural flame luminosity is lower for alcohol fuels, suggesting their potential to reduce carbon soot production and support low-carbon combustion. These experimental results contribute to advancing research on cleaner, more efficient and renewable fuels, thereby reducing reliance on conventional fossil fuels.

Experimental study on multi-point ignition of NH3/air by high-frequency nanosecond dielectric barrier discharge

Non-equilibrium plasma ignition technology, with its ability to expand ignition limits and increase ignition volume, is considered an important development direction of advanced ignition systems, and has significant advantages in improving ignition stability and combustion rate. This study investigates the ignition and combustion assistance effect of high-frequency nanosecond surface dielectric barrier discharge (nSDBD) on NH3/air mixture in a constant volume combustion chamber (CVCC). The study reveals the influence of high-frequency nSDBD on the growth process of the flame kernel in NH3/air mixture. As the discharge pulse number (PN) increases, the flame kernel develops from the middle position of the discharge filament to the head of the discharge filament, while there is no obvious flame at the root and middle of the discharge filament. Continuous discharge causes the flame kernel to appear concave and the center of the flame kernel to shift towards the wall of the CVCC. In the NH3/air mixture, the initial flame kernels exhibit dissipation phenomenon, resulting in a discrepancy between the number of initial flame kernels and the number of stable combustion flame kernels. As the discharge frequency or pulse number increases, and the number of stable combustion flame kernel increases. The adjustment of discharge frequency and pulse number can effectively control the flame development time (FDT) and flame rise time (FRT) of NH3/air mixture. As PN increases, both FDT and FRT are shortened. When discharge frequency is 20 kHz, the maximum shortening of FDT and FRT are 30 ms and 14 ms, respectively, about 55 % and 30 %. The effects of discharge frequency on FDT and FRT exhibit a non-monotonic variation pattern, and it is necessary to comprehensively consider various discharge parameters to achieve the best ignition effect. The ignition success rate curve of high-frequency nSDBD in NH3/air mixture is steep. The study results of this paper provide new discoveries and experimental data for advanced ignition systems.

Optical study on spray mixing, flame propagation and jets evolution within visible methanol active pre-chamber for turbulent jet ignition

Methanol spray impingement, mixing, flame propagation and jet evolution within the narrow-confined active pre-chamber (APC) with complex walls were experimentally observed by optical method for the first time. The effects of injection pressure and duration was investigated on an actual-geometry optical APC assembled in constant volume combustion chamber (CVC). Exploration on APC internal processes within static environments forms the basis for optimization of APC and analysis of jet formation. Mie scattering coupled with flame natural luminosity imaging were used to record spray mixing and combustion. The results show that in the APC with narrow-confined space, methanol spray undergoes three wall impingements, inducing a tumble that promotes mixing. High injection pressure enhances rapid spray tip penetration, while long injection duration slows methanol diffusion. In longer injection duration cases, the spray tip after the third impingement interferes with subsequent sprays. For higher injection pressure, this interference occurs in the APC cone section due to a larger spray cone angle, whereas for lower pressure, it happens in the APC duct section. Higher injection pressure also causes more spray to impact the APC bottom after the first wall impingement, hindering flame acceleration in the duct section. Irregular flame propagation is observed in the APC cone section due to wider space and uneven mixture conditions, while the convergent geometry from the APC throat to the duct section significantly accelerates flame propagation. The APC jet appears due to the pressure difference between the APC and the main chamber, with the brightness and length of the visible flame jet increasing with APC flame luminosity and pressure difference. A Mach ring structure is observed initially, but the jet velocity decreases as the Mach ring disappears during the APC inner flame extinguishing process. Through this study, the actual spraying and combustion process in APC is experimentally captured and revealed, which are an important contribution for APC optimization and development.

