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The application of compressed natural gas (CNG) as fuel for compression ignition (CI) engines under dual-fuel (DF) mode operation is not attempted in countries like India for commercial purposes. A commercial heavy-duty turbocharged six-cylinder common-rail direct-injected diesel engine has been converted into a DF mode of operation using CNG and diesel for its potential usage and study on its performance along with Selective Catalytic Reduction (SCR). CNG is inducted through the intake manifold at varying energy substitution rates (ESR) with a flow rate of 0.67-1.54 kg/h while diesel fuel is controlled through the engine electronic control unit (ECU). For a maximum ESR of 10.2% with CNG, an increase in power by 8.9% and a 5.8% increase in torque were observed. While there was an increase in brake thermal efficiency (BTE), volumetric efficiency marginally decreased, therefore, to have higher brake power with a DF engine, a dedicated turbocharging system is necessary. The brake-specific energy (BSEC)/fuel consumption (BSFC) has marginally reduced by 1%, and optimum engine speed for better fuel economy was in the range of 1250-2250 rpm. The brake-specific carbon monoxide (BSCO) and carbon dioxide (BSCO₂) emissions have considerably reduced while brake-specific non-methane hydrocarbon (BSNMHC), oxides of nitrogen (BSNOx), and methane (BSCH₄) emission was marginally higher with CNG substitution; however, within Euro 4 emission norms. Unregulated emissions like ammonia (NH₃), propane, and sulfur dioxide (SO₂) have reduced while formaldehyde, acetylene, ethylene, and formic acid have marginally increased. SCR has been useful in reducing mass emissions out from the diesel engine and in conversion.

This study presents a comparative analysis of energy consumption and gaseous emissions from a compressed natural gas (CNG)-fueled vehicle under real driving emissions (RDE) conditions and values predicted using machine learning (ML) models developed from chassis dynamometer data. The analyzed components included energy consumption (EC) as well as carbon dioxide (CO ), carbon monoxide (CO), total hydrocarbons (HC), methane (CH ), and nitrogen oxides (NO ). The models were trained using a limited set of easily accessible predictors, namely vehicle speed and acceleration. A hybrid modelling approach was proposed, combining laboratory data with validation under real-world conditions. Additionally, road load power ( ) was introduced as a novel predictor representing vehicle operating load. The results demonstrate that the models effectively capture emission trends, with the highest agreement obtained for CO, CO . The inclusion of improved prediction accuracy, which increased from approximately 64% to 71% for CO and from 57% to 61% for HC. For CO , the model achieved about 80-82% agreement with RDE measurements, with analogous levels obtained for EC. A key advantage of the proposed methodology is its reliance on a limited number of input variables, which enhances practical applicability while maintaining satisfactory accuracy. Furthermore, the use of precise laboratory data improves model robustness, and the approach enables the estimation of methane (CH ), which is typically not measured by standard portable emissions measurement systems (PEMSs). The results confirm the effectiveness of the hybrid ML framework and highlight the importance of incorporating load-related parameters in real-world emissions and energy consumption modeling.

Compressed Natural Gas (CNG) is a promising alternative fuel for application in diesel engines operating on dual-fuel mode. However, its application for a commercial heavy-duty engine has been limited due to difficulty in modification and in altering the engine control unit (ECU) settings. In this investigation, an attempt has been made to optimize the CNG flow rate for different speed and load conditions for operating a commercial heavy-duty turbocharged intercooled engine under diesel- CNG dual fuel based on engine performance and emission parameters on an eddy current engine dynamometer. CNG was inducted through the intake manifold at varying mass flow rates of 0.65-4.0 kg/hr for different speed and load conditions while operating the engine at the Speed/ Torque (NT) mode of the dynamometer-engine control. The results show that diesel-CNG dual fuel (DDF) has better performance in terms of power, brake thermal efficiency, volumetric efficiency (VE), and exhaust temperature, making it suitable for commercial usage. While for regulated mass emissions like carbon monoxide (CO), total hydrocarbon (THC), and NOx, though DDF has shown higher emission compared to normal diesel, certain CNG flow rates were within the Euro 4 emission limit. Based on different criteria including engine performance and emissions, a matrix of CNG flow rates between 0.65 kg/hr and 3.0 kg/hr suitable for different loads and speeds has been optimized for the diesel engine.

