Addition Of Methane Research Articles

Experimental Study of the Dynamics of Lean Premixed Hydrogen Flames in a Multi Jet Combustor

Abstract In this study, the flame dynamics of lean premixed hydrogen jet flames are experimentally investigated. Acoustic and optical measurements are used to capture the response of a bundle of jet flames to acoustic forcing. Using helium as a fuel surrogate, we simulate the change in acoustic properties in the burner during the determination of cold burner transfer matrix measurements. We investigate the influence of the equivalence ratio and the addition of methane as well as the interaction of the individual flames to evaluate the scalability of the results to systems with more flames. It is shown that the changes in the dynamic flame response can primarily be explained by the flame length, which changes both with the methane share and with the equivalence ratio. It can be observed that with small changes in the equivalence ratio, the flame length and the flame transfer function (FTF) change in the same way as with a small change in gas composition. To assess the scalability of these results, we deactivate some of the jet flames and analyze how the overall response to acoustic forcing changes. We find that the FTF phase is not affected by the number of active flames. Analyzing the respective gain values, significantly stronger responses are measured for a few flames, but only small difference can be measured above a certain number of neighboring flames so that the lab scale results can also be expected to be valid for industrial configurations with a high number of flames.

Effect of methane addition on supercritical water oxidation of poultry manure in the flow mode

The paper presents the research results of the supercritical water oxidation (SCWO) of poultry manure continuously fed into a tubular reactor both in the absence and presence of methane as an auxiliary fuel. The tests were conducted at a temperature gradient along the vertical axis of the reactor (top to bottom: 390–600 °C), a pressure of 25 MPa, and varying reagent flow rates. It is shown that due to heat generation during methane oxidation the energy consumption from external sources is reduced by 1.3–1.5 times depending on the ratio of reagent flow rates. The gas products contain CO2, N2, and trace amounts of N2O. The ash residues are predominantly composed of calcite and hydroxyapatite. The addition of methane results in a reduction in the content of phenols and polycyclic aromatic hydrocarbons present in the aqueous effluent, while content of N-bearing aromatics increases. The formation of nitrophenols was observed at elevated oxygen concentrations in the reaction mixture. It was revealed that excess oxygen plays a pivotal role in the efficacy of organic nitrogen removal. The formation of mineral acids and a high level of ammonia in the reaction mixture during the SCWO of poultry manure result in corrosion of stainless steel and copper seals, which in turn leads to an increased concentration of chromium and copper in the aqueous effluent. The results obtained indicate the potential for utilizing natural gas in an environmentally friendly and resource-saving manner for poultry manure processing by SCWO in autothermal mode.

The effect of methane addition on reacting hydrogen jets in crossflow

The combustion characteristics in a jet in crossflow configuration are numerically investigated using Large Eddy Simulation (LES) with subgrid scale modelling for partially premixed combustion. The time-averaged statistics are compared with the experimental measurements. Both the temperature and velocity comparisons show good agreement with measurements. The distribution of reaction regions of nitrogen-diluted hydrogen fuel jet is then examined in both physical and mixture fraction space. The results demonstrate that the fuel consumption in potential core, near-field and far-field regions occurs at various mixture fraction ranges. In the potential core region, reactions predominantly occur between the lean and stoichiometric mixture fraction range. This range broadens to include fuel-rich conditions in the near-field region and narrows again to fuel-lean combustion in the far-field region. With these changes in the mixture fraction range, the fractional contribution from different combustion modes also changes. A closer study of these changes reveals that the fractional contribution from the non-premixed mode is highest at the end of the potential core region. The dependency of these combustion modes on the fuel composition is studied by increasing the volume fraction of methane in the jet. This resulted in altered chemical kinetics and thereby increased the fractional contribution of the non-premixed mode, particularly in the potential core region.

Microbial anabolic and catabolic utilization of hydrocarbons in deep subseafloor sediments of Guaymas Basin.

