Browse Topic: Methane

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Methane Emission Mitigation in Large-Bore Dual-Fuel Engines via Negative Valve Overlap Diesel Injection: Thermochemical Pathways and Reactivity Control2026-37-00456/9/2026
Low-load natural gas–diesel reactivity controlled compression ignition (RCCI) in medium-speed marine engines is constrained by an insufficient charge thermal state. This limitation leads to partial fuel oxidation, producing high methane emissions. This work evaluates the use of negative valve overlap (NVO) combined with NVO diesel injection as an in-cylinder reactivity enhancement strategy. The simulation study was performed using the University of Vaasa’s advanced thermo-kinetic multi-zone model (UVATZ), extended for reactive simulations during NVO. The extended framework was validated against test-bench data from a prototype Wärtsilä 6L20 dual-fuel engine operating in RCCI mode. The baseline low-load operating point for reforming simulations was defined by reducing the intake manifold temperature to replicate conditions close to partial misfire with 52% combustion efficiency. The parametric sweeps of NVO injection timing and ratio showed that the strategy can be used for in-cycle fast thermal management, effectively restoring complete combustion on an individual cycle basis. In simulated conditions, the best performance was obtained with an NVO injection ratio of 0.3, with the injection scheduled before top dead center. In contrast, increasing the NVO fraction beyond ~0.3 provided no benefit and led to complete misfire due to excessive reduction of main-event high-reactivity fuel. The simulations revealed a coupled thermal–chemical control mechanism. Early NVO injections stabilize combustion through recompression heat release and an increased next-cycle intake valve closing temperature. Sufficiently late injections stabilize combustion by carrying unreacted diesel into the subsequent cycle. Injections near NVO TDC primarily undergo fuel conversion to CO, H2O, and unsaturated light/mid-range hydrocarbons with negligible thermal boost, yielding an overall reactivity deficit.
Soleimani, Amir, Nurmi, Mikael, Hunicz, Jacek, Kim, Jeyoung, Hyvonen, Jari, Mikulski, Maciej
Development of a Diesel Combustion System for Next-Generation Heavy-Duty Engines Using a Synergistic Analysis-and-Testing Approach2026-37-00046/9/2026
Regulators and policymakers have introduced increasingly stringent limits on tailpipe CO₂ and pollutant emissions to accelerate the decarbonization of heavy-duty vehicle applications. The development of innovative propulsion technologies — such as advanced combustion systems, low-friction reciprocating components, and improved aftertreatment solutions — combined with hybridization and the adoption of alternative fuels (e.g., biogas, HVO, green hydrogen), is a key pathway for meeting future emission and GHG targets. In this study, advanced combustion systems were developed for a 13-liter diesel engine for heavy-duty truck applications, with the objective of meeting forthcoming Euro VII regulations while maximizing thermal efficiency. The combustion system architecture—including open-bowl geometry with high aspect ratio, injector nozzle with wider spray opening angle, and reduced swirl ratio—was optimized using a Machine Learning–algorithm trained on high-fidelity 3D CFD combustion data. The method enabled the identification of two optimized combustion-system “recipes”, one of which was evaluated through engine tests, which refined nozzle specifications and injection strategies, using a structured Design of Experiments (DoE) approach. Results were benchmarked against a MY24 baseline combustion system, assessing efficiency, NOx–soot trade-offs, and combustion behaviors. Based on 3D-CFD results, the advanced combustion concept achieved an improvement in Brake Thermal Efficiency (BTE) of up to +0.8% points and delivered substantial NOx reductions of up to 45%, while maintaining smoke emissions at or below baseline levels. The experimental results indicate that the advanced combustion system developments designed for next-generation heavy-duty engines can further increase BTE by up to ~1% relative to the baseline combustion system, without deteriorating the soot–NOx trade-off.
Belgiorno, Giacomo, Centini, Maria Pia, Pezza, Vincenzo, Cozza, Ivan F., Pesce, Francesco C., Vassallo, Alberto, Colombo, Giovanni, Gallo, Alessandro, Mirzaeian, Mohsen, Borg, Jonathan
Numerical Simulation of Spark-Ignited Flame Kernels towards Prospective Application to Hydrogen SI Engines2026-37-00156/9/2026
The ongoing energy transition demands the decarbonization of the transport sector, for which the use of premixed hydrogen in spark-ignition (SI) engines appears very promising. However, modeling the combustion of the lean hydrogen/air mixtures required for safe, efficient, and low-NOx engine operation involves multiple open issues. Correct prediction of flame kernel initiation and growth is a difficulty that hydrogen shares with hydrocarbon fuels, while properly accounting for the instabilities that characterize lean hydrogen flames is an additional demanding task. In this work, a 1D kernel expansion model of general validity recently proposed by the authors is implemented into OpenFOAM, an open-source 3D CFD software package, to enable numerical simulation of expanding spark-ignited flame kernels. Firstly, the OpenFOAM framework is presented focusing on XiFluid, its flame propagation model based on a regress variable whose evolution depends on the laminar flame speed. Then, the authors’ kernel expansion model, based on the transient thermo-diffusive theory, is briefly recalled to highlight its capabilities and outputs. The coupling between OpenFOAM and authors’ model is split into two stages, namely ignition and expansion. During the ignition stage, an artificial profile of the regress variable is temporarily imposed to ensure a stable numerical solution, following which the kernel expansion is simulated by feeding into XiFluid an equivalent flame speed extracted from the 1D model. The coupling is currently formulated for laminar kernels, simulations of which are conducted firstly for conventional fuels (methane and propane) and then for hydrogen. The results are validated against outcomes of experimental tests performed in a constant-volume combustion chamber operated by engine manufacturer Wärtsilä. The validation is satisfactory for all fuels, although minor disagreements appear in case of intense flame stretch. These will be addressed in future developments, which will also extend this approach to unstable turbulent hydrogen flames in SI engines.
Dotteschini, Enrico, Pretto, Marco, Giannattasio, Pietro, Gadalla, Mahmoud
Impact of Hydrogen on Methane and Pollutant Emissions over Three-Way Catalysts with Natural Gas–Hydrogen Blends2026-01-03574/7/2026
Blending natural gas (NG) with hydrogen (H₂) can improve combustion and engine performance while potentially facilitating the catalytic conversion of methane and other pollutants, resulting in cleaner tailpipe emissions. This study evaluates the impact of H2 on the conversion of methane, CO, and NOx emissions on a commercial three-way catalyst (TWC) in a flow reactor using synthetic gas mixtures that simulate stoichiometric engine exhausts with NG or NG+H₂ combustion. The work examines whether, and how, the additional amount of H₂ in the exhaust stream affects the conversion efficiency of methane and other pollutants. Experiments were conducted with both degreened and aged catalysts under controlled conditions, systematically varying temperature, the air-to-fuel equivalence ratio (λ), and λ modulation. Test conditions covered λ values from 0.996 to 1.000 to represent nominally stoichiometric engine operation with different λ modulation amplitudes, as well as a range of temperatures to inform control strategies for effective CH₄, CO, and NOₓ reduction. Overall, the results show that hydrogen addition significantly improves the conversion efficiency of CH₄ and NOₓ, particularly at temperatures below 500 °C. More significantly, this study highlights that exhaust gas composition, operating temperature, λ management, and the oxygen storage capacity of the TWC all play major roles in affecting the tailpipe emissions from NG and NG+H₂ combustion.
Prikhodko, Vitaly, Wang, Min, Park, Yeonshil, Chen, Hai-Ying, Pihl, Josh
Improving Late Pilot Injection Strategy in Dual-Fuel Diesel/Methane Engines through Supercharging and Hydrogen Enrichment03-18-08-004912/24/2025
In this study, a novel dual-fuel combustion strategy is investigated, employing late pilot injection in diesel–methane engines to improve performance and reduce emissions. The engine was first tested with conventional diesel and methane, exploring a wide range of pilot injection timings, injection pressures, and intake boost pressures. Subsequently, experiments were repeated using a methane/hydrogen blend to assess the influence of hydrogen addition. Results show that, when using only methane, delayed pilot injections have minimal effects on engine performance. In naturally aspirated operation, unburned hydrocarbons and carbon monoxide are reduced, while in supercharged conditions, emissions increase; however, they remain within acceptable limits. Nitrogen oxides and particulate matter reach their lowest levels with delayed injection. Introducing hydrogen reduces engine performance and hydrocarbons and carbon monoxide emissions; notably, it suppresses the typical nitrogen oxides increase associated with hydrogen, while also lowering particulate matter. These findings demonstrate that combining late pilot injections with hydrogen addition and supercharging is a promising strategy for improving dual-fuel engine efficiency and emissions, offering a potential pathway toward cleaner combustion.
