Browse Topic: Methane

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Dragonfly : Defining Environments for Rotorcraft Flight on TitanF-0076-2020-1630110/5/2020
Dragonfly is an X-8 octocopter designed to explore Saturn's moon Titan, and is currently under development for launch in 2026. Titan is a uniquely favorable body for atmospheric flight, in that it has a low gravity (1/7 Earth's) and a dense atmosphere (4x Earth's) which reduce the energetic requirements for heavier-than-air flight. Dragonfly will make multiple (autonomous) flights over several years with ranges of the order of 10km to explore different sites on Titan. The key features of the Titan environment are reviewed. These include the characteristics of the landing site terrain, resembling dune fields in terrestrial deserts. Winds are generally very low, ∼ 1m/s. Stronger winds, and methane rainfall, can occur in rare rainstorms, but these are not expected at the latitude and season of Dragonfly's arrival. Brownout and triboelectric charging due to surface dust lofted by rotor downwash is possible, and these hazards and their mitigations are discussed.
Lorenz, Ralph
In-Situ Resource Utilization (ISRU): Methylotrophic Microorganisms Expressing Soluble Methane Monooxygenase ProteinsTBMG-358121/1/2020
Long-duration missions to planetary bodies and deep space will require new technological developments that support human habitation in transit and on distant bodies. Microorganisms are unique from the standpoint that they can be employed as self-replicating bio-factories to produce both native and engineered mission-relevant bio-products. Methane (CH4) usage in In-Space Manufacturing (ISM) platforms has been discussed previously for human exploration and has been proposed to be used in physicochemical systems as a propulsion fuel, supply gas, and in fuel cells.
Methane Detector Sniffs Out LeaksTBMG-351569/1/2019
Methane is everywhere on Earth. It’s the main ingredient in the natural gas that powers heating, cooking, and electricity. It’s also a potent greenhouse gas. The presence of methane is also interesting for a different reason: because the biggest source of the gas on Earth is bacterial life. That means when NASA planetary scientists caught a glimpse of it on Mars, it merited a closer look.
Mobile, Dual-Comb Device for Methane Leak DetectionTBMG-351459/1/2019
Accurately detecting, locating, and quantifying leaks of methane — the main component of natural gas and a major fuel source worldwide — is critically important for both environmental and economic reasons. Unfortunately, traditional methods are slow, labor-intensive, limited to small coverage areas, and expensive to operate over time.
The Use of Ozone in Low Temperature Methane Control for Natural Gas Applications2018-01-17029/10/2018
Lean operating natural gas heavy duty applications have advantages in terms of lower CO2 and PM compared to Diesel applications. This makes operating heavy duty applications on natural gas attractive and currently, they do not have to implement an exhaust particulate filter. However, the challenge is controlling methane emissions over a range of vehicle operating conditions. Methane is extremely stable and light off occurs at temperatures above 400 °C, with high efficiency occurring >500 °C and requires high precious metal loaded catalysts in the range of 150 - 200 g/ft3. Under stoichiometric conditions, 500 °C can be met in many engine operating points however, for lean operating applications, the exhaust temperature can be significantly lower than 500 °C posing a significant challenge for exhaust catalytic CH4 control. This paper will discuss synthetic gas reactor study results using ozone in the feed gas to perform low temperature methane control. A range of catalysts were characterised for the development of low temperature methane control and a non-precious metal catalyst was found to give high efficiency at low temperatures. The best catalyst screened did not contain PGM and was a current production catalyst that gave >60% CH4 control at 220 °C, in the presence of water. All other catalysts screened gave no significant methane control activity at low temperatures. The feed gas composition played a key role in the peak efficiency obtained. The data shows a significant improvement in ozone enhanced catalysis compared to more traditional precious metal based CH4 control routes.
Keenan, Matthew, Nicole, Jacques, Poojary, Damodara
Experimental Study on Combustion Characteristics of Methane/Gasoline Dual-Fuel in a SI Engine at Different Load Conditions2018-01-11404/3/2018
Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO2 emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions. Under large load conditions, methane addition showed good knocking resistance and the potential of knocking limit extension. Through advancing spark-ignition timing, methane/gasoline dual-fuel combustion was able to provide sufficient torque output with optimized combustion phasing. Current research results shall give insights into combustion optimization of methane (or natural gas) and gasoline dual-fuel engines.
