Natural Gas Hydrogen Blends Research Articles

Energy storage and multi energy systems in local energy communities with high renewable energy penetration

Abstract This study investigates how a district with a high capacity of non-controllable renewable electricity generation can entirely self-consume its production at a community level either directly or for heating and cooling, thus potentially fulfilling the concept of Renewable Energy Community. It investigates the potential role of storage systems and polygeneration in renewables self-consumption, by also exploiting the synergies among different energy networks in a real residential district with high PV penetration. Two scenarios were modeled other than the baseline: the first one evaluating the optimal portfolio of energy conversion and storage technologies, and a second one achieving the same goal only using batteries. Both scenarios proved to be a viable solution to exploit the excess of electricity production from the PV plants in the district only through local self-consumption. The results show that a multi-energy system is the most cost-effective solution in doing so, exploiting polygeneration technologies (CHP) and the storage of energy as thermal, electrical, and chemical through power-to-gas. In particular, the least cost solution entails a 42 kWe CHP micro gas engine fueled by a natural gas-hydrogen blend, a 135 kWh battery system, and a 2830 kWh hydrogen storage.

A comprehensive study on using new hydrogen-natural gas and ammonia-natural gas blends for better performance

This study presents a novel configuration using the hydrogen-natural gas and ammonia-natural gas blends for practical applications and investigates the system performance comprehensively. Natural gas is blended with hydrogen and ammonia to investigate performance improvement. Wind energy source is employed to the proposed configuration for power generation using wind turbines. The power generated by the wind turbine is employed to the proton exchange membrane (PEM) electrolyser for hydrogen production. A part of hydrogen is employed to the PEM fuel cell for power production. The proposed system is used to investigate the effect of hydrogen and ammonia blends with natural gas to achieve better performance. In order to investigate the H2-CH4 blends, a part of the produced hydrogen is supplied to the mixing chamber from the hydrogen storage tank while ammonia input is supplied to the mixing chamber to improve the performance under NH3-CH4 blends. The results revealed that the combustion energy and exergy efficiencies increase from 84.8% to 94.8% and 62.5%–70.2% respectively and the overall energetic and exergetic efficiencies increase from 37.4% to 40.3% and 36.8%–39.8% respectively with hydrogen addition from 0 to 20%. In the case of ammonia-natural gas blends, the combustion energy and exergy efficiencies increase from 84.8% to 92.9% and 58.9%–64.4% respectively and overall energetic and exergetic efficiencies increase from 37.4% to 39.1% and 36.8%–38.5% respectively.

Performance investigation of adding clean hydrogen to natural gas for better sustainability

This paper presents a novel system of adding clean hydrogen to the natural gas for more effective and more efficient combustion. The proposed system includes a wind-photovoltaic hybrid system where both wind and solar energy sources are simultaneously utilized. A partial amount of electrical power produced by the wind turbines, PEM fuel cell and PV array is fed to the PEM electrolyser while the additional electricity is supplied to the community for use. In the hydrogen-natural gas blends, the fraction of hydrogen is taken from 0% to 20%, respectively, and the natural gas is reduced from 100% to 80% simultaneously to explore hydrogen addition effect in the combustion process. Although natural gas is cleaner than other fossil fuels, adding hydrogen to the natural gas makes it much cleaner and more environmental friendly. The blends of natural gas and hydrogen helps increase the combustion efficiency, decrease oxygen and reduce the emissions, in particular CO2. The results further reveal that the energetic efficiency of the combustion unit rises from 84.83% to 94.83% while the exergetic efficiency rises from 62.52% to 70.16% with the rise in hydrogen fraction from 0% to 20%. It is also found that the CO2 emissions decrease with the rise in hydrogen fraction in hydrogen-natural gas blends.