Guaymas Basin, located in the Gulf of California, is a hydrothermally active marginal basin. Due to steep geothermal gradients and localized heating by sill intrusions, microbial substrates like short-chain fatty acids and hydrocarbons are abiotically produced from sedimentary organic matter at comparatively shallow depths. We analyzed the effect of hydrocarbons on uptake of hydrocarbons by microorganisms via nano-scale secondary ion mass spectrometry (NanoSIMS) and microbial sulfate reduction rates (SRR), using samples from two drill sites sampled by IODP Expedition 385 (U1545C and U1546D). These sites are in close proximity of each other (ca. 1km) and have very similar sedimentology. Site U1546D experienced the intrusion of a sill that has since then thermally equilibrated with the surrounding sediment. Both sites currently have an identical geothermal gradient, despite their different thermal history. The localized heating by the sill led to thermal cracking of sedimentary organic matter and formation of potentially bioavailable organic substrates. There were low levels of hydrocarbon and nitrogen uptake in some samples from both sites, mostly in surficial samples. Hydrocarbon and methane additions stimulated SRR in near-seafloor samples from Site U1545C, while samples from Site U1546D reacted positively only on methane. Our data indicate the potential of microorganisms to metabolize hydrocarbons even in the deep subsurface of Guaymas Basin.

Directed Evolution of Protein-Based Sensors for Anaerobic Biological Activation of Methane.

Microbial alkane degradation pathways provide biological routes for converting these hydrocarbons into higher-value products. We recently reported the functional expression of a methyl-alkylsuccinate synthase (Mas) system in Escherichia coli, allowing for the heterologous anaerobic activation of short-chain alkanes. However, the enzymatic activation of methane via natural or engineered alkylsuccinate synthases has yet to be reported. To address this, we employed high-throughput screening to engineer the itaconate (IA)-responsive regulatory protein ItcR (WT-ItcR) from Yersinia pseudotuberculosis to instead respond to methylsuccinate (MS, the product of methane addition to fumarate), resulting in genetically encoded biosensors for MS. Here, we describe ItcR variants that, when regulating fluorescent protein expression in E. coli, show increased sensitivity, improved overall response, and enhanced specificity toward exogenously added MS relative to the wild-type repressor. Structural modeling and analysis of the ItcR ligand binding pocket provide insights into the altered molecular recognition. In addition to serving as biosensors for screening alkylsuccinate synthases capable of methane activation, MS-responsive ItcR variants also establish a framework for the directed evolution of other molecular reporters, targeting longer-chain alkylsuccinate products or other succinate derivatives.

Flame propagation dynamic characteristics and mechanisms of methane–syngas–air mixtures in a semi-enclosed duct

The composition of syngas is complex, often leading to the generation of methane, which impacts the explosive characteristics of syngas. The analysis focused on the kinetic characteristics and mechanisms of flame propagation in methane–syngas–air mixtures in a semi-enclosed duct under various equivalence ratios (φ = 0.8–1.4) and methane volume ratios (R = 0 %–70 %) under ambient temperature and pressure. The results indicated that the flame speed and pressure propagation of methane–syngas–air mixtures could be divided into three stages: a stable stage, an oscillatory increase stage, and an oscillatory decrease stage. In the stable stage, as the methane proportion in the premixed gas increased, the oscillations in the flame and pressure decreased. Turbulent flow of the mixed gas was observed due to restrictions and obstructions within the duct. This led to an increase in the peak pressure and flame speed of the mixed gas, thereby resulting in an oscillatory increase stage. Distorted tulip-shaped flames were also formed in the semi-enclosed duct. The flame of the pure syngas/air mixture exhibited a hemispherical shape and a finger-shaped and slope-shaped propagation structure. When 30 %, 50 %, or 70 % of the methane in the methane–syngas–air mixtures was added, the flame exhibited a propagation structure characterized by a hemispherical shape, finger shape, slope shape, flat shape, tulip shape, or distorted tulip shape. The flame front evolved with time from a linear growth stage to a nonlinear growth stage. The flame front speed of the methane–syngas–air mixtures was closely related to the pressure and flame structure. With the increase in the methane proportion in the methane–syngas–air mixtures, the concentration of key radicals and the rate of OH* generation and consumption gradually decreased. Sensitivity analysis revealed that with increasing methane proportion in the premixed gas, the most important reaction dominating OH* consumption changed from R15 (H + O2(+M) <=> HO2(+M)) to R138 (CH4 + OH <=> CH3 + H2O) and then to R112 (2CH3(+M) <=> C2H6(+M)); moreover, the most important reaction dominating OH* generation remained R1 (H + O2 <=> O + OH). The addition of methane interrupted the hydrogen–oxygen chain reaction of the methane–syngas–air explosion process.

