Hydrogen-compressed Natural Gas Research Articles

A LoRa-based safety monitoring system for hydrogen compressed natural gas (HCNG)

Abstract Hydrogen compressed with natural gas pipeline for gas mixture delivery is an effective way to realize large-scale, low-cost delivery of hydrogen. The Internet of Things (IoT) technology is one of the important supporting technologies for smart energy transformation, and the low power wide area network (LPWAN) represented by LoRa will play a key role. In this paper, a LoRa-based hydrogen compressed natural gas safety monitoring system is designed, which can collect, transmit, and analyze multiple types of data, such as ambient temperature and humidity, gas concentration, pipeline and equipment vibration, etc., and store the data and configure the alarm thresholds through the cloud server, and finally complete the real-time safety monitoring in the application layer. The system is characterized by high efficiency, high precision, low power consumption, and intelligence, which will have a positive effect on the safe transportation of hydrogen.

Performance analysis of combining solid oxide electrolysis cell hydrogen production and marine hydrogen compressed natural gas engine system

Natural gas holds promise as an alternative energy source for ships, and its combustion blended with hydrogen can achieve better beneficial of energy saving and emission reduction. Nevertheless, the current challenges in hydrogen, characterized by its high cost and difficulties in storage and transportation, hinder its application in maritime technology. To address the issue, this study proposes a system that integrates a marine hydrogen compressed natural gas (HCNG) engine, a supercritical carbon dioxide Brayton cycle (SCBC), and a solid oxide electrolysis cell (SOEC). In this system, SCBC is capable of recovering waste heat for electricity generation, while SOEC serves as an energy storage device to adjust engine load and enhance fuel economy. The generated hydrogen can be utilized as a source of hydrogen in HCNG fuel, thereby improving engine performance and reducing pollutant emissions. Various system numerical simulation schemes with different engine hydrogen volume fractions were studied. The results show that the electrical efficiency of SOEC is improved by 17.86% by heating the feed stream with engine exhaust gas. In addition, the hydrogen fraction in which SOEC can act as a complete hydrogen source ranges from 30% to 40%. The results of the sensitivity analysis show that the cycle efficiency reaches a peak of 31.5% at a compressor outlet pressure of 16 MPa, while the efficiency of the whole system reaches a maximum of 50.8% at 21 MPa. The optimal operating temperature for the SOEC falls within the range of 650–700 °C for the 30, 40 HCNG schemes, and between 750 and 800 °C for the 50, 60 HCNG schemes.

Comparative analysis of different heat transfer models, energy and exergy analysis for hydrogen-enriched internal combustion engine under different operation conditions

The implementation of hydrogen as a fuel in internal combustion engines is widely considered a favorable optimal due to its zero-carbon emissions and high energy content. Heat transfer from engine cylinder walls has a major role on engine combustion, performance and emission characteristics. In this study, heat transfer analysis conducted by different heat transfer models and identify the best model to analyse the energy and exergy analysis of hydrogen enriched internal combustion engine. A series of experiments were conducted on a compressed natural gas internal combustion engine across varying hydrogen fractions, EGR ratios, engine speeds and load conditions to capture in-cylinder pressure data and heat transfer rate. The authors compared six distinct models for heat transfer based on absolute percentage errors of maximum pressure and indicated mean effective pressure. These models systematically incorporated into a quasi-dimensional combustion model (QDCM) on MATLAB for hydrogen-compressed natural gas engine, accounting for diverse operating conditions. Convective heat transfer models, including Woschni, Nusselt, Hohenberg, Han, Eichelberg, and Assanis correlations were employed. Comparative analyses were undertaken to identify the most precise correlation for predicting engine in-cylinder pressure and heat transfer rates with experimental results across a broad spectrum of operational conditions. The Woschni model, as presented, is most suitable for the QDCM of the hydrogen-compressed natural gas fuel blend. This suitability is indicated by the close alignment of Taylor length and turbulent intensity coefficients to 1, as well as the minimal absolute percentage error observed for indicated mean effective pressure. It is also observed that heat transfer rate is increased by increasing the engine load 25 %, 50 %, 75 % and 100 % as 49.57 J/deg, 129.26 J/deg, 245.35 J/deg and 250.62 J/deg respectively and heat transfer rate is decreased by increasing the speed of engine 1100 rpm, 1200 rpm, 1500 rpm and 1700 rpm as 137.34 J/deg, 134.21 J/deg, 95.33 J/deg and 48.57 J/deg respectively. The energy and exergy analyses revealed that elevating the engine load corresponds to a reduction in exergy destruction. Brake energy increased 15 % by increasing the load conditions from 25 % to 100 % and decreased 7 % by increasing the speed from 1100 rpm to 1700 rpm. Another significant finding from this study is that the values of both energy and exergy efficiencies were 38.42 % and 40.12 % respectively obtained by thermodynamic analyses.

