Effects Of Equivalence Ratio Research Articles

Effects of total temperature and equivalence ratio on n-decane/air two-phase rotating detonation wave

The Eulerian–Lagrangian method is used to conduct the numerical simulation of the non-premixed two-phase rotating detonation wave (RDW) fueled by n-decane/air. The stratified spray detonation transient phenomena, as well as the effects of total temperature (850, 900, 1000 K) and equivalence ratio (0.5, 0.7, 1.0) on the RDW dynamics and propagation characteristics are discussed in detail. The results indicate that the velocity difference caused by separate injection of fuel and air generates the low-temperature zone behind the oblique shock wave, which hinders the direct contact between the droplets and the detonation products. Droplets in the refilled zone are broken by the shear effect and evaporate in high total temperature air, forming the stratified distribution structure of droplets and vapor. In addition, the coupling–decoupling–recoupling dynamic mechanism is observed between the leading shock front and the heat release zone, which leads to the local decoupling of RDW during the propagation. Moreover, the spatial variation of high-pressure zones at the leading shock front leads to multiple leading shock fronts and transverse pressure waves. It is revealed that the increase in total temperature broadens the lower boundary of equivalence ratio to obtain two-phase RDW. RDW velocity and velocity deficit are insensitive to the total temperature in the considered parameter range. However, the increase in the total equivalence ratio not only improves the mean velocity significantly but also enlarges the velocity deficit. With the increasing total temperature and equivalence ratio, the stability of pressure becomes worse. Furthermore, the stability of velocity declines with the increasing equivalence ratio at the total temperature of 1000 K.

Numerical investigation and optimization of the ammonia/diesel dual fuel engine combustion under high ammonia substitution ratio

This study investigated the effects of initial temperature, equivalence ratio, and diesel injection timing on engine combustion and emission characteristics at high ammonia substitution ratios. Increased compression temperature and pressure significantly reduce ignition delay, enhance combustion speed and efficiency, and decrease N2O and unburned NH3 emissions. A strong correlation exists between the amount of N2O produced and the mass of unburned NH3 when ammonia combustion efficiency is high. The N2O distribution is concentrated near the cylinder walls and the bottom surface of the piston platform, in areas with high concentrations of unburned NH3. As the equivalence ratio increases from 0.6 to 0.75, flame propagation speed and indicated thermal efficiency (ITE) increase, while NOx, N2O, and unburned NH3 emissions decrease. The combustion performance and emissions were optimized by advancing the diesel injection timing and increasing the equivalence ratio to accelerate the combustion speed. This adjustment increases ITE to 47.6% at an 80% ammonia energy ratio. Post-optimization results show a reduction in unburned NH3 emissions from 51.7 g/kW·h to 5.9 g/kW·h and a decrease in N2O emissions from 0.930 g/kW·h to 0.370 g/kW·h, culminating in a 60.4% reduction in greenhouse gas (GHG) emissions.

Investigation of NO emission characteristics from co-combustion of methane and ammonia at high-altitude areas

The high-altitude areas of China are abundant in renewable energy and have a natural advantage in ammonia production. Based on this advantage, this paper proposes a co-combustion strategy for methane and ammonia to reduce carbon emissions in these areas. However, the NO emission characteristics associated with this strategy remain uncertain. A custom-designed combustion system capable of simulating high-altitude environments was used to investigate the effect of ammonia mixing ratio, equivalence ratio, and pressure on NO emission in methane/ammonia/air flames. Additionally, chemical kinetic calculations were conducted to explore the mechanisms of how sub-atmospheric pressure influences NO emission. The results indicate that for stoichiometric flames, NO increases with the ammonia mixing ratio. In fuel-rich flames, NO remains nearly constant once the ammonia mixing ratio exceeds 10%. Sub-atmospheric pressure leads to higher NO, particularly in fuel-rich flames, where the increase can reach up to 24.4%. Analysis of nitrogen reaction pathways and key radical concentrations reveals that sub-atmospheric pressure has a minimal effect on nitrogen conversion pathways. The variation in NO is achieved by altering the pathway contributions and the concentrations of H, NH, and N. This work provides direction and guidance for improving the application of methane and ammonia co-combustion in high-altitude areas.

