Methane Number Research Articles

Effect of the turbulence intensity on knocking tendency in a SI engine with high compression ratio using biogas and blends with natural gas, propane and hydrogen

This research presents the test results carried out in a diesel engine converted to spark ignition (SI) using gaseous fuels, applying a geometry change of the pistons combustion chamber (GCPCC) to increase the turbulence intensity during the combustion process; with similar compression ratio (CR) of the original diesel engine; the increase in turbulence intensity was planned to rise turbulent flame speed of biogas, to compensate its low laminar flame speed. The research present the test to evaluate the effect of increase turbulence intensity on knocking tendency; using fuel blends of biogas with natural gas, propane and hydrogen; for each fuel blend the maximum output power was measured just into the knocking threshold before and after GCPCC; spark timing (ST) was adjusted for optimum generating efficiency at the knocking threshold. Turbulence intensity with GCPCC was estimated using Fluent 13, with 3D Combustion Fluid Dynamics (CFD) numerical simulations; 12 combustion chamber geometries were simulated in motoring conditions; the selected geometry had the greatest simulated turbulent kinetic energy (TKE) and Reynolds number (Re) during combustion. The increased turbulence intensity was measured indirectly through the periods of combustion duration to mass fraction burn 0–5%, 0–50% and 0–90%; for almost all the fuel blends the increased turbulence intensity of the engine, increased the knocking tendency requiring to reduce the maximum output power to keep engine operation just into the knocking threshold. Biogas was the only fuel without power derating by the conditions of higher pressure and higher turbulence during combustion by GCPCC and improve its generating efficiency. Peak pressure, heat release rate, mean effective pressure and exhaust temperature were lower after GCPCC. Tests results indicated that knocking tendency was increased because of the higher turbulent flame speed; fuel blends with high laminar flame speed and low methane number (MN) had higher knocking tendency and lower output power.

Predicting the methane number of gaseous fuels using an artificial neural network

Methane number (MN) is a critical gas quality parameter for gaseous-fueled engines. It is a measure of knock resistance for gaseous fuels, as is the octane number for gasoline. Therefore, a priori knowledge of the MN of gaseous fuel is important to avoid any structural damage to the engine due to knock. In the present study, a model was developed to predict the MN of gaseous fuels using an artificial neural network (ANN). The model utilized measured MNs of 1202 different gaseous fuel compositions, out of which 90% of the data (randomly) was used to train the ANN model using the Levenberg–Marquardt algorithm. In order to obtain the best performance, the number of neurons in the hidden layer and the transfer function of the hidden and output layers were changed. The ANN model incorporating hyperbolic tangent sigmoid function in the hidden layer with 53 neurons, and linear function in the output layer, showed the best performance – with mean square error and correlation coefficient of 0.055 and 1, respectively. The MNs of the remaining 10% of the data were determined using the ANN model, and were compared with those determined by the AVL (Anstalt für Verbrennungskraftmaschinen List) model. The model was able to predict MN accurately (R = 0.999).

ENERGY EFFICIENT USAGE OF NATURAL GAS CRITERIAS

The article suggests that Wobbe Index is one of the main criteria when determining quality of natural gas for natural gas Interchangeability from different sources ДСТУ ISO:13686:2016. For effective natural gas combustion the Wobbe Index Ws gas of should not differ form Ws of gas G20 by more than 2 percent. Especially in cases where equipment designed precisely to work with G20 gas. In that case it is necessary to adjust gas pressure or substitute machine design for different gas usage. Methane number that is corrected by Wobbe Index could be another criteria of quality of gas determination. Authors suggest minimal methane number of MN=65 defined by EN 16726:2015 is not sufficient. It is proven that even in case of higher combustion energy output for gas with Wobbe Index significantly lower of G20 gas test values the overall efficiency of using this gas in particular burner system is much lower. Flame flow for natural gas in streams M166 and M208 is closer to wrinkles due to chemical mixture of gas and natural gas in M1204 stream creates yellow tipping due to incomplete combustion, sulfur content similar to G21 test gas. With mediocre combustion energy output same burners consume more natural gas to provide same amount of energy. Natural gas from stream M404 has almost ideal mixture of components. Its Wobbe Index is 50,41 MJ/Nm3 but hydrocarbon dew point of 15.3 °C at P=3.92 MPa. That indicates relative humidity of 100%. Specific humidity of gas in stream is 0.44 grams per cubic meter that is dangerous for creating natural gas hydrates, solid clathrate compounds that may damage machinery or obstruct pipeline flow. Authors suggest to provide certain set of actions to process natural gas into so called clean “pipeline quality dry gas” at wells or gas-processing plants to improve gas parameters to be closer to European Union standards. As for government policies they have to be reworked from using “energy saving” term to “energy efficiency” term and start improving on efficient usage of natural gas by approving and applying newest energy efficient technologies and machinery into gas transport\consumer network.