Carlucci, Antonio Paolo, Strafella, Luciano, Ficarella, Antonio
Optimization of Biogas Combustion in SI Engines Applied to the Pre-Chamber Ignition System2025-36-020912/18/2025
The diversification of the energy matrix, combined with the use of renewable and less polluting fuels in internal combustion engines, has encouraged numerous research efforts both nationally and internationally. In this context, the utilization of waste for biofuel production stands out as a promising alternative, offering a clean and economically viable energy source. Biogas is one of the most sustainable options and has been widely used in the industry. However, it presents low lower heating values (LHV) and difficulties in burning stoichiometric mixtures, which compromise engine performance, resulting in higher specific fuel consumption and lower power output compared to fossil fuels. To address this challenge, this study aimed to improve biogas combustion in internal combustion engines by investigating the application of a new pre-chamber ignition system in the combustion process and engine performance parameters. For this, experimental tests were conducted with two biofuel concentrations for evaluation: (100% CNG) and (85% CNG + 15% CO2), enriching the stoichiometric mixture and applying calibration methodologies in a single-cylinder engine adapted to operate with biogas, assessing engine performance parameters and gas emissions. The application of pre-chamber ignition showed significant improvements in energy efficiency, resulting in approximately a 12% torque gain in stoichiometric mixtures, contributing to more efficient combustion and a reduction in hydrocarbon emissions. The use of mixtures in the range of 1.0 to 1.2 led to emission reductions between 60% and 35% compared to the engine without the pre-chamber, demonstrating the pre-chamber’s ability to promote more complete combustion even in leaner mixtures. The data obtained provide valuable insights for the development and application of new technologies in biogas-powered internal combustion engines, contributing to advancements in this research area.
Siqueira, Caio Henrique Moreira, Ázara, Luiz Eduardo Martins, Ribeiro, José Vitor Puttini, Soares, Gabriel Faria, Silva, Fábio Moreira, Alvarez, Carlos Eduardo Castilla
Review of the Potential for Utilizing Organic Waste for Biogas Production in Latin American Countries2025-36-008312/18/2025
Environmental agreements and the urgent need to mitigate greenhouse gas emissions have positioned biogas as a sustainable alternative for bioenergy production. Biogas is a highly versatile fuel that can be used for heat and electricity generation, as well as a substitute for fossil fuels. However, its contribution to the global energy matrix remains limited. This study presents a literature search aimed at assessing the potential for biogas and bioenergy production in Latin American countries, with an emphasis on agro-industrial, agricultural, and urban waste sources. This source was conducted using articles retrieved from the CAPES Journals Portal. Based on the findings, Brazil stands out due to its extensive agro-industrial sector, while countries such as Argentina, Colombia, and Mexico also offer substantial opportunities which biogas could meet a significant share of regional energy demand. The review showed that sugarcane residues in Colombia could replace up to 44% of gasoline consumption, whereas in Cuba, agricultural residues may supply approximately 18% of national electricity demand. Sanitary landfills in countries such as Ecuador and Mexico demonstrated the potential to power thousands of households and significantly reduce methane emissions. Furthermore, biogas production and utilization could prevent the emission of 38,294 tCO2eq in Colombia. In Mexico, the implementation of energy recovery systems in landfills could avoid up to 134,688 tCO2eq. The region possesses abundant resources to drive biogas production, aligning energy generation with sustainability goals. Despite its potential, several challenges must still be addressed, including investments in infrastructure, upgrading technologies, and public policies that promote biogas development. These measures are essential to enable decentralized energy generation, reduce costs, and mitigate methane emissions.
Rodrigues, Jônatas Soares, Moreira, Thiago Augusto Araújo, Souza Pereira, Felipe Augusto de, Castro, Daniel Enrique
Visualization Study on Combustion Characteristics of Ammonia/Methane/Air Mixtures Ignited by Diesel Pilot in Rapid Compression and Expansion Machine2025-32-005411/3/2025
The application of ammonia fuel in engines can significantly reduce carbon emissions, serving as a crucial method for achieving carbon neutrality. However, its potential is hindered by the challenges of ammonia's difficulty in ignition and slow combustion rate. An effective solution to these drawbacks is to blend methane into ammonia mixtures and use a small amount of diesel for ignition. This study investigates the effects of mixture equivalence ratio and gas composition on the combustion characteristics of diesel-ignited NH3/CH4/Air mixtures. Pressure measurements and visual observations were conducted using a rapid compression expansion machine (RCEM). Experimental results reveal that the combustion process exhibits two distinct stages: initial intense diesel combustion followed by mixture combustion. Higher equivalence ratios prolong ignition delay while accelerate secondary combustion. Pure ammonia mixtures show incomplete lean combustion, while richer mixtures achieve more vigorous and complete burning. Notably, the two phases demonstrate an inverse relationship in the trends of flame luminance variation with respect to equivalence ratio changes. Methane addition (40% energy ratio) significantly improves overall performance, enhancing heat release rates, chamber pressure, flame characteristics, and heat release efficiency while reducing ignition delays. The research provides a systematic analysis of combustion phasing, flame development, and efficiency parameters under varying mixture conditions, highlighting methane's role in optimizing ammonia-based combustion systems.
Yin, Shuo, Dai, Zhizhuo, Zhou, Qingxing, Cui, Zechuan, Zhang, Xiaolei, Ye, Mingyuan, Ren, Yifang, Wang, Zhanpeng, Nishida, Keiya
Experimental Study on Hydrogen-Methane Co-Combustion in Small Gas Engines2025-32-005511/3/2025
Hydrogen fuel has garnered significant attention as a key method for adapting internal combustion engines to a carbon-neutral society. Hydrogen is a carbon-free fuel that does not produce CO2 emissions during combustion. However, its wide flammability range and extremely low ignition energy present technical challenges when applied to internal combustion engines, such as the frequent occurrence of abnormal combustion phenomena like pre-ignition and knocking. Furthermore, the low energy density of hydrogen makes it difficult to achieve high power output. Additionally, hydrogen’s high adiabatic flame temperature and short quenching distance result in increased NOx emissions and cooling loss, which are further obstacles to its use. To address these issues, this study focuses on methane blending as a remedial approach. Experiments were conducted using a naturally aspirated engine with a premixed intake method to investigate the effects of methane-hydrogen blending. The following key findings were obtained: 1 The heat release rate can be controlled by adjusting the blending ratio. 2 Pre-ignition and knocking can be suppressed. 3 Power output can be improved. 4 NOx emissions can be reduced. 5 Thermal efficiency can be enhanced by optimizing the blending ratio based on engine load conditions. The insights gained through this study demonstrate the potential of internal combustion engines in achieving a low-carbon and decarbonized society.
Tanaka, Kenta, Tani, Toshihiro, Sako, Takahiro
Experimental and Kinetic Study of Methane Blending on The Laminar Combustion and Emission Characteristics of Ammonia Under Various Oxygen Contents at High Temperature and Pressure2025-32-006011/3/2025
As a carbon-free fuel, ammonia is one of the alternatives to traditional fossil fuels, but its combustion characteristics are poor, and it is usually optimized by blending methane and increasing oxygen content. However, there are few relevant studies under different conditions. In this study, the laminar burning velocities (LBV) and flame instability of NH3/CH4/O2/N2 mixture at high initial temperature (T), high initial pressure (p), various oxygen contents (Ω) and methane energy ratios (α) are analyzed using a constant volume combustion chamber (CVCC). Through numerical simulation, how various oxygen contents and methane energy ratios affect the combustion characteristics of NH3/CH4/O2/N2 mixture and NO emission is analyzed. The results show that LBV is positively correlated with T, α and Ω, and negatively correlated with p. Markstein length (Lb) does not change significantly with T, but increases with α and decreases with p and Ω. Both oxygen enrichment and methane blending significantly increase the hydrodynamic instability of the flame and decrease the buoyancy instability of the flame. Oxygen enrichment and methane blending have little effect on the thermal diffusion instability of the flame. Oxygen enrichment and methane blending are effective in increasing the generation of NHi, O, H, OH, and other radicals and the chemical reaction rate. The main factor of oxygen enrichment and methane blending to increase LBV is the thermal effect, but it also leads to the increase of NO, which is mainly thermal NO. The reaction path and sensitivity analysis of NO show that HNO + H <=> NO + H2, N + NO <=> N2 + O play an important role in the production and consumption of NO, respectively. With the change of Ω and α, the concentration of NO increases and the time of NO production decreases.
YU, Yuantao, Dai, Zhizhuo, Hou, Chunlei, Ye, Mingyuan, Zhang, Xiaolei, Cui, Zechuan, Yin, Shuo, Nishida, Keiya
Effect of Flow Speed and Turbulence on Methane Combustion in a Rapid Compression Machine2025-01-039310/7/2025
Recent experimental work from the authors’ laboratory demonstrated that applying a boosted current ignition strategy under intensified flow conditions can significantly reduce combustion duration in a rapid compression machine (RCM). However, that study relied on spark anemometry, which provided only localized flow speed estimates and lacked full spatial resolution of velocity and turbulence near the spark gap. Additionally, the influence of turbulence on combustion behavior and performance across varying flow speeds and excess air ratios using a conventional transistor-controlled ignition (TCI) system was not thoroughly analyzed. In this study, non-reactive CFD simulations were used to estimate local flow and turbulent velocities near the spark gap for piston speeds ranging from 1.2 to 9.7 m/s. Simulated local velocities ranged from 0.7 to 96 m/s and were used to interpret experimentally observed combustion behavior under three excess air ratios (λ = 1.0, 1.4, and 1.6). Combustion was analyzed using pressure-based normalized cumulative heat release (NCHR) durations and high-speed shadowgraph imaging. At stoichiometric conditions (λ = 1.0), combustion duration decreased by over 70% with increasing flow speed, with optimal behavior observed between 33 and 72 m/s. At 96 m/s, durations increased again due to early spark kernel displacement and greater convective losses. For λ = 1.4, the shortest durations occurred near 23 m/s, corresponding to an 87% reduction in flame initiation time. At higher flow speeds, ignition consistency declined, with complete misfires at 72 m/s. For ultra-lean mixtures (λ = 1.6), stable combustion was only observed at low flow speeds (≤ 9 m/s); beyond this, ignition failed entirely due to heat loss and limited mixture reactivity. Shadowgraph imaging confirmed that larger, faster-growing flame kernels formed at optimal flow speeds, correlating with shorter combustion durations and higher peak pressures. At excessive flow intensities, however, early flame kernel disruption and elevated convective losses led to slower combustion or complete misfire.