Heat propagation phenomenon of compressed natural gas /air premixed laminar flame impinging on a flat surface

In this paper the heat transfer characteristics have been determined theoretically using heat propagation phenomena of compressed natural gas (CNG)/air premixed laminar flames impinging on flat surfaces. Effects of varied equivalence ratios (Ф), Reynolds numbers (Re), separation distances (H/d) and burner diameters (d) on stagnation point heat flux have been investigated. The simulation findings were validated with the available experimental data. The flat plate with the maximum heat flux at the stagnation position is located close to the margin of the innermost premixed reaction zone (i.e., at H/d, Re and d are 5, 1000, 8 mm). The flow of heat steadily decreases in axial direction as the separating distance from the inner reaction zone's tip increases. Greater separation lengths at the stagnation region cause a subsequent increase in heat flux. The objective of this investigation is to get an idea about the impact of existence of the plate on the flame and temperature distribution and to get clarity about the reason behind higher amount of heat flux owing to tip of the innermost reaction area at stagnation region.

Investigating the impacts of charge composition and temperature on ammonia/hydrogen combustion in a heavy-duty spark-ignition engine

Ammonia, as a hydrogen carrier with mature production technology and convenient storage, has become one of the most promising zero carbon fuels in recent years. The use of ammonia/hydrogen mixture fuel in spark ignition (SI) engines has drawn significant attentions since it solves the problems of low flame speed, high ignition energy requirement and narrow flammable range of pure ammonia. In this study, the combustion and emission processes of an ammonia/hydrogen port fuel injection (PFI) engine at high load operation are numerically analyzed to investigate the effects of intake hydrogen energy ratio (HER), equivalence ratio (φ), intake temperature and combustion chamber wall temperature on energy distribution and pollutants. The results indicate that under the same HER of 25%, the lean-burned mode provides favorable thermal efficiency compared to stoichiometric mode due to reduced combustion and wall heat loss. However, lower cylinder temperature at lean condition inhibits the participation of NH3 in the reduction reactions and the consumption of N2O, increasing the residuals of both pollutants. The NOx emission is promoted by excessive O radicals at lean conditions, and the pathways of fuel NOx and thermal NOx are also discussed using an isotope labeling method. At stoichiometric mode, increasing fuel HER (10%–25%) only has minor impacts on improving thermal efficiency, but can promote the consumption of NH3 and N2O by increasing H radicals and cylinder temperature. The study also shows that optimizing the intake and wall temperatures can effectively reduce NH3 and N2O emissions by 87.5% and 71.7%, respectively, while slightly reducing NOx.

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.

Experimental study on the equivalence ratio effects in ammonia–hydrogen–air premixed gas duct-vented explosions

To explore the combustion characteristics of ammonia‒hydrogen‒air flame, explosion venting experiments of ammonia‒hydrogen‒air mixtures with different equivalence ratios (ϕ), in the range of 0.6–1.7, are carried out in a 2 m long duct. The results show that the pressure‒time histories inside the duct have a three-peak structure (Pb, Pout, and Pext), which is caused by the burst of the vent cover, venting of burned mixtures, and counterflow flame generated by the external explosion, respectively. Pout evolves into three pressure peak types with increasing ϕ. The pressure peak value Pe is generated at the pressure measuring point outside the duct because of the external explosion. The change in Pe with ϕ is consistent with Pout and Pext, all of which increase first and then decrease with increasing ϕ and reach a maximum value at ϕ = 1.3. This study provides basic theoretical support for the promotion and application of ammonia mixed fuel.