Numerical Investigation of Methane Number and Wobbe Index Effects in Lean-Burn Natural Gas Spark-Ignition Combustion

A larger use of natural gas in internal combustion engines will reduce the dependence upon petroleum imports. However, large variations in gas composition as a result of the gas origin and/or gas t...

Development of a natural gas Methane Number prediction model

The methane number (MN) of natural gas is predicted using mathematical modeling and machine learning techniques which can be incorporated into a sensor. Natural gas quality is known to vary seasonally and regionally depending on the geological region. MN is defined by the gas composition and also related to the knocking resistance in a natural gas engine. This article presents the results of two different methods to predict MN, which are Multiple Regression (MR) and Support Vector Regression (SVR) that can be further specified by three kernel types: linear, polynomial, and Gaussian distributions. The analysis of the 4 methods - MR, linear SVR, polynomial SVR, and Gaussian SVR - shows that each predicts MN with a root mean square error of ±1.06, ±1.08, ±0.54, and ±0.20 respectively. About 37% of the predictions made by MR are under the ±0.5 error range. 40% of linear SVR, 52% of polynomial SVR, and 98% of Gaussian SVR predictions are within the ±0.5 error range. The SVR using Gaussian kernel outperforms the other three methods in accuracy. The results can enable the technology needed to develop an intelligent sensor that can estimate the MN of natural gas online and in real-time, economically and reliably, overall increasing fuel efficiency and emission performance.

The effect of electric fields in methane hydrate growth and dissociation: A molecular dynamics simulation

Molecular dynamics simulation was employed to examine the growth and dissociation process of methane hydrate in the presence of static/oscillation electric fields at T = 260 K and P = 100 bars. The intensity of electric field was in range of 1.0–2.0 v/nm, and the frequency of applied e/m field was in range of 2.45 GHz–1.0 THz. Electric field would be a factor controlling the hydrate growth and dissociation because the migration of water molecules may be affected. Total energy of simulation system, final system configurations, hydrate-like methane numbers, radial distribution functions, H-bond numbers with simulation time, and dipole moment were analyzed. There is intensity threshold for e-field to exert an effect on methane hydrate. Static electric fields above the intensity threshold (1.5 v/nm) could push hydrate dissociation by inducing the arrangement of water molecules along the field. Cosine oscillation electric fields could promote both methane hydrate growth and dissociation, and there are different critical field magnitudes for different frequency e-fields to play positive roles in methane hydrate growth or dissociation. In order to promote methane hydrate dissociation, higher the e-field magnitude will need as the e-field frequency is higher.

Algorithm for Determining the Knock Resistance of LNG

This paper reports the development of a next-generation algorithm to calculate the knock resistance for LNG compositions. This so-called PKI Methane Number is developed and tested for a lean-burn, medium-BMEP gas engine. The algorithm itself is a polynomial equation based on thousands of simulations performed using an experimentally verified engine knock model. Comparison of the PKI MN calculated using the gas-input-only algorithm and measurements on the test engine show very good agreement. A comparison with two existing methods for calculating the methane number (AVL and MWM Method as defined in EN 16726) with experimental engine data show reasonable agreement with predictions using AVL method but substantial differences with predictions from MWM method are observed. Additionally, the current methods such as AVL and MWM need a dedicated solver to calculate the methane number. In contrast, the algorithm described here is a polynomial equation that is very easy to implement in gas composition sensors for fast real-time methane number calculations. This opens possibilities for smart-phone methane number calculation during bunkering and fuel-adaptive control systems that could optimize engine performance for a broad range of fuel compositions. Furthermore, given the experimentally verified reliability and ease of implementation of the PKI MN algorithm, we assert that it is an excellent, open-source candidate for international standards for specifying the knock resistance of LNG.