Haider, Muhammad.Shaheer, Jin, Long, Yu, Xiao, Reader, Graham, Zheng, Ming
Combined Biological and Electrochemical Process to Produce Ammonia Fuel from High-Strength Blackwater2025-01-04839/16/2025
This study develops a biological-electrochemical process for ammonia fuel production from high-strength blackwater, integrating enhanced ammonification, anaerobic digestion (AD), and electrodialysis (ED). The system achieved 90% COD removal, with Bacillus subtilis increasing NH3-N concentrations by 113%, enhancing nitrogen recovery. AD reduced volatile solids by 60%, producing 200 mL/day of biogas with 70% methane content, and increased NH3-N from 215 to 308 mg/L in the effluent. ED concentrated ammonia to 3 g NH3-N/L with an energy consumption of 1.8 Wh/L, while diluted effluent contained <30 mg NH3-N/L. The system generated a net energy output of 20.48 kWh-e/day, transforming wastewater from an energy sink into an energy-positive process. This approach enables high-efficiency nitrogen recovery, converting waste into ammonia fuel for reformation efforts, while supporting decentralized sanitation solutions.
Thomas, Benjamin, Emerson, Emilia, Smerigan, Blake, Monson, Carter, Liu, Yan, Boltersdorf, Jonathan, Hill, Caroline, Dillon, Robert J., Baker, David R., Dusenbury, James, Liao, Wei
Optical Diagnostic Analysis of Methane Combustion Performance and Emissions While Incorporating Ammonia and Multiple Flames In A Spark-Ignition Engine2025-24-00239/7/2025
The utilization of methane–ammonia fuel blends in spark-ignition engines represents a viable strategy for reducing carbon emissions while capitalizing on the high hydrogen content and carbon-free nature of ammonia. Methane, characterized by its high octane number and low carbon content, offers improved thermal efficiency, higher compression ratios, and reduced pollutant emissions relative to conventional gasoline fuels. Ammonia, despite its advantageous energy density and zero carbon content, suffers from low flame speed and high ignition temperature, which pose challenges for stable combustion. Blending ammonia with methane addresses these limitations by enhancing ignition characteristics and flame stability while simultaneously reducing carbon-based emissions. This study examines the combustion and emission behavior of methane–ammonia blends in a single-cylinder, four-stroke engine under varying spark ignition configurations. Experiments were conducted across a range of ammonia energy fractions from 20% to 50%, with results compared to baseline pure methane combustion. Findings indicate that increasing ammonia content results in prolonged ignition delay and combustion duration due to ammonia's lower reactivity. Pure methane exhibited stable combustion and higher power output, whereas higher ammonia fractions led to increased cycle-to-cycle variability and reduced engine performance. However, the implementation of multiple spark plugs significantly improved combustion stability and engine performance by promoting faster heat release. Nitrogen oxides emissions increased with ammonia fraction, peaking at 30% and declining thereafter, while carbon-based emissions showed a marked reduction. High-speed natural flame luminosity imaging was employed to visualize flame front propagation across different blend conditions, providing insight into the influence of fuel composition and ignition strategy on combustion dynamics.
Uddeen, Kalim, Tang, Qinglong, Shi, Hao, Turner, James
Enhancing Ammonia Combustion in Heavy-Duty SI Engines: A 3D-CFD Study on Pre-Chamber Ignition, Methane Addition, and Spark Timing Optimization2025-24-00069/7/2025
Ammonia is a promising fuel for achieving zero-carbon emissions in internal combustion engines. However, its low flame speed and heat of combustion pose significant challenges for efficient combustion. The pre-chamber (PC) spark-ignition (SI) system offers a viable solution by generating multiple ignition points in the main chamber (MC), enhancing combustion efficiency and enabling at the same time lean-burn operation. This study investigates the combustion characteristics and emissions of an active PC spark-ignition heavy-duty engine fueled with ammonia and ammonia-methane mixtures through numerical 3D-CFD simulations performed using the CONVERGE software. These simulations provide an accurate representation of the complex chemical and physical phenomena occurring within the combustion chamber. The study starts from a fully methane-fueled case, validated against experimental data, and subsequently explores different ammonia-methane mixtures. Then, a detailed spark timing (ST) analysis is conducted, varying the ST from 14° to 50° BTDC, to determine the optimal ignition timing for each fuel blend in terms of both performance and emissions. The findings contribute to the ongoing efforts to improve the efficiency and environmental sustainability of heavy-duty spark-ignition engines, aligning with increasingly stringent emissions regulations. The results indicate that optimal performance is achieved with the PC entirely fueled by methane and the MC operating with a 80% NH3 – 20% CH4 mixture, with a ST of 38° BTDC.
Palomba, Marco, Salahi, Mohammad Mahdi, Cameretti, Maria Cristina, Mahmoudzadeh Andwari, Amin
Life Cycle Assessment of Hydrogen Generation through Steam Methane Reforming: A Focus on Co-Product Allocation between Steam and Electricity2025-01-01816/16/2025
This research presents a numerical analysis of the environmental impacts associated with using hot steam as a co-product in hydrogen production through Steam Methane Reforming (SMR) of renewable gas sources. As hydrogen production technology advances rapidly, reducing emissions and addressing environmental concerns, particularly greenhouse gas (GHG) emissions, have become essential. This study examines the SMR process with a focus on the environmental effects of utilizing hot steam as a co-product for electricity generation or facility heating. The analysis evaluates renewable feedstocks, including landfill gas, animal waste, food waste, and wastewater sludge, to determine their viability for sustainable hydrogen production. Key pollutants, such as carbon monoxide and nitrogen oxides, along with GHGs, are assessed to identify the most environmentally advantageous feedstock options. This work aims to provide insights to promote sustainable hydrogen production practices.
Rosyadi, Ahmad Adib, Lim, Ocktaeck
Heat Transfer Characteristics of Lean Methane Flame in the Region near the Wall Boundary Layer2024-32-01204/18/2025
Since proportion of wall heat loss takes as high as 20-30% of the total engine heat loss, the reduction of wall heat loss is considered as an effective way to improve the engine thermal efficiency. The heat transfer near the wall boundary layer plays a significant role on the exploration about the mechanism of wall heat transfer which contributes to figuring out the approach to the reduction of wall heat loss. However, the near wall characteristics of heat transfer are still unclear. In this study, the premixed lean methane flame propagation was captured by the high-speed schlieren and the flame behavior in the near-wall region was investigated by the micro CH* chemiluminescence. The temporal histories of the wall temperature and the heat flux are measured by the co-axial thermocouple. The factors including the convective heat transfer coefficient and non-dimensionless numbers, Nusselt number and Reynolds number, were used to characterize the near wall characteristics. Also, the characteristics of near-wall heat transfer were confirmed under various ambient pressures and lean mixtures. In addition, the flame temperature and thermal gradient near wall boundary layer were revealed by CFD simulation using Chemkin Code. The experimental and simulation results show that the moment of wall temperature rising becomes earlier with the increase of equivalent ratio. The corresponding near-wall thermal gradient derived from the heat flux shows a significant positive correlation with the mixture concentration. The increased ambient pressure leads to a faster flame propagation speed due to the strong buoyancy effect. However, the laminar burning velocity turns decreasing because of the low reactivity of the lean combustion at elevated pressures, leading to a small variation of wall heat flux. The flow field within the near-wall region becomes intense at elevated ambient pressures, resulting in increasing convective heat transfer with the flame. The wall boundary layer characteristics show a strong correlation with the wall heat transfer process, then greatly affecting the heat loss and flame quenching at near-wall region.
Xuefeng, Xue, Run, Chen, Tie, Li
Operating the Tour Split-Cycle Engine on Hydrogen/Methane Fuel Blends to Achieve High Efficiency and Reduction of Both GHG and NOx Emissions2025-01-84224/1/2025
Decarbonized or low carbon fuels, such as hydrogen/methane blends, can be used in internal combustion engines to support ambitious greenhouse gas (GHG) emission reduction goals worldwide, including achieving carbon neutrality by 2045. However, as the volumetric concentration of H2 in these fuel blends surpasses 30%, the in-cylinder flame propagation and combustion rates increase significantly, causing an unacceptable increase in nitrogen oxides (NOx) emissions, which is known to have substantial negative effects on human health and the environment. This rise in engine-out NOx emissions is a major concern, limiting the use of H2 fuels as a means to reduce GHG emissions from both mobile and stationary power generation engines. In this study, an experimental investigation of the combustion performance and emissions characteristics of a 4th generation Tour split-cycle engine was undertaken while operating on 100% methane and various hydrogen/methane fuel blends (30%, 40%, and 50% by volume of hydrogen). Taking advantage of the Tour engine’s superior operating flexibility and its inherent capability to manipulate combustion phasing, the results demonstrate that the Tour split-cycle engine operating on hydrogen/methane fuel blends is capable of high brake thermal efficiency and reduced GHG emissions, while at the same time exhibiting reduced engine-out NOx emissions.