Effect of Feedstock Blends and Equivalence Ratio on the Thermal Arc Plasma Assisted Co-Gasification of Biomass and Plastic using Air-Blown Downdraft Reactor

Plastic waste is known to cause an emerging environmental pollution, posing risks to both terrestrial and aquatic ecosystems. Co-gasification method is an alternative way to reduce municipal solid waste and plastic waste by converting it into useful gas fuel energy. The present study used empty fruit bunch biomass (EFB), plastic waste of low-density polyethylene (LDPE) and Polyethylene terephthalate (PET) as a feedstock for thermochemical conversion process into syngas fuel energy via plasma co-gasification method. The effect of multiple feedstocks mixture between biomass and plastic and equivalence ratio on the compositions of produced syngas, high heating value (HHV), lower heating value (LHV), cold gas efficiency (CGE) and carbon conversion efficiency (CCE) were critically investigated. A reactor of air-blown downdraft arrangement was used in these experiments. The gasifying agent flow rate of air was set at the frequency range of 10 to 22Hz to achieve equivalence ratio between 0.15 to 0.30. The blending ratio (BR) between biomass and plastic (EFB:Plastic) were set as E90:P10, E80:P20 and E70:P30. The results indicate that H2 and CO composition is typically decrease as ER increase for the mixture of EFB and LDPE. In contrast, the composition of H2 and CO is generally increase as ER increases. However, the maximum value of H2 and CO is dominated by the mixture of EFB and LDPE at any blending ratio and lower ER condition. This is due to the higher element of H, C and O in the raw material of EFB and LDPE compared to PET. This study is crucial in understanding the synergistic effect of co-gasification assisted with plasma reaction between biomass and plastic waste.

Turbulent flame acceleration and deflagration-to-detonation transitions in ethane–air mixture

The deflagration-to-detonation transition (DDT) poses significant risks in the oil, gas, and nuclear industries, capable of causing catastrophic explosions and extensive damage. This study addresses a critical knowledge gap in understanding the DDT of ethane–air mixtures on a large scale, amid increasing industrial utilization and production of ethane. A novel computational framework is introduced, utilizing the finite-volume code named Morris Garages, which incorporates reactive compressible Navier–Stokes equations, adaptive mesh refinement, and correlations of turbulent burning velocities. This model integrates the most recent data on laminar and turbulent burning velocities for premixed ethane–air mixtures, simulating flame acceleration and DDT within a two-dimensional large-scale setting, measuring 21 m in length and 3 m in height, with obstacles mimicking pipe congestion. Two mixture scenarios, lean and near-stoichiometric, are analyzed to evaluate the effects of equivalence ratios on flame propagation and DDT. The simulations, validated against large-scale experimental data from Shell, show reasonable agreement and provide critical insights into the onset conditions of DDT, such as temperature, pressure, flame speed, and turbulent kinetic energy. Furthermore, the ξ–ε detonation peninsula diagram is utilized to explore autoignition and detonation behaviors in ethane–air mixtures.

The effect of jet disturbance on flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel

Gas explosions mostly occur in turbulent environments in practical situations. Meanwhile, the current research on the explosion characteristics of hydrogen-doped natural gas is mostly methane/hydrogen mixed fuel, ignoring the influence of other components of natural gas on the explosion characteristics of the actual situation. Therefore, the effects of different jet intensities (Pjet), hydrogen-doping ratios (XH2) and equivalence ratios (φ) on the explosion characteristics of multi-component natural gas/hydrogen mixed fuel are experimentally investigated in cylindrical tanks of 30 L. Additionally, it extensively explored the dual influence of jet disturbance and gas inerting effect on the flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel. With the increase of Pjet, both Pmax and (dp/dt)max initially increase and then decrease, while τ continuously decreases. When Pjet = 0.4 MPa, the promotion effect on Pmax and (dp/dt)max is most significant. The lifting of XH2 leads to a gradual increase in Pmax and decreasing τ. (dp/dt)max exhibits a trend of initially increasing and then decreasing with the elevation of XH2, reaching its maximum at XH2 = 40%. The introduction of jet flow significantly reduces the promotion or inhibition effect on explosions of high hydrogen blending ratio mixtures. Furthermore, the introduction of jet flow is more effective in promoting the explosive performance of multi-component natural gas/hydrogen mixed fuel with high equivalence ratios and low hydrogen doping ratios under rich fuel conditions. This study can provide a key reference for the explosion hazard assessment during the practical application of natural gas/hydrogen mixed fuel.

