Methane Number Research Articles

A rotating detonation engine using methane-ethylene mixture and air

Most of hydrocarbon fuels often have larger methane numbers than hydrogen. It is more difficult to detonate the mixture of hydrocarbon fuels and air at room temperatures in non-premixed engines since the mixing is slower than hydrogen-air mixing and the mixing is slower at lower temperatures. Ethylene–air rotating detonation operations have been successful, but methane-ethylene-air mixture at room temperatures is more difficult to detonate for rotating detonation engines since methane is more chemically stable. The hollow combustor channel here had an outer diameter of 220 mm and a length of 163 mm. Methane-ethylene mixture was injected axially into the combustor from cylindrical orifices in a diameter of 0.8 mm, and air was injected radially through a convergent-divergent circular channel with a throat width of 0.8 mm. Non-premixed rotating detonation waves were obtained for methane-ethylene-air mixture at total temperatures of 280–285 K in the present study. Both high-speed images and pressure traces show that three-wave mode has a higher detonation speed than five-wave mode. The rotating detonation speed is increased with the increased detonation height.

Development of the chemical kinetic mechanism and modeling study on the ignition delay of liquefied natural gas (LNG) at intermediate to high temperatures and high pressures

In the past decade, liquefied natural gas (LNG) has attracted attention as a sustainable energy resource. The composition of LNG is one of the primary factors that has an influence on the engine knock and determines the fuel reactivity and the heat release in the combustion processes due to the presence of C1-C5 alkanes. The knocking behavior of LNG in gas engines is derived by the methane number (MN) which is directly related to the composition of the mixtures and the operating conditions. The determination of the methane number therefore demands a comprehensive characterization of a fuel mixture towards its auto-ignition properties such as ignition delay time (IDT) based on chemical kinetics of the fuel oxidation.In this study, a detailed chemical kinetic mechanism was developed to discover a correlation between the MNs and IDTs. The comparison of the modeling and experiments results of the ignition of different LNG mixtures containing C1-C5 alkanes and N2, and reference mixtures containing only CH4 and H2 with known MN were carried out in the temperature range 850–1550 K, at pressures of 10, 20 and 40 bar, and equivalence ratios (ϕ) of 0.4 and 1.2. The newly developed model demonstrates very good performance in simulating the IDT of various LNG mixtures, while the improvement in reduction of the maximal discrepancies between model and experiments is from factor 7–10 to 1–2. Moreover, the modeling studies provided a deeper understanding of the oxidation chemistry of the investigated mixtures.

Modeling the natural gas knocking behaviour using gas-phase infrared spectra and multivariate calibration

To assess the knocking properties of natural gas (NG) when it is used as fuel for vehicles is vital to optimize the design and functioning of their motors. Analytical efforts in this field are needed as the engines used to define it empirically are not available anymore, and existent mathematical algorithms yield different accuracy. The hybridization of gas-phase infrared spectrometry and partial least squares multivariate regression is presented first time to address the determination of the methane number (MN) of NG samples. It circumvents the need for the previous knowledge of the NG composition required to apply dedicated equations. The use of true NG samples to develop the models is also quite new in the field. Proof-of-concept studies were made with synthetic spectra and, then, a collection of liquefied NG samples for which MN values were computed by the National Physics Laboratory algorithm (NPL) from their sample composition were used to develop operative models. Additional validation was made with a collection of synthetic standard mixtures prepared for two European projects (EMRP LNG II and EMPIR LNG III) whose service methane numbers (SMN) were measured with an engine. The FTIR-PLS approach yielded statistically unbiased predictions with average standard errors around 0.4% MN when compared to the NPL-MN and SMN values, and standard deviations of the means ca. 1% MN. The approach is fast, cost effective as it involves standard instrumentation, and can be considered compliant with the green chemistry principles.