Evaluating the potential performance of methane in lean conditions and examining the variations in combustion in a gasoline direct injection engine

The present work investigates the effect of methane addition on a direct injection spark-ignition engine's performance, combustion, cycle-to-cycle variation, coefficient of variation, and emission characteristics. Equivalence ratio of the engine is varied from λ = 1.0, 1.02, 1.08, 1.15, and 1.22. Methane addition for the equivalence ratios (λ = 1.0, 1.02, and 1.08) close to the stoichiometric condition does not support the methane addition. Decrease in peak pressure is seen in minimum to the maximum methane addition of 19.5 %. Adding the gaseous fuel to the intake manifold causes charge displacement, as the fuel is inducted at the suction top dead center. This effect is consistent with the increase in flame initiation and combustion durations. The same methane addition fraction for the equivalence ratios of λ = 1.15 and 1.22 provides better combustion stability and efficiency. The peak pressure attainment for λ = 1.22 is a 25 % increment with the maximum methane addition. Emission formation of carbon monoxide and unburnt hydrocarbons drops as the fuel is leaner towards λ = 1.22, even with the addition of methane. The oxides of nitrogen emissions decrease initially for the equivalence ratio close to the stoichiometric condition but increase for the leaner equivalence ratio with the methane addition fraction.

A review of methane-driven two-step thermochemical cycle hydrogen production

Solar thermochemical cycling is a promising approach to utilizing solar energy to produce H2 and CO, which can be further synthesized into liquid fuels via Fischer-Tropsch reactions, making storage and transportation easier. Despite the potential high theoretical efficiency, factors such as the high temperature and low oxygen partial pressure required for the reduction restrict the large-scale application of this technology. In the near-to-medium term, in order to accelerate the popularization and application of this technology, according to Le Chatelier's principle, the assisted reduction of methane can greatly reduce the demand for high-temperature materials and ultra-low oxygen partial pressure. However, the addition of methane will also bring additional challenges, such as carbon emissions and carbon deposition. Reducing the influence of factors such as material sintering and irreversible loss on system efficiency in the experiment will be essential for the development of this technology. This paper focuses on the methane-driven two-step thermochemical cycle hydrogen production process, summarizes its reaction mechanism, thermodynamic analysis, kinetic analysis, oxygen carrier material doping, and experimental research in detail, and comprehensively analyzes the effect of material properties and irreversible loss on the system. According to thermodynamic and kinetic analysis, rational selection and doping of metal oxygen carrier materials can effectively reduce the reaction temperature, improve gas production rates, and enhance structural stability. Analyzing and trying to reduce various irreversible losses of the system, such as reradiation energy loss, conduction energy loss, etc., and taking appropriate heat recovery measures will help to improve the system efficiency of the actual cycle. This paper would be valuable for the development of this technology and for achieving the goal of carbon neutrality.

Low-carbon fuel reburning for CO2 and NOx reduction in pulverized coal firing system

Using low- or zero-carbon fuels is necessary to reduce CO2 emissions. Gas reburning technology can be applied to existing coal boilers to reduce not only CO2 but also NOx emissions. In this study, we confirmed the gas reburning effect using lab-scale equipment based on the consumption coal used in real-scale boilers, with the aim of practical application. Bituminous coal was used as the reference fuel, and sub-bituminous coal was blended to determine whether coal blending has an effect on NOx emissions. This was conducted to optimize the coal blending ratio and gas reburning technology for NOx emission reduction and quantify the NOx reduction by the two methods. Blending sub-bituminous coal reduced the unburned carbon (UBC) content, because of its high volatile matter content. Moreover, NOx emissions decreased as the ratio of sub-bituminous coal increased. In terms of the reburning effect, although UBCs increased with the addition of methane, NOx emission decreased by up to 96.05 %. The conversion ratio, defined as the NOx formation ratio of the total fuel N injection, was used to separate the NOx reduction effects of the two methods. Thus, gas reburning in the ammonia co-firing system of coal-fired power plants can significantly reduce NOx emissions.