Compressed natural gas (CNG) is a promising alternative fuel for compression ignition (CI) engines under dual━fuel (DF) mode operation. Its application on commercial heavy━duty multicylinder diesel engines is scarcely reported, and its potential usage is investigated through a research study. The focus of this research was to study the in━cylinder combustion and its effect on emissions with an increasing energy fraction of CNG at different speeds (1000 rpm━2500 rpm) and load conditions (Speed━Torque mode), inducted through the intake manifold at different mass flow rates ranging from 0.67 kg/h to 4.0 kg/h corresponding to an energy substitution rate (ESR) of 1.9%━60.2% while using diesel as pilot fuel. In━cylinder pressure, heat release rate (HRR), and pressure rise rate (PRR) increased with the increase in CNG mass flow rate (CMFR). Combustion duration is prolonged under diesel━CNG DF (DDF) mode while ignition delay (ID) is reduced with an increase in CNG flow rate. Carbon monoxide (CO) and total hydrocarbon (THC) emissions reduced with a longer fuel burn rate (FBR), combustion duration, and diesel injection duration (DID), and was lower at higher indicated mean effective pressure (IMEP) alternately; nitric oxides (NOx) and carbon dioxide (CO₂) emission were lower at shorter above combustion parameters. The combustion characteristics of DDF engines and their effect on emission performance have been studied and used for the optimization of the heavy━duty diesel engine.

Hydrogen, an emerging low-carbon energy carrier, is pivotal for high-penetration renewable energy and integrated energy systems, yet the coupling of hydrogen with electricity and gas for hydrogen production and enriched compression-integrated systems remains a key issue for energy transition. This study establishes the architecture and analyzes the energy flow of an urban hydrogen production and enriched compressing-integrated energy system, as well as models its hydrogen production-enriched compressing, power, and hydrogen-enriched compressed natural gas subsystems based on water electrolysis, hydrogen storage, hydrogen fuel cells (HFCs), and hydrogen-enriched compressed natural gas (HCNG) technology, and develops a low-carbon optimal scheduling model with demand response to minimize intraday economic dispatch costs. Scenario comparisons verify the model’s effectiveness, showing that the system boosts wind-solar utilization by 6.81% and cuts carbon emissions by 1.89%.

Compressed natural gas (CNG) taxis represent the most ubiquitous and dynamically active passenger vehicles in urban settings. The pollutant emission characteristics of in-use CNG taxis driving on a typical mountain city before and after three-way catalyst (TWC) replacement was examined using a modular on-board portable emissions measurement system (PEMS), the OBS-ONE developed by Horiba. The results showed that the exhaust NO of CNG taxis equipped with deactivation TWC exceeded the emission limits, even higher than gasoline vehicles. The high emission rate of CNG taxis is mainly concentrated on road slopes between a 2% and 6% gradient and a deceleration rate in the interval of [0.5, 4], respectively, which results in higher emissions from CNG taxis traveling in the mountain city of Chongqing than other cities and vehicles. Moreover, the pollutant emission rates of the in-use CNG taxis were highly correlated with the velocity and the vehicle specific power (VSP). After a new TWC replacement, the emission factors of carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NOx), and particle number (PN) decreased by 85.21–89.11%, 68.71–85.49%, 60.91–81.11%, and 62.26–68.39%, respectively. Our results will provide guidance for urban environments to carry out the comprehensive management of in-use vehicles and emphasize the importance of TWC replacement for CNG taxis.

Transporting green hydrogen by existing natural gas networks has become a practical means to accommodate curtailed wind and solar power. Restricted by pipe materials and pressure levels, there is an upper limit on the hydrogen blending ratio of hydrogen-enriched compressed natural gas (HCNG) that can be transported by natural gas pipelines, which affects whether the natural gas network can supply energy safely and reliably. To this end, this paper investigates the effects of the intermittent and fluctuating green hydrogen produced by different types of renewable energy on the dynamic distribution of hydrogen concentration after it is blended into natural gas pipelines. Based on the isothermal steady-state simulation results of the natural gas network, two convection–diffusion models for the dynamic simulation of hydrogen injections are proposed. Finally, the dynamic changes of hydrogen concentration in the pipelines under scenarios of multiple green hydrogen types and multiple injection nodes are simulated on a seven-node natural gas network. The simulation results indicate that, compared with the solar-power-dominated hydrogen production-blending scenario, the hydrogen concentrations in the natural gas pipelines are more uniformly distributed in the wind-power-dominated scenario and the solar–wind power balance scenario. To be specific, in the solar-power-dominated scenario, the hydrogen concentration exceeds the limit for more time whilst the overall hydrogen production is low, and the local hydrogen concentration in the natural gas network exceeds the limit for nearly 50% of the time in a day. By comparison, in the wind-power-dominated scenario, all pipelines can work under safe conditions. The hydrogen concentration overrun time in the solar–wind power balance scenario is also improved compared with the solar-power-dominated scenario, and the limit-exceeding time of the hydrogen concentration in Pipe 5 and Pipe 6 is reduced to 91.24% and 91.99% of the solar-power-dominated scenario. This work can help verify the day-ahead scheduling strategy of the electricity-HCNG integrated energy system (IES) and provide a reference for the design of local hydrogen production-blending systems.

