Gas Engine Research Articles

Reactive molecular dynamics simulations of poly(vinyl alcohol) gasification in supercritical carbon dioxide

Supercritical fluid gasification technology, as an environmentally friendly technology, can convert organic components of plastic waste into fuels and chemical materials. Moreover, the utilization of CO2 as the gasification environment holds significant importance for reducing carbon emissions. To better comprehend the microscopic mechanism of plastic gasification in supercritical environment, this sthdy used the Reactive Force Field (ReaxFF) molecular dynamics method to study the gasification process of long-chain poly(vinyl alcohol) molecule in supercritical H2O/CO2 under different reaction conditions. The result illustrated that during the gasification process, poly(vinyl alcohol) initially depolymerized into multiple long carbon chain (C5+) molecular fragments. Subsequently, these fragments underwent cleavage into short carbon chains and various gaseous small molecules. In this reaction, O radicals generated by CO2 decomposition play a crucial role in promoting the cleavage of plastic C–C bonds. In addition, through the analysis of the products and chemical bonds, we found that increasing temperature and prolonging reaction time significantly enhance the gasification efficiency and hydrogen production of plastics. Conversely, exceedingly high pressure inhibits the gasification reaction.

Study of Efficient and Clean Combustion of Diesel–Natural Gas Engine at Low Loads with Concentration and Temperature Stratified Combustion

The approach for achieving efficient and clean combustion in a diesel–natural gas (NG) heavy-duty engine at low loads was studied by computational fluid dynamics simulation. This study proposed the concentration and temperature-stratified combustion technology and clarified its mechanism. The results revealed that different stratified combustions can be organized by controlling the pressures, timings, and durations of diesel and NG injections, and stratified combustion can be classified into moderate, lean, and rich stratified combustion modes. Efficient and clean combustion can be realized simultaneously at low engine loads: the gross indicated thermal efficiency (ITEg) of engine breakthrough was improved to 47.9%, and the indicated-specific emissions of unburned hydrocarbon (ISUHC) were greatly reduced to 1.6 g/kWh, while the indicated-specific emissions of nitrogen oxide (ISNOx) remained at 0.6 g/kWh. Moreover, the detailed analysis of three typical stratified combustion modes demonstrates that coupling control of the concentration and temperature of the charge is the key to obtaining excellent engine performance. Most of the NG-stratified mixture should burn in the react ratio range of 0.4 to 0.8 for low unburned hydrocarbon emissions, low nitrogen oxides emissions, and rapid combustion. The proper temperature stratification should ensure that a high-temperature charge is around the over-lean NG mixture. This study can provide the fundamentals of stratified combustion control and feasible solutions for commercial applications of NG engines.

An innovative sustainable multi-generation energy system (electricity, heat, cold, and potable water) based on green hydrogen-fueled engine and dryer

Increasing renewables' portion in energy matrix around the world has made the scientists to propose innovative techniques for recovering the available waste heat of energy systems to produce excess energies in the Waste-to-X framework. This study proposes a green sustainable multi-generation energy system (MES), producing power, heat, cold, and potable water, driven by a hydrogen-fueled gas engine. The engine's heating potential is recovered to run some bottoming systems comprising proton exchange membrane electrolyzer (PEME), absorption/electrical chiller cycles (ACC/ECC), organic Rankine cycle (ORC), dryer unit, heat pump cycle (HPC), and reverse osmosis desalination unit. The combination of ACC with dryer and HPC is an innovative idea which utilized to produce heating load in this study. A detailed sustainability evaluation framework (technical and eco-environment) is derived to approve performance of the MES. The construction feasibility of the MES in different climatic conditions is sought by considering 5 case study cities around the world. Afterwards, best working fluid of the ECC/HPC and ORC is selected and then the sensitivity of the MES performance to design variables is investigated trough a comprehensive parametric study. Results illustrated that the MES shows the best performance in the city of Willington in which the emission of 84.8 tons of CO2 is prevented annually which is equivalent to saving of 16,291.6 m3 natural gas. The working fluid selection outputs proved that considering R22 and R123 for ECC/HPC and ORC leads the best techno-economic performance. The sensitivity study demonstrated that the highest and lowest influence of the MES's techno-economic performance is related to the ECC evaporator and ORC turbine temperatures, respectively. So that, increasing ECC evaporator temperature led to a relative variation of 8.2%, 4.5%, and 7.5% in energy recovery factor, exergy efficiency, and levelized cost of productions, respectively.