A Comparative Study on Influence of Natural Gas Composition on the Performance of a CNG Engine

Natural gas is the cleanest fossil fuel and it has high energy conversion efficiencies for power generation in internal combustion engines. Natural gases have varying composition depending on the place where they are produced. This paper studies the effects of natural gas composition on the combustion and emissions characteristics of CNG engines and presents the overall combustion characteristics obtained from running a 1.65 L, 4-cylinder EF 7 CNG engine. Engine power, Torque, BMEP and BSFC were measured under steady state operation conditions at full load conditions. The obtained simulation results were compared with experimental ones in the literature and showed that the CNG composition had a considerable influence on engine performance and fuel economy. A correlation has been proposed to help gain insight into the relationship between the Methane Number (MN) and engine power, and it provides a practical method for estimating the engine power when the composition of natural gases varies.

Methane number measurements of hydrogen/carbon monoxide mixtures diluted with carbon dioxide for syngas spark ignited internal combustion engine applications

A comprehensive analysis of the autoignition tendency of binary mixtures of hydrogen and carbon monoxide diluted with carbon dioxide is carried out in this paper. Methane Number (MN) measurements of these mixtures were performed by using a method analogous to the standard method for Octane Number (ON) measurement. The experimental MNs ranged from 46.0 to 139.1 according to experimental data. These results are compared with the MNs calculated by programs released for natural gas MN estimations. A comparative analysis concluded that these programs are not suitable to calculate MN of syngas. A method to isolate the effect of carbon dioxide on the autoignition tendency of binary mixtures of hydrogen and carbon monoxide is proposed. Results reveal that increments of carbon dioxide concentration in the mixtures, exponentially increase the MN of the mixtures. At low carbon dioxide concentration, the MN of the ternary mixtures can be approximated by the MN of their equivalent binary mixtures of hydrogen and carbon monoxide. Based on this observation, the MNs of coal gases reported in the literature are estimated.

Operational tests of an innovative fuel supply system for an industrial 4-stroke gas engines

The modern power generation solutions focus on several key factors: economy, efficiency, reliability as well as environmental impact. The natural way to protect environment and secure project feasibility is to move from more and more expensive conventional fuels like oil, coal and natural gas towards unconventional and more environment friendly fuels. That group includes many fuels that are currently mainly disposed without usage which means creating direct pollution without any direct value. The main problem is that there are many problems with such fuels and practical usage requires lot of investments and operational costs. The innovative fuel supply system HE-MUZG designed for 4-stroke gas engine developed together by Horus-Energia and Cracow University of Technology enables wide range of gas fuels to be used for power generation. This paper will present results from operational tests of the HE-MUZG system installed on gas genset. The test program covered many various fuels, which are problematic for typical modern gas engines, due to fuel low calorific value, low methane number or wide and rapid fluctuations of fuel properties. The presented results show main achievements obtained during HE-MUZG system development. Additionally the article describes some engine modifications implemented to optimise engine operation and to improve the efficiency.

3D CFD simulation of a CI engine converted to SI natural gas operation using the G-equation

The conversion of heavy-duty CI engines to natural gas (NG) SI operation have the potential to increase the use of NG in the transportation sector in the United States. More, the increased turbulence of a bowl-in-piston combustion chamber can increase the flame speed under more efficient lean conditions. The main objective of this study was to investigate if a 3D G-equation-based RANS simulation (i.e., reasonable computational costs and running times) can predict the efficiency and emissions of such converted engine, for various NG compositions and operating conditions. The model was validated with experimental data from a single-cylinder CI research engine that replaced the fuel injector with a spark plug and fumigated NG inside the intake manifold using a low-pressure gas injector. Using a unique set of model tuning parameters, the model was able to qualitatively predict the effect of NG composition on engine performance and emissions over a range of operating conditions that changed spark timing, equivalence ratio, and engine speed. The model also captured the double-peak heat release rate seen at advanced spark timing in the experiments. The results showed that a lower methane number (MN) increased peak pressure and indicated mean effective pressure. Higher H/C ratio advanced combustion phasing. More, higher MN lowered nitrogen oxides but increased unburned hydrocarbons emissions. However, while a lower MN increased carbon monoxide (CO) production during the combustion process, there was no clear trend for engine-out CO emissions. Overall, the predicted gas composition effects on engine efficiency and emissions were relatively small, at least for the range of operating conditions investigated here. However, the results suggest that the 3D CFD model described here is suitable for combustion phenomena analysis such the flame behavior in a bowl-in-piston combustion chamber.