Hydrogen separation from hydrogen-compressed natural gas blends through successive hydrate formations

With hydrogen gaining prominence as a future decarbonization tool, the practice of “Hydrogen Blending” – the integration of hydrogen into natural gas pipelines – has swiftly emerged to curb carbon emissions. However, before hydrogen pipelines become widespread, in-depth research into “Hydrogen Deblending” – the separation of hydrogen from HCNG (Hydrogen-Compressed Natural Gas) – is essential to ensure the availability of pure hydrogen when required. In this context, our study introduces an innovative gas separation technique based on clathrate hydrates. Clathrate hydrates are crystalline inclusion compounds in which guest molecules are accommodated within the cage of water-framework constructed by hydrogen bonding. The water-based nature of clathrate hydrates enables a scalable and sustainable process for gas storage and separation. We propose an innovative gas separation system that utilizes successive hydrate formations to store natural gas within hydrates, while enhancing the purity of hydrogen in the vapor phase. Employing in-situ gas chromatography, we analyzed gas compositions at stage 1 of hydrate formation and quantified gas storage capacities (mmol/mol of water) for individual guest species. Our study confirmed that the designed successive hydrate formation could achieve around 79.32% of hydrogen recovery with a purity of 98.73%, demonstrating the viability of hydrate-based separation process.

Numerical investigation of performance, combustion, and emission characteristics of spark-ignition engine fuelled with compressed natural gas and hydrogen

The combustion of gasoline engines running on blends of compressed natural gas and hydrogen fuels was investigated using the quasi-dimensional and two-zone model. This model could investigate and predict the combustion characteristics, emissions, and performance parameters of petrol engines using MATLAB software. The impact of hydrogen inclusion to compressed natural gas on the cylinder temperature, pressure, cumulative work done, and heat transfer related to compressed natural gas was investigated. The engine’s thermal efficiency and output power were increased while specific fuel consumption was decreased when hydrogen was blended up to 20%. The highest decline in specific fuel consumption of 20% hydrogen was 25.1% for compressed natural gas. The torque values are 4.25, 4.34, 4.42, 4.51, and 4.60 N·m for compressed natural gas, hydrogen with compressed natural gas HCNG 5%, HCNG 10%, HCNG 15%, and HCNG 20%, respectively, at rated speed of 2500 r/min. The peak decreases in peak cylinder temperature and pressure for HCNG 20% compared to compressed natural gas are 5.9% and 5.2%, respectively. For HCNG 20%, the greatest cylinder pressure, temperature, and cumulative work done were 7.9 MPa, 2309.97 K, and 190.88 J, respectively. NO x emissions were increased for hydrogen-compressed natural gas blends but hydrocarbon emissions were decreased. In comparison to compressed natural gas, the highest hydrocarbon emission reduction is up to 2.64% for HCNG 20%. The model's validity was examined in comparison to the findings from the literature and the Diesel RK program. The results show that the MATLAB code is appropriate. Several alternative fuels can be used using this mathematical model.

How the cylinder initial conditions affect the HCNG refuelling process - A thermodynamic analysis to determine the most effective filling parameters

The hydrogen compressed natural gas (HCNG) blends play a key role in the European Hydrogen Roadmap targets achievement. The HCNG refuelling stations can be built up by upgrading the existing compressed natural gas stations. This work investigates the thermodynamic of HCNG refuelling processes to determine the impact on gas temperature due to the Joule-Thomson effect, heat transfer through the cylinder wall, the kinetic energy conversion in internal energy, and compression contribution during the fast fill-up. Specifically, the vehicle tank initial conditions and the refuelling parameters have been analysed, evaluating how they affect the final refuelling temperatures, filled mass, relative states of charge, and refuelling times. With an average pressure ramp rate of 0.18 MPa/s, at initial cylinder conditions of 10 °C and 9 MPa, the 0.065 m3 and 0.15 m3 tanks reach a SOC of 93.83% and 65.32% and final temperature of 82.5 °C and 44.5 °C, respectively.