Bhanage, Pratik, Cho, Kukwon, Anderson, Bradley, Kemmet, Ryan, Tour, Gilad, Atkinson, Chris, Tour, Hugo, Tour, Oded
The Numerical Study of Methane Flame Characteristics in the Ammonia/Air Environment at Sub-Atmospheric Pressure2025-01-84504/1/2025
The low emission of carbon and minimum level of soot formation in combustion engines and turbines strategy is adopted by many countries to counteract global warming and climate change. The use of ammonia with hydrocarbon fuels can limit the formation of soot and carbon emissions due to non-carbon atoms. The current study explores the use of ammonia with air at coflow flame conditions, which was not tested before. It may give the choice for diesel cycle engines to use the ammonia either with air or fuel. The combustion and emission characteristics of methane coflow flame were studied at low pressure and air polluted by ammonia conditions. The results showed that a significant decline in carbon formation was observed when ammonia was boosted, 5-10%. The impact of sub-atmospheric pressure, 90-70 KPa, on COx development was higher than that of NH3 addition, 0-5%, thanks to the lower formation of hydroxymethylium, formaldehyde, and aldehyde radical. In the environment of lower pressure, the reaction rates were reduced due to increasing molecules' interaction space. The sub-atmospheric pressure had more impact on the reduction of nitric oxide than that of nitrous oxide, and ammonia impact was greater on the increment of nitric oxide than that of nitrous oxide. The maximum reduction and increment in the profile of nitric oxide were observed ~ 42.1% at 5% NH3 and 182% at 80 KPa. The acetylene species was more affected by sub-atmospheric pressure rather than cyclopropenyl radical, while ammonia highly reduced acetylene species compared to cyclopropenyl radical. The acetylene species has a lower C-H ratio, which transformed easily with another lower species after reacting with ammonia. The peak reduction was observed by ammonia 19% at 90 KPa, and by sub-atmospheric pressure 13% at 5-10% NH3 acetylene profiles. The lower formation of acetylene and cyclopropenyl radicals reduced the precursor formation. The peak reduction of 14.4% at 70 KPa was observed in pyrene by ammonia enrichment and of 11.1% at 10% NH3 in benzene by sub-atmospheric pressure. The impact of ammonia and sub-atmospheric pressure on soot particle number density formation in methane flame was dominant over soot volume fraction because the soot particle reaction rates were more active than that of soot volume. The peak reduction was observed about 35% at 5% NH3 by pressure impact.
Hina, Anam, Akram, M Zuhaib, Shafa, Amna, Akram, M Waqar
Cryogenic Flux CapacitorTBMG-524772/1/2025
NASA's Cryogenic Flux Capacitor (CFC) capitalizes on the energy storage capacity of liquefied gases. By exploiting a unique attribute of nano-porous materials, aerogel in this case, fluid commodities such as oxygen, hydrogen, methane, etc. can be stored in a molecular surface-adsorbed state. This cryogenic fluid can be stored at low to moderate pressure densities, on par with liquid, and then quickly converted to a gas, when the need arises. This solution reduces both safety-related logistics issues and the limitations of complex storage systems.
Experimental Investigation of Hydrogen or Methane Injection in Active Pre-Chamber on a Lean Combustion Gasoline Engine2025-01-71061/31/2025
With the global promotion of carbon neutrality policies, internal combustion engine (ICE) of traditional fossil fuel is gradually transitioning to carbon neutral fuel ICE, and hybrid dedicated engines are gradually replacing traditional internal combustion engines in the passenger car market. Ultra-lean combustion supported by active pre-chamber is one of the key technologies for achieving high thermal efficient over 45% BTE. However, there are still issues like cold start and PN emissions caused by impingement of liquid fuel injection in pre-chamber, and there is still room for improvement in thermal efficiency by less energy of pilot ignition fuel. Gaseous fuel such as hydrogen or methane have no wetting issues, and can be more easily controlled in terms of the injection amount in pre-chamber, thereby using a less amount of gaseous fuel as the pilot ignition fuel could be a solution. Due to the above situation, this article conducted experiments on a lean burn gasoline engine by injecting hydrogen or methane instead of gasoline into the pre-chamber to ignite the gasoline in the main chamber, and investigate its performance, combustion and emissions. The results show that, there is a best value for both the equivalent calorific value substitution ratio of hydrogen or methane injection in pre-chamber and global lambda, which results in lowest fuel consumption. Due to the fact that hydrogen has a higher activity and none carbon molecule while methane has a lower activity and property of easily generating soot precursors through C1 radicals, the performance of hydrogen and methane injection in the pre-chamber is significantly different: Compared to gasoline injection in pre-chamber, hydrogen injection in pre-chamber can reduce ISFC and significantly decrease PN. Methane injection in pre-chamber increases ISFC and PN, the more retarded the SOI is, the higher the PN results. Hydrogen injection in pre-chamber can breaking through the limitation of ignition angle being too forward of traditional pre-chamber in cold start. This article provides data and solutions for the transition from fossil fuels to carbon neutral fuel step by step.
Liu, Yaodong, Liu, Mingli, He, Zhentao, Li, Xian, Zhao, Chuan, Qian, Dingchao, Qu, Hanshi, Li, Jincheng
Effect of Gasification Temperature on Biohydrogen Derived from Waste Agro Products for Alternative Fuel Application2024-01-52601/28/2025
Hydrogen fuel is becoming a popular choice in many energy applications because of its innovative green technology, which produces zero carbon emissions. It also offers better efficiency than fossil fuels. Current research focuses on obtaining hydrogen energy from agricultural waste using a gasification process. This process involves heating the waste at gasification temperatures 300, 400, 500, 600, and 700°C, maintaining a residence time of 60 minutes, and applying a gasification pressure of 20 bar. The effects of gasification temperature on the effectiveness of hydrogen production are examined. At a high gasification temperature of 700°C and a residence time of 60 minutes, the processed agro feedstock showed impressive results. It achieved a molar fraction of 12% carbon dioxide (CO2), 31% methane (CH4), and 55% hydrogen (H2), leading to an improved hydrogen yield of 15.2 mol/kg. Additionally, it demonstrated better hydrogen selectivity at 8.1 and a higher gasification efficiency of 61%, outperforming results from other gasification temperatures. Bio-green hydrogen is used as an alternative fuel for energy purposes.
Venkatesh, R., De Poures, Melvin Victor, Raguraman, B., Marimuthu, S., Devanathan, C., Baranitharan, Balakrishnan, Madhu, S., Kaliyaperumal, Gopal, Manickaraj, Pethuraj
Fuel Design Concept to Improve Both Combustion Stability and Antiknocking Property Focusing on Ethane2024-01-427611/5/2024
For realizing a super-leanburn SI engine with a very-high compression ratio, it is necessary to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for some contribution to stable combustion. C2H6 has a very-long ignition delay time at a low temperature, close to that of CH4, but a short ignition delay time at a high temperature, close to that of gasoline. C2H6 also has a laminar burning velocity about 1.2 times higher than that of gasoline. C2H6 addition to gasoline could be a good example of fuel design to improve both combustion stability and antiknocking property. In the present study, the antiknocking effect of adding CH4, C2H6, or C3H8 with the RON of 120, 115, or 112, respectively, to a regular-gasoline surrogate fuel with the RON of 90.8 has been investigated in an SI engine with a stoichiometric mixture. With the energy fraction of the gaseous fuel of less than 0.35, knocking limit CA50 is advanced further in the order of C2H6 addition > C3H8 addition > CH4 addition, which is conflict with the order of RON of CH4 > C2H6 > C3H8. The effect is dependent on not the RON of the gaseous fuel, but the rate of OH consumption by the gaseous fuel. The effect of adding each gaseous fuel to a premium-gasoline surrogate fuel with the RON of 100.2 has been also investigated. The effect is not dependent on the cool-flame reactions of the liquid fuel.
Kuwahara, Kazunari, Shimizu, Taisei, Okada, Atsuki
A Hydrogen-Powered Airship Sets Course for Greener Aerial InspectionsTBMG-5184110/16/2024
Pipeline inspection is a crucial aspect of maintaining the integrity, safety, and reliability of the planet’s energy infrastructure. However, due to cost and scale challenges, infrastructure operators struggle to conduct accurate, large-scale inspections. A French startup, HyLight, offers a solution to precisely detect issues on the infrastructure, such as methane leaks on pipelines and defects on power lines at an industrial scale, without emitting greenhouse gases.
Numerical Study of Catalytic Methanation Reactions Using a Kinetic Model2024-24-00229/18/2024
Even if huge efforts are made to push alternative mobility concepts, such as, electric cars (BEV) and fuel cell powered cars, the importance and use of liquid fuels is anticipated to stay high during the 2030s. The biomethane and synthetic natural gas (SNG) might play a major role in this context as they are raw material for chemical industry, easy to be stored via existing infrastructure, easy to distribute via existing infrastructure, and versatile energy carrier for power generation and mobile applications. Hence, biomethane and synthetic natural gas might play a major role as they are suitable for power generation as well as for mobile applications and can replace natural gas without any infrastructure changes. In this paper, we aim to understand the direct production of synthetic natural gas from CO2 and H2 in a Sabatier process based on a thermodynamic analysis as well as a multi-step kinetic approach. For this purpose, we thoroughly discuss CO2 methanation to control emission in order to maximize the methane formation and minimize the CO formation and to understand the complex methanation process. We have considered an equilibrium and kinetic modelling study on the NiO-SiO2 catalyst for methanation focusing on CO2 derived SNG. In this work, a comprehensive thermodynamic analysis of CO2 hydrogenation is preformed to define the optimum process parameters followed by the kinetic simulations. Further, the simulations can be performed at various conditions, for example, catalyst mass, mass flow, pressure, temperature etc. to optimize the methanation process.