Autoignition studies of Liquefied Natural Gas (LNG) in a shock tube and a rapid compression machine

Liquefied Natural Gas (LNG) has become an increasingly important world energy resource and is a part of the European Union clean fuel strategy launched in 2013. Therefore, there are currently several ongoing measurement strategies considering quality specification of LNG. In this context, for application in gas engines, it is essential to understand the combustion behavior of these natural gas mixtures. The methane number (MN) which represents a scale for the knocking propensity, is one of the main indicators for this combustion behavior. In this study, we investigated the influence of the LNG composition on the ignition delay time and thus the knocking behavior of prototypical LNG Mixtures. Several LNG typical mixtures containing CH4/C2H6/C3H8/n-C4H10/i-C4H10/n-C5H12/i-C5H12/N2 were studied in the temperature range 850–1450 K, with pressures of 20 and 40 bar and at equivalence ratios of 0.4 and 1.2. The use of a shock tube and a rapid compression machine facility allowed us to study the ignition behavior over a wide range of operating conditions relevant to gas engines. We report a detailed investigation of LNG autoignition with respect to temperature, pressure and equivalence ratio thereby providing crucial validation data for chemical kinetic models for real applications.

Predicting Wobbe Index and methane number of a renewable natural gas by the measurement of simple physical properties

This study describes a fuel quality prediction strategy that predicts the fuel quality parameter and component composition of Renewable Natural Gas (RNG) containing CH4, C2H6 and CO2. Onsite measurement of the gas properties in a renewable natural gas (RNG) fuel is necessary to ensure an expected level of quality, which must be maintained for better combustion efficiency. The Wobbe Index (WI) and methane number (MN) are the natural gas quality indicators used. To predict the WI, MN, and component composition, a data set that consists of WI, MN, thermal conductivity and sound velocity of the gaseous fuel mixture as a function of its temperature, pressure and composition, was created. Through a regression analysis of the data set, a model that estimates the WI, MN and composition of the gaseous fuel mixture from its physical properties (temperature, pressure, thermal conductivity and sound velocity), was developed. The results of the study including the data set and the prediction model that can accurately estimate the WI, MN, and gas composition, is presented in this paper.

Jovian Auroral Ion Precipitation: Field‐Aligned Currents and Ultraviolet Emissions

AbstractA model is described for the transport of magnetospheric oxygen ions with low charge state and energies up to several MeV/nucleon (MeV/u) as they precipitate into Jupiter's polar atmosphere. A revised and updated hybrid Monte Carlo model originally developed by Ozak et al. (2010, https://doi.org/10.1029/2010JA015635) is used to model the Jovian X‐ray aurora. The current model uses a wide range of incident oxygen ion energies (10 keV/u to 5 MeV/u) and the most up‐to‐date collision cross sections. In addition, the effects of the secondary electrons generated from the heavy ion precipitation are included using a two‐stream transport model that computes the secondary electron fluxes and their escape from the atmosphere. The model also determines H2 Lyman‐Werner band emission intensities, including a predicted spectrum and the associated color ratio. Implications of the new model results for interpretation of data from National Aeronautics and Space Administration's Juno mission are discussed. In particular, the model predicts that for a 2 MeV/u oxygen ion energy input of 10 mW/m2: (1) escaping electrons are produced with an energy range from 1 eV to 4 keV, which is a smaller range than previous models by Ozak et al. (2013, https://doi.org/10.1002/2013GL50812) predicted, (2) H2 band emission rates of 75 kR are generated, similar to previous estimates, and (3) a newly calculated Lyman and Werner band color ratio of 10 is expected. The color ratios are put into a context of various methane number density distributions.