Waste management optimization with NLP modeling and waste-to-energy in a circular economy

This work presents a methodology integrating Non-Linear Programming (NLP) for multi-objective and multi-period optimization, addressing sustainable waste management and energy conversion challenges. It integrates waste-to-energy (WtE) technologies such as Anaerobic Digestion (AD), Incineration (Inc), Gasification (Gsf), and Pyrolysis (Py), and considers thermochemical, technical, economic, and environmental considerations through rigorous non-linear functions. Using Mexico City as a case study, the model develops waste management strategies that balance environmental and economic aims, considering social impacts. A trade-off solution is proposed to address the conflict between objectives. The economical optimal solution generates 1.79M$ with 954 tons of CO2 emissions while the environmental one generates 0.91M$ and reduces emissions by 54%, where 40% is due to gasification technology. Moreover, the environmentally optimal solution, with incineration and gasification generates 9500 MWh/day and 5960 MWh/day, respectively, demonstrates the capacity of the model to support sustainable energy strategies. Finally, this work presents an adaptable framework for sustainable waste management decision-making.

Ab initio calculations of Nb-based MAX phases as bond coats for thermal barrier coatings

Thermal barrier coatings (TBCs) are essential to the reliable high-temperature operation of gas turbines and engines. They comprise a ceramic top coat (TC), a metallic bond coat (BC), and a superalloy substrate. Metallic BCs are common, but they require a minimal difference in the coefficient of thermal expansion (CTE) between the TC and substrate. Among ceramic materials, MAX phases have high CTE. This study reports our use of ab initio calculations to assess the suitability of MAX phases as TBCs. We model Nb-based MAX phases with 211 and 312 structures that have Al or Si at the A sites and C or N at the X sites. We use the quasi-harmonic approximation to calculate the Young's moduli and CTEs of the materials with respect to temperature. The Nb2SiN MAX phase appears as the most suitable for use as a BC between various ceramic TCs and an Inconel-718 substrate. It is predicted to be effective in relieving thermal stresses due to its high CTE of 10.882 × 10−⁶ K−1 at 1273 K. The results indicate that carbide MAX phases with high Young's modulus and low CTE should be used with caution. They may not accommodate thermal stresses as effectively, potentially leading to material failure or reduced performance. Overall, our study indicates the potential of Nb-based MAX structures for use as BCs.

A study on misfire detection by calculating crank angular velocity considering in-cylinder gas properties

Misfire detection using a new crank angular velocity calculation was studied for high efficiency and robust engine ignition performance and combustion stability control. An applying production was achieved by applying in-cylinder gas properties prediction and its correction to the misfire index and verifying it under various conditions. The relationship between the misfire index and torque fluctuation was consistent depending on the combustion control factors EGR, injection timing, pilot injection quantity change, and environmental change factors water temperature and intake gas temperature. On the other hand, it was found that the piston speed changes due to the in-cylinder pressure with respect to the intake pressure, and the crank angular speed needs to be corrected. Commonly used sensors for engine cooling water temperature, intake gas temperature, intake pressure, and engine speed were used as representative values for in-cylinder pressure, and the cooling loss was subtracted from the polytropic index and the reduction in specific heat ratio due to EGR was corrected. By building a new model that calculates the compression end pressure model from the polytropic index and adding corrections to the misfire index, we applied logic that can be calculated for each cycle to the ECU onboard. Conventionally, compression end pressure prediction requires calculations that take combustion conditions into account, which requires the number of sensors and their accuracy, and a long calculation time. However, in this study, Authors focused on the fact that the pressure at TDC during a misfire does not include ignition and combustion phenomena and expressed the necessary physical phenomena using the minimum sensor information. As a result of the above, a control structure at a level that can be applied to products was obtained.