Ensuring natural gas infrastructure is suitable for hydrogen service

AbstractThis paper compares hazard and risk factors related to transporting hydrogen in natural gas pipelines. Properties of hydrogen‐compressed natural gas (HCNG) blends and typical materials for the construction of transmission and distribution systems are evaluated to address the key properties that might impact hazard and risk factors. ASME (American Society of Mechanical Engineers) standards B31.8 and ASME B31.12 are reviewed for key differences applicable to HCNG blends. A methodology to identify compliance gaps and mitigate deficiencies if HCNG blends are transported in natural gas transportation systems is proposed.

Investigation on a diesel engine fueled with hydrogen‐compressed natural gas and Kusum seed biodiesel: Performance, combustion, and emission approach

AbstractThe objective of the present study is to evaluate the performance, combustion, and emission characteristics of a compression‐ignition engine using hydrogen‐compressed natural gas (HCNG)‐enriched Kusum seed biodiesel blend (KSOBD20). The flow rate of HCNG was set at 5, 10, and 15 liters per minute (lpm), and the injection pressure was varied in the range of 180–240 bar. Brake thermal efficiency (BTE) and brake‐specific fuel consumption (BSFC) were improved when HCNG was added to the KSOBD20. Combustion characteristics, namely, cylinder pressure (CP) and net heat release rate (NHRR), were also improved. Emissions of carbon monoxide (CO), hydrocarbons (HC), and smoke were also reduced, with the exception of nitrogen oxides (NOx). The higher injection pressure (240 bar) had a positive effect on operating characteristics. At an injection pressure of 240 bar, for KSOB20 + 15 lpm HCNG, the highest BTE and the lowest BSFC were found to be 32.09% and 0.227 kg/kWh, respectively. Also, the CP and NHRR were 69.34 bar and 66.04 J/deg. CO, HC, and smoke levels were finally reduced to 0.013%, 47 ppm, and 9%, respectively, with increased NOx levels of 1623 ppm. For optimum results in terms of engine characteristics, the fuel combination KSOBD20 + 15 lpm HCNG at fuel injection pressure 240 bar is recommended. Thus, HCNG‐enriched KSOBD20 can be used as an alternative fuel in diesel engines without requiring any modifications to increase performance and reduce emissions.

Environmental Economical Dispatching of Electric–Gas Integrated Energy System Considering Hydrogen Compressed-Natural Gas

As a high-quality secondary energy, hydrogen energy has great potential in energy storage and utilization. The development of power-to-hydrogen (P2H) technology has alleviated the problem of wind curtailment and improved the coupling between the power grid and the natural gas grid. Under the premise of ensuring safety, using P2H technology to mix the produced hydrogen into the natural gas network for long-distance transmission and power generation can not only promote the development of hydrogen energy but also reduce carbon emissions. This paper presents a new model for incorporating hydrogen into natural gas pipelines. To minimize the sum of wind curtailment cost, operation cost and carbon emission cost, an electric–gas integrated energy system (EGIES) model of hydrogen-compressed natural gas (HCNG) containing P2H for power generation is constructed. Aiming at the problem of global warming caused by a lot of abandoned wind and carbon emissions, the economy and environmental protection of the system model are analyzed. The results show that the model of EGIES considering HCNG can not only absorb excess wind power but also reduce carbon emission costs and system costs, which can reduce the total cost of the environmental economic dispatch of the EGIES by about 34.1%. In the context of the EGIES, the proposal of this model is of great significance to the economical and environmentally friendly operation of the system.

Green Hydrogen-Compressed natural gas (bio-H-CNG) production from food waste: Organic load influence on hydrogen and methane fusion

Biogenic hydrogen (bioH2) enriched compressed natural gas (bio-H-CNG or biohythane) is emerging interest due to its feasibility to use in the existing transportation infrastructure with induced environmental benefits. This study evaluated the production of bioH2and biomethane (bioCH4) towards bio-H-CNG formation at a varying organic load (OL: 30,40,50 g COD/L) of food waste (FW). Acidogenic reactor operated with FW at 40 g COD/L showed the highest cumulative bioH2production while elevated OL (50 g COD/L)showedhigher cumulative bioCH4production (CMP: 11.92 L) from the methanogenic reactor. BioH2 and bioCH4 produced at different time intervals were combined to assess bio-H-CNG. The nature of biocatalyst and OLsignificantly regulated the composition of bio-H-CNG varying between 0.1 and 0.3 of H2/(H2+CH4) ratio accounting for5–12.6 kJ/g COD. Chain elongation, converting short (C2-C4) to medium-chain fatty acids(Caproic acid,1.16 g/L) was specifically observed during the acidogenic process.