Mauss, Fabian
Mimicking 'Plant Power' Through Artificial PhotosynthesisTBMG-512148/1/2024
Solar panels are an increasingly popular way to generate electricity from the sun’s energy. Although humans are still figuring out how to reliably turn that energy into fuel, plants have been doing it for eons through photosynthesis. Now, a team reporting in ACS Engineering Au has mimicked the process to produce methane, an energy-dense fuel, from carbon dioxide, water and sunlight. Their prototype system could help pave the way toward replacing nonrenewable fossil fuels.
Effect of Dithering on Post-Catalyst Exhaust Gas Composition and on Short Time Regeneration of Deactivated PdO/Al 2 O 3 Catalysts under Real Engine Conditions2024-37-00026/12/2024
Fossil fuels such as natural gas used in engines still play an important role worldwide which however is also exacerbating climate change as a result of carbon dioxide emissions. Although natural gas engines show an overall low pollutant emissions level, methane slip due to incomplete combustion occurs, causing methane emissions with a more than 20 times higher global warming potential than CO2. Additionally, further tightening of emissions legislation is to be expected bringing methane emissions even more into focus making exhaust gas aftertreatment issues remain relevant. For lean gas applications, (Pd)-based catalysts turned out to convert CH4 most efficiently usually being supported by metal oxides such as aluminium oxide (Al2O3). Water (H2O) contained in the exhaust gas causes strong inhibition on Pd catalysts. In real exhaust gases, not only water vapour but also pollutants and sulphur-containing compounds such as hydrogen sulphide (H2S) or sulphur oxides (SOx) are poisoning the catalytic converter. Rich pulses decomposing sulphur species adsorbed on Pd-Pt methane oxidation catalysts, enable efficient regeneration of heavily poisoned catalysts. A strategy similar to operation with rich pulses, but with a different motivation, is the use of high-frequency oscillations between lean and rich exhaust gas, so-called dithering, to improve pollutant conversion. A combination of a stoichiometric pulse while simultaneously dithering shows better results in recovery as well as emissions during regeneration than a pure rich pulse.
Tomin, Sebastian, Wagner, Uwe, Koch, Thomas
Dimethyl Ether Biogas Reactivity-Controlled Compression Ignition for Sustainable Power Generation with Low Nitrogen Oxide Emissions03-17-07-00544/22/2024
Biogas (60% methane–40% CO2 approximately) can be used in the reactivity-controlled compression ignition (RCCI) mode along with a high-reactivity fuel (HRF). In this work dimethyl ether (DME) that can also be produced from renewable sources was used as the HRF as a move toward sustainable power generation. The two-cylinder turbocharged diesel engine modified to work in the DME–biogas RCCI (DMB-RCCI) mode was studied under different proportions of methane (45–95%) in biogas since the quality of this fuel can vary depending on the feedstock and production method. Only a narrow range of biogas to DME ratios could be tolerated in this mode at each output without misfire or knock. Detailed experiments were conducted at brake mean effective pressures (BMEPs) of 3 and 5 bar at a speed of 1500 rpm and comparisons were made with the diesel–biogas dual-fuel and diesel–biogas RCCI modes under similar methane flow rates while the proportion of CO2 was varied. The DMB-RCCI mode exhibited superior brake thermal efficiency (25.3% as against 22% and 31.5% as against 29% at the BMEPs of 3 and 5 bar) as compared to the other modes and was not sensitive to the concentration of methane. The NOx and soot emissions were also negligible and the lowest CH4 emission levels were also attained. The cyclic fluctuations in IMEP were lower than 5% in this mode. Thus, DME can be used along with biogas to enhance its reactivity for sustainable power generation in the RCCI mode.
Gopa Kumar, S., Mohan, Aneesh, Ramesh, A.
Sulfur Impact on Methane Steam Reforming over the Stoichiometric Natural Gas Three-Way Catalyst2024-01-26334/9/2024
The steam reforming of CH4 plays a crucial role in the high-temperature activity of natural gas three-way catalysts. Despite existing reports on sulfur inhibition in CH4 steam reforming, there is a limited understanding of sulfur storage and removal dynamics under various lambda conditions. In this study, we utilize a 4-Mode sulfur testing approach to elucidate the dynamics of sulfur storage and removal and their impact on three-way catalyst performance. We also investigate the influence of sulfur on CH4 steam reforming by analyzing CH4 conversions under dithering, rich, and lean reactor conditions. In the 4-Mode sulfur test, saturating the TWC with sulfur at low temperatures emerges as the primary cause of significant three-way catalyst performance degradation. After undergoing a deSOx treatment at 600 °C, NOx conversions were fully restored, while CH4 conversions did not fully recover. Experimental data under fixed lambda conditions reveal that sulfur stored on the catalyst leads to reduced CH4 conversions by steam reforming at high temperatures under rich conditions. In contrast, CH4 conversions by oxidation at high temperatures under lean conditions remain consistent, indicating a greater impact of sulfur on CH4 steam reforming. Analysis using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the potential for sulfur-induced deterioration of active sites and oxygen storage capacity, resulting in the formation of carbonaceous species on the catalyst surface.
Kim, Mi-Young, Dadi, Karthik Venkata, Gong, Jian, Kamasamudram, Krishna
Modeling and Analysis of the Hydrogen Production via Steam Reforming of Ethanol, Methanol, and Methane Fuels2024-01-21794/9/2024
The global transition to alternative power sources, particularly fuel cells, hinges on the cost-effective production and distribution of hydrogen fuel. While green hydrogen produced through water electrolysis using renewable energy sources holds immense promise, it currently falls short of meeting the burgeoning demand for hydrogen. To address this challenge, alternative methods, such as steam reforming and partial oxidation of hydrocarbon fuels with integrated carbon capture, are poised to bridge the gap between supply and demand in the near to midterm. Steam reforming of methane is a well-established technology with a proven track record in the chemical industry, serving as a dependable source of hydrogen feedstock for decades. However, to meet the demand for efficient hydrogen storage, handling, and onboard reforming, researchers are increasingly exploring liquid hydrocarbon fuels at room temperature, such as methanol and ethanol. In this work, we have developed reformer models for ethanol, methanol, and methane within the GT-SUITE software, drawing on data from the existing body of research. We examine fuel conversion and hydrogen yield under varying conditions, including different feed temperatures, flow rates, and catalyst loadings. These reactor models hold the potential for seamless integration into system-level models, designed to investigate onboard fuel reforming, startup and shutdown procedures, carbon capture, and more.
Hariharan, Deivanayagam, Chhatija, Harish, Brown, Jonathan, Gundlapally, Santhosh
Add-On Device Makes Home Furnaces Cleaner and SaferTBMG-498191/1/2024
Natural gas furnaces not only heat your home, they also produce a lot of pollution. Even modern high-efficiency condensing furnaces produce significant amounts of corrosive acidic condensation and unhealthy levels of nitrogen oxides, carbon monoxide, hydrocarbons, and methane. These emissions are typically vented into the atmosphere and end up polluting our soil, water, and air.
Coil-On-Plug Igniter for Reliable Engine StartsTBMG-4959812/1/2023
Innovators at NASA Johnson Space Center have developed a coil-on-plug ignition system for integrated liquid oxygen (LOX)/liquid methane (LCH4) thermal-vacuum environment propulsion systems operating in a thermal vacuum environment. The innovation will help quell corona discharge issues and reduce overall mass.
Experimental Investigation on Biogas Operated Electric Vehicle Charging Station2023-28-017811/10/2023
Biogas is developing as a possible replacement for fossil fuels as the globe shifts to sustainable energy sources. Organic waste, including food waste, agricultural waste, and sewage, decomposes to produce biogas. Biogas is a fuel that can be used to create electricity, heat homes, and power vehicles. The popularity of electric cars (EVs) is rising as a result of their zero emissions. EVs and biogas can work together to create a sustainable transportation option. The viability of EV charging stations powered by biogas is the main topic of this techno-economic inquiry. The study involves the evaluation of the technical and economic elements of the proposed system. The technical aspects cover power generation, the EV charging system, the biogas storage system, the biogas production process, and the biogas purification process. The capital cost, operating cost, and revenue from the charging station are all considered economic factors. The collection and processing of organic waste is a step in the creation of biogas. Impurities from the biogas are removed during the purification process, including carbon dioxide and hydrogen sulphide. The compressed version of the purified biogas is next stored in a storage system before being used to power a biogas generator. EVs are charged using the electricity generated. The economic study of the proposed system covers the capital cost, which includes the cost of equipment, installation, and site purchase. The cost of producing biogas, producing power, and performing maintenance are all included in the operational cost. The revenue earned from the charging station comprises the income generated from charging EVs. According to the study, an EV charging station powered by biogas is a workable option for sustainable transportation. Due to the high cost of equipment and installation, the system has a high capital cost. But so far, because power and biogas production are inexpensive, the system has low operational costs. Over time, the charging station's revenue may yield a return on investment. In order to increase system efficiency and lower system costs, the study suggests additional research on the optimization of the biogas production process, the biogas purification process, and the power generation system.