Hydrogen-natural gas combustion in a marine lean-burn SI engine: A comparitive analysis of Seiliger and double Wiebe function-based zero–dimensional modelling

With increasingly stringent emission regulations, marine natural gas engines need to improve their performance. Various proven advantages of hydrogen-natural gas (H-NG) blends make them a promising enhanced fuel solution. Although modelling of H-NG combustion has been investigated before, mostly using CFD models, the literature on the modelling capabilities of Seiliger-based and Wiebe-based zero-dimensional (0-D) models is limited for H-NG combustion. Especially for the application of marine lean-burn spark-ignited (SI) engines. Therefore, the aim of this paper is to compare the capabilities of Seiliger-based and double Wiebe function-based 0-D models to capture H-NG combustion in a marine SI engine for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads.In this work, measurements on a turbocharged, SI marine natural gas engine were used to develop a heat release rate model, which was subsequently used as a basis for the Seiliger and double Wiebe function-based H-NG combustion characterization models. Results from the two combustion modelling approaches were compared for different H-NG fuel blends, engine leaning (lean-burn operation) and engine loads. The modelling results were also compared against engine measurements for different experimental conditions.This paper shows that the Seiliger modelling approach can be used to define different physical phenomenon in H-NG combustion, while accurately capturing the effects of hydrogen addition and engine leaning on the H-NG combustion process at varying engine loads. This research also found that the variations in late burn phase present in lean-burn NG and H-NG combustion can be captured using the double-Wiebe modelling approach, however, clear trends of the Wiebe combustion parameters for varying fuel blends and engine loads could not be identified to accurately capture the H-NG combustion process. Furthermore, Wiebe-based modelling approach produced larger errors in the estimations of work output and combustion heat for all test conditions.

On the possibility to simulate the operation of a SI engine using alternative gaseous fuels

A thermodynamic combustion model developed in AVL BOOST software was used in order to evaluate the pollutant emissions, performance and efficiency parameters of a spark ignition engine Renault K7M-710 fueled with compressed natural gas, hydrogen and blends of compressed natural gas and hydrogen (hythane). Multiple research studies have concluded that for the near future hythane could be the most promising alternative fuel because it has the advantages of both its components. In our previous work the model was validated for the performance and efficiency parameters by comparison of simulation results with experimental data acquired when the engine was fueled with gasoline. In this work the model was improved and can predict the values of pollutant emissions when the engine is running with the studied alternative fuels. As the percentage of hydrogen in hythane is increased, the power of the engine rises, the brake specific fuel consumption, carbon dioxide, carbon monoxide and total unburned hydrocarbon emissions decrease while nitrogen oxides increase. The values of peak fire pressure, maximum pressure derivative and peak fire temperature in cycle are higher, leading to an increased probability of knock occurrence. To avoid this phenomenon an optimum correlation between the natural gas-hydrogen blend, the air-fuel ratio, the spark advance and the engine operating condition needs to be found.

The correlation between the cylinder pressure and the ion current fitted with a Gaussian algorithm for a spark ignition engine fuelled with natural-gas–hydrogen blends

An investigation was conducted of the ion current characteristics at various excess air ratios λ in a spark ignition engine fuelled with natural-gas–hydrogen blends. The Gaussian mathematical method was employed to fit the pure ion current signal without a spark tail generated by the ignition discharge. The cylinder pressure was recorded, and the Pauta criterion static threshold was used to deal with the outlier errors in the testing data for given cycles. The results show that the spark tail and the ion current can be separated by fitting the ion current with the Gaussian method, and the fitted pure ion current includes the flame-front stage and the post-flame stage. The timing with respect to the flame-front peak exhibits an irregular variation with λ. The maximum current in the flame-front stage increases with increasing λ.The timing of the maximum current in the post-flame stage occurs earlier at the stoichiometric ratio than at other air-to-fuel ratios. The correlation coefficient between the ion current in the post-flame stage and the pressure data treated with the Pauta criterion method increases. In addition, there are high correlation coefficients between the ion current and the pressure.

Effect of spark plug protrusion on the performance and emission characteristics of an engine fueled by hydrogen-natural gas blends

Mixtures of hydrogen and natural gas are promising for improving efficiency and reducing harmful emissions in spark ignition engines, since limits of flammability can be extended while stable combustion is secured. In this research, the combustion characteristics of long electrode spark plugs were evaluated in a hydrogen blended with natural gas (HCNG) engine. Decreases in the flame propagation distance through the use of spark plugs can lead to increased burning rates and further improvement of fuel economy in HCNG engines. An 11-liter heavy duty lean burn engine was employed and performance characteristics including emissions were assessed according to the spark timing of the minimum advance for best torque (MBT) for each operating condition. Retarded MBT spark advance timing with long electrode spark plugs due to increased burning speed supported increases in engine efficiency and reductions of nitrogen oxide (NOx) emissions. The lower positions of initial flame kernels due to the use of long electrode spark plugs were preferable to improvements of cyclic variability due to reduced flame front quenching, and carbon monoxide (CO) emissions at the flammability limit were also improved.