Effects of methane addition on the laminar burning velocity and Markstein length of methanol/air premixed flame

Adding methane to methanol can solve the problem of difficult cold starts of methanol engines. Therefore, it is important to understand the combustion of methane and methanol fuel blends. Because of this, this study explores the effect of methane addition on the laminar burning velocity and Markstein length of methanol/methane premixed flames under stoichiometric conditions at the initial temperatures of 353 K, 373 K, and 393 K, initial pressures of 1 bar, 2 bar, and 4 bar, using methane addition ratios of 0%, 25%, 50%, 75%, and 100% in a constant volume combustion chamber. The results show that the laminar burning velocity decreases linearly with the increase of methane addition ratio due to the linear decrease of the Arrhenius factor. The sensitivity analysis revealed that the kinetic effect is the main reason for the inhibition of laminar burning velocity, which is insensitive to initial temperature but enhanced at a high initial pressure. The Markstein length decreases with the addition of methane and the increase of initial pressure, which is mainly caused by the high mass diffusivity of methane and the decrease of flame thickness due to the increase of initial pressure.

The influence of methane blending ratio on the spontaneous combustion characteristics of high-pressure hydrogen leakage

Adding CH4 to high-pressure H2 is considered one of the effective and convenient measures to reduce high-pressure H2 leakage and spontaneous combustion, which is conducive to improving the safety of H2 energy storage. Based on the independently built high-pressure hydrogen leakage and self ignition experimental platform, the influence of CH4 on the critical self ignition pressure and flame of high-pressure H2 leakage and self ignition was tested. The results indicate that the addition of methane can effectively increase the critical spontaneous combustion pressure. When 20% CH4 is added, the critical self ignition pressure can be increased by 151.58%. Under similar discharge pressure conditions, the flame velocity in the pipeline decreases from 1224.64m/s for pure H2 to 1024.07m/s for 10% CH4. In addition, after mixing CH4, the dispersion time of the jet flame is advanced, the flame duration is shortened, and the flame brightness is reduced. There are two main reasons for the mixed inhibition of spontaneous combustion by CH4. On the one hand, it reduces the Mach number of shock wave propagation, thereby lowering the ignition temperature. On the other hand, the activity of the fuel system decreases, and the heat required for self ignition increases.

Selective monoborylation of methane by metal-organic framework confined mononuclear pyridylimine-iridium(I) hydride.

Chemoselective monoborylation of methane in high yield is a grand challenge. We have developed a metal-organic framework confined pyridylimine-iridium hydride catalyst, which is efficient in methane C-H borylation using bis(pinacolato)diboron to afford methyl boronic acid pinacol ester in 98% GC-yield at 130 °C with a TON of 196. Mechanistic investigation suggests the oxidative addition of methane to IrIII(Bpin)2(H) species to form IrV(Bpin)2(CH3)(H)2 as the turnover limiting step.

Suppression of polycrystal nucleation by methane addition at moderate timing to maintain GaN crystal growth on point seeds in the Na-flux method

We have grown low-dislocation, large-diameter GaN substrates using small seed crystals, called as point seeds (PSs) in the Na-flux method. To further reduce dislocation density and improve wafer bowing, reducing the PS diameter is effective. However, it was found that crystals did not start to grow on a small diameter PS. In this study, we also found that a growth on a small diameter PS can be carried out in the condition without graphite addition. However, graphite is conventionally added to suppress polycrystals, so those could not be avoided at the latter process to planarize crystal surface by raising and lowering the crystal, called the flux film coated (FFC) process, in which polycrystals are likely generated. Thus, in this study, we newly proposed to suppress polycrystals by adding methane gas before the FFC process, instead of graphite which cannot be added during the middle of growth.