Phenomenological Analysis of the Combustion of Gaseous Fuels to Measure the Energy Quality and the Capacity to Produce Work in Spark Ignition Engines

Abstract Combustion at the knocking threshold (KT) was tested using fuels with different methane numbers (MN) in a modified spark ignition (SI) engine, with high compression ratio (CR) with high turbulence intensity to the combustion process; also, fuels were tested in a cooperative fuel research (CFR) engine to measure MN and critical compression ratio (CCR); in both engines, tests were performed just into the KT. It is proposed that MN to gaseous fuels will be considered similarly to octane number (ON) to liquid fuels, to indicate the energy quality and the capacity to produce work. According to the tests, biogas has better combustion properties than the others fuels; biogas is the fuel with the highest knocking resistance; biogas is the cleanest fuel with the best energy quality measured with the energy density (ED) and adiabatic flame temperature (Tad); biogas has the highest capacity to produce work in SI engines, because of its high MN, low ED, low laminar flame speed (SL), and low Tad. Fuel combustion phenomenological characteristics were compared using CCR versus: output power, generating efficiency, ED, SL, and Tad. It is suggested that the strategies to suppress knocking are the key to improve the performance of SI engines; the knocking phenomenon is the engine limit to electrical energy generation in SI engines; two equations are proposed to define quantum generating efficiency and maximum electrical energy generated; knocking was defined as a quantum phenomenon using the entropy concepts as filter of the second law of thermodynamics.

The effects of natural gas composition on conventional dual-fuel and reactivity-controlled compression ignition combustion in a heavy-duty diesel engine

The use of natural gas (NG) in dual-fuel heavy-duty engines has the potential to reduce pollutant and greenhouse gas (GHG) emissions from the transport sector when compared to the conventional diesel engines. However, NG composition and methane slip are of interest because both can adversely affect the benefits of NG as an alternative fuel, especially when considering GHG emissions. Therefore, this study experimentally investigated the effects of NG fuel properties on the performance and emissions of both conventional dual-fuel and reactivity-controlled compression ignition (RCCI) engine operations. Three different gas mixtures were selected to simulate typical NG compositions available in the world market, with methane numbers (MN) of 80.9, 87.6 and 94.1. These fuels were tested in a single-cylinder compression ignition engine operating at 0.6, 1.2 and 1.8 MPa net indicated mean effective pressure (IMEP). A high-pressure common rail system allowed for the use of various diesel injection strategies while a variable valve actuation system enabled the effective compression ratio to be adjusted via late intake valve closing (LIVC). The RCCI combustion was found to be more sensitive to changes in MN than the conventional NG-diesel dual-fuel operation. The gas mixture with the lowest MN reduced both total unburned hydrocarbons emissions and methane slip at the expense of higher nitrogen oxides (NOx) emissions. The effects of MN on the net indicated efficiency were more significant at 0.6 MPa IMEP, yielding differences of up to 4.9% between the RCCI operations with the lowest and highest MN fuels. Overall, this work revealed that the combination of the RCCI combustion and LIVC can achieve up to 80% lower methane slip and NOx emissions and relatively higher net indicated efficiency than the conventional dual-fuel regime, independent of the NG composition.

Impact of Grid Gas Requirements on Hydrogen Blending Levels

Abstract The aim of the article is to determine what amount of hydrogen in %mol can be transferred/stored in the Estonian, Latvian and Lithuanian grid gas networks, based on the limitations of chemical and physical requirements, technical requirements of the gas network, and quality requirements. The main characteristics for the analysis of mixtures of hydrogen and natural gas are the Wobbe Index, relative density, methane number, and calorific value. The calculation of the effects of hydrogen blending on the above main characteristics of a real grid gas is based on the principles described in ISO 6976:2016 and the distribution of the grid gas mole fraction components from the grid gas quality reports. The Wärtsila methane number calculator was used to illustrate the effects of hydrogen blending on the methane number of the grid gas. The calculation results show that the maximum hydrogen content in the grid gas (hydrogen and natural gas mix), depending on the grid gas quality parameters (methane number, gross heat of combustion, specific gravity, and the Wobbe Index), is in the range of 5–23 %mol H2. The minimum hydrogen content (5 %mol H2) is limited by specific gravity (>0.55). The next limitation is at 12 %mol H2 and is related to the gross heat of combustion (>9.69 kWh/m3). It is advisable to explore the readiness of gas grids and consumers in Estonia, Latvia and Lithuania before switching to higher hydrogen blend levels. If the applicability and safety of hydrogen blends above 5 %mol is approved, then it is necessary to analyse the possible reduction of the minimum requirements for the quality of the grid gas and evaluate the associated risks (primarily related to specific gravity).