Deepan Kumar, Sadhasivam, PC, Murugan, S, Jayakrishnan, Arun, M U, L, Naveen, R, Poomani
Efficiency Enhancement and Lean Combustion Performance Improvement by Argon Power Cycle in a Methane Direct Injection Engine2023-01-161810/31/2023
Argon Power Cycle (APC) is an innovative future potential power system for high efficiency and zero emissions, which employs an Ar-O2 mixture rather than air as the working substance. However, APC hydrogen engines face the challenge of knock suppression. Compared to hydrogen, methane has a better anti-knock capacity and thus is an excellent potential fuel for APC engines. In previous studies, the methane is injected into the intake port. Nevertheless, for lean combustion, the stratified in-cylinder mixture formed by methane direct injection has superior combustion performances. Therefore, based on a methane direct injection engine at compression ratio = 9.6 and 1000 r/min, this study experimentally investigates the effects of replacing air by an Ar-O2 mixture (79%Ar+21%O2) on thermal efficiencies, loads, and other combustion characteristics under different excess oxygen ratios. Meanwhile, the influences of varying the methane injection timing are studied. Results indicate that by replacing air with an Ar-O2 mixture, thermal efficiencies and loads have a significant improvement, the operation boundary of excess oxygen ratio is extended from 1.73 to 2.91, the combustion duration period is shortened 3.5 - 7.0 °CA, and the cycling stability is significantly improved. For the APC, when the excess oxygen ratio is 1.34 and the methane injection timing is -130 °CA ATDC, the highest net indicated thermal efficiency of 51.1% and the gross indicated thermal efficiency of 53.1% are achieved, which are elevated by approximately 27.8% compared to the air cycle. Meanwhile, the maximum net indicated mean effective pressures of APC increases by 17.6% from 0.80 MPa to 0.68 MPa. The improvements in thermal efficiency are mainly attributed to the increase of thermal conversion efficiency. Moreover, compared to the air cycle, the higher in-cylinder temperature and pressure of APC allows for easier ignition and faster combustion, also leading to an increase in the thermal efficiency.
Wang, Chenxu, Deng, Jun, Su, Xiang, Cui, Wenyi, Tang, Yongjian, Li, Liguang
Impact of Hydrogen Energy Fractions on Cycle-to-Cycle Variations in Biogas-Fueled Spark Ignition Engine2023-01-507510/25/2023
The limitations related to the cost-effectiveness and technological feasibility of upgrading biogas to bio-methane for rural power generation applications have prompted researchers to explore alternative approaches for improving the quality of biogas fuel. This study focuses on evaluating the effect of hydrogen enrichment on combustion characteristics and cycle-to-cycle combustion variations in a single-cylinder spark ignition engine fueled with biogas (60% CH4 and 40% CO2). The engine was run at a constant operating load of 6 Nm, with a compression ratio of 10:1 and an engine speed of 1500 rpm. To establish a baseline for comparison, engine characteristics were initially assessed using pure methane fuel. Subsequently, the share of hydrogen in the biogas fuel mixture was incrementally increased on the volumetric basis from 0% to 30% and experiments were performed to study the effects of these variations on combustion behavior. The statistical approach was adopted for analyzing cycle-to-cycle variations by considering 120 consecutive engine cycles. The results of this study showed that increasing the H2 share from 0% to 30% in an SI engine powered by biogas improved the combustion characteristics (increment in peak in-cylinder pressure; reduction in COVIMEP from 9.9% to 1.7%; improvement in combustion phasing). With the addition of H2, flame propagation speed increased and combustion time decreased. Results indicated that hydrogen enrichment resulted in lower cycle-to-cycle variations (CCVs) of pressure and combustion-related parameters.
Sagar, Abhinandan, Kurien, Caneon, Mittal, Mayank
Study on Knocking Intensity and Autoignitive Propagation Velocity with the Same Methane Number Mixtures of Methane/Ethane and Methane/ n -Butane2023-01-180310/24/2023
Although methane number is widely used to predict knocking occurrence and its intensity, it does not determine a fuel composition uniquely, that means, the knocking intensity by the different composition fuel must show difference even if the same methane number fuels are employed. To establish a novel index, the knocking intensity and the autoignitive propagation velocity, as consequence of spontaneous ignition process, are investigated both experimentally and numerically by using the different composition gaseous fuels with same methane number. Methane/ethane/air and methane/n-butane/air mixtures with the same methane number of 70 and the equivalence ratio of 0.5 were employed. They are rapidly compressed and ignited spontaneously by a Rapid Compression Machine. Ignition delay times, autoignitive propagation velocities, and knocking intensity were measured by acquired pressure histories and high-speed imaging. To survey detail, zero-dimensional and quasi-one-dimensional numerical simulations are involved in this work. Since the temperature dependency on the ignition delay time of each fuel may influence the autoignitive propagation velocity correlated with the knocking intensity, Arrhenius plots of each fuel mixture are acquired by the zero-dimensional reaction simulation to clarify the influence of the mixture composition on the autoignitive propagation velocity. It is necessary to take into account compressible fluid dynamics to predict pressure growth during the spontaneous ignition, the quasi-one-dimensional numerical simulation was carried out. From the above approaches, it was found that the different composition mixture shows the different temperature dependency on the spontaneous ignition delay time, |dτi/dT|, in spite of the same methane number. Meanwhile, the autoignitive propagation velocity takes the same level with the same |dτi/dT|. In other words, autoignitive propagation velocity can change in spite of the same methane number mixture. Since the knocking intensity increases with increase in the autoignitive propagation velocity, it is thought that the knocking for the same methane number mixture is different depending on the temperature range.
Saito, Masanori, Kato, Ryo, Komatsu, Yuma, Takagi, Keigo, Otani, Masaki, Tanabe, Mitsuaki
The Effect of Methane Addition on the Low-Temperature Oxidation Preparation and the Thermal Ignition Preparation of Dimethyl Ether Under Representative Engine In-Cylinder Thermal Conditions2023-32-01509/29/2023
Dimethyl ether (DME) is a highly reactive diesel substitute that can be used as a pilot fuel to ignite low- reactivity methane (CH4) in heavy-duty engines. To optimize the efficiency and emissions of CH4/DME dual-fuel engines, it is crucial to study the fundamental combustion characteristics of DME mixed with methane. This study focuses on the influence of CH4 addition on the low-temperature oxidation (LTO) preparation stage and the thermal ignition (TI) preparation stage of DME in the two-stage ignition process, as these two stages respectively control the ignition delay of the first and second stages. The comparison is made between pure DME and a 50% CH4 and 50% DME blended fuel, operating under thermodynamic conditions representing the engine in- cylinder environment at 30 atm pressure, 650K temperature, and a stoichiometric equivalence ratio. The results show that the addition of methane hardly affects the control mechanism of the two-stage ignition of DME. Specifically, the LTO preparation stage is still promoted by the increase in OH radicals in the DME’s low-temperature oxygenation pathways to form KET, and the second stage is still controlled by the H2O2 loop mechanism. The kinetic analysis also reveals that methane addition can compete for some of the OH radicals in the LTO preparation stage, which has a suppressing effect on ignition. However, in the TI preparation stage, methane can promote the loop reaction of OH→HO2→H2O2→OH and promote ignition. For the operating conditions studied here, although methane consumes a total of 7.24% prior to thermal ignition, it only consumes 0.63% of the total amount in the LTO preparation stage and 1.81% of the total amount in the TI preparation stage. This indicates that methane is mainly consumed in the LTO stage, accounting for 65% of the total methane consumption amount. It can be concluded that the kinetic effect of methane has a relatively small impact on the ignition delay of the DME, at least for the conditions investigated here. In other words, the dilution and thermal effects caused by adding methane are the main reasons for the prolonged time of LTO/TI preparation. Overall, more fundamental research is warranted to understand the role of methane in the two-stage ignition process of DME, which could facilitate the development of CH4/DME dual-fuel engines.
Ou, Juan, Yang, Ruomiao, Yan, Yuchao, Liu, Zhentao, Liu, Jinlong
Study on Influences of Hydrogen addition and Turbulence on Ignition Characteristics of Hydrocarbon Mixtures2023-32-01479/29/2023
This study is performed to experimentally examine the effects of hydrogen addition and turbulence on the ignition and the flame-kernel development characteristics in isotropic and homogeneous turbulence for methane or propane mixtures. First, in order to investigate the ignition and flame-kernel development in quiescence, the minimum ignition energy MIE and the relationship between the flame radius and the burning velocity of meso-scale laminar flames are examined by using sequential schlieren photography in a constant volume vessel. Then, the properties of MIE are examined for three turbulence level. Additionally, the transition region of MIE could be summarized by using the proposed turbulent Karlovitz number based on the burning velocity of the meso-scale flame in quiescence.