Pan, Jiaying, Wei, Haiqiao, Shu, Ge-Qun, Feng, Dengquan
Investigation of Combustion Knock Distribution in a Boosted Methane-Gasoline Blended Fueled SI Engine2018-01-02154/3/2018
The characteristics of combustion knock metrics over a number of engine cycles can be an essential reference for knock detection and control in internal combustion engines. In a Spark-Ignition (SI) engine, the stochastic nature of combustion knock has been shown to follow a log-normal distribution. However, this has been derived from experiments done with gasoline only and applicability of log-normal distribution to dual-fuel combustion knock has not been explored. To evaluate the effectiveness and accuracy of log-normal distributed knock model for methane-gasoline blended fuel, a sweep of methane-gasoline blend ratio was conducted at two different engine speeds. Experimental investigation was conducted on a single cylinder prototype SI engine equipped with two fuel systems: a direct injection (DI) system for gasoline and a port fuel injection (PFI) system for methane. The experiments were conducted at 1500 rpm and 2000 rpm, 12.0 bar net indicated mean effective pressure wherein the engine was boosted using compressed air. E10 gasoline and methane were used in this study. The results from blending two fuels show that the log-normal distribution provides a good fit to the measured distribution and captures the knock characteristics. The independency of log-normal distribution to the knock distribution at different spark timings was examined. The distribution parameters (log normal mean (μ) and standard deviation (σ)) show a linear correlation with the spark timing from knock borderline (BD) to 1.75° crank angle retarded. A μ and σ fit based log-normal (calculation-based log-normal) distribution model was proposed. The coefficients of multiple determination (CoMD) for the calculation-based log-normal model are all above 0.8 over the tested conditions. The validation of calculation-based log-normal was also conducted for all blending ratios and speeds.
Yang, Zhuyong, Rao, Sandesh, Wang, Yanyu, Harsulkar, Jaideep, Ansari, Ehsan, Miganakallu Narasimhamurthy, Niranjan, Dice, Paul, Naber, Jeffrey, Lonari, Yashodeep, Szwaja, Stanislaw
Optical Investigation of Sooting Propensity of n-Dodecane Pilot/Lean-Premixed Methane Dual-Fuel Combustion in a Rapid Compression-Expansion Machine2018-01-02584/3/2018
The sooting propensity of dual-fuel combustion with n-dodecane pilot injection in a lean-premixed methane-air charge has been investigated using an optically accessible Rapid Compression-Expansion Machine (RCEM) to achieve engine-relevant pressure and temperature conditions at the start of pilot injection. A Diesel injector with a 100 μm single-hole coaxial nozzle, mounted at the cylinder periphery, has been employed to admit the pilot fuel. The aim of this study was to enhance the fundamental understanding of soot formation and oxidation processes of n-dodecane in the presence of methane in the air charge by parametric variation of methane equivalence ratio, charge temperature, and pilot fuel injection duration. The influence of methane on ignition delay and flame extent of the pilot fuel jet has been determined by simultaneous excited-state hydroxyl radical (OH*) chemiluminescence and Schlieren imaging. The sooting behavior of the flame has been characterized using the 2D-DBI imaging methodology. The apparent soot black-body temperature has been measured 1D resolved along the injector axis by applying an imaging spectrograph. Addition of methane into the air charge considerably prolongs the ignition delay with an increasing effect under less reactive conditions and with higher methane equivalence ratios. Therefore, the influence of methane on the formation of soot is twofold: in case of short pilot injection, the presence of methane was found to decrease the soot formation due to the leaner pilot fuel mixture at the time of ignition. For longer pilot fuel injections, methane enhances the soot production by decreasing oxygen availability and introducing additional carbon. In all cases, methane strongly defers the oxidation of soot due to the lower availability of oxygen.
Srna, Aleš, Bruneaux, Gilles, von Rotz, Beat, Bombach, Rolf, Herrmann, Kai, Boulouchos, Konstantinos
An Optical Characterization of Dual-Fuel Combustion in a Heavy-Duty Diesel Engine2018-01-02524/3/2018
Dual fuel (DF) combustion technology as a feasible approach controlling engine-out emissions facilitates the concept of fuel flexibility in diesel engines. The abundance of natural gas (90-95% methane) and its relatively low-price and the clean-burning characteristic has attracted the interest of engine manufacturers. Moreover, with the low C/H ratio and very low soot producing tendency of methane combined with high engine efficiency makes it a viable primary fuel for diesel engines. However, the fundamental knowledge on in-cylinder combustion phenomena still remains limited and needs to be studied for further advances in the research on DF technology. The objective of this study is to investigate the ignition delay with the effect of, 1) methane equivalence ratio, 2) intake air temperature and 3) pilot ratio on the diesel-methane DF-combustion. Combustion phenomenon was visualized in a single cylinder heavy-duty diesel engine modified for DF operations with an optical access. The high-speed natural luminosity (NL) imaging technique was employed to record the temporally resolved in-cylinder combustion event at an operating load of approx. 10 bar IMEP at 1400 rpm. The results show that flame propagation becomes stable and sustained with an increase in either of the methane equivalence ratio, intake air temperature, or diesel amount. However, the sensitivity of each effect on the flame propagation and ignition delay was observed to be different. The effect of these parameters on DF combustion has been characterized with the help of NL images and corresponding cylinder pressure and net heat-release rate (HRR) data. The study also presents a detailed discussion on the analyzed ignition delay trends.