Pyrolysis gases produced from individual and mixed PE, PP, PS, PVC, and PET—Part II: Fuel characteristics

The current energy industry relies heavily on fossil fuels. As reserves of fossil fuels are diminishing, the demands for alternative forms of energy are growing. Therefore, the search for alternative fuels is crucial. This article discusses pyrolysis gases generated from major plastics as possible future successors to fossil fuels. The novelty of this study lies in the comprehensive discussion of the fuel characteristics of different pyrolysis gases that are so far unpublished. The article builds on Part I, which predominantly focused on the production and physical properties of pyrolysis gases from plastics. Various properties are determined by combining experimental and mathematical methods. An interesting aspect of the gases produced from poly(ethylene terephthalate) (PET) is their high upper flammability limits, which are 61.46% on average. Gases from poly(vinyl chloride) (PVC) are characterized by very high laminar burning velocities, with an average value of 178.62 cm s−1, which is about five times higher than that of natural gas (NG). Gases produced from PVC at 500 and 700 °C have autoignition temperatures almost identical to that of NG. Furthermore, the results presented in this article show that, according to standards proposed by the California Air Resources Board and the Gas Research Institute, none of the pyrolysis gases are suitable fuels for gas engines, because the methane number of no gas meets the minimum value of 65 required in the EU and USA. This article discusses results valuable for determining the potential suitability of pyrolysis gases for use in power-engineering facilities, including combustion engines, and includes information on further research prospects.

Numerical evaluation of the effect of methane number on natural gas and diesel dual-fuel combustion

Natural gas and diesel dual-fuel combustion is a promising technology for efficiently utilizing natural gas in a compression ignition engine. Natural gas composition varies depending on the geographical source, which affects engine performance. The methane number is an indicator of natural gas fuel quality to assess the variation in composition. In this study, the influences of methane number on natural gas/diesel dual-fuel combustion were numerically examined using computational fluid dynamic simulations. The differences between natural gases with the same methane number but different components were also compared. Two dual-fuel combustion strategies, diesel pilot ignition, and reactivity controlled compression ignition were evaluated. The results show that for both diesel pilot ignition and reactivity controlled compression ignition, the ignition delay increases and the combustion duration decreases as the methane number is increased. The retarded trend of ignition of reactivity controlled compression ignition is more significant than that of diesel pilot ignition, while the decreased trend in combustion duration is less significant. To understand this trend, a chemical kinetics study of ignition delay characteristic of natural gas and n-heptane mixture was conducted. The result reveals that introducing ethane, propane, or an ethane–propane mixture into pure methane shortens the ignition delay in the entire temperature range. However, for the methane and n-heptane mixture, adding ethane, or propane, or an ethane–propane mixture shortens the ignition delay in the high temperature range, while increases the ignition delay in the low temperature range. These observations in combination with the analysis of air–fuel mixture formation and combustion provide the evidence to interpret the different ignition and combustion behaviors between diesel pilot ignition and reactivity controlled compression ignition combustion. In addition, a temperature A-factor sensitivity study was carried out to explain the result of the chemical kinetics study. Furthermore, the responses of emissions to methane number were also investigated. The results show that for diesel pilot ignition, the hydrocarbon and carbon monoxide emissions decrease with the decreased methane number. However, for reactivity controlled compression ignition, the variations of hydrocarbon and carbon monoxide emissions with the methane number are not so obvious as for diesel pilot ignition combustion. For both diesel pilot ignition and reactivity controlled compression ignition combustion, the nitrogen oxides emissions show a strong dependence on combustion phasing rather than natural gas composition. Overall, to control diesel pilot ignition combustion, the methane number should be considered together with other parameters. However, attention should be paid to other control parameters for the reactivity controlled compression ignition combustion. The engine performance of reactivity controlled compression ignition is not sensitive to the variation of natural gas composition, so it can adapt to the natural gas from different sources.