Optical study on the spray and combustion characteristics of diesel-biodiesel-alcohol blend fuels on a constant volume combustion chamber

The rapid increase in automobile ownership has brought about an increase in pollutant emissions, the blending of alcohols can effectively reduce conventional pollutant emissions from diesel engines. However, alcohols have poor inter-solubility with diesel fuel. This study investigates the effects of blending different alcohols on the spray and combustion characteristics of diesel, with biodiesel as the cosolvent. The results show that among the three alcohols, blending methanol has the best improvement in the gas-liquid phase spray characteristics, followed by ethanol and propanol. The GL-SCA and GL-SPA of the methanol blends are 8.2 % and 2.3 % larger than those of the ethanol blends, and 19 % and 11.9 % larger than those of the propanol blends, respectively. Among the four fuels, fuel blended with methanol emits the least normalized sum KL, 45 % less than that of diesel, 23.8 % less than that of ethanol blended fuel, and 35.3 % less than that of propanol blended fuel.

Regulation of Catalysts on Tightly Packaged Solid Propellant Energetic Particles: High Combustion Performance with Low Temperature Sensitivity.

Although the effectiveness of combustion catalysts promoting the combustion performance of solid propellant (SP) was identified in many research studies, its regulation on the temperature sensitivity coefficient of burning rate (δp) has been rarely explored, where SP with low δp is a big challenge with little progress. Herein, several ammonium perchlorate (AP)-enriched (>70 wt %) pomegranate-structured SP energetic particles (SPPs), AP/nitrocellulose (NC)/Al (SPP), SPP/CoWO4-rGO (SPP-Co), SPP/Bi2WO6-rGO (SPP-Bi), and SPP/CuCo2O4/GO (SPP-Cu), were prepared by the electrospray granulation method, tightly packaging AP with high-efficiency catalysts to promote its reactivity and reduce temperature sensitivity. The pressurization rates of SPPs in a constant volume combustion chamber at 50, 0, and -40 °C were obtained to determine δp. The burning rates of SPP-Co, SPP-Bi, and SPP-Cu loose strips are 0.319, 0.312, and 0.356 m/s, which are increased by 11.1%, 8.7%, and 24.0% compared to that of SPP (0.287 m/s), respectively. The peak pressures and pressurization rates of SPP-Co, SPP-Bi, and SPP-Cu at 0 °C are increased by 18.8%, 10.1%, and 9.1% and 62.3%, 67.1%, and 64.1% compared with SPP, respectively, indicating that these catalysts significantly accelerate the combustion process. Compared with SPP, the δp of SPP-Co, SPP-Bi, and SPP-Cu decreased by 26.6%, 60.6%, and 24.7% at 0-50 °C and 19.5%, 61.6%, and 27.6% at -40-0 °C, respectively. It suggests that the Bi2WO6-rGO catalyst reduces the δp by 61% at -40-50 °C, exhibiting the optimal δp regulation performance. This research introduces a novel approach to lower the δp from the chemical by tightly packaging temperature-sensitive AP with high-efficiency catalysts.

Laser ignition of hydrogen/air mixtures in a constant-volume combustion chamber using a pulse-burst Nd:YAG/Cr4+:YAG laser spark plug

In this study, characteristics of laser ignition of H2/air mixtures are investigated in a constant-volume combustion chamber using a compact, passively Q-switched Nd:YAG/Cr4+:YAG laser spark plug. Ignition was conducted at a single point, with precise timing achieved through two laser modes of operation: delivering a single laser pulse and operating in pulse-burst mode, emitting trains of up to five laser pulses. Experiments covered a wide range of relative equivalence ratios (λ= 1.5 to 5.0) at 1 bar initial pressure and extended to 9 bar. Under similar pressure conditions, igniting H2/air mixtures with higher λ values (lean mixtures) results in a reduction of maximum pressure and a slower combustion process. Conversely, maintaining the same λ value for H2/air mixtures, while elevating the initial pressure, yields higher maximum pressures, but concurrently decelerates the combustion process. Pulse-burst mode laser ignition expedited combustion, especially for lean mixtures (λ> 4.0), showcasing advantages over single-pulse laser ignition. Additionally, lean ignition limits were determined at different pressures, revealing pressure-dependent differences between single pulse and pulse-burst modes laser ignition. These results provide insights into the features of laser ignition with pulse trains of H2/air mixtures and the use of this ignition technique in hydrogen-powered reciprocating engines.