Progress in hydrogen enriched hydrocarbons combustion and engine applications

The paper summarized the work on hydrogen enriched hydrocarbons combustion and its application in engines. The progress and understanding on laminar burning velocity, flame instability, flame structure flame and chemical kinetics were presented. Based on fundamental combustion, both homogeneous spark-ignition engine and direct-injection spark-ignition engine fueled with natural gas-hydrogen blends were conducted and the technical route of natural gas-hydrogen combined with exhaust gas recirculation was proposed which experimentally demonstrated benefits on both thermal efficiency improvement and emissions reduction.

HCNG 엔진의 터보차저 변경에 따른 전부하 출력 및 배출가스 특성 연구

Hydrogen-natural gas blends(HCNG) engine is optimizing technology of performance and emission characteristics with use of hydrogen's fast flame speed and wide flammability limit. As lean-burn limit is extended, the improvement in thermal efficiency and harmful emissions can be achieved. However, the extension of lean-burn limit under a wide open throttle operation point could be realized with the increase in boosting capacity in a lean-burn engine with turbo-charging system. In the present study, the power output characteristics of HCNG engine with turbo-charger change is assessed and feasibility of the increase in boost- ing capacity is evaluated. The turbo-charger design with high efficiency at higher flow rate rather than higher boosting pressure makes efficient operation possible at relatively rich mixture condition.

Effects of the ignition timing retard and the compression ratio on the full-load performance and the emissions characteristics of a heavy-duty engine fuelled by hydrogen–natural-gas blends

Heavy-duty natural-gas vehicles contribute towards environmental improvement in the air quality of downtown areas because the particulate matter emissions are quite low and lean combustion facilitates improvement in the efficiency and reduction in the harmful emissions. However, because stronger emission regulations such as Euro VI cannot be satisfied using the current technology, new technology is required. Hydrogen–natural-gas blend engines have been investigated as an alternative in preparation for the hydrogen era. Such engines make further emission reductions and efficiency improvements possible by extending the lean-combustion limit. However, they do have some disadvantages such as the degradation in the full-load performance, which can limit the reduction in the nitrogen oxide emissions or the operation range because the extension of the lean-burn limit requires a larger amount of intake air even under a wide-open throttle operating condition. In the present study, the full-load performance and emissions characteristics of a hydrogen–compressed-natural-gas engine were evaluated using hydrogen–compressed-natural-gas fuel with a hydrogen content of 30 vol %. In order to achieve performance improvement, a spark timing retard strategy was employed, together with a change in the compression ratio. After examining the full-load performance for each parameter change, the emission characteristics were assessed to analyse the commercialization potential and feasibility of this hydrogen–compressed-natural-gas engine. For a higher compression ratio, the specified torque value could be achieved with spark timing retard; an excess air ratio of 1.8 was found to be preferable, and the nitrogen oxide emissions standard of Euro VI was satisfied.

압축비 변화에 따른 HCNG 엔진의 배기 특성

Abstract : Compression ratio is an important factor affecting engine performance and emission characteristics since thermal efficiency of spark ignition engine can be theoretically improved by increasing compression ratio. In order to evaluate the effect of compression ratio change in HCNG engine, natural gas engine was employed using HCNG30 (CNG 70 vol%, hydrogen 30 vol%). Combustion and emission characteristics of CNG and HCNG fuel was analyzed with respect to the change of compression ratio at each operating condition. The results showed that thermal efficiency improved and CH 4 , CO 2 emission decreased with the increase in compression ratio while NO x emissions were decreased at a certain excess air ratio condition. Higher thermal efficiency and further reduction of exhaust emissions can be achieved by the increase of compression ratio and the retard of spark timing. Key words : Compression ratio(압축비), Emission characteristics(배기특성), Hydrogen-natural gas blends(수소-천연가스 혼합연료), Power output(출력성능), Excess air ratio(공기과잉률)