Investigation of the end-gas autoignition process in natural gas engines and evaluation of the methane number index

Engine knock and misfire are barriers to pathways leading to high-efficiency Spark-Ignited (SI) Natural Gas (NG) engines. The general tendency to knock is highly dependent on engine operating conditions and the fuel reactivity. The problem is further complicated by the wide range of chemical reactivity in pipeline quality NG, represented by the Methane Number (MN) (65< MN<95). Understanding the underlying phenomena responsible for engine knock can support the development of predictive tools capable of identifying knock onset/intensity as well as a fuel's propensity to knock, allowing engine manufacturers to expand the knock envelope and design more efficient/robust SI NG engines. Additionally, there is an opportunity for increased efficiency by controlling levels of end-gas autoignition if this can be predicted and controlled. This work focuses on the development of a novel methodology to understand/predict a fuel's propensity to knock. This methodology is based on the charge fraction undergoing autoignition, namely fractional end-gas autoignition (F-EGAI), and was developed based on first order laminar flame speeds and ignition delay analysis combined with a 0-D homogeneous batch reactor model. This methodology proved to be suitable to predict a fuel's propensity to knock, even under conditions when light knock was observed. The simple modeling approach was used to explain the results from a series of MN tests with multiple NG compositions exhibiting a wide range of reactivity compositions and providing insight on why fuels of very different chemical compositions can have the same MN. Lastly, a CFD model was developed was used to confirm the methodology capability and provide further insights in the physical and chemical phenomena behind end gas autoignition.

Impact of Liquefied Natural Gas Composition Changes on Methane Number as a Fuel Quality Requirement

The one of main quality requirements of natural gas as an engine fuel is the methane number (MN). This parameter indicates the fuel’s capability to avoid knocking in the engine. A higher MN value indicates a better natural gas quality for gas engines. Natural gas with higher methane content tends to have higher MN value. This study presents analysis of deviation of liquefied natural gas (LNG) composition and its impact on LNG quality as an engine fuel. The analysis of higher hydrocarbons and nitrogen content impact on LNG parameters was considered for several samples of LNG compositions. Most engine manufacturers want to set a new, lower limit value for methane number at 80. This fact causes significant restrictions on the range of variability in the composition of liquefied natural gas. The goal of this study was to determine the combination of the limit content of individual components in liquefied natural gas to achieve the strict methane number criterion (MN &gt; 80). To fulfill this criterion, the methane content in LNG would have to exceed 93.7%mol, and a significant part of the LNG available on the market does not meet these requirements. The analysis also indicated that the methane number cannot be the only qualitative criterion, as its variability depends strongly on the LNG composition. To determine the applicability of LNG as an engine fuel, the simultaneous application of the methane number and Wobbe index criteria was proposed.