Experimental characterization of ammonia, methane, and gasoline fuel mixtures in small scale spark ignited engines

In this study, gaseous anhydrous ammonia is blended with fuels like gasoline and methane and tested in an instrumented, low-technology single cylinder carbureted engine. In-cylinder pressure and emissions are monitored with the various mixtures and their performance is then compared with pure gasoline. With the addition of ammonia, the stability of combustion inside the combustion chamber was affected. But with the addition of a combustion modifier, the overall variability was reduced. At higher substitutions of ammonia, Initial results show an increase in indicated thermal efficiency of the engine. There is also a substantial decrease in the heat release rate (HRR) of the engine when substituting gasoline with ammonia. With the addition of methane, the change in the fuel reactivity helped improve HRR. Increasing ammonia substitution also resulted in an increase in indicated efficiency when compared to pure gasoline by approximately 12% with 50% substitution of ammonia in gasoline. Adding ammonia to the fuel mixtures also showed an initial reduction in unburnt hydrocarbon emission, followed by a sudden increase with further increasing concentration, suggesting incomplete combustion of the fuel mixture. The addition of methane with gasoline also showed a reduction in overall NOx emissions. Furthermore, methane was also tested as the main fuel with ammonia substitution of up to 50%. This ammonia and methane blend also showed comparable results to the gasoline, ammonia, and methane blends tested. From the emissions data, the catalyzing effects of ammonia were also seen with some cases showing varying trends with increasing ammonia substitution. Results from this study can be used to design small-scale engine based power generation systems that need very little modifications to accept ammonia based mixed fuels. Furthermore, this study lays the groundwork for using fuels blends with methane sourced using carbon neutral technologies and ammonia to power engine based systems.

Mass spectrometry and in situ x-ray photoelectron spectroscopy investigations of organometallic species induced by the etching of germanium, antimony and selenium in a methane-based plasma

Organometallic positive ions were identified in inductively coupled plasmas by means of mass spectrometry during the etching of Ge, Sb, Se materials. A preliminary study was focused on identifying M x H y + (M = Ge, Sb, Se) positive ion clusters during a H2/Ar etching process. The methane addition to the H2/Ar mixture generates CH x reactive neutral species. The latter react with the metalloids within gas phase to form M x C y H z + organometallic ions. In addition, the etching of Sb2Se3 and Ge19.5Sb17.8Se62.7 bulk targets forms mixed products via ion-molecule reactions as evidenced by the presence of SeSbC x H y + ion clusters. Changes in surface composition induced by the newly formed organometallic structures were investigated using in situ x-ray photoelectron spectroscopy. In the case of the Ge and Sb surfaces, (M)–M–C x environments broadened the Ge 2p3/2, Ge 3d, Sb 3d and Sb 4d spectra to higher values of binding energy. For the Se surface, only the hydrogen and methyl bonding could explain the important broadening of the Se 3d core level. It was found that the Ge39Se61 thin film presents an induced (Ge)–Ge–Se entity on the Ge 2p3/2 and Ge 3d core levels.

Molecular mechanism in the solubility reduction of elemental sulfur in H2S/CH4 mixtures: A molecular modeling study

The solubility evolution of elemental sulfur in sour gas is key to study the occurrence and inhibition of sulfur deposition in the exploitation of high-sulfur gas reservoirs. Elemental sulfur mainly dissolves in H2S, and its solubility decreases dramatically in the presence of methane. As both methane and H2S are the main components in high-sulfur gas, it is essential to understand the molecular mechanism of the solubility reduction in H2S/CH4 mixtures. Molecular dynamics simulations are carried out for the S8, H2S and CH4 mixtures to reproduce the solubility reduction upon methane addition, and then used to reveal the reduction mechanism at the level of intermolecular interaction. The simulations reveal that both the strong competitiveness and high collision probability of H2S–CH4 pairs reduce the average densities of H2S–S(S8) and H2S–H2S pairs, which reduce the sulfur solubility in a direct/indirect but cooperative way. The role of methane in the solubility reduction is then discussed and the molecular mechanism of sulfur dissolution and precipitation in the sour gasses is addressed.