Study on the microscopic characteristics of pentanol/highly active fuel spray based on high-speed droplet tracking velocimetry technology

Pentanol blending with highly reactive fuels for internal combustion engines holds considerable promise. The atomization of sprays closely influences the efficiency and combustion characteristics of the system. Based on Particle Tracking Velocimetry and high-speed shadow imaging technology, we propose a method termed High-speed Droplet Tracking Velocimetry for analyzing spray particle size. Prior to conducting our study, we validated the reliability of High-speed Droplet Tracking Velocimetry through comparisons with the Malvern and Phase Doppler methods. This study utilized long working distance micro high-speed shadow imaging technology in a visualized constant volume combustion chamber to investigate the spray micro-characteristics of pentanol blended with highly reactive fuels, including Fatty Acid Methyl Ester, Hydrogenated Catalytic Biodiesel, and Diesel. The results indicate that under all operating conditions, the droplets of P20H80 (the volume fraction of 20 % n-pentanol mixed with 80 % Hydrogenated Catalytic Biodiesel) are smaller and more uniformly distributed, demonstrating the minimum Sauter Mean Diameter, characteristic diameter, and width of droplet size distribution. The droplet velocities of P20H80 are the lowest, followed by P20Di80 (the volume fraction of 20 % n-pentanol mixed with 80 % Diesel), and P20B80 (the volume fraction of 20 % n-pentanol mixed with 80 % Fatty Acid Methyl Ester) exhibits the highest velocities. These velocity differences among the three fuels generally remain within 10 %-20 % across various injection pressures. P20Di80 shows the highest Reynolds and Weber numbers, followed by P20H80, with P20B80 having the smallest values due to its intermediate physical properties. The gaps between each fuel type range from 20 % to 30 %.

Laser ignition versus conventional spark ignition system performance for hydrogen-enriched natural gas-air mixtures in a constant volume combustion chamber

This study compares the performance of a laser ignition system vis-à-vis a conventional electrical spark ignition system in a constant volume combustion chamber. A custom-built constant-volume combustion chamber was used to compare the performance of the laser and spark ignition systems. A combination of three lenses in the optical path was used to create laser plasma in the constant volume combustion chamber. Initial chamber pressure and temperature were maintained constant at 4 bar and 150 °C during the experiments. The effect of hydrogen enrichment of compressed natural gas on combustion was assessed for three relative air–fuel mixture strengths (λ: 1.0, 1.2 and 1.4) to compare the performance of both ignition systems. The laser ignition system exhibited superior combustion characteristics to the spark ignition system. The combustion duration of laser ignition was considerably lower than spark ignition. Three hydrogen-enriched natural gas blends (10HCNG, 20HCNG and 40HCNG) were assessed and compared with baseline compressed natural gas. Hydrogen enrichment improved the combustion characteristics, increasing the excess chamber pressure and reducing the combustion duration. Two locations were taken for assessing the performance of the laser ignition system in this study. The first location was the same as the spark from a conventional electrical spark ignition system, and the second was at the centre of the constant volume combustion chamber. The central location of laser ignition showed a higher reduction in the combustion duration than baseline spark ignition and its corresponding laser ignition, indicating its superiority. The ability to choose an ignition location centrally in the engine combustion chamber emerged to be a main advantage of laser ignition systems.

Visualization study on the flame propagation and distribution characteristics and exploration of optimal injection strategy in ammonia/diesel dual direct injection mode

With the increasing shortage of fossil fuels and the worsening carbon emission problems, ammonia has been attracted widely to alleviate the current challenges faced by internal combustion engines. Igniting direct injection of liquid ammonia by diesel may be a measure to achieve effective ammonia application, while the research on the characteristics of combustion and the unburned ammonia emission is little. Therefore, this paper studies the effects of ambient parameters and injection parameters on the characteristics of diesel ignition and flame propagation and distribution based on a constant volume combustion chamber, through the shadow method. The results indicate that the premise to ensure that ammonia can fully participate in combustion is that the flame can backpropagate to the junction of the two sprays. The current optimal injection strategy is the simultaneous injection of diesel and ammonia combined with a complete ammonia injection before the maintained flame. At a low temperature and high diesel injection pressure, ammonia will participate in combustion after a delay, which may result in a relatively low heat release rate and high unburned ammonia emissions. Overall, the paper can provide important references for professional researchers which is of great significance for the development of diesel/ammonia engines.