Research Progress and Suggestions on Natural Gas Industry Technology Revolution in the Context of Energy Revolution

The energy revolution is an important driving force for the progress of productivity and civilization in human society. As a big country in global energy consumption and carbon emission, promoting the energy revolution is a strategic choice to ensure the sustainable development of China's energy industry, which is in line with China's national conditions of the construction of modern energy system. Based on the strategic background of the energy revolution, this paper combines China's natural gas production capacity and consumption demand in the context of national conditions, and from the perspective of technological revolution, we have sorted out the research results of relevant scholars on the natural gas industry and the technological development of the whole industry chain of “production, supply, storage and marketing”, and discussed the technological development of China's natural gas industry in the context of the energy revolution. The results of the study show that: (1) the innovative technology of natural gas industry is diversified, low-carbon and green development, but from the dimension of safety, stability and economy, the performance is relatively weak. (2) The overall synergistic development of the whole industrial chain technology is uneven, the gap between supply and demand is increasing, and the degree of information and intelligence is low. And then for the development of China's natural gas industry technology puts forward proposals: (1) to promote innovative natural gas technology breakthroughs, integration of new areas of technology, to achieve the dual objectives of low-carbon economic development and environmental protection; (2) to increase natural gas exploration and development efforts, breakthroughs in the integration of the digital transformation of traditional exploration technology, and continue to support the increase in storage and production; (3) to accelerate the upgrading of natural gas supply and demand, and the establishment of a synergistic, intelligent, diversified pipeline network system. (4) Boost the construction of gas storage system, pay attention to the standardized gas storage management system, and play the role of valley cutting and peak leveling; (5) Build a new comprehensive energy service system, and build a multi-species, multi-link intelligent technology integration to create a new service system.

Modeling and Experimental Validation of Pre-Chamber Jet Penetration Considering Jet Density and Ejection Pressure Variations

Abstract Although pre-chamber (PC) is regarded as a promising solution to enhance ignition in lean-burn gas engines, a lack of comprehensive understanding of PC jet penetration dynamics remains. This study proposed a zero-dimensional (0-D) model for PC jet penetration, considering the mixing of combustion products and unburned gases and floating ejection pressure. A combustion completion degree was defined employing fuel property and heat release to estimate varying jet density. Pressure differences between PC and the main chamber (MC) were referred to as the ejection pressure. Then, this model was validated against experiments from a constant volume chamber and a rapid compression and expansion machine with CH4-H2 blends at different equivalent ratios. Results showed that the proposed model can provide a good prediction in stationary and turbulent fields with the calibrated model coefficient. The overall jet penetration exhibits a t0.5 dependence due to its single-phase characteristic and the relative lower density compared to ambient gas in MC. The flame propagation speed and heat release in PC influence the combustion completion degree at the start of jet ejection, the mass fraction of burned gas in jet increases with the equivalent ratio. Jet penetration is primarily driven by ejection pressure, with tip dynamics barely affected by the pressure difference after the peak. Tip penetration intensity increases with increased fuel equivalent ratio and H2 addition, owing to the faster flame propagation. These findings can offer useful suggestions for model-based design and combustion model development for gas engines.

An experimental study on fuel reforming waste heat recovery engine system fueled with methane

The effects of various operating parameters on a fuel reforming waste heat recovery engine system fueled with methane were experimentally investigated. Steam methane reforming was employed in the system because it is endothermic. Experiments were conducted on the parameters of methane flow rate to reformer and steam-to-carbon ratio to study their effects on the conversion of methane and resulting the overall thermal efficiency of the system. The components of the reformed gas were analyzed, and their effects on the combustion characteristics and thermal efficiency factors of a spark-ignition gas engine were discussed. The effects of engine operating parameters such as spark timing and excess air ratio on the exhaust gas heat recovery effect by fuel reforming and the improvement of system thermal efficiency were also investigated through experiments.