Bench-Scale Gasification of Olive Cake in a Bubbling Fluidized Bed Reactor

The gasification of olive cake is a promising method for converting this material into valuable energy. This work offers interesting results about the effect of equivalence ratio and temperature on the composition and quality of the produced gas obtained during olive cake gasification in a fluidized bed plant with air as a gasification agent. Additionally, the efficiency of the gasification process was evaluated. The results show that, for a specific temperature, an equivalence ratio of 0.3 showed a higher cold gas efficiency. For example, at 850 °C and an equivalence ratio of 0.1, the cold gas efficiency was 22.7%; however, at the same temperature but at an equivalence ratio of 0.3, the cold gas efficiency was increased to 61.2%. In addition, for a constant equivalence ratio, by increasing the operating temperature, there was no significant increase in the lower heating value of the exit gas, and the gas flow was practically constant with temperature, but it varied substantially with the equivalence ratio, reaching values in the range of 3.44–14.89 NL/min (825.6–3573.6 NL/kg feed). Finally, the production of CO, H2, and CH4 is estimated to be higher for tests conducted with an equivalence ratio of 0.3.

Optimizing micro power generation with blended fuels and porous media for H2-fueled combustion

To enhance the combustion stability and thermal performance of micro-thermophotovoltaic system, a combustor inserted porous media and varying channel heights for premixed H2/CH4/Air burning is proposed. The experimental and numerical methods are conducted to investigate the effects of CH4 addition, equivalence ratio, porous media, and chamber setting on combustion characteristics, heat transfer, and flame stability. The results indicate that a small fraction of CH4 addition and porous media insertion both enhance heat release and transfer of H2-fueled combustion, and the optimal CH4 blending ratio is influenced by chemical energy input. Appropriately increasing the equivalence ratio under high flow rates contributes to stabilize the flame and improve the combustor thermal performance. Furthermore, porous media effectively promotes flame stability and heat transfer efficiency, with longer porous media enhancing heat conduction and convection processes, thereby increasing the radiation temperature. Besides, increasing the channel height of the porous media combustor appropriately enhances the electrical power output of the power system. Besides, the maximum electrical output of 9.7 W is obtained in the porous media combustor with a channel height of 11 mm at mc = 20 %, Ф = 1.0 and mf = 9.448 × 10−5 kg/s, which is 7.2 W higher than the free flame combustor with h = 7 mm.

Thermodynamic and entropy generation analyses of Telsa-valve structured meso-scale combustors fuelled with hydrogen for thermophotovoltaic applications

The present work numerically examed the effects of hydrogen volume flow rates (Qv) and equivalence ratios (Φ) on thermal performances of meso-scale combustors structured with Tesla-vale type flow channels. Four distinct Tesla-valve configurations are implemented and then subsequently compared. The reverse-flow Tesla valve with counter-flow combustor (RC) structure shows a remarkable improvement of 72.6 % to the combustor wall temperature at Qv = 100 mL/min. The diodicity (Di) of the Tesla valve is found to be increased with a higher Qv, and a lower Φ contributes to a higher Di. Besides, Di is decreased when Φ goes up, stabilizing at Φ = 0.9. The reverse-flow Tesla valve exhibits a more uniform pressure distribution and entropy production than the forward-flow Tesla valve. At Φ = 0.9, the hydrogen-to-air ratio maximized heat release, producing the highest entropy. Tesla-valve structured combustors demonstrate near complete combustion before Φ reaching 0.9, the combustion efficiency (ηcombustion) is gradually decreased after Φ getting to 1.0. The RC construction achieved maximum combustion efficiency under conditions of insufficient oxygen. This present study demonstrates the feasibility of enhancing thermal and overall performances of meso-scale combustors structured with Tesla-valve channels, and revealing the key parameters effects on the combustion characteristics in these combustors.