Experiments and modeling of the thermal spray-chasing phenomenon during split injection processes

Spray chasing is a specific manifestation of the interaction between split injections, where the mass and heat transfer between the pilot and main sprays significantly influence fuel mixing and ignition processes. In this study, a spray-chasing model is developed and validated based on optical diagnostic results, aiming to theoretically support the development of injection strategies that are more environmentally adaptive and offer improved performance. A series of optical diagnoses of diesel split injection is performed in a constant volume combustion chamber using diffused back-illumination imaging and high-speed schlieren imaging. The extent of the spray-chasing phenomenon is modulated by regulating the injection dwell time (DT) and ambient temperature. For inert sprays, when the background temperature exceeds 790 K, the liquid spray-chasing phenomenon can be disregarded owing to the premature evaporation of the pilot spray. Although shortening the DT can promote the development and mixing of the main spray, the lack of evaporation in the pilot fuel pocket leads to a higher local fuel concentration in the interaction zone after spray chasing, which will hinder the subsequent ignition of the main spray. For reactive sprays, the variations in spray chasing patterns under different operating parameters are determined and their impact on the ignition process is evaluated by combining optical test results with theoretical models. Under cold start conditions, the ignition delay and ignition location of the main spray exhibit a non-monotonic trend with increasing injection dwell time. Optical diagnosis observes that compared to DT of 200 us and 1500 μs, the main spray exhibits both valley in ignition delay time and ignition location at DT = 900 μs. The spray-chasing model identifies approximately 1020 μs as the optimal theoretical DT, expected to best facilitate ignition of the main spray. However, under hot-start conditions, even though the spray-chasing mode varies with different injection dwell times, the ignition characteristics remain essentially unchanged due to the limited promotion effect of split injection on ignition.

Investigation on the Regulation of the Combustion Characteristics of a Propane/Air Mixture by Repetitive nSDBD Pretreatment.

This paper investigates the effect of the transient repetitive nanosecond surface dielectric barrier discharge (nSDBD) pretreatment on the combustion characteristics of combustible mixtures. A method of using nSDBD online pretreatment of a combustible mixture to regulate the combustion characteristics of the mixture is proposed. The study is conducted in a constant-volume combustion chamber at atmospheric pressure and temperature using a propane/air mixture as fuel. The discharge characteristics of repetitive nSDBD and the effects of pretreatment discharge energy and interval time between the pretreatment and ignition on combustion rate are discussed. The results show that (1) For 12.5 kHz pulses, the filament length generated with the annular dielectric barrier electrode discharge can reach up to 7 mm, and the number of discharge filaments per pulse can reach 40. (2) Pretreating mixtures using repetitive nSDBD at millisecond time scale can significantly improve the combustion process. (3) Repetitive nSDBD pretreatment can enhance the activity of the mixture near the surface of nSDBD electrode, which leads to obvious wrinkles on the flame surface and significantly improves the combustion rate. (4) The flame rise time decreases with the increase of discharge energy and increases with the increase of the interval time between the pretreatment and ignition. The effect of the repetitive nSDBD pretreatment on flame propagation during the flame development period becomes more pronounced with the increase of the excess air coefficient. The research results of the paper reveal the law of online regulation of combustion characteristics of combustible mixtures by the nSDBD, providing experimental data support for the mechanism research of online regulation of combustion characteristics of combustible mixtures by the nSDBD.

Electrical ignition of ADN-based green liquid propellant in constant volume combustion chamber and continuous flow

Ammonium dinitramide (ADN) propellant for green space propulsion is perceived as a focal point in space propulsion research. The development of electrical ignition methods to realize the ignition for ADN-based liquid propellant can overcome the technical bottleneck of the catalytic ignition methods currently applied to ADN-based space thrusters. This work presents an experimental investigation of the electrical ignition and combustion characteristics of an ADN-based liquid propellant in a constant volume combustion chamber, considering ignition voltages and initial pressures. It is observed that increasing the ignition voltage and initial pressure reduces the flame retardation period, combustion duration, droplet lifetime, ignition energy, and total energy. Also, the combustion peak pressure decreases with an increase in the ignition voltage but increases with higher initial pressures. The energy consumption is mainly concentrated in the ignition stage, with the ignition energy accounting for approximately 76% to 96% of the total energy. The measurement of the concentrations of the keycombustion products are reported, highlighting that the mole fraction of CO decreases with an increase in ignition voltage and pressure. The ignition and combustion of the ADN-based liquid propellant in continuous flow were achieved for the first time through a combination of resistive ignition and high-temperature arc-assisted combustion. During the testing of the propellant ignition in continuous flow, there is a need for a continuous supply of electrical energy, and the combustion cannot be self-sustaining.