The effect of pure methane energy fraction on combustion performance, energy analysis and environmental - economic cost indicators in a single-cylinder common rail methane-diesel dual fuel engine

Although methane-diesel dual fuel implementation is a very effective method in reducing high NOx and smoke emissions, which are the main problems of diesel engines, this implementation still suffers from high level of HC and CO emissions at low-medium load conditions. Considering this problem of dual-fuel engines, it is very important to examine the effects of pollutant emissions resulting from combustion on the environment and human health to see the usability of methane gas in dual fuel mode, and the current literature is quite limited. Therefore, in this study, the effect of methane energy fraction on combustion, emissions and environmental-economic costs was investigated in a dual fuel engine with optimum diesel injection timing.The tests were conducted in a single-cylinder, air-cooled, common rail diesel engine at constant engine speed and variable engine loads. The operation was carried out in two different modes as diesel and methane-diesel dual fuel. In the first mode, the optimum diesel injection timing of common rail diesel engine was determined. Five different injection timings from 11°CA to 19°CA before top dead center (bTDC) were used to determine the optimum diesel injection timing. The second mode was carried out at varying methane energy fraction (MEF) levels with %0, %25, and %50 contributions to the total fuel energy of methane. In the optimum injection timing experiments, the lowest ignition delay period, combustion duration, lower emission values, and better engine performance were obtained with 11°CA bTDC under all load conditions. The methane energy fraction significantly reduced the maximum combustion pressure, especially under low load conditions. However, combustion pressure values of diesel and methane-diesel dual fuel studies under high load conditions were obtained close to each other due to late injection timing, high injection pressure, and higher combustion temperature. Moreover, COVIMEP values of all test fuels were obtained below 5% under medium and high load conditions. On the other hand, NO and smoke emissions, which are the main problems of diesel engines, decreased significantly. With the increase of MEF level in methane-diesel dual fuel application, NO emissions showed an improvement up to 67%. Similarly, smoke emissions improved up to 82%. Despite the high HC and CO emissions, which is one of the main problems of the dual fuel mode, the significant reduction of NO emissions due to methane addition has significantly improved the environmental and economic costs. This situation clearly demonstrated the usability of high methane substitution in terms of emissions in dual fuel mode. In addition, exhaust energy loss for all load conditions in methane-diesel dual fuel mode showed an average improvement of 13.5% compared to diesel mode. As a result, high methane substitution is promising because it significantly reduces NO and smoke emissions, which are the main problems of diesel engines, and the low-performance data is at a compensable level.

Influence of hydrogen and methane addition in laminar ammonia premixed flame on burning velocity, Lewis number and Markstein length

The use of Ammonia (NH3) and blends with either Methane (CH4) or Hydrogen (H2) obtained by in-situ NH3 cracking, seem to be promising solutions to partially or fully decarbonise our energy systems. To strengthen understanding of fundamental combustion characteristics of these NH3 blends, the outwardly propagating spherical flame configuration was employed to determine the flame speeds and Markstein lengths. The air/fuel mixtures were varied across a large range of compositions and equivalence ratios. In general addition of CH4 or H2 results in a linear and exponential increase in measured laminar burning velocity, respectively. Of the appraised mechanisms, Stagni and Okafor kinetics mechanisms yielded best agreement with NH3/H2 and NH3/CH4 flame speed measurements. With respect to measured Markstein length, for a fixed equivalence ratio, addition of CH4 to NH3 resulted in a linear reduction in stretch sensitivity for the tested conditions. For lean NH3/H2 flames, an initial decrease in Markstein length is observed up to 30–40% H2 addition, at which point any further addition of H2 results in an increase in Markstein Length, with a non-linear behaviour accentuated as conditions get leaner. Above stoichiometry similar stretch behaviour is observed to that of NH3/CH4. Different theoretical relationships between the Markstein length and Lewis Number were explored alongside effective Lewis Number formulations. For lean NH3/H2 mixtures, a diffusional based Lewis Number formulation yielded a favourable correlation, whilst a heat release model resulted in better agreement at richer conditions. For NH3/CH4 mixtures, a volumetric based Lewis Number formulation displayed best agreement for all evaluated equivalence ratios. For NH3/H2, changes in measured Markstein Length were demonstrated to potentially be the result of competing hydrodynamic and thermo-diffusive instabilities, with the influence of the thermo-diffusional instabilities reducing as the equivalence ratio increases. On the other hand, the addition of CH4 to NH3 results in the propensity of moderating hydrodynamic instabilities, resulting in a stabilising influence on the flame, reflected by increasing positive Markstein number values. Finally, a systematic analysis of the flame speed enhancements effects (kinetic, thermal, diffusive) of CH4 and H2 addition to NH3 was undertaken. Augmented flame propagation of NH3/CH4 and NH3/H2 was demonstrated to be principally an Arrhenius effect, predominantly through the reduction of the associated activation energy.