A method for determining hydrogen–methane–nitrogen mixtures for laboratory tests of syngas-fuelled internal combustion engines

An original method for formulating surrogate fuels from actual syngas mixtures is presented and formalised. The method is the first example in the scientific literature of a rather complete tool for planning and setting up a laboratory syngas-fuelled engine test when some components of the syngas mixture are not available. Basically, the method allows a map to be built that provides the composition for a surrogate fuel once the composition of a syngas mixture is assigned, the components of a surrogate fuel are selected and the equivalence parameters are defined. The laminar flame speed, the energy density of the fuel–air mixture and the methane number are identified as equivalence parameters in the study. In particular, the proper laminar flame speed and energy density ensure that an engine fuelled by the surrogate mixture produces the same indicated power as it would when fuelled by the original syngas. Instead, the methane number allows for checking the fact that the tendency of the engine to knock is the same or greater than the knock tendency during syngas operation. In this article, the method is used to determine the hydrogen–methane–nitrogen mixtures corresponding to six five-component syngas mixtures, resulting from actual gasification processes. The laminar flame speed and methane number of each syngas mixture are estimated by means of simple original models aimed at either improving the predicting capabilities of existing models or allowing for a prompt application of the procedure. The results show that four of the six surrogate fuels are equally or more knock-prone than the original syngas mixtures, whereas only one of the two remaining surrogate fuels likely imposes a retardation of the spark advance in the final setup of the engine for actual syngas operation.

Numerical assessment of methane number and critical compression ratio of gaseous alternative fuels: CFR engine quasi dimensional simulation approach

The development of a quasi-dimensional engine model and its adaptation for CFR configuration for Methane Number assessment of gaseous fuel mixtures is reported. The stochastic model based on eddy entrainment and laminar burn-up concept for turbulent combustion adopts full reaction kinetics with detailed reaction mechanism in the unburned mixture region for auto-ignition. Adaptive time step solver is invoked for the solution of the stiff system of equations. Modular validation of the developed engine simulation model is performed by independently validating an iso-choric system and an HCCI engine module followed by complete engine simulation model validation based on experimental results over a range of operating conditions and different engine frames. The model is extended to replicate a CFR engine as per ASTM D2700-16a/ASTMWK54121 and validated based on literature reported data. The use of flame quench limit for knock recognition in lieu of equivalence ratio independence, as adapted in the ASTM standards, is a particular case in point example.The developed model is used for knock rating assessment of eight different syngas compositions. Preliminary analysis suggests the model to over-predict the critical CR to the tune of 1 ± 0.5 with the over-prediction attributed to aspects like turbulence, heat transfer, fame propagation etc. Relaxing the flame out limit by 2° crank angle improves the critical CR prediction to within 0.75 ± 0.25. The estimated Methane Number remains within 5 units of the experimental results establishing the capability of the proposed model for assessment of gaseous fuel knock rating. The proposed approach can be extended to evaluate other fuels for knock quality assessment by incorporating appropriate fuel specific features.

Experimental and Modeling Studies on the Correlation Between Auto-Ignition Delays and the Methane Number of Liquefied Natural Gas (LNG) and Liquefied Biogas (LBG)

Liquefied natural gas (LNG) and liquefied biogas (LBG) as transport fuel constitute one of the pillars of the European clean fuel strategy. LNG and LBG often contain higher hydrocarbons up to C5 that lead to more complex ignition properties when utilizing them in gas engines. Therefore, it is essential to understand their combustion behavior and to quantify the abnormal combustion such as knocking propensity with correlation to the methane number (MN). Currently, there is no traceable standard to define the MN and the literature algorithms give no consistent results for the same LNG/LBG mixtures. In this study, the correlation between MN and ignition delays of several LNG/LGB mixtures containing C1 to C5 alkanes and nitrogen were investigated at temperatures between 870 and 1550 K at 10, 20, and 40 bar and with equivalence ratios of 0.4 and 1.2. Good correlations have been observed for mixtures with MN 50 to 90 at high temperatures. At intermediate temperatures, discrepancies were found between mixtures with same MN but different C1 to C3 compositions. Moreover, addition of butane and propane isomers at low vol.% showed no effect on the IDTs at intermediate temperatures.

Mobile-Platform Measurement of Air Pollutant Concentrations in California: Performance Assessment, Statistical Methods for Evaluating Spatial Variations, and Spatial Representativeness.