A new fractal pore-throat chain model for non-Darcy flow through porous media

Non-Darcy flow through porous media is of great significance in hydraulics, oil and gas engineering, biomedical science, chemical and civil engineering etc. However, it is difficult to fully grasp the nature of fluid flow through porous media from macroscopic scale alone. Based on the statistically fractal scaling laws of pore structures, a new fractal pore-throat chain model (FPTCM) for non-Darcy flow through the isotropic porous media is developed. The analytical expressions for the Darcy and non-Darcy permeability as well as non-Darcy coefficient are derived accordingly. In order to explore the local flow field of high-speed non-Darcy flow through porous media, the finite element method is also carried out on an equivalent pore-throat unit. The predicted permeability by FPTCM shows better agreement with present numerical results and available experimental data, compared with commonly used semi-empirical formulas including Kozeny-Carman and Ergun equations. It has been found that both Darcy and non-Darcy permeability as well as non-Darcy coefficient strongly relate to the pore structures of porous media. The non-Darcy permeability is positively correlated to porosity, pore fractal dimension and Darcy permeability, while it is negatively related to tortuosity fractal dimension and pore size range. The non-Darcy coefficient shows opposite correlation with these parameters. The present work can provide theoretical basis for oil and gas development, nuclear waste treatment, carbon dioxide geological sequestration etc.

Experimental study on comprehensive detection technology of shallow gas in deep soft soil layer

This study focuses on the underground shallow gas detection project in the Lingkun Island area of the northern entrance tunnel of the Wenzhou City Light Rail S2 line. Based on geological exploration data of shallow gas, we chose the technique of controlled-release gas with static pressure as the experimental foundation, integrating various technologies such as multi-functional in-situ probing, electrical methods, and seismic waves, comprehensively researching shallow gas detection technology in the Lingkun Island area. We conducted field probing experiments to accurately obtain the physical and mechanical properties of gas-rich soil layers and further studied the possibility of determining gas-rich locations. By applying parallel electrical methods, we can accurately identify and distinguish areas of anomalous resistivity in shallow geological structures. Based on abnormal changes in acoustic impedance in strata, we used seismic wave methods, including seismic CT and seismic wave scattering technology, to accurately reveal the presence and depth of shallow gas, providing reliable basis for accurate determination of shallow gas. Finally, we summarized a comprehensive plan for underground shallow gas detection technology, covering on-site data collection, data processing, and image interpretation of results, which will provide valuable references for future shallow gas exploration in relevant areas.

Exploiting Lubricant Formulation to Reduce Particle Emissions from Gas Powered Engines

The present paper illustrates the results of an experimental study aimed at evaluating the effect of lubricant oil features on the emissive behaviour of a heavy duty spark ignition engine fuelled with methane. The activity was performed within a research project between CNR-STEMS and TotalEnergies in which oils with different formulations were characterized, focusing on their potentiality in particle emission reduction. Considering the ultralow particle emission level in the exhaust of gas engines, a specific testing procedure was designed to guarantee highly reliable and accurate results. In particular, the engine was operated under transient conditions, along the World Harmonized Transient Cycle in cold- and hot-start conditions. The results of the test campaign clearly highlight that the lubricant formulation is a key technology for the control of particles, revealing this as an important aspect in view of the upcoming severe regulation limits on particle emissions. The experimental findings show the capability of reformulated oils to drop down the total particle number to 60–70% with respect to a baseline standard oil. The interest in the present study also lies in providing information extendable to more sustainable fuels, like hydrogen or biomethane, nowadays of great interest as alternative energy sources.

A novel approach to integrate CCHP systems with desalination for sustainable energy and water solutions in educational buildings.

This study presents a novel approach to integrating combined cooling, heating, and power (CCHP) systems with water desalination for enhanced energy and water management in educational buildings. Two distinct layouts for CCHP and desalination systems are introduced: one prioritizing efficient power generation to meet electricity demands while providing waste heat for desalination, and the other focusing on balancing cooling and heating loads alongside water desalination. Both layouts are tailored to meet the building's energy and water demands while considering operational efficiency. Optimization of these layouts against traditional systems using the bat search algorithm emphasizes economic viability and the gas engine's operational flexibility, which are crucial for partial load operation. In addition, an environmental assessment compares the proposed CCHP-desalination systems with conventional setups, assessing CO2 emission reductions and overall sustainability. The evaluation encompasses key environmental metrics, such as resource consumption and the integration of renewable energy sources. Results highlight significant CO2 emission reductions across various gas engine capacities, with notable enhancements in economic and environmental performance achieved by selecting a 3,250 kW gas engine within the CCHP-desalination system. This choice not only maximizes the annual profit but also reduces CO2 emissions by 57% compared to conventional systems, underscoring the system's sustainability benefits.