Ahmad, Zeeshan, Aryal, Janak, Ranta, Olli, Kaario, Ossi, Vuorinen, Ville, Larmi, Martti
Study on Auto-Ignition Characteristics of High Pressure Methane Jet for Compression Ignition Engine Application2018-01-02744/3/2018
Natural gas has been considered as an alternative fuel for a heavy duty diesel engine with its lower pollutant and carbon dioxide emissions than its counterpart. However, due to the high auto-ignition temperature of methane, this alternate fuel has been mainly used in spark-ignited engine with relatively lower compression ratio, losing full potential of achieving high efficiency. To overcome these limitations, high-pressure direct injection of the natural gas in a compression ignition engine has been proposed, and there have been several attempts to understand physical behaviors and ignition of methane jet. In this study, auto-ignition characteristics of high-pressure methane jet were investigated both through the experiment and the multi-zone modeling to suggest the applicability to such engine. In the experiments, constant volume combustion chamber equipped with a single-hole, gasoline-direct-injector was used to understand the jet behavior and the ignition characteristic of the high-pressure (~90 bar) methane injection. To visualize the shape of jet and combustion, shadowgraph/schlieren photography and natural luminosity imaging were carried out. From the experimental results, the penetration distance of 15~25 mm is achieved in ~1.5 msec and the first apparent ignition of methane jet occurs around 1.3 to 5.5 msec after start-of-injection, as background temperature decreases from 1300 K to 1150 K in the background pressure of 50 ± 5 bar. In the multi-zone modeling, jet penetration model based on Abramovich concentration and velocity gradient profile was adapted for overall penetration calculation, while the species transfer by convection and the GRI 3.0 mechanism were adapted for calculating the chemical reaction kinetics and validated against the experimental result. The model was used to study the effects of fuel and background conditions (pressure, temperature and composition) on ignition characteristic of high pressure methane jet, and the applicability to a compression ignition engine was evaluated based on the results.
Lee, Tae Kyung, Min, Hyungeun, Song, Han Ho
CFD Analysis of the Combustion Process in Dual-Fuel Diesel Engine2018-01-02574/3/2018
Dual-fuel technology has the potential to offer significant improvements in the emissions of carbon dioxide from light-duty compression ignition engines. The dual-fuel (diesel/natural gas) concept represents a possible solution to reduce emissions from diesel engines by using natural gas (methane) as an alternative fuel. Methane was injected in the intake manifold while the diesel oil was injected directly into the engine. The present work describes the results of a numerical study on combustion process of a common rail diesel engine supplied with natural gas and diesel oil. In particular, the aim is to study the effect of increasing methane concentration at constant injected diesel amount on both pollutant emissions and combustion evolution. The study of dual-fuel engines that is carried out in this paper aims at the evaluation of the CFD potential, by a 3-dimensional code, to predict the main features of this technology. In fact, to better understand the phenomena that take place during the dual-fuel operation (flame propagation throughout the premixed methane-air medium activated by the early self-ignition of the diesel fuel), the fluid-dynamic calculations could be extremely useful. The model calibration has been done referring to experimental data obtained in a single cylinder of an optically accessible engine. The experiments provided reference data in terms of pressure cycles, pollutant and unburned species and detailed visualization of the combustion development. Such data represented an effective validation check of the CFD based calculations. The latter allowed a deeper investigation of the combined diesel oil - methane combustion process. The numerical results also confirm that the OH radical plays a significant role for the detection of the regions with the highest combustion reactivity.
Mancaruso, Ezio, Sequino, Luigi, Vaglieco, Bianca Maria, Cameretti, Maria Cristina, De Robbio, Roberta, Tuccillo, Raffaele
Experimental and Kinetic Analyses of Thermochemical Fuel Reforming (TFR) with Alcohol Enrichment in Plug Flow Reactor: a Verification of In-Cylinder TFR2017-01-227810/8/2017
In-cylinder thermochemical fuel reforming (TFR) in spark ignition natural gas engine was developed to reveal that thermochemical fuel reforming could increase H2 and CO concentration in reformed gas, leading to an increase of thermal efficiency and engine performance. Moreover, ethanol enrichment has been proved to have great potential to optimize TFR performance. In order to explain TFR phenomenon chemically, methane oxidation experiments were conducted in a laminar flow reactor with addition of ethanol and methanol at equivalent ratios of 1.5, 1.7, 1.9 and 2.1 from 948K to 1098K at atmospheric pressure. Experimental results showed that methanol have great ability to facilitate the oxidation of methane than that of ethanol. Meanwhile, the degree of methane conversion became more significantly as the equivalent ratio increased. Kinetic analysis of oxidation of methane with alcohol enrichment in a plug flow model was also conducted in this study. There was good agreement between experimental and computational results. The oxidation of methanol or ethanol released plenty of radicals such as H, OH and HO2, which further reacted with CH4 more intensively in fuel rich condition. Rate of production and sensitivity analyses showed that methanol could produce more reactive radicals, which were involved in a series of initial oxidation reactions of methane. It indicated that methanol have great potential to improve in-cylinder TFR performance.