Mobile platform measurements provide new opportunities for characterizing spatial variations of air pollution within urban areas, identifying emission sources, and enhancing knowledge of atmospheric processes. The Aclima, Inc. mobile measurement and data acquisition platform was used to equip four Google Street View cars with research-grade instruments, two of which were available for the duration of this study. On-road measurements of air quality were made during a series of sampling campaigns between May 2016 and September 2017 at high (i.e., 1-second [s]) temporal and spatial resolution at several California locations: Los Angeles, San Francisco, and the northern San Joaquin Valley (including non-urban roads and the cities of Tracy, Stockton, Manteca, Merced, Modesto, and Turlock). The results demonstrate that the approach is effective for quantifying spatial variations of air pollutant concentrations over measurement periods as short as two weeks. Measurement accuracy and precision are evaluated using results of weekly performance checks and periodic audits conducted through the sampler inlets, which show that research instruments located within stationary vehicles are capable of reliably measuring nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3), methane (CH4) black carbon (BC), and particle number (PN) concentration with bias and precision ranging from <10 % for gases to <25 % for BC and PN at 1-s time resolution. The quality of the mobile measurements in the ambient environment is examined by comparisons with data from an adjacent (< 9 m) stationary regulatory air quality monitoring site and by paired collocated vehicle comparisons, both stationary and driving. The mobile measurements indicate that U.S. EPA classifications of two Los Angeles stationary regulatory monitors' scales of representation are appropriate. Paired time-synchronous mobile measurements are used to characterize the spatial scales of concentration variations when vehicles were separated by <1 to 10 kilometers (km). A data analysis approach is developed to characterize spatial variations while limiting the confounding influence of diurnal variability. The approach is illustrated using data from San Francisco, revealing 1-km scale differences in mean NO2 and O3 concentrations up to 117 % and 46 %, respectively, of mean values during a two-week sampling period. In San Francisco and Los Angeles, spatial variations up to factors of 6 to 8 occur at sampling scales of 100 - 300m, corresponding to 1-minute averages.

Capacitive and Infrared Gas Sensors for the Assessment of the Methane Number of LNG Fuels.

Liquid Natural Gas (LNG) is an energy source that is becoming more important in energy transition, as the world is facing lower the CO2 emissions and backup sources for wind and solar energy are needed. LNG is becoming a major player not only as fuel for power plants, but also in transport and mobility. However, the composition of LNG varies significantly between the various production locations around the world, and the layering of hydrocarbons with different molecular weights takes place even in LNG containers. This is especially critical for LNG engines, in which the ignition properties of the gas depend heavily on the fuel quality or Methane Number (MN) of the gas. For optimized engine operation and motor management, this fuel quality should be measured regularly, preferably online and by a small and low-cost sensor. This paper presents two sensor solutions for the assessment of the full gas composition. For both sensors, the standard deviation in the composition of the relevant hydrocarbons was low enough to calculate the Methane Number with an accuracy of approximately 1 MN unit. It was demonstrated that the electronic capacitive sensor was better suited to assess the higher hydrocarbons, whereas the infrared sensor showed higher selectivity for the lower hydrocarbons.

Methane Number Control of Fuel Gas Supply System Using Combined Cascade/Feed-Forward Control

Liquefied natural gas began to attract attention as a ship fuel to reduce environmental pollution and increase energy efficiency. During this period, highly efficient internal combustion engines emerged as the new propulsion system instead of steam turbines. However, Otto-cycle engines must use fuel that meets the methane number that was given by the engine makers. The purpose of this study was to develop a system configuration and a control method of methane number adjustment using combined cascade/feed-forward controllers for marine Otto-cycle engines to improve reference tracking and the disturbance rejection. The main principle involves controlling the downstream gas temperature of the fuel gas supply system to meet the required methane number. Three controllers are used in the combined cascade/feed-forward control for adjusting the downstream of the gas temperature: the cascade loop has two controllers and the feed-forward has one controller. The two controllers in the cascade loop are designed with proportional–integral (PI) controllers. The remaining controller is based on feed-forward control theory. A simulation was conducted to verify the efficacy of the proposed method, focusing on the disturbance rejection and set-point tracking, in comparison with a single PI controller, a single PI controller with feed-forward, and cascade control.