Experimental optimization of engine performance of a dual-fuel compression-ignition engine operating on hydrogen-compressed natural gas and Moringa biodiesel

Non admixed Natural gas-fuelled diesel engines are usually associated with harsh engine emissions as well as low performances at moderate to high engine loads. However, the use of Moringa biodiesel as additive in hydrogen-compressed natural gas (HCNG) is a viable novel strategy for reducing toxic emissions such as hydrocarbons and nitrogen oxides in CI engines. In this study, five hybrid HCNG–Moringa biodiesel (MB) oil samples labelled A–E were analysed for their abilities to improve the overall performance of a CI engine (Petter PH1W diesel engine). The fuels had a fixed volume by volume hydrogen : carbon ratio of 87:13% respectively, and the HCNG–MB hybrid samples consisted of 0, 5, 7, 10 and 13 %v/v MB for samples A, B, C, D and E, respectively. At higher engine loads (i.e. 58%–100%), the engine performance improved thus giving higher BTEs in the range of 19–33.9% for all the fuel blends relative to the BTE (15.1%–19%) of the unblended HCNG fuel; this confirms the suitability of MB as an additive for improving the brake thermal efficiency of CI engines; there were also reductions in HC, O2, CO2, CO and NOx emissions for all the MB–HCNG fuels relative to the case of the unblended HCNG fuel. At optimum condition, the fuel that gave the best results in terms of the aforementioned engine characteristics is the MB–HCNG fuel blend having 10% MB.

Optimized operation method of small and medium-sized integrated energy system for P2G equipment under strong uncertainty

This paper studies an Integrated Energy System (IES) and the application of Hydrogen Compressed Natural Gas (HCNG) and Power to Gas (P2G) equipment in IES. Based on the C&CG algorithm, this paper establishes a two-stage robust optimization(TRO) model of the system operating in uncertain environments. Introducing HCNG and P2G equipment into IES can improve the system’s ability to accommodate renewable energy, reduce system operation cost and reduce interaction fluctuation between the system and the main grid. Robust optimization can effectively reduce the risk of system operation in uncertain environments and improve the stability of system operation. Under the compensation of the real-time market, the financial performance of the robust optimization model is better than the deterministic optimization model according to the numerical simulation. This study is helpful to the study of the operation and scheduling of IES in remote areas with weak power system infrastructure and abundant renewable energy resources.

Development of hydrogen-compressed natural gas blend engine for heavy duty vehicles

Natural gas fuel, as an alternative energy source of transportation, has been used widely since it has an advantage of low emission levels. However, new technologies are required in order to meet the reinforced emission regulations. For this purpose, research into the development of hydrogen-compressed natural gas (HCNG) blend engine was carried out to evaluate its feasibility and emission characteristics. The Engine Research Department at the Korea Institute of Machinery and Materials carried out a large number of tests based on various parameter changes that could affect the performance and emission of HCNG engine in different operating conditions. An earlier stage of the research project focused on the lean combustion of a HCNG engine for heavy duty vehicles to meet the EURO-VI standards. An 11-L/6-cylinder CNG engine was used for the test. The effects of the excess air ratio change were assessed based on various content ratios of hydrogen in the natural gas fuel. In the later part of the HCNG research, a stoichiometric mixture operation was suggested to meet reinforced emission regulation without requiring a De-NOx system. Additionally, an exhaust gas recirculation (EGR) system was introduced for the purpose of improving thermal efficiency and durability. The optimal operating conditions were selected to achieve the best thermal efficiency to meet the required emission levels. In this paper, we demonstrate that a HCNG engine can achieve a significant decrease in NOx emissions, as compared to that of a CNG engine, while meeting the requirements of the EURO-VI standards during a transient mode cycle test. EGR can suppress the weakness of stoichiometric mixture combustion strategy, such as the deterioration of the durability and thermal efficiency, while the emission level can be lowered with the use of a three-way catalyst. The possibility of further reduction of emissions and CO2 with EGR was evaluated to access practical application of a HCNG engine in the field. From that evaluation, the HCNG engine with stoichiometric mixture operation for heavy duty vehicles was developed. The emission levels of HCNG engine were 50 % lower when compared to the EURO-VI standards with a greater than 10 % decrease in CO2 compared to that of a natural gas engine.