Deng, Zhiwei, Li, Ang, Zhu, Lei, Huang, Zhen
Direct Numerical Simulation of Methane Turbulent Premixed Oxy-Fuel Combustion2017-01-219210/8/2017
A 3-D DNS (Three-Dimensional Direct Numerical Simulation) study with detailed chemical kinetic mechanism of methane has been performed to investigate the characteristics of turbulent premixed oxy-fuel combustion in the condition relevant to Spark Ignition (SI) engines. First, 1-D (one-dimensional) laminar freely propagating premixed flame is examined to show a consistent combustion temperature for different dilution cases, such that 73% H2O and 66% CO2 dilution ratios are adopted in the following 3-D DNS cases. Four 3-D DNS cases with various turbulence intensities are conducted. It is found that dilution agents can reduce the overall flame temperature but with an enhancement of density weighted flame speed. CO2 dilution case shows the lowest flame speed both in turbulent and laminar cases. Reaction path analysis based on an in-house post-processing tool is performed to show that the chemical effect of dilution agent H2O leads to an increase of the key elementary reactions; however the total effect is endothermic compared with the counterparts for air condition case. This also results in a lower temperature of the oxy-fuel combustion. Furthermore, weak and strong levels of turbulent intensities 0.8 and 2.4 m/s are studied to show that the higher turbulent intensity leads to higher pressure rise rate, more flame surface wrinkling and higher displacement speed.
Zhong, Shenghui, Peng, Zhijun, Li, Yu, Li, Hailin, Zhang, Fan
Correlation between Simulated Volume Fraction Burned Using a Quasi-Dimensional Model and Flame Area Measured in an Optically Accessible SI Engine2017-01-05453/28/2017
Multi-fuel operation is one of the main topics of investigative research in the field of internal combustion engines. Spark ignition (SI) power units are relatively easily adaptable to alternative liquid-as well as gaseous-fuels, with mixture preparation being the main modification required. Numerical simulations are used on an ever wider scale in engine research in order to reduce costs associated with experimental investigations. In this sense, quasi-dimensional models provide acceptable accuracy with reduced computational efforts. Within this context, the present study puts under scrutiny the assumption of spherical flame propagation and how calibration of a two-zone combustion simulation is affected when changing fuel type. A quasi-dimensional model was calibrated based on measured in-cylinder pressure, and numerical results related to the two-zone volumes were compared to recorded flame imaging. Gasoline, ethanol, methane and hydrogen were used as fuels and the aforementioned comparison was performed for each case. In order to identify the influence of specific properties, intake pressure, air-fuel ratio and spark timing were kept constant for al fuel types. Overall the spherical flame assumption was found to ensure acceptable results and the correlation between turbulence intensity and flame propagation emphasized the importance of proper description of localized scales at which chemical reactions occur behind the flame front.
Irimescu, Adrian, Di Iorio, Silvana, Merola, Simona Silvia, Sementa, Paolo, Vaglieco, Bianca Maria
Surface Functional Groups and Graphitization Degree of Soot in the Sooting History of Methane Premixed Flame2017-01-10033/28/2017
The evolution of surface functional groups (SFGs) and the graphitization degree of soot generated in premixed methane flames are studied and the correlation between them is discussed. Test soot samples were obtained from an optimized thermophoretic sampling system and probe sampling system. The SFGs of soot were determined by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) after removing the soluble impurities from the soot samples, while the graphitization degree of soot was characterized by Raman spectrum and electron energy loss spectroscopy (EELS). The results reveal that the number of aliphatic C-H groups and C=O groups shows an initial increase and then decrease in the sooting history. The large amount of aliphatic C-H groups and small amount of aromatic C-H groups in the early stage of the soot mass growth process indicate that aliphatic C-H groups make a major contribution to the early stage of soot mass growth. The higher graphitization degree of soot appears at low height above the burner when the graphite core is formed. The graphitization degree of soot rapidly decreases in the early mass growth stage then increases in the maturation process. The results from transmission electron microscopy (TEM), SFGs, and the graphitization degree verify the assumption that the nascent soot consists of a graphite-like core and an aliphatic shell. There is a strong correlation between SFGs and graphitization degree in the early stage of the soot mass growth process. During the soot maturation process, the correlation between SFGs and graphitization degree weakens. The SFGs may be related to the aggregate soot particle properties, such as fractal dimension.