Stability and combustion characteristics of dual annular counter-rotating swirl oxy-methane flames: Effects of equivalence and velocity ratios

An experimental study was carried out to investigate flow/flame interactions, stability, combustion, and emissions properties of CH4/O2/CO2 stratified flames stabilized on a dual annular counter-rotating swirl (DACRS) burner for gas turbine combustion applications. The effects of two targeted parameters, namely equivalence ratios (for primary - ϕp, secondary - ϕs, and global - ϕg streams) and velocity ratio (Vr = Vp/Vs: primary to secondary stream inlet velocity ratio), are studied at fixed volumetric oxygen fraction (OF) in the oxidizer mixture (O2 + CO2) of both primary and secondary streams of 34 % at fixed Vp of 5 m/s. The experimental results indicated that no flame flashback was recorded in the domain of any operational ϕp up to stoichiometric operation of the secondary stream (ϕs = 1.0). At near stoichiometric operation of the primary stream, the main secondary flame can persist in extremely lean conditions (ϕs = 0.45 @ Vr = 3), thereby extending the thresholds of flame blowout. Moreover, raising ϕp from 0.4 to 1.0 results in significant reduction of ϕs at blowout from 0.595 to 0.456, corresponding to reducing the combustor ϕg at blowout from 0.577 to 0.499. At lower ϕp, the oxy-methane flame tends to lift and extinguish earlier.

Numerical study on laminar burning velocity and ignition delay time of ammonia/methanol mixtures

As a carbon-free hydrogen-carrying fuel, ammonia can effectively alleviate the problem of CO2 emissions and has great application potential in marine engines. The low laminar burning velocity and calorific value, and the narrow flammability limit range make the combustion of pure ammonia difficult. Ammonia/methanol mixed combustion is a feasible method to improve ammonia combustion and mitigate CO2 emissions. It is difficult to accurately predict the laminar burning velocity (LBV) and ignition delay time (IDT) of ammonia/methanol combustion simultaneously by the existing chemical kinetic mechanisms. This study aims to develop a detailed chemical kinetic mechanism that can simultaneously predict the LBV and IDT. The new-developed mechanism was fully validated based on experimental data. Furthermore, it was employed to investigate the effects of methanol blending ratios and equivalence ratios on the LBV and IDT in NH3/CH3OH mixed flames. Besides, chemical kinetic analyses were conducted to elucidate the influence of methanol mixing ratios and equivalence ratios on LBV and IDT. Reaction pathway analysis revealed that the NH3 and CH3OH chemistry interacted by the sharing of H, OH and O radicals in fuels’ decomposition, and chemical interactions of N-containing radicals with the C1 species. The reactions involving C-containing species can notably improve the LBV of NH3/CH3OH mixed combustion. At low equivalence ratio, LBV increases in proportion to the fuel proportion. Conversely, at high equivalence ratio, the effect of oxygen concentration on LBV becomes the dominant factor.

Micron-sized aluminum particle combustion under elevated gas condition: Equivalence ratio effect

Micron-sized aluminum (Al) particle combustion under elevated gas condition is critical for improving energetic material performance, impacting propulsion and explosives technology. This study utilizes Eulerian-Lagrangian method to investigate Al particle combustion dynamics, encompassing both heterogeneous reaction (HTR) and homogeneous reaction (HMR). It focuses on the critical role of the equivalence ratio in single Al particle combustion, highlighting the interplay between HTR and HMR, aiming to optimize energy release and emission control. Our study identifies four stages in the combustion of a single Al particle, where the highest heat release is attributed to HTR, succeeded by HMR, and the minimal from unburned Al vapor. We observe a decline in the total heat release rate with an increasing equivalence ratio, primarily due to the differential impacts of heterogeneous and homogeneous reactions. The thermal-runaway stage in HTR is governed by the particle temperature, while the subsequent decaying stage is influenced by either the diminishing effective Al droplet diameter or the availability of oxygen, contingent upon the fuel conditions. Utilizing Cantera software to analyze HMR allows us to elucidate the thermal effects of elementary reactions and the key reaction pathways. These findings underscore the complex interactions between Al particles and the surrounding gas, providing insights into optimizing the conditions for Al-containing reaction systems.