Operation optimization of propane pre-cooled mixed refrigerant LNG Process: A novel integration of knowledge-based and constrained Bayesian optimization approaches

Liquefied natural gas (LNG) technology, particularly the propane precooled mixed refrigerant (C3MR) process, has demonstrated efficiency and emerged as a distinctive dual-refrigerant technology widely used in LNG production. However, the liquefaction process is the highest energy-intensive stage within its supply chain as it consumes about 8 % of the LNG energy content. Thus, for the first time, this study proposes systematic knowledge-based and constrained Bayesian optimization approaches to identify the optimal operation of the C3MR process. These approaches optimize both the operational parameters (pressures and flow rates) and the composition of the mixed refrigerant with practical equipment specifications and rigorous constraints. The results show that the specific energy consumption (SEC) is reduced to 0.264 kWh/kgLNG, which is 14.6 %, and 26 % lower than the basic C3MR process (unoptimized case) and typical industrial C3MR processes, respectively. In addition, the optimized SEC in this study is 14.5 % to 38.6 % lower than those reported in the literature. At large-scale LNG production (10,000 tons per day), the reduction in the SEC is translated into an 18 MW decrease in compression power, saving approximately 4.7 million $ per year for each C3MR train. Moreover, the coefficient of performance (COP) of the C3MR process was improved by about 15 %, and the CO2 emissions were reduced by 17 % (7 tons per year) compared to the basic C3MR process, indicating potential advancements in large-scale LNG liquefaction processes.

Hydrogen Blending in Natural Gas Grid: Energy, Environmental, and Economic Implications in the Residential Sector

The forthcoming implementation of national policies towards hydrogen blending into the natural gas grid will affect the technical and economic parameters that must be taken into account in the design of building heating systems. This study evaluates the implications of using hydrogen-enriched natural gas (H2NG) blends in condensing boilers and Gas Adsorption Heat Pumps (GAHPs) in a residential building in Rome, Italy. The analysis considers several parameters, including non-renewable primary energy consumption, CO2 emissions, Levelized Cost of Heat (LCOH), and Carbon Abatement Cost (CAC). The results show that a 30% hydrogen blend achieves a primary energy consumption reduction of 12.05% and 11.19% in boilers and GAHPs, respectively. The presence of hydrogen in the mixture exerts a more pronounced influence on the reduction in fossil primary energy and CO2 emissions in condensing boilers, as it enhances combustion efficiency. The GAHP system turns out to be more cost-effective due to its higher efficiency. At current hydrogen costs, the LCOH of both technologies increases as the volume fraction of hydrogen increases. The forthcoming cost reduction in hydrogen will reduce the LCOH and the decarbonization cost for both technologies. At low hydrogen prices, the CAC for boilers is lower than for GAHPs; therefore, replacing boilers with other gas technologies rather than electric heat pumps increases the risk of creating stranded assets. In conclusion, blending hydrogen into the gas grid can be a useful policy to reduce emissions from the overall natural gas consumption during the process of end-use electrification, while stimulating the development of a hydrogen economy.