Liu, Ye, Lv, Gang, Fan, Chenyang, Li, Na, Wang, Xiaowei
The Effects of Charge Preparation, Fuel Stratification, and Premixed Fuel Chemistry on Reactivity Controlled Compression Ignition (RCCI) Combustion2017-01-07733/28/2017
Engine experiments were conducted on a heavy-duty single-cylinder engine to explore the effects of charge preparation, fuel stratification, and premixed fuel chemistry on the performance and emissions of Reactivity Controlled Compression Ignition (RCCI) combustion. The experiments were conducted at a fixed total fuel energy and engine speed, and charge preparation was varied by adjusting the global equivalence ratio between 0.28 and 0.35 at intake temperatures of 40°C and 60°C. With a premixed injection of isooctane (PRF100), and a single direct-injection of n-heptane (PRF0), fuel stratification was varied with start of injection (SOI) timing. Combustion phasing advanced as SOI was retarded between -140° and -35°, then retarded as injection timing was further retarded, indicating a potential shift in combustion regime. Peak gross efficiency was achieved between -60° and -45° SOI, and NOx emissions increased as SOI was retarded beyond -40°, peaking around -25° SOI. Optimal cases in terms of both gross efficiency and peak pressure rise rate (PPRR) were in the mid-range SOI timings centered about -50° SOI, while late SOI resulted in decreased gross efficiency, decreased combustion efficiency, and high NOx. To assess the effect of the premixed fuel chemistry on RCCI combustion, a representative reformed fuel referred to as syngas (50% H2, 50% CO by volume), and methane were substituted for PRF100. A reference baseline PRF condition with an SOI timing of -50° at Tin = 40°C and ϕ = 0.30 was used for comparison purposes. Matching combustion phasing to the baseline case by adjusting the premixed percent or SOI timing resulted in reduced gross efficiency (ηg) and increased NOx emissions for both the syngas and methane cases. Matching the bulk heat release rate (HRR) characteristics by fixing the DI SOI quantity and duration and adding a premixed injection of n-heptane was able to regain most of the lost efficiency while decreasing NOx emissions close to the baseline level.
DelVescovo, Dan, Kokjohn, Sage, Reitz, Rolf
Parametric Analysis of Compression Ratio Variation Effects on Thermodynamic, Gaseous Pollutant and Particle Emissions of a Dual-Fuel CH 4 -Diesel Light Duty Engine2017-01-07643/28/2017
The paper reports the results of an experimental campaign aimed to assess the impact of the compression ratio (CR) variation on the performance and pollutant emissions, including the particle size spectrum, of a single cylinder research engine (SCE), representatives of the engine architectures for automotive application, operated in dual-fuel methane-diesel mode. Three pistons with different bowl volumes corresponding to CR values of 16.5, 15.5 and 14.5 were adopted for the whole test campaign. The injection strategy was based on two injection pulses per cycle, as conventionally employed for diesel engines. The test methodology per each CR included the optimization of both 1st injection pulse quantity and intake air mass flow rate in order to lower as much as possible the unburned methane emissions (MHC). The testing points were selected in order to analyse the CR impact on SCE performance at partial and high loads, including the performance estimation over the New European Driving emission homologation Cycle (NEDC) of a real four-cylinder automotive multi-cylinder engine. The results evidence benefits on combustion noise, MHC and particle size spectrum when lowering the CR in DF mode. However, with respect to the tested engine class, a CR of 15.5 appears to be the best compromise among energy efficiency and global pollutant emissions.
Di Blasio, Gabriele, Belgiorno, Giacomo, Beatrice, Carlo
Efficiency and Emissions Characteristics of Partially Premixed Dual-Fuel Combustion by Co-Direct Injection of NG and Diesel Fuel (DI 2 ) - Part 22017-01-07663/28/2017
The CO2 advantage coupled with the low NOX and PM potential of natural gas (NG) makes it well-suited for meeting future greenhouse gas (GHG) and NOX regulations for on-road medium and heavy-duty engines. However, because NG is mostly methane, reduced combustion efficiency associated with traditional NG fueling strategies can result in significant levels of methane emissions which offset the CO2 advantage due to reduced efficiency and the high global warming potential of methane. To address this issue, the unique co-direct injection capability of the Westport HPDI fuel system was leveraged to obtain a partially-premixed fuel charge by injecting NG during the compression stroke followed by diesel injection for ignition timing control. This combustion strategy, referred to as DI2, was found to improve thermal and combustion efficiencies over fumigated dual-fuel combustion modes. In addition, DI2 provided significant thermal efficiency improvement over the baseline diffusion-controlled combustion strategy (HPDI) where NG injection occurs after diesel injection. The DI2 combustion process was analyzed using 3D-CFD and indicated that additional CH4 reductions from the crevice region may be possible by reducing the NG nozzle spray angle. To evaluate the potential reduction available, modified injection nozzles with narrow NG spray angles were tested on the engine. This paper reports the CFD and experimental results obtained with the modified injection nozzles which confirmed that significant CH4 emission reductions can be achieved while maintaining high BTE with DI2.