Experimental and numerical study of hydrogen addition in a natural gas heavy duty engine for a bus vehicle

Hydrogen added to natural gas improves the process of combustion with the possibility to develop engines with higher performance and lower environmental impact. In this paper experimental and numerical analyses on a multi cylinder stoichiometric heavy duty engine, fuelled with natural gas–hydrogen blends, are reported. Some constrains on hydrogen content and maximum load achievable have limited the scope of investigation. A specific modelling of the reference engine was developed to extend the study at full load condition and at higher hydrogen content. The results showed a higher combustion speed when hydrogen content in the fuel is increased. However, the positive effect of shorter combustion duration on thermal efficiency is mitigated by higher wall heat loss, due to higher combustion temperatures. Therefore lower CO2 emissions are due only to the substitution of natural gas with hydrogen, making crucial the way of hydrogen producing to have a benefit on well-to-wheel CO2 emissions.

HCNG 엔진의 공기과잉율 변화에 따른 노킹 특성에 관한 연구

자동차 배기가스 규제가 강화됨에 따라 천연가스에 수소를 첨가하는 수소-천연가스 혼합연료(HCNG)를 기존의 압축천연가스(CNG) 엔진에 적용하려는 많은 연구들이 진행되고 있다. 그러나 수소의 높은 연소 속도로 인한 역화, 조기착화, 노킹(knocking) 등의 이상연소 발생 가능성은 엔진의 가열 또는 열효율 및 출력의 저하를 야기하는 문제점이 발생할 수 있다. 본 연구에서는 CNG 연료에 수소를 일정 부분 혼합한 HCNG 연료를 기존의 CNG 엔진에 적용하여 희박연소 한계 확장을 통해 연소 성능 개선을 확인하고, CNG와 HCNG 연료의 노킹 특성을 파악하고자 하였다. 공기과잉율의 변화에 따른 노킹 발생 조건을 관찰함으로써 HCNG 연료의 적용성 및 노킹마진을 평가하고자 하였다. HCNG 연료 사용 시 최적운전조건에서 노킹 문제없이 엔진을 운전할 수 있었으나 노킹이 일어날 수 있는 가능성이 높아져 이에 대한 대비가 필요할 것으로 판단된다. As emission regulation for vehicle has been reinforced, many researches carried out for HCNG(hydrogen-natural gas blends) fuel to the conventional compressed natural gas (CNG) engine. However, abnormal combustion such as backfire, pre-ignition or knocking can be caused due to high combustion speed of hydrogen and it can result in over heating of engine or reduction of thermal efficiency and power output. In the present study, improvement of combustion performance was observed with HCNG fuel since it can extend a flammability limit. Knocking characteristics for CNG and HCNG fuel were investigated. Feasibility of HCNG fuel was evaluated by checking the knock margin according to excess air ratio. The operation of engine with HCNG was stable at minimum advance for best torque(MBT) spark timing and knock phenomena were not detected. However, it is necessary to prepare higher knock tendency since possibility of knock is higher with HCNG fuel.

Combustion analysis of a spark ignition i. c. engine fuelled alternatively with natural gas and hydrogen-natural gas blends

This paper describes an experimental activity performed on a passenger car powered by a spark ignition engine fuelled alternatively with natural gas (CNG) and hydrogen-natural gas blends, with 15% (HCNG15) and 30% (HCNG30) of hydrogen by volume. The vehicle was tested on a chassis dynamometer over different driving cycles, allowing the investigation of more realistic operating conditions than those examined on an engine test bed at steady state conditions. Fuel consumption was estimated using the carbon balance methodology, allowing the comparison of engine average efficiency over the driving cycles for the tested fuels. Furthermore, cylinder pressure was measured and, by processing the pressure signal, a combustion analysis was performed allowing to estimate the burning rate and combustion phasing. Ignition timing was the same for all the tested fuels, in order to assess their interchangeability on in-use vehicles. Results showed CO2 emission reduction between 3% and 6% for HCNG15 and between 13% and 16% for HCNG30 respect to natural gas. Fuel consumption in MJ/km did not show significant differences between CNG and HCNG15, while reductions between 3% and 7% have been observed with HCNG30. The heat release rate increased with hydrogen content in the blends, reaching values higher than those attained using CNG. The combustion duration, calculated as the angle between 10% and 90% of heat released, has been shortened, with 16% reduction for HCNG15 and 21% for HCNG30 respect to CNG at 2.5 bar imep and 2400 rpm. As a consequence, hydrogen addition resulted in a combustion phasing advance respect to CNG. Cycle-by-cycle variability decreased, particularly at low loads, due to the positive effect of hydrogen on combustion stability.