Effect of Passive Pre-chamber Igniting Position on the Large Bore Natural Gas Engine Combustion Characteristics

Effect of Passive Pre-chamber Igniting Position on the Large Bore Natural Gas Engine Combustion Characteristics

Experimental study on combustion instability characteristics in a pre-chamber natural gas engine under lean burn conditions

Pre-chamber jet ignition is a key technology for future high-efficiency natural gas (NG) engines. It can achieve fast and stable combustion through excellent ignition performance. However, there are still some challenges, such as high combustion instability near the lean burn limit and the narrow engine operating range. Therefore, this paper investigates the combustion instability of a pre-chamber NG engine under ultra-diluted conditions by experimental method. At two engine loads, experiments are carried out with different jet ignition intensity schemes to study the effect of jet ignition intensity on the cyclic combustion variations. Then, the combustion instability characteristics of the pre-chamber NG engine are studied by cyclic variation analysis and phase space reconstruction. The results show that with the increase in the jet ignition intensity, the cyclic combustion variations decrease, and the cyclic variation coefficient of the indicated mean effective pressure decreases to below 2%. The lean burn limit of the pre-chamber natural gas engine is extended to an excess air ratio of 2.0. The operation instability of the pre-chamber NG engine is mainly due to cyclic variations in the ignition and combustion process. The nonlinear dynamic analysis shows that the combustion process in the lean burn pre-chamber NG engine behaves with chaotic characteristics under the operating conditions of low jet ignition intensity. As the jet ignition intensity increases, the combustion stability is improved and the cycle-to-cycle variations change from fairly deterministic to more stochastic behavior. The chaotic characteristics of the combustion process become weaker. In conclusion, it is of great importance to generate stable and high ignition intensity jets for reducing combustion instability and improving combustion efficiency in lean burn pre-chamber NG engines.

Energy efficiency research of propulsion system for series-parallel hybridization of amphibious vehicles

The series-parallel hybrid system has attracted much attention from scholars for its effective integration of the power advantages and operating characteristics of different power sources, which is influenced by international emission regulations, energy-saving and emission reduction policies. As such, a series-parallel hybrid powertrain is introduced to the amphibious vehicle, and an innovative powertrain topology architecture is proposed. Meanwhile, the operation mode and energy efficiency characteristics are investigated during the working process. Firstly, the energy flow simulation model of a series-parallel gas-electric hybrid propulsion system is constructed using a modular modeling approach. Secondly, four operating modes, namely mechanical propulsion, electric propulsion, hybrid propulsion and charging mode, were formulated due to the fact that the propulsion system has multiple forms of power sources in the form of natural gas engine and reversible motor. Meanwhile, the energy flow states were investigated under different operating modes. Meanwhile, a comprehensive investigation of the energy efficiency associated with propulsion, storage and start-up energy was conducted for each specific mode. The results of the research indicated that the energy efficiency of the electric propulsion mode can reach up to 35.15 %, which is the gain from the wide operating range of the motor's high efficiency. The hybrid propulsion mode can obtain the highest energy efficiency of 35.88 %, which fully demonstrates the advantages of coordinating and complementing the two power sources, the natural gas engine and the reversible electric motor. This investigation also provides theoretical and empirical support for optimizing energy matching and formulating energy management strategies.

Penetration state recognition for tungsten inert gas welding via an alternating cusp-shaped magnetic field-assisted molten pool-oscillation

To ensure optimal penetration in direct current (DC) argon tungsten arc welding, a method was proposed to recognize the molten pool penetration during molten pool oscillation under alternating cusp-shaped magnetic field (ACSMF). An arc discharge model is established to analyze the oscillation mechanism of the molten pool under ACSMF. The periodic variation of arc shape induces the periodic oscillation to establish a mapping relationship with the fluctuation of arc voltage waveform. At the excitation current of 3 A and frequency of 10 Hz, the arc voltage waveform undergoes abrupt changes at 1.26 V and 1.37 V, corresponding to the critical and the full penetration states, respectively. The errors in identifying moving penetration are 0.8 % and 0.7 %, with a full penetration weld, demonstrating a penetration rate of 100 %, indicating effective penetration recognition. Arc sensing technology for tungsten inert gas (TIG) welding under ACSMF is poised for gradual application in single-side welding and double-side forming of medium and thick plates. It is anticipated to evolve towards real-time identification technology for molten pool penetration monitoring.

A Review of Exploration and Development Technologies for Coal, Oil, and Natural Gas

Energy is the fundamental prerequisite for human survival and development, as well as the driving force behind the progress of human civilization [...]