Impact of natural gas quality on engine performances during a voyage using a thermodynamic fuel system model

Liquefied Natural Gas (LNG) as a fuel is seen as a solution to curb harmful emissions in shipping and its quick uptake is now significant. As heat leaks into the LNG fuel tanks, composition of the vapor and liquid phase change. This process, known as ageing, alters the fuel properties and can impact negatively the main engine performance. In this paper, a dynamical model to assess the methane number at engine inlet from the bunkered composition is presented. The fuel system is made of a 40 ft container tank and two heat exchangers. The model considers the two-phase real mixture in the tank and solves explicitly the heat and mass conservation laws. Then a strategy is developed to avoid “off-spec” methane number at engine inlet. The approach is tested on two bunkered compositions, one from Libya and one from Australia. The simulations have been conducted for a concept LNG/wind electric ship using multiple removable 40 ft container LNG tanks. Results show that with the proposed mixing strategy, the methane number remains above its limit value at engine inlet, insuring optimal operating conditions of engines.

Prediction of the knock propensity of biogenous fuel gases: Application of the detonation theory to syngas blends

Prediction of the knock propensity is crucial for design and control of engines operating on syngas from thermo-chemical conversion. Classical fuel rating methods such as the methane number or the propane knock index were found to fail for the syngas compositions encountered in practice. A detailed chemical kinetics simulation of the critical compression ratio in an ideal homogenous auto-ignition reactor was tested as an alternative rating method, but was found to also have serious drawbacks and provoke misleading results due to overlying thermodynamic effects. Thus, a novel methodology based on the detonation theory was successfully adopted. The method centres on the two dimensionless parameters ξ and ε which characterise the possible regimes of auto-ignition propagation originating from hot spots. The ξ-ε diagram was applied to a total of 38 fuel blends including reference fuels and syngas compositions determined with a statistical mixture plan supplemented by measured data. The gas measurements were taken at an industrial scale intermediate pyrolysis plant featuring the Thermo-Catalytic Reforming technology of Fraunhofer UMSICHT. Practically all syngas blends showed to be more prone to knock than methane or biogas, albeit not more than propane, which is a standard fuel used in gas engines. Admixtures of higher hydrocarbons were found to substantially increase the knock propensity. Lean equivalence ratios, exhaust gas recirculation and the addition of water vapour were effective measures to mitigate the risk of knock. The anti-knock effect of dilution could be primarily attributed to a reduction of the amount of energy transferred into the acoustic front of an auto-ignition wave.

A Versatile Capacitive Sensing Platform for the Assessment of the Composition in Gas Mixtures.

The energy market is facing a major transition, in which natural gas and renewable gasses will play an important role. However, changing gas sources and compositions will force the gas transporters, gas engine manufacturers, and gas grid operators to monitor the gas quality in a more intensive way. This leads to the need for lower cost, smaller, and easy to install gas quality sensors. A new approach is proposed in this study that is based on the chemical interactions of the various gas components and responsive layers applied to an array of capacitive interdigitated electrodes. For Liquid Natural Gas (LNG), containing a relative high concentration of higher hydrocarbons, an array of ten capacitive chips is proposed, that is sufficient to calculate the full composition, and can be used to calculate energy parameters, such as Wobbe Index, Calorific Value, and Methane Number. A first prototype was realized that was small enough to be inserted in low and medium pressure gas pipes and LNG engine fuel lines. Adding the pressure and temperature data to the chip readings enables the determination of the concentrations of the various alkanes, hydrogen, nitrogen, and carbon dioxide, including small fluctuations in water vapor pressure. The sensitivity and selectivity of the new sensor is compared to a compact analyzer employing tunable filter infrared spectrometry.