Operating strategy for exhaust gas reduction and performance improvement in a heavy-duty hydrogen-natural gas blend engine

Hydrogen-natural gas blends (HCNG) have the advantage of lower emission levels, because of their lean combustion characteristics, compared to a direct injection diesel engine equipped with a high-cost fuel supply system and an aftertreatment system for heavy-duty vehicles. The HCNG engine has superior fuel economy with extension of the flammability limit. However, the performance and emission characteristics vary with the content of hydrogen in fuel gases and the operating strategy at each operating condition.The present study assesses the applicability of the HCNG engine (which has a hydrogen content of 30 vol% and adheres to the EURO-VI standard) according to operating strategies. The flammability limit is extended by 0.2 of the excess air ratio with HCNG compared to CNG (compressed natural gas), while combustion stability is secured so that the thermal efficiency is improved by an average of about 0.74%, and an average NOx (nitrogen oxides) level of 2.6 g/kWh is measured at the optimal excess air ratio and the minimum advance for best torque spark timing. The operating strategy that uses retarded spark advance timing and richer combustion is effective to satisfy the NOx limit of the EURO-VI standard, while the thermal efficiency decreases by 1–2%.

Effect of mixing CO2 with natural gas–hydrogen blends on combustion in heavy-duty spark ignition engine

Because further reduction in carbon dioxide (CO2) will require upgrading the existing engine technology or developing a new type of engine, the addition of hydrogen to natural gas is considered as an alternative that could meet the required emission standards. However, the carbon monoxide/CO2 generated in the reforming process of natural gas can affect the engine performance and emissions characteristics. The content of CO2 in the reformed gas can be varied by varying the ingredients or the conditions of the process. Therefore, it is essential to control the air-fuel mixture condition and combustion phasing. In this research, the performance and emission characteristics of an 11 L spark ignition engine using natural gas–hydrogen blends with various CO2 contents were examined, and an optimization strategy for controlling the excess air ratio and the spark advance timing was assessed. The thermal efficiency decreased with the increased content of CO2 under a given excess air ratio condition. The increased heat capacity of the mixture reduced the combustion temperature, so that the generation of nitrogen oxides was suppressed. However, total hydrocarbon (THC) emissions and the methane portion of the THC emissions were increased by the introduction of CO2. The decrease in the exhaust gas temperature also resulted in low conversion efficiency of the oxidation catalyst.

CO2 emissions from a spark ignition engine operating on natural gas–hydrogen blends (HCNG)

The addition of hydrogen to natural gas could be a short-term alternative to today’s fossil fuels, as greenhouse gas emissions may be reduced. The aim of this study is to evaluate the emissions and performance of a spark ignition engine fuelled by pure natural gas, pure hydrogen, and different blends of hydrogen and natural gas (HCNG). Increasing the hydrogen fraction leads to variations in cylinder pressure and CO2 emissions. In this study, a combustion model based on thermodynamic equations is used, considering separate zones for burned and unburned gases. The results show that the maximum cylinder pressure rises as the fraction of hydrogen in the blend increases. The presence of hydrogen in the blend leads to a decrease in CO2 emissions. Due to the properties of hydrogen, leaner fuel–air mixtures can be used along with the appropriate spark timing, leading to an improvement in engine emissions with no loss of performance.