Neely, Gary D., Florea, Radu, Miwa, Jason, Abidin, Zainal
A Study of HCCI Operating Range Expansion by Applying Reaction Characteristics of Low-Carbon Alternative Fuels2016-32-001111/8/2016
Issues that must be addressed to make Homogeneous Charge Compression Ignition (HCCI) engines a practical reality include the difficulty of controlling the ignition timing and suppression of rapid combustion under high load conditions. Overcoming these issues to make HCCI engines viable for practical application is indispensable to the further advancement of internal combustion engines. Previous studies have reported that the operating region of HCCI combustion can be expanded by using DME and Methane blended fuels.(1), (2), (3), (4), (5) The reason is that the reaction characteristics of these two low-carbon fuels, which have different ignition properties, have the effect of inducing heat release in two stages during main combustion, thus avoiding excessively rapid combustion. However, further moderation of rapid combustion in high-load region is needed to expand the operation region. This study focused on supercharging and use of blended fuels. For the purpose of promoting the practical implementation of HCCI engines, experiments were conducted in the present study with the aim of expanding the HCCI operating range over a wide region of combustion loads by using the reaction characteristics of a fuel blend of DME/methane. The results revealed that the pressure rise rate was substantially reduced while maintaining the indicated mean effective pressure level. It was also observed that HCCI operation over a wide range of engine loads was possible by making use of two-stage heat release during main combustion.
Agui, Keito, Suzuki, Hirotaka, Takamura, Yuki, Iijima, Akira, Shoji, Hideo
Numerical Simulation of Heat Transfer Characteristics of Swirling Turbulent Flame Impinging on Flat Surface2016-01-13404/5/2016
This paper presents a CFD simulation methodology for solving complex physics of methane/air swirling turbulent flame impinging on a flat surface. Turbulent Flow in burner is simulated using Re-Normalized Group k-ε model while Stress-omega Reynolds Stress Model is used for flame structure. Methane/air combustion is simulated using global combustion reaction mechanism. To account for Turbulence-Chemistry Interaction of methane/air combustion, Eddy - Dissipation Model is used. The effect of varying plate distance to burner exit nozzle diameter is also investigated and comparisons of simulated results with experiments are discussed. Change in flame structure is observed with variation of plate distance from burner exit. A dip in the heat flux distribution is observed for all cases. This is due to the presence of central weak flow region created at and around the central axis due to swirl.
Dang, Vikram, Chander, Subhash
Numerical Investigation of Spark Ignition Events in Lean and Dilute Methane/Air Mixtures Using a Detailed Energy Deposition Model2016-01-06094/5/2016
It is beneficial but challenging to operate spark-ignition engines under highly lean and dilute conditions. The unstable ignition behavior can result in downgraded combustion performance in engine cylinders. Numerical approach is serving as a promising tool to identify the ignition requirements by providing insight into the complex physical/chemical phenomena. An effort to simulate the early stage of flame kernel initiation in lean and dilute fuel/air mixture has been made and discussed in this paper. The simulations are set to validate against laboratory results of spark ignition behavior in a constant volume combustion vessel. In order to present a practical as well as comprehensive ignition model, the simulations are performed by taking into consideration the discharge circuit analysis, the detailed reaction mechanism, and local heat transfer between the flame kernel and spark plug. The energy profile and the energy source geometry are investigated in detail to represent the physics of electrical discharge. It was observed in the experiments that a sufficiently high ambient pressure is necessary for a successful ignition event in the lean and dilute mixture when the spark plug gap size and primary energy input are held constant. By adopting realistic energy levels, this detailed energy deposition model showed the capability to reasonably present such ignition behavior transition. The unique combination of energy deposition profile and geometry reveals the complexity of electrical discharge during the spark ignition event. The response of the combustible gas to the energy deposition showed dependency on the volumetric energy density, energy source’s surface area, temperature gradient at the energy source boundary, as well as the heat transfer condition local to the flame kernel.