Nakahara, Masaya, Matsushita, Yuki, Kishiura, Kensuke, Abe, Fumiaki, Tokunaga, Kenichi
Effects of Engine Speed on Prechamber-Assisted Combustion2023-24-00208/28/2023
Lean combustion technologies show promise for improving engine efficiency and reducing emissions. Among these technologies, prechamber-assisted combustion (PCC) is established as a reliable option for achieving lean or ultra-lean combustion. In this study, the effect of engine speed on PCC was investigated in a naturally aspirated heavy-duty optical engine: a comparison has been made between analytical performances and optical flame behavior. Bottom view natural flame luminosity (NFL) imaging was used to observe the combustion process. The prechamber was fueled with methane, while the main chamber was fueled with methanol. The engine speed was varied at 1000, 1100, and 1200 revolutions per minute (rpm). The combustion in the prechamber is not affected by changes in engine speed. However, the heat release rate (HRR) in the main chamber changed from two distinct stages with a faster first stage to more gradual and merged stages as the engine speed increased. NFL imaging revealed that lower mean piston speed allowed for longer free jet propagation inside the combustion chamber resulting in faster and stronger HRR stages. At higher speeds, the jet-piston interaction started earlier and was dispersed in radial directions, resulting in a relatively prolonged HRR. Finally, the study emphasizes the importance of prechamber jet and piston interaction in shaping HRR.
Palombi, Lucia, Sharma, Priybrat, Cenker, Emre, Magnotti, Gaetano
Fuel Stratification to Improve the Lean Limit in a Methane-Fueled Heavy-Duty Spark-Ignition Optical Engine2023-24-00458/28/2023
Natural gas is an attractive fuel for heavy-duty internal combustion engines as it has the potential to reduce CO2, particulate, and NOx emissions. This study reports optical investigations on the effect of methane stratification at lean combustion conditions in a heavy-duty optical diesel engine converted to spark-ignition operation. The combination of the direct injector (DI) and port-fuel injectors (PFI) fueling allows different levels of in-cylinder fuel stratification. The engine was operated in skip-firing mode, and high-speed natural combustion luminosity color images were recorded using a high-speed color camera from the bottom view, along with in-cylinder pressure measurements. The results from methane combustion based on port-fuel injections indicate the lean burn limit at λ = 1.4. To improve the lean limit of methane combustion, fuel stratification is introduced into the mixture using direct injections. Two different volume fractions of direct injections (20% and 40% by volume) were tested in addition to the port-fuel injections. With stratification, the combustion phasing is shifted towards the TDC, and combustion duration decreases, indicating a faster combustion process. The stratification strategy obtained by combining the direct injection of 40 % methane by volume and port-fuel injection of 60 % methane by volume, shows highly stable combustion with COV of IMEPg as 2.85 %, rapid heat release, and shorter burn duration. The high-speed color images provide insights into the spatial and temporal evolution of flame propagation, while a HSV-model (Hue Saturation Value) analysis enables the identification of different combustion regions based on observed color changes during the combustion process.
Panthi, Niraj, Sharma, Priybrat, Magnotti, Gaetano
CFD Analysis of Different Biogas Upgrading Levels for Dual-Fuel Operation in Diesel Engines2023-24-00558/28/2023
As the transportation sector continues to increase its energy demand and present stricter environmental regulations, the use of biofuels has been gaining more attention. Among them, one of the most promising options is biomethane - a methane-rich fuel produced from biogas upgrading. Despite presenting excellent combustion properties and composition comparable to natural gas, this green fuel requires a proper biogas processing technology that may lead to a high final cost. On the other hand, the direct use of unprocessed biogas may cause operational issues in the engine, since it may present corrosive contaminants and a high CO2 concentration that affects the combustion and decrease storage efficiency. Therefore, a balance between upgrading level and good engine operation could lead a reliable engine performance without the need of high processing costs. In this sense, the present study aims to discuss the effect of different biogas upgrading levels over engine performance and pollutant formation, focusing on fuels with distinct methane concentrations and their use as a partial energy source in dual-fuel diesel engines. For this analysis, a CFD simulation was carried out using a multi-component, 178-species reaction mechanism, which was experimentally validated for biogas and biomethane at various energy substitution fraction (ESF). Compared to diesel operation, all tested fuels led to delayed combustion, more homogeneous temperature profiles, and lower NOx emissions. Biogas upgrading level did not visually affect temperature and NOx distribution inside the cylinder, but final NOx emissions were up to 24.2% lower for biogas with lower methane concentrations. Finally, slightly delaying the diesel injection led to lower NOx, lower UHC, and increased power, but the optimal delay was lower for dual-fuel operation due to the delayed combustion of both biogas and biomethane.
Zucareli de Souza, Túlio Augusto, Frez, Gustavo V., Pinto, Gabriel, Costa, Roberto, Roque, Luis Filipe A., Coronado, Christian J. R., Vidigal, Luís Pedro V.
Repetitive Multi-pulses Enabling Lean CH 4 -Air Combustion Using Surface Discharges03-16-08-00616/20/2023
The development of efficient and reliable ignition systems for lean fuel-air mixtures is of great interest for applications associated with the use of combustion in transportation, electricity production, and other heavy industries. In this study, we report the use of repetitive nanosecond pulsed surface discharges for the ignition of lean methane (CH4)-air mixtures at pressures above 1 bar. Powered by ten 10-ns voltage pulses at 10 kHz, a commercially available non-resistive spark plug was used to generate surface discharges, which were able to ignite CH4-air mixtures at 1.5 bar and with equivalence ratios (ϕ) ranging from 1.0 to 0.5. At the leanest conditions, e.g., ϕ ≤ 0.6, nitric oxide (NO) and nitrogen dioxide (NO2) emission were reduced to <10% of their values at ϕ = 1.0, demonstrating the advantage of lean burn in emission reduction. Consistent ignition was obtained under extremely lean conditions (e.g., ϕ = 0.5) with a minimum of five pulses and a minimum Coulomb transfer of 82 μC. Additionally, the surface plug durability was tested for 114 hours or over 12 million pulse trains by operating the surface plug in 3.5 bar of dry air at 30 pulse trains per second. This study shows that the use of repetitive nanosecond pulses with surface discharge-based plugs holds promise for a durable ignition solution.
Umstattd, Ryan J., Jiang, Chunqi
Ignition Characteristics of Dielectric Barrier Discharge Ignition System under Elevated Pressure and Temperature in Rapid Compression and Expansion Machine03-16-08-00606/15/2023
A rapid compression and expansion machine (RCEM) was used to experimentally investigate the ignition phenomena of dielectric-barrier discharge (DBD) in engine conditions. The effect of elevated pressure and temperature on ignition phenomena of a methane/air premixed mixture was investigated using a DBD igniter. The equivalence ratio was changed to elucidate the impact of DBD on flame kernel development. High-speed imaging of natural light and OH* chemiluminescence enabled visualization of discharges and flame kernel. According to experimental findings, the discharges become concentrated and the intensity increases as the pressure and temperature rise. Under different equivalence ratios, the spark ignition (SI) system has a shorter flame development time (FDT) as compared with the DBD ignition system.
Agrawal, Saurabh, Yamamoto, Shuya, Horibe, Naoto, Hayashi, Jun, Kawanabe, Hiroshi
Experimental and Modeling Study on the Thermal Aging Impact on the Performance of the Natural Gas Three-Way Catalyst2023-01-03754/11/2023
The prediction accuracy of a three-way catalyst (TWC) model is highly associated with the ability of the model to incorporate the reaction kinetics of the emission process as a lambda function. In this study, we investigated the O2 and H2 concentration profiles of TWC reactions and used them as critical inputs for the development of a global TWC model. We presented the experimental data and global kinetic model showing the impact of thermal degradation on the performance of the TWC. The performance metrics investigated in this study included CH4, NOx, and CO conversions under lean, rich, and dithering light-off conditions to determine the kinetics of oxidation reactions and reduction/reforming/water-gas shift reactions as a function of thermal aging. The O2 and H2 concentrations were measured using mass spectrometry to track the change in the oxidation state of the catalyst and to determine the mechanism of the reactions under these light-off conditions. The experimental data indicate that the NOx and CH4 conversions were higher under rich lambda conditions, thereby generating more NH3 than that observed under lean lambda conditions. Conversely, the NH3 formation was mitigated under the dithering conditions resulting from the recovery of redox properties. The measured O2 and H2 concentration profiles indicated that the conversion of CH4 was attributed to its reaction with O2 until O2 was fully consumed. Further, it was converted through a reforming reaction that produced H2 when O2 was depleted. Consequently, dithering conditions with a substantial amount of O2 showed a delayed onset of reforming chemistry and NH3 formation than those observed under rich conditions. The global kinetic model was developed based on the O2 and H2 data obtained under lean and rich conditions as inputs. The model predicted the NOx reduction chemistry in the presence of CO and H2, steam reforming, and the total oxidation of methane reasonably well. We also discussed an approach to improve the model predictions for the partial oxidation reaction of methane.
Kim, Mi-Young, Dadi, Rama Krishna, Gong, Jian, Kamasamudram, Krishna
Operation of a Natural Gas Direct Injection Compression Ignition Single Cylinder Research Engine2023-01-02604/11/2023
The medium and heavy-duty powertrain industry trend is to reduce reliance on diesel fuel and is aligned with continued efforts of achieving ultra-low emissions and high brake efficiencies. Compression Ignition (CI) of late cycle Directly Injected (DI) Natural Gas (NG) shows the potential to match diesel performance in terms of brake efficiency and power density, with the benefit of utilizing a lower carbon content fuel. A primary challenge is to achieve stable ignition of directly injected NG over a wide engine speed and load range without the need for a separate ignition source. This project aims to demonstrate the CI of DI NG through experimental studies with a Single Cylinder Research Engine (SCRE), leading to the development of a mono-fueled NG engine with equivalent performance to that of current diesel technology, 25% lower CO2 emissions, and low engine out methane emissions. The SCRE has a single cylinder displacement of 2.5L and utilizes a high-pressure direct-injection gaseous injector with pilot gas injection capabilities. This is combined with technologies targeting the end-of-compression temperatures required to achieve the autoignition of late cycle injection of NG. These technologies include increased compression ratio and auxiliary charge air heating. The SCRE experimental studies have been successful in demonstrating robust ignition of DI NG, producing high efficiency, stable operation with acceptable pressure rise rates, and good combustion stability. The technology offers direct control of combustion phasing and heat release rate through injection strategy, including pilot and main injection timing and injection pressure. Studies have been conducted to expand the operating range of the SCRE and characterize the interactions of response variables to achieve high efficiency and low emissions operation at increased engine loads, with a final target of 24 bar BMEP.