Reduced-order modellin for high-pressure transient flow of hydrogen-natural gas mixture

In this paper the transient flow of hydrogen compressed-natural gas (HCNG) mixture which is also referred to as hydrogen-natural gas mixture in a pipeline is numerically computed using the reduced-order modelling technique. The study on transient conditions is important because the pipeline flows are normally in the unsteady state due to the sudden opening and closure of control valves, but most of the existing studies only analyse the flow in the steady-state conditions. The mathematical model consists in a set of non-linear conservation forms of partial differential equations. The objective of this paper is to improve the accuracy in the prediction of the HCNG transient flow parameters using the Reduced-Order Modelling (ROM). The ROM technique has been successfully used in single-gas and aerodynamic flow problems, the gas mixture has not been done using the ROM. The study is based on the velocity change created by the operation of the valves upstream and downstream the pipeline. Results on the flow characteristics, namely the pressure, density, celerity and mass flux are based on variations of the mixing ratio and valve reaction and actuation time; the ROM computational time cost advantage are also presented.

Experimental validation of accuracy of dynamic hydrogen-compressed natural gas mixing system using a single cylinder spark ignition engine

Natural gas is considered as one of the best alternate fuels because of its lower emissions and highest H/C ratio amongst hydrocarbons. Its usage requires minimum modifications in the existing engine hardware. Addition of hydrogen to the compressed natural gas (CNG) improves its combustion, performance and emission characteristics. In the present study, a compression ignition (CI) engine was modified to operate on hydrogen enriched compressed natural gas (HCNG) mixtures using port fuel injection in spark ignition (SI) mode. HCNG engine technology is not widespread and HCNG is not available commercially hence there is need of developing an online HCNG mixing system, which can deliver desired HCNG compositions dynamically on demand so that a wide range of experiments can be carried out to determine the optimum mixture composition. Very few researchers have made efforts to develop such a system and because of lack of such a system, majority of HCNG investigations are confined to 3–4 premixed HCNG mixtures. In this study, a dynamic HCNG mixing system was developed for producing different HCNG mixtures. The working of this dynamic mixing system was validated on a single cylinder SI engine for its performance and accuracy in delivering desired HCNG compositions. Experiments were performed for comparing combustion, performance and emission characteristics of dynamic HCNG mixtures with premixed blends, prepared using conventional method, employing Dalton's law of partial pressures. Results showed satisfactory performance of the dynamic mixing system at all engine loads. The HCNG mixture quality was the best at higher engine loads.

Performance, Combustion and Emission characteristics of a Manifold Injected HCNG-Biodiesel Dual Fuel Operation / Bir Manifolda Enjekte Edilen HCNG-Biyodizelin Çift Yakıtlı Çalışmasının Performans, Yanma ve Emisyon Karakteristikleri

Vehicular exhaust emission control and engine efficiency are the most important parameters in current engine design. The Euro V emission norms aredirecting the research towards developing new technologies for combating engine emissions. Natural gas has become a widely used alternative fuel due to its many advantages including its ready availability and its low emission levels. Addition of hydrogen in CNG improves the composition and properties of base fuel CNG. In the present work adiesel engine was converted to operate in dual fuel engine mode in which Hydrogen-compressed natural gas (HCNG) was injected into the intake manifoldusing a specially developed electronic control unit (ECU) while diesel/biodiesel was injected directly inside the combustion chamber during the compression stroke. Experimental investigations were then carried out on a single cylinder four stroke CI engine test rig operatedin dual fuel mode using Diesel, Honge methyl ester (HOME),Jatropha methyl ester (JOME)as injected pilot fuels and HCNG as injectedprimary fuel.ECU was used for varying the injectiontimings and injection durations for HCNG injection while the optimum injection timing for diesel/biodieselwas maintained at 27°bTDC.The pilot fuel injection pressure was maintained at 230 bar. Engine was operated with constantcompression ratio of 17.5 and HCNG flow rate was maintained at 0.5kg/h. The experimental results showedthat an injection timing of 5obTDC and injection duration of 40obTDCfor HCNG injection was found to be optimum based on the improved performance, combustion and emission characteristics. The brake thermal efficiency formanifold injected HCNGdual fuel operation with diesel, HOME and JOME at 80% load was found to be 28.1%, 27.2% and 26.2% respectively. The Smoke emissions, Carbon monoxide (CO), Carbon dioxide (CO2) emissions were found to be lesser with aninjection timing of 5obTDC and injection duration of 40o bTDCin HCNG injected dual fuel operation.The use of HCNG manifold injection in the dual fuel operatedCI engine improves the performance and reduces the exhaust emissions from the engine except for HC and NOX emissions.