Algorithm for Determining the Knock Resistance of Pipeline Natural Gases

A next-generation algorithm to calculate the PKI methane number is reported. The algorithm is suitable for a wide range of fuel compositions encountered in natural gas pipelines, including admixture of hydrogen and carbon monoxide from renewable sources. Comparison with measurements of knock in a commercial engine shows that the algorithm allows sharp distinction between fuel compositions that do or do not cause engine knock under given operating conditions. Moreover, the algorithm presented here demonstrates superior performance as compared to the existing methods from MWM and AVL. The methane numbers calculated using the PKI MN algorithm for a wide range of fuel compositions are within the uncertainty of the experimental knock measurements. In contrast, methods that are currently used do not predict the knock behavior of the measured gas compositions reliably. A major benefit of the algorithm presented here is that it consists of a simple polynomial equation that can be easily integrated into real-time gas-quality sensing equipment to calculate the PKI MN for assessment of pipeline gas quality or into engine management systems to allow next-generation feed-forward, fuel-adaptive control. In contrast, the current methods such as AVL and MWM need dedicated (and for AVL, proprietary) solvers that iteratively calculate the methane number. 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 gaseous fuels.

Dynamic simulation of fuel tank aging for LNG‐fueled ship apparatus in an X‐DF Otto cycle engine

AbstractThe increased density in a liquefied natural gas (LNG) tank caused by boil‐off gas (BOG) is a key factor to consider for LNG‐fueled ships with Otto cycle engines. This study conducted dynamic simulation using Aspen HYSYS to solve LNG aging in the fuel gas supply system (FGSS) of an extra‐long stroke dual fuel (X‐DF) engine. The aging phenomenon is severe in the Otto cycle internal combustion engine because heavy hydrocarbon (HHC) components must be removed during the process to satisfy the methane number (MN) requirement. HHC components such as ethane, propane, butane are separated in the HHC removal process so that HHC can be returned to the LNG storage or fuel tank without increased risk of equipment failure relative to steady‐state design conditions. Dynamic process simulations for four cases were conducted to verify the behavior of LNG aging for two fuel compositions and two fuel tank capacities. The results indicate that the different composition of LNG affects the pump duty, the duty of heat exchanger and BOG compressor in steady‐state simulation. Additionally, based on the analysis results, solutions to the problem caused by LNG aging for the FGSS in an X‐DF engine were provided.

Experimental investigation of natural gas reactivity using a fuel substitution method

Fuel substitution tests using reference fuels of methane/hydrogen and methane/propane were performed for the pure test fuels hydrogen, ethane, ethylene, propane, n-butane, n-heptane, and isooctane using HCCI combustion. The reactivity of each test fuel relative to the reference fuels was quantified with a newly defined hydrogen index (HI) and propane index (PI). It was observed that the common hydrocarbon fuels tested show a strong sensitivity of HI and PI to temperature and pressure, and that the reactivity relative to the reference fuels can change substantially at different operating conditions. The fuels that have similar low temperature chemistry (n-butane, n-heptane, and isocotane) exhibited PI that were independent of operating condition. Ethane, ethylene, and hydrogen exhibited PI that were strongly dependent on operating condition, with the relative reactivities increasing with increasing temperature. Fuel substitution tests performed with two multi-component methane number (MN) gas mixtures followed trends similar to those observed for the pure hydrocarbon fuel testing, exhibiting similar relative reactivity trends as for propane relative to the reference fuels for the different operating conditions. A linear energy-based blending rule was used to predict the HI of each fuel mixture from the individual fuel components and seen to match experimental trends; however, predicted HI were lower than experimental HI across all operating conditions. The MN was also used to predict the HI of each fuel mixture and was seen to match experimental results only at low pressure/high temperature conditions but not at high pressure/low temperature conditions.