Investigations of emission characteristics and thermal efficiency in a spark-ignition engine fuelled with natural gas-hydrogen blends

This paper presents the experimental results of a single cylinder Enfield engine using an electronically controlled fuel injection system which was developed to carry out exhaustive tests using neat compressed natural gas (CNG), and mixtures of hydrogen in CNG (HCNG) as 5, 10, 15 and 20% by energy. Experiments were performed at 2000, 2400 and 2800 rpm with wide open throttle and varying the equivalence ratio. Hydrogen, which has a fast burning rate, when added to CNG, enhances its flame propagation rate. The emissions of HC, CO, decreased with increasing percentage of hydrogen but NOx was found to increase. The results indicated a marked improvement in the brake thermal efficiency with the increase in percentage of hydrogen added. The improved thermal efficiency was clearly observed to be more in lean regions when compared with rich regions.

Numerical evaluation of internal combustion spark ignition engines performance fuelled with hydrogen – Natural gas blends

The dependence of road transportation from fossil fuels and the related economic and environmental consequences imposes the diversification of energy sources. Hydrogen can strongly contribute to this goal because it can be produced from different renewable energy sources. In order to boost the development of hydrogen technology and reduce the dependence from conventional fossil fuels, hydrogen can be used in internal combustion engines added to natural gas (NG). Hydrogen-natural gas blends, commonly named HCNG, can be distributed using the natural gas infrastructures without significant modifications if hydrogen content is lower than 30% in volume. In this paper a numerical model has been developed to predict the performance and emissions of an internal combustion engine fuelled by natural gas and hydrogen – natural gas blends. The analysis displayed the impact of hydrogen addition on engine brake efficiency and NOx emission. Stoichiometric air-to-fuel ratio was considered for each fuel in order to assure an efficient exhaust after-treatment adopting a three-way catalyst. Exhaust gas recirculation (EGR) was investigated with the aim at improving engine efficiency and reducing NOx emissions respect to undiluted charge. In fact, HCNG blends combustion properties are particularly suitable for EGR, assuring a stable combustion also when the charge is diluted. Maximum brake torque (MBT) ignition timing has been adopted for all fuels and operating conditions investigated. Simulations were performed at conditions reproducing engine operation on a passenger car over the New European Driving Cycle (NEDC). Results were displayed in terms of fuel consumption in MJ/km and NOx emissions in g/km. The results showed that HCNG blends improved engine brake efficiency, particularly at low loads and for the highest hydrogen content, with fuel consumptions on energy basis over NEDC 2.5%, 4.7% and 5.7% lower than CNG, for HCNG 10, 20 and 30 respectively. NOx emissions increased of about 4% for HCNG 10, 11% for HCNG 20 and 20% for HCNG 30, due to the higher in-cylinder gas temperatures. Further investigations, performed adopting 10% EGR for HCNG blends, showed a large reduction of NOx emission, over 80% compared with natural gas (without EGR), with a positive effect also on engine efficiency. The decrease in fuel consumption using HCNG blends together with EGR, compared with natural gas, was 5.4%, 6.6% and 7.7% for HCNG 10, 20 and 30, respectively.

Performance and emission characteristics of a hydrogen-enriched compressed-natural-gas direct-injection spark ignition engine diluted with exhaust gas recirculation

Compressed natural gas (CNG) has been widely used in city buses or taxis because of its relatively low price and great abundance. Most of the CNG engines externally mix the natural gas with the intake air and utilize a lean-burn strategy to achieve low nitrogen oxide (NO x) emissions and high fuel economy. However, the well-examined external mixing of gas fuel with the intake air will result in a volumetric efficiency loss at high engine loads and may cause backfire when the natural gas is enriched with hydrogen. Also, the lean-burn technique may not sufficiently satisfy increasingly restricted future legislation. In this paper, the use of the stoichiometric equivalence ratio with exhaust gas recirculation (EGR) was investigated experimentally on a direct-injection spark ignition engine fuelled with hydrogen–natural-gas blends. Attention is focused on the advantages of combining EGR with hydrogen enrichment. The results show that hydrogen enrichment increases the brake mean effective pressure, which dramatically deteriorates under high-level EGR. Optimal efficiencies are achieved with an EGR rate of 5–10 per cent; the NO x emissions can be decreased by about 80 per cent with 25 per cent EGR dilution, but the combustion variation increases simultaneously. With hydrogen enrichment, the combustion variation can be controlled under 5 per cent, while the NO x, hydrocarbon, and carbon monoxide emissions are kept at a low level. Worse EGR tolerance was exhibited for the late-injection-timing case.