Zhang, Anqi, Scarcelli, Riccardo, Lee, Seong-Young, Wallner, Thomas, Naber, Jeffrey
Characterization and Potential of Premixed Dual-Fuel Combustion in a Heavy Duty Natural Gas/Diesel Engine2016-01-07904/5/2016
Natural Gas (NG) is currently a cost effective substitute for diesel fuel in the Heavy-Duty (HD) diesel transportation sector. Dual-Fuel engines substitute NG in place of diesel for decreased NOx and soot emissions, but suffer from high engine-out methane (CH4) emissions. Premixed Dual-Fuel Combustion (PDFC) is one method of decreasing methane emissions and simultaneously improving engine efficiency while maintaining low NOx and soot levels. PDFC utilizes an early diesel injection to adjust the flammability of the premixed charge, promoting more uniform burning of methane. Engine experiments were carried out using a NG and diesel HD single cylinder research engine. Key speeds and loads were explored in order to determine where PDFC is effective at reducing engine-out methane emissions over Conventional Dual-Fuel which uses a single diesel injection for ignition. PDFC has shown significant reductions in methane as well as CO emissions when compared with Conventional Dual-Fuel combustion. Medium loads enjoy the largest benefit from PDFC. At higher load, the amount of diesel injected early was limited in order to stay within the constraints for cylinder pressure. At lighter loads, the benefits of PDFC are reduced due to higher in-cylinder global lambda (λ) and lower temperature and pressure to promote auto-ignition. Overall, the PDFC mode of operation observes the potential to minimize the need for exhaust after-treatment as well as increase engine efficiency.
May, Ian, Pedrozo, Vinícius, Zhao, Hua, Cairns, Alasdair, Whelan, Steve, Wong, Hoi, Bennicke, Paul
Advanced Infrared Camera Maps Methane "Hot Spots"TBMG-243003/1/2016
Methane often appears in the atmosphere at an irregular rate, puzzling researchers challenged with the task of tracking the gas’s sources in the landscape. An advanced infrared camera developed by Linköping University and Stockholm University researchers, in collaboration with the infrared imaging manufacturer Telops, allows users to both film and photograph methane emissions.
Non-Thermal, Plasma-Assisted Catalytic Reactor for CO2 MethanationTBMG-224137/1/2015
Converting in-situ resources such as CO2, which is the main component of the Mars atmosphere, into methane for rocket propellants can significantly reduce the cost and risk of human exploration while at the same time enabling new mission concepts and long-term exploration sustainability. Methanation of CO2, also called a Sabatier reaction, is hence a key enabling technology required for sustainable and affordable human exploration of Mars.
Domain-Engineered Magnesium-Oxide-Doped Lithium Niobate for Lidar-Based Remote SensingTBMG-224287/1/2015
There are several frequency conversion applications associated with lidar-based remote sensing that would benefit from the use of high-quality, complex (i.e., chirped, multi-section, or otherwise modulated) domain-engineered magnesiumoxide- doped lithium niobate (MgO:LN). While congruently melting lithium niobate (CLN) has been explored in detail over the last decades, it is known to be highly susceptible to photorefractive damage, which has limited the achievable performance of some QPM-assisted (quasi phase matching) structures that are commercially available. The demand for high-performance engineered nonlinear optical (NLO) materials, in terms of power handling, efficiency, conversion bandwidth, and accessible wavelength range, has driven the development of high-quality, large-area wafers of MgO:LN. While commercial outlets for these materials exist, there is still a need to expand the achievable performance of these structures (i.e. larger aperture bulk structures, higher efficiency waveguide structures, and implementation of sophisticated poling designs that increase achievable conversion bandwidths).
NASA, UCF Professor Send Sensor to StratosphereTBMG-221425/1/2015
Planetary Atmospheres Minor Species Sensor (PAMSS) University of Central Florida Orlando, FL
Study of an On-board Fuel Reformer and Hydrogen-Added EGR Combustion in a Gasoline Engine2015-01-09024/14/2015
To improve the fuel economy via high EGR, combustion stability is enhanced through the addition of hydrogen, with its high flame-speed in air-fuel mixture. So, in order to realize on-board hydrogen production we developed a fuel reformer which produces hydrogen rich gas. One of the main issues of the reformer engine is the effects of reformate gas components on combustion performance. To clarify the effect of reformate gas contents on combustion stability, chemical kinetic simulations and single-cylinder engine test, in which hydrogen, CO, methane and simulated gas were added to intake air, were executed. And it is confirmed that hydrogen additive rate is dominant on high EGR combustion. The other issue to realize the fuel reformer was the catalyst deterioration. Catalyst reforming and exposure test were carried out to understand the influence of actual exhaust gas on the catalyst performance. Fresh catalyst showed good performance in generating hydrogen, but an aged catalyst generated only half as compared to a fresh catalyst. So we considered measures to improve catalyst performance. According to EGR reforming performance test with single-cylinder engine using conventional catalyst and an improved catalyst, the improved catalyst showed good performance. Finally, in order to confirm the performance of hydrogen generation and the effects of real reformate gas on EGR combustion, a single-cylinder engine with the fuel reformer was developed. It is confirmed that hydrogen is generated from gasoline and EGR gas by the fuel reformer, and combustion stability under high EGR rate is enhanced by reformate hydrogen.