Methane Number Improvement of Gas from LNG Regasification Unit

Methane Number (MN) is one of quality requirement of gas as fuel for gas engine, which indicates fuel capability to avoid knocking in the engine. Higher MN provides better quality of gas for gas engine. Natural gas with higher methane (CH4) and fewer higher hydrocarbon, tends to have higher MN score. This study aims to obtain heating methods of LNG to produce vapor that has appropriate MN as a fuel gas supply to gas engine. The simulation for LNG regasification prepared is an approach to the design of the existing regasification facility of the power plant in Bali. The temperature ranges for LNG heating simulation were obtained based on saturated temperatures of LNG phase envelopes. In the simulation. to obtain a certain MN value can be conducted by adjusting the temperatures at two different values i.e. above -110 ° and below - 80 °. To produce LNG vapor that has MN of 80 either through higher temperature of heating (HT heating) or lower temperature of heating (LT heating) requires more energy than direct heating without MN improvement. Heat loading for LT heating is higher than HT heating due to more temperature defference between LT and heating fluid temperatures. The ability of engine to produce power decreased with decreasing fuel gas MN. The power increment increases for lower MN gas if MN improvement is conducted.

Effect of natural gas composition on methane number: A case of gas reservoirs in Serbia

ABSTRACTNatural gas is considered as the most environmentally acceptable fossil fuel, thus it is an alternative to petroleum derivate, dominantly used in internal combustion engines. Physical properties of a fuel as well as behavior during combustion process are affected by its composition. This article presents analysis of effect of natural gas composition on methane number (MN), conducted for natural gas deposits in Serbia. For empirically determination of MN: California air resources board(CARB) method and Linear and Anstalt für Verbrennungskraftmaschinen list (AVL) method have been applied. Effect of reactive hydrogen and carbon ratio, Wobbe index and content of inert matter on MN is discussed. For compositions characterized with total share of inert compounds higher than 5%, impact of inert components becomes significant, without observed dependency between reactive hydrogen and carbon and MN. An analysis has shown that carbon dioxide and nitrogen have differently affect MN. Carbon dioxide affects the increase of MN due to higher molar specific heat, appearance of dissociation, and higher activation energy.

New Potentialities for Utilization of Associated Petroleum Gases in Power Generation and Chemicals Production

New possibilities for the utilization of associated petroleum gases (APG) and monetization of small-scale and remote Natural Gas resources by power generation and chemicals production are considered and tested. One possibility is the oxycracking of APG. This technology allows selective transformation of heavier hydrocarbons that have low octane (methane) numbers and inclined to soot and tar formation, into lighter compounds with higher octane numbers, thus producing gas suitable to feed different types of power engines. Another possibility is the small-scale conversion of APG to syngas to produce more easily transportable and more valuable chemicals or liquid fuels via well-known Fischer–Tropsch process or catalytic synthesis of methanol. For this purpose we have suggested principally new technology for natural gases conversion into syngas, based on the use of 3D (volumetric) matrixes. It allows the relative simple and very compact non-catalytic reformers to be designed for small-scale gas-to liquid (GTL) technologies. Their main advantages are autothermal character of the process without any need in additional heating or power supply, absence of catalyst that allows processing hydrocarbon gases of practically any composition, including APG, without additional pretreatment, very high specific volume capacity, at any rate 10 times higher than that of steam reforming, and simplicity in construction and operation.

Characteristics of Auto-Ignition in Internal Combustion Engines Operated With Gaseous Fuels of Variable Methane Number

This paper explores the feasibility of using Syngas with low methane number as fuel for commercial turbocharged internal combustion engines. The effect of methane number (MN), compression ratio (CR), and intake pressure on auto-ignition tendency in spark ignition internal combustion engines was determined. A nondimensional model of the engine was performed by using kinetics mechanisms of 98 chemical species in order to simulate the combustion of the gaseous fuels produced from different thermochemical processes. An error function, which combines the Livengood–Wu with ignition delay time correlation, to estimate the knock occurrence crank angle (KOCA) was proposed. The results showed that the KOCA decreases significantly as the MN increases. Results also showed that Syngas obtained from coal gasification is not a suitable fuel for engines because auto-ignition takes place near the beginning of the combustion phase, but it could be used in internal combustion engines with reactivity controlled compression ignition (RCCI) technology. For the case of high compression ratio and a high inlet pressure at the engine's manifold, fuels with high MN are suitable for the operating conditions proposed.