운전조건 변화가 HCNG 엔진용 삼원촉매 전환효율에 미치는 영향

Abstract - Stoichiometric combustion engine with Three-way catalyst had an advantage that can reduce the harmful emissions effectively. Fuel equivalence ratio controlled from engine is very important because Fuel equivalence ratio with high conversion efficiency was narrow. This study analyzed the conversion efficiency under whole range of operating area for to evaluate the performance of three-way catalyst. In order to identify the Optimum conversion efficiency, the conversion efficiency due to change the control value of fuel equiv-alence ratio was investigated. The result show that conversion efficiency of emissions(more than 95%) has dis-covered by means of fuel equivalence ratio control at each test condition. As engine power increases, optimal fuel equivalence ratio tended to increase linearly under operating conditions of similar exhaust gas temperature. Key words : HCNG(Hydrogen- Compressed Natural gas Blends), stoichiometri c, TWC(Three-way Catalyst), conversion efficiency, equivalence ratio

HCNG용 수소제조장치 실험 및 결과분석

Pollution emission control of the 20th century, for transportation energy, are being enhanced, and then as alternative to this, because hydrogen emit only water gas emissions to be environmentally friendly energy, so hydrogen as a sustainable clean energy is in the limelight. Used in compressed natural gas engines to mix hydrogen and natural gas in both domestic and international technology development and demonstration is being carried out. The hydrogen-compressed natural gas(HCNG) charging infrastructure can be used to build a hydrogen infrastructure in the transitional aspects of a future hydrogen economy society. In this paper, for a demonstration of HCNG charging infrastructure we made and operated a <TEX>$30Nm^3/h$</TEX> hydrogen generating unit and analyzed the result of the operation. We was identified the operating conditions of a reforming reactor and water gas shift reactor from an analysis result, the thermal efficiency was calculated according to the operating conditions of the total hydrogen production process.

수소-천연가스엔진에서 밸브오버랩 감소가 배기특성에 미치는 영향

현행 배기가스규제인 유로6을 대응하기 위해선 질소산화물과 메탄의 배출량을 크게 저감시켜야 하는 실정이다. 본 연구에서는 부분부하운전조건에서 밸브오버랩 감소가 수소-천연가스엔진의 연소 및 배기특성에 미치는 영향을 살펴보았다. 각 연료와 기존캠 및 밸브오버랩이 감소된 변경캠에 대하여 연소 및 배기특성을 분석하였다. 실험결과 변경캠을 사용하였을 때 열효율이 감소하고 연료유량이 증가하였다. 열효율 감소로 인하여 메탄과 이산화탄소의 배출량은 증가하였다. 희박한 운전조건에서 질소산화물 배출량은 기존캠 대비 감소하였다. 동일한 연료 및 운전조건에서는 효율과 배기특성에 악영향을 미치는 것을 알 수 있었다.

Full load performance and emission characteristics of hydrogen-compressed natural gas engines with valve overlap changes

Natural gas vehicle engines are preferred over diesel engines because they release significantly lower amounts of nitrogen oxides (NOx) and carbon dioxide emissions. Hydrogen-compressed natural gas (HCNG) technology is a promising alternative to that used in conventional compressed natural gas engines because hydrogen possesses stable lean combustion characteristics. Although the NOx emissions requirements are satisfied, methane emissions must be filtered using an oxidation catalyst. An alternative is required for methane reduction because improving the conversion efficiency of methane is expensive. In this study, the strategy of varying the valve overlap was employed to reduce methane emissions. Although a torque valve cannot meet engine emission specifications, the hydrocarbon and methane emissions were reduced by approximately 41% by decreasing the valve overlap duration while using HCNG fuel. The level of NOx emissions was approximately equivalent to or slightly higher than that of a conventional camshaft.