Influence of Ambient Pressure on the Jet-Ignition Combustion Performance and Flame Propagation Characteristics of Gasoline in a Constant Volume Combustion Chamber

Based on a constant volume combustion chamber, the initial ambient pressure effect on gasoline combustion performance and flame propagation of the active and passive pre-chamber ignition systems were studied. Compared with the passive pre-chamber, the active pre-chamber can significantly expand the lean combustion limit from 1.2 to 1.5, enhance the ignition and combustion performance, and speed up the combustion of the main combustion chamber. At slightly lean combustion conditions, the heat release performance has a positive correlation with the initial ambient pressure. As the premixed λ increases, the heat release performance and the initial ambient pressure begin to become negatively correlated. Ignition delay can be decreased by approximately 50% at an initial pressure of 0.75 MPa, premixed lambda of 1.2 with APC compared with PPC. The high ambient pressure (1.0 MPa) in the constant volume chamber greatly reduces the mixture entrainment ability of the jet flame at lean combustion conditions, thereby reducing the combustion speed and peak heat release rate.

Study on ignition mode transition of methanol pre-chamber jet ignition system controlled by boundary condition parameters

Optimizing boundary condition parameters is an effective means to substantially improve the combustion performance of methanol pre-chamber turbulent jet ignition systems. In this study, an optically accessible constant-volume combustion chamber was employed to delve deeply into the impacts of critical boundary condition parameters on the combustion performance of the pre-chamber jet ignition system. The findings suggest that adjusting the pre-chamber boundary condition parameters can lead to various jet ignition modes, including jet flame ignition, jet direct ignition, jet delayed ignition, jet wake ignition, and dual jet ignition. Different jet ignition modes result in variations in ignition timing, ignition location, combustion rate, and lean burn limits. Under identical initial temperature and pressure conditions, compared to jet flame ignition with the lowest combustion velocity and jet wake ignition with almost no lean burn capability, dual jet ignition can reduce the combustion duration by about 50% and elevate the lean burn limit by more than double. Unlike the patterns observed in traditional spark ignition systems, within the range of experimental tests, lowering the temperature and increasing the pressure significantly improved the lean combustion limit of the pre-chamber system and reduced the probability of jet wake ignition. This performance enhancement is attributed to the increase in the density of the mixture in the main combustion chamber.

Spray autoignition study of bio-oxygenated additives blended with aviation kerosene under engine-like cold-start conditions

Abstract Bio-oxygenated fuels are expected to be used as a clean alternative energy source to improve the ignition behavior and pollutant emissions of RP-3 kerosene in compression ignition engines. In this study, the spray autoignition of PR-3 blended with different types of oxygenated fuels (including n-pentanol (PeOH), methyl propionate (MP), methyl ethyl ketone (MEK), 1,2-dimethoxyethane (1,2-DME), and 2-Ethylhexyl nitrate (EHN)) was measured using a constant-volume combustion chamber. Experiments were performed on three sets of blended fuels with different oxygen contents (2.5 wt%, 5 wt%, 10 wt%) in the temperature range of 723∼863 K and at ambient pressures of 2.2 and 4 MPa. A kinetic analysis utilized a merged RP-3 low-temperature kinetic model containing various oxygenated components. The ignition delay of blended fuels increases with the addition of PeOH, MP, and MEK, particularly PeOH, which demands more energy absorption at low temperatures due to its higher specific heat and latent heat of vaporization. As ambient pressure increased, the ignition delay period shortened for all blended fuels; however, PeOH and MEK demonstrated more significant low-temperature suppression. The combined kinetic model can reasonably predict the trend of the effect of oxygenated additives. 1,2-DME showed significantly more low-temperature reactivity versus PeOH, MP, and MEK. The variability is because the products of secondary O2 addition and isomerization of 1,2-DME undergo low-temperature branched chain reactions, but other oxygenated fuels produce more inert components.