White, Tyler, Eggart, Brian, Naber, Jeffrey, Turcios, Marco, Singh, Ashish, Munshi, Sandeep
Enhanced Combustion by Photo Ignition of Carbon Nanotubes in a Constant Volume Chamber2023-01-04064/11/2023
Using ammonia as fuel in retrofitted large marine vessels or heavy-duty vehicles has the potential to reduce CO2 emissions. However, ammonia is hard to burn in an internal combustion engine (ICE) due to its poor combustion properties, i.e. having high autoignition temperatures and low flame speeds. This results in the need for a highly reactive secondary fuel or an improved ignition system for achieving complete and stable combustion. This study investigates a radical technology for the ignition of a fuel-air mixture using carbon nanotubes. The technology consists of injecting a mixture of multi-walled carbon nanotubes and ferrocene (CNT-Fe) into a fuel-air mixture and subjecting the particles to a bright flash of light. Due to the photochemical properties of CNT-Fe particles, the absorbed light initiates ignition. The burning particles thereby ignite the gas mixture at multiple points in the chamber, resulting in a flame front propagating faster compared to when using conventional methods like spark plugs. This study investigates the concept in a constant volume chamber filled with mixtures of methane and air, where the CNT-Fe is dispersed inside the chamber and ignited by an externally located xenon flash tube through a quartz window. The aim of the study was to provide a proof of concept, showing that an external light source can initiate combustion in a chamber by CNT-Fe, potentially demonstrating that the technology can be transferred to an engine. Different mixtures of methane/air and chamber pressures were tested. The results show that photo ignition of methane/air is achieved for mixtures with equivalence ratios of 0.65-0.9, whilst for spark ignition the equivalence ratio range was 0.7-1.4. A qualitative assessment of the flame spread is made through optical measurements of the flame front, showing that dispersed CNT-Fe achieves faster burn rates.
Bjorgen, Karl Oskar Pires, Saanum, Inge, Bratsberg, Stian, Jørgensen, Patrick, Lovas, Terese, Emberson, David
Investigation of Premixed Fuel Composition and Pilot Reactivity Impact on Diesel Pilot Ignition in a Single-Cylinder Compression Ignition Engine2023-01-02824/11/2023
This work experimentally investigates the impact of premixed fuel composition (methane/ethane, methane/propane, and methane/hydrogen mixtures having equivalent chemical energy) and pilot reactivity (cetane number) on diesel-pilot injection (DPI) combustion performance and emissions, with an emphasis on the pilot ignition delay (ID). To support the experimental pilot ignition delay trends, an analysis technique known as Mixing Line Concept (MLC) was adopted, where the cold diesel surrogate and hot premixed charge are envisioned to mix in a 0-D constant volume reactor to account for DPI mixture stratification. The results show that the dominant effect on pilot ignition is the pilot fuel cetane number, and that the premixed fuel composition plays a minor role. There is some indication of a physical effect on ignition for cases containing premixed hydrogen. The results also show that the HC and CO emissions for the methane/ethane and methane/propane mixtures decrease despite an increase in the molar carbon content of the fuel with substitution of methane. For the methane/hydrogen mixture, the decrease is caused by both the reduction in carbon content and the improvement in background mixture reactivity.
Tyrewala, Daanish, Rothamer, David, Ghandhi, J.
Effective Ignition of Lean Methane/Hydrogen Mixture in a Rapid Compression Machine2023-01-02554/11/2023
The use of renewable natural gas and green hydrogen can significantly reduce the carbon footprint of engines. For future spark ignition engines, lean burn strategy and high compression ratio need to be adopted to further improve thermal efficiency, reducing energy consumption. The efficacy of the ignition system is essential to initiate self-sustainable flame under those extreme conditions. In this work, a rapid compression machine is employed to compress air-fuel mixture to engine-like boundary conditions before the spark event to experimentally investigate the ignition and combustion characteristics of the methane-air mixtures under extreme lean conditions. Hydrogen is also added to support the ignition process and enhance flame propagation speed. Lean methane-air mixtures with excess air ratio up to 2.8 are used, with 10 vol% hydrogen addition into the methane fuel. The ignition criteria under various ignition strategies are explored. Both in-cylinder pressure and high-speed direct imaging are collected to analyze combustion parameters, such as heat release rate and flame propagation speed. The impact of discharge current amplitude and duration on the lean burn limit of the fuel-air mixture is investigated.
Yu, Xiao, Jin, Long, Reader, Graham, Wang, Meiping, Zheng, Ming
Performance and Emission Characteristics of Direct Injection DME Combustion under Low NOx Emissions2023-01-03274/11/2023
Compression ignition internal combustion engines provide unmatched power density levels, making them suitable for numerous applications including heavy-duty freight trucks, marine shipping, and off-road construction vehicles. Fossil-derived diesel fuel has dominated the energy source for CI engines over the last century. To mitigate the dependency on fossil fuels and lessen anthropogenic carbon released into the atmosphere within the transportation sector, it is critical to establish a fuel source which is produced from renewable energy sources, all the while matching the high-power density demands of various applications. Dimethyl ether (DME) has been used in non-combustion applications for several decades and is an attractive fuel for CI engines because of its high reactivity, superior volatility to diesel, and low soot tendency. A range of feedstock sources can produce DME via the catalysis of syngas. In this work, DME is applied in a direct injection compression ignition combustion application. A novel plunger-type injection system was used to pressurize DME to 415 bar. Each set of operating conditions was subject to exhaust gas dilution to lower NOx emissions below the current regulatory standards. The results focused on the combustion characteristics and exhaust emissions, with matching conditions under diesel-fueled operation as a baseline reference for proper comparison. Non-regulated exhaust species were compared, specifically hydrogen, methane, and formaldehyde. The ultra-low smoke characteristic of DME avoided the classical NOx-soot trade-off of diesel-fueled engines, allowing for combustion optimization through stronger exhaust gas dilution. DME showed improved combustion completeness likely owing to the self-containing oxygen and higher volatility minimizing the dependency on mixing with the in-cylinder surrounding compressed charge.
Leblanc, Simon, M, Murugesa Pandian, Han, Xiaoye, Tjong, Jimi, Zheng, Ming
AI Super-Resolution-Based Subfilter Modeling for Finite-Rate-Chemistry Flows: A Jet Flow Case Study2023-01-02004/11/2023
Large-eddy simulation (LES) can be a very important tool to support and accelerate the energy transition to green technologies and thus play a significant role in the fight against climate change. However, especially LES of reactive flows is still challenging, e.g., with respect to emission prediction, and perfect subfilter models do not yet exist. Recently, new subfilter models based on physics-informed generative adversarial networks (GANs), called physics-informed enhanced super-resolution GANs (PIESRGANs), have been developed and successfully applied to a wide range of flows, including decaying turbulence, sprays, and finite-rate-chemistry flows. This technique, based on AI super-resolution, allows for the systematic derivation of accurate subfilter models from direct numerical simulation (DNS) data, which is critical, e.g., for the development of efficient energy devices based on advanced fuels. This paper describes a case study demonstrating PIESRGANA for a finite-rate chemical methane jet flow using transfer learning. A priori and a posteriori results are presented and discussed. Since the training process is very crucial for the successful application of this new LES technique, a detailed description of possible strategies is provided.
Bode, Mathis
Analysis of Combustion Cycle-to-Cycle Variation in an Optical Single Cylinder Dual-Fuel Engine2023-01-02794/11/2023
This study aims to improve the dual fuel combustion for low/zero carbon fuels. Seven cases were tested in a single cylinder optical engine and their ignition and combustion characteristics are compared. The baseline case is the conventional diesel combustion. Four cases are diesel-gas (compressed natural gas) dual-fuel combustion operations, and two cases are diesel-hythane combustion. The diesel fuel injection process was visualized by a high-speed copper vapour laser. The combustion processes were recorded with a high-speed camera at 10000 Hz with an engine speed of 1200 rpm. The high-speed recordings for each case included 22 engine cycles and were postprocessed to create one spatial overlapped average combustion image. The average combustion cycle images were then further thresholded and these images were then used in a new method to analyze the cycle-to-cycle variation in a dimensionless, for all cases comparable value. Furthermore, the ignition delay and heat release profile of each case are analyzed. The results showed the lowest deviation from the complete overlap for the pure Diesel case and the Hythane Cases since the flames are more concentrated in these. From these studies, it can be concluded that the cyclic variation for the pure diesel combustion is mostly caused by the different swirl speeds in the piston bowl. The diesel-gas dual-fuel combustion with earlier pilot injections have lower cyclic variation due to a wider spread of the combustible mixture. The usage of hythane as main fuel instead of methane results in a about 10% faster combustion and more concentrated flames areas.
Lauterkorn, Alexander Michael, Wang, Xinyan, Zhao, Hua
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