Experimental study on the effect of piston bowl geometry on the combustion performance and pollutant emissions of methane-diesel common rail dual-fuel engine

In dual-fuel operations, high methane substitution negatively affects combustion performance and creates high hydrocarbon (HC) and carbon monoxide (CO) pollutant emissions. Piston bowl geometry is proven an effective method for improving combustion performance and emissions. In the available study, combustion chamber geometry is experimentally indicated to succeed in dramatically reducing HC and CO pollutant emissions uncompromising nitrogen monoxide (NO) and smoke pollutant emissions.In this study, the effect of piston bowl geometry on the combustion performance and pollutant emissions of a single-cylinder methane-diesel common rail dual-fuel engine was studied experimentally. High-performance piston bowl geometries (Toroidal and Toroidal re-entrant) of conventional diesel operations were used versus original combustion chamber (OCC) geometry in diesel and dual fuel operation for enhancing combustion performance and reducing pollutant emissions. The experiments were conducted at constant 1850 r/min and five different engine loads. The methane energy fraction was set to 50% of the total energy fraction in dual fuel operations. Experimental results showed that the Toroidal re-entrant combustion chamber (TRCC) geometry reduced the long ignition delay period that was due to the methane addition and ensured more stable combustion at all torque conditions. In dual fuel operation, the TRCC geometry improved smoke, HC, and CO pollutant emissions by an average of 18%, 10%, and 3% for all loads, respectively, compared to the OCC geometry. However, NO pollutant emissions were an average of 2.5% higher than OCC geometry for the TRCC geometry. In sum, use of the TRCC geometry is an effective way for providing more complete combustion and reducing emissions under dual fuel operations at all torque conditions between 3 and 9 Nm.

Visualization study on the effects of pre-chamber jet ignition and methane addition on the combustion characteristics of ammonia/air mixtures

As a carbon-free green fuel, ammonia has recently attracted more and more attention. However, the application of ammonia as an alternative fuel in internal combustion engines is a challenge due to its low chemical reactivity. Thus, more fundamental researches on the combustion characteristics of ammonia are necessary to enhance the ignition and combustion of ammonia in internal combustion engines. In this study, the effects of pre-chamber jet ignition and different methane additions on the combustion characteristics of ammonia/air mixtures were investigated experimentally. The experimental results showed that pre-chamber jet ignition could improve the combustion performance of the premixed ammonia/air and ensure combustion stability at a low equivalence ratio, compared with spark direct ignition. For the jet ignition mode, the optimal equivalence ratio of the ammonia/air mixtures was between 1.0 and 1.1. The combustion duration was determined by the flame transverse propagation velocity, which was minimally influenced by the jet flame. For both jet ignition and direct ignition modes, a higher initial pressure would hinder the flame propagation resulting in a longer combustion duration, while an increase in the maximum pressure led to an increase in the average pressure rise rate. And for both ignition modes, the promotion of increasing methane addition from 0 to 10% on the pure ammonia combustion was higher than that of increasing methane addition from 10% to 20% on the combustion, and small amounts (10% and 20%) of methane addition had a less promotion on pure ammonia combustion at a higher initial pressure.