Effects of equivalent ratio and initial temperature on the explosion characteristics of ethanol, acetone, and ethyl acetate

In this paper, the effects of equivalence ratio (0.8–2.0) and temperature (30°C–120°C) on ethanol, acetone, and, ethyl acetate vapors explosion characteristics through experimental and numerical studies were investigated. The explosion overpressure and flame propagation velocity were recorded through the pressure transducer and high-speed camera. The results showed that the flame propagation velocity, peak explosion overpressure, and peak growth rate of explosion overpressure increased first and then decreased with the increase of equivalence ratio. The cracks on the flame surface enhanced with the increase of the equivalence ratio. As the initial temperature increased, peak explosion overpressure, the flame propagation velocity, and peak growth rate of explosion overpressure gradually increased. The sensitivity analysis of laminar burning velocity indicated that with the change of equivalence ratio and initial temperature, the shared elementary reactions that increased the reactivity were H + O2 <=> O + OH, HCO + M <=> H + CO + M, and CO + OH <=> CO2 + H, and the shared elementary reaction that reduced the reactivity was H + OH + M <=> H2O + M. The main factor affecting laminar burning velocity was the mole fraction of H and OH radicals.

Biosolid Gasification Performance Prediction Using a Stoichiometric Thermodynamic Model.

The gasification process can recover energy from biosolids produced in wastewater treatment. This paper developed a stoichiometric thermodynamic equilibrium model for biosolid gasification based on the biosolid properties, thermodynamic database, and equilibrium constants. If the calculation result showed that the quantity of char was negative, the quantity of char was put to zero, and the simulation was carried out again. The model was first verified by woody gasification under isothermal conditions, and the influence of a given temperature on biosolid gasification was simulated. The model further investigated the effects of different feedstock types, moisture contents, equivalence ratios, and reaction extensions on the adiabatic temperature, exergy efficiency, and syngas properties under autothermal conditions. The four factors were all the main factors for adiabatic temperature. The exergy efficiency depended more on the operation conditions than on the feedstock type. The H2 concentration of the dry syngas in biosolid gasification exhibited a curve both against the given temperature under isothermal conditions and against the moisture content under autothermal conditions.

Jet ignition characteristics of ammonia-hydrogen passive pre-chamber: Emphasis on equivalence ratio and hydrogen/ammonia ratio

Ammonia-hydrogen blend fuels offer the potential for zero-carbon emissions in internal combustion (IC) engines. To improve combustion performance, considerable attention has been focused on pre-chamber jet ignition technologies. Passive pre-chamber featuring a simple structure can be installed in the spark plug hole without modifying the cylinder head. However, the jet ignition characteristics of ammonia-hydrogen passive pre-chambers are not fully understood, and there is a lack of visualized evidence on how critical parameters (e.g., equivalence ratio and hydrogen/ammonia ratio) impact ignition processes. This work investigated the effects of equivalence ratio and hydrogen/ammonia ratio on ammonia-hydrogen jet ignition characteristics in a rapid compression machine with passive pre-chamber. High-speed photography and instantaneous pressure acquisition were employed to capture detailed ignition and combustion evolutions. Results show that under low hydrogen/ammonia ratio conditions, there exists a combustion regime with noticeable fluctuations in jet penetration, indicating degenerate ignition performance. As the hydrogen/ammonia ratio increases from 0 % to 20 %, the ignition delay time of mixtures in the main chamber is reduced by 70 %, suggesting an improved overall ignition performance. Regarding the equivalence ratio, more pronounced effects on jet ignition and flame propagation are identified under lean-burning conditions. For mixtures at the hydrogen/ammonia ratio of 20 %, as the equivalence ratio increases from 0.6 to 0.8 and from 0.8 to 1.0, the decay rates for 10 %–90 % combustion duration are 82.5 % and 20.6 %, respectively. Besides, with the increase of equivalence ratio, flame initiation is shifted from the jet head to the side surface. The role of hydrogen/ammonia ratio and equivalence ratio is different, with the former modifying mixture reactivity while the latter affecting ignition energy.