Because of their direct contact with society, urban buses are prioritized targets for air quality improvement. In this study, a sample group of in-use urban old buses powered by compressed natural gas (CNG) and diesel engines was chosen for particle emission analysis. The CNG buses do not have any type of after-treatment, while diesel ones are equipped with a diesel particulate filter (DPF). To measure the lung deposited surface area (LDSA), a possible physical metric of exhaust particles’ toxicity, a diffusion charger-based analyzer was utilized. The measurements were done at different engine speeds in stationary conditions. The results revealed that although the particle mass emission of CNG buses remains at a low level, the number of emitted particles for 75% of the CNG buses (depending on their maintenance conditions) is 10 to 100 times more than the retrofitted diesel ones, with the range of 10 6 to 10 7  p/cm 3 . The rest 25% of the CNG buses were performing the same as the retrofitted diesel ones in terms of exhaust particle number in the range of 10 5  p/cm 3 . In addition, the lowest LDSA parameter at low idle engine speed was measured to be 97.8 and 229.4 μm 2 /cm 3 for a CNG and a DPF retrofitted diesel bus, respectively. This result indicates the same and even lower LDSA and surface area and thus the lower possible toxic potentiality of exhaust particles of CNG buses compared to diesel vehicles at DPF downstream. Investigation on the different behavior of the CNG buses in the emission of particles showed the correlation of some aging parameters such as lubricant oil aging mileage with the released particles and the importance of periodic maintenance interval. Graphical abstract

The article analyzes the modern theory and practice of transportation and storage of compressed natural gas. The expediency of the inclusion of a floating storage berth for the loading of gas carriers and container ships into the infrastructure of marine transportation of compressed natural gas is considered. Requirements for storage berth are formulated. It is shown that without using a marine mooring storage facility, the loading time of a gas carrier will considerably increase, and the economic efficiency of compressed gas transportation will lower due to the considerable time of loading and unloading of a gas carrier. The construction of a storage berth is proposed, and calculations of storage parameters and calculation of its buoyancy are made. The possibility of using the REFPROP vs. 9.1 software package to automate the selection of the composition of a multicomponent hydrocarbon mixture for further use at the selected range of temperatures and pressures is substantiated. The use of the system is considered in the example of phase equilibrium of a multicomponent hydrocarbon mixture.

Metal hydrides are an interesting group of chemical compounds, able to store hydrogen in a reversible, compact and safe manner. Among them, A2B7-type intermetallic alloys based on La-Mg-Ni have attracted particular attention due to their high electrochemical hydrogen storage capacity (∼400 mAh/g) and extended cycle life. However, the presence of Mg makes their synthesis via conventional metallurgical routes challenging. Replacing Mg with Y is a viable approach. Herein, we present a systematic study for a series of compounds with a nominal composition of La2-xYxNi6.50Mn0.33Al0.17, x = 0.33, 0.67, 1.00, 1.33, 1.67, focusing on the relationship between the material structural properties and hydrogen sorption performances. The results show that while the hydrogen-induced phase amorphization occurs in the Y-poor samples (x < 1.00) already during the first hydrogen absorption, a higher Y content helps to maintain the material crystallinity during the hydrogenation cycles and increases its H-storage capacity (1.37 wt.% for x = 1.00 vs. 1.60 wt.% for x = 1.67 at 50 °C). Thermal conductivity experiments on the studied compositions indicate the importance of thermal transfer between powder individual particles and/or a measuring instrument.