Ashida, Koichi, Maeda, Hirofumi, Araki, Takashi, Hoshino, Maki, Hiraya, Koji, Izumi, Takao, Yasuoka, Masayuki
Fuel-Independent Particulate Emissions in an SIDI Engine2015-01-10814/14/2015
The fuel-independent particulate emissions of a direct injection gasoline engine were investigated. This was done by running the engine with reference gasoline at four different loads and then switching to hydrogen or methane port fuel operation and comparing the resulting particulate emissions and their size distribution. Differences in the combustion characteristics of hydrogen and gasoline were accounted for by diluting the inlet air with nitrogen and matching the pressure or heat release traces to those of gasoline operation. Methane operation is expected to generate particulate emissions lower by several orders of magnitude compared to gasoline and hydrogen does not contribute to carbon soot formation because of the lack of carbon atoms in the molecule. Thus, any remaining particulate emissions at hydrogen gas operation must arise from non fuel related sources, e.g. from lubrication oil, metal abrasion or inlet air. With methane and hydrogen operation, only a very small amount of particles larger than 30 nm could be measured. The comparison between CEC reference fuel and hydrogen operation showed similar size distributions for particles smaller than 10 nm at low loads, which was also consistent with the comparison between methane and gasoline operation. The tentative conclusion is that particles smaller than 10 nm do not, for the most part, originate from the combustion of the fuel. However, at higher loads, the differences between gasoline and hydrogen operation were more pronounced at all particle sizes. Thus, while there seems to be a fuel-independent baseline of particulate emissions, the contribution of the fuel combustion itself is also important and is the dominant contribution at higher engine loads.
Maier, Axel, Klaus, Ulrike, Dreizler, Andreas, Rottengruber, Hermann
Low Er-Doped Yttrium Gallium Garnet (YGG) as Active Media for Solid-State Lasers at 1651 nmTBMG-218074/1/2015
The typical approach for producing laser output at the 1651-nm wavelength is via nonlinear frequency conversion. Lasers based on nonlinear conversion are complex, and it is very difficult to provide stability over time and over a wide range of operating temperatures. The efficiency of such optical sources is also low. A much more promising approach is the use of active media that allows for the development of solid-state lasers (SSL) with spectral emission at 1651 nm. An important requirement for this active medium is the ability to support in-band pumping with a low quantum defect since this approach leads to significant improvement in efficiency of SSLs and excellent beam characteristics due to low thermal stress of the active media.
Prediction of Ignition and Combustion Development in an HCCI Engine Fueled by Syngas2014-32-000211/11/2014
To determine the auto-ignition and combustion mechanisms and the components of syngas that are applicable to homogeneous charge compression ignition (HCCI) engines, the combustion characteristics and the chemical reaction process in an HCCI engine were studied numerically and experimentally using mock syngas with various mixtures of the fuel components. The mock syngas consisted of hydrogen (H2) and carbon monoxide (CO) as the main combustible components, nitrogen (N2) and carbon dioxide (CO2) as incombustible components and a small amount of methane (CH4), assuming the composition of the gas was produced from wood by thermochemical conversion processes. The oxidation reaction process was analyzed numerically using CHEMKIN-PRO. Further experiments were conducted to investigate the validity of the calculated results. Primarily, the effects of hydrogen and carbon monoxide on auto-ignition and combustion were investigated. Auto-ignition timing mainly depends on the in-cylinder gas temperature and the auto-ignition temperature is approximately 1100 K, which is the same as that of hydrocarbon fuels. It has been shown that the rate of combustion following auto-ignition is mainly determined by the hydrogen and carbon dioxide contents. The time interval from 10% to 90% conversion is longer for hydrogen than for carbon monoxide. The amount of hydrogen begins to decrease before that of carbon monoxide. The amount of carbon monoxide, however, decreases rapidly. The combustion duration can be roughly estimated from the ratio of H2 to CO2 in the fuel.
Yamasaki, Yudai, Kaneko, Shigehiko
Titan Lake and Shore SamplerTBMG-2093911/1/2014
A lake and shore sampling and sample distribution system was developed for a Titan lake environment (93.7 K, in liquid hydrocarbons). The Titan Lake and Shore Sampler (TLASS) would enable the chemical analysis of hydrocarbon lake samples via a Dual Rectilinear Ion and Orbitrap Mass Spectrometer and Nuclear Magnetic Resonance (NMR) Spectrometry.
Thermodiffusive Effect on the Flame Development in Lean Burn Spark Ignition Engine2014-01-263010/13/2014
In Spark Ignition engines, the heat release rate is not only piloted by the mixture reactivity but also by its sensitivity to stretch effects. Only few results can be found in the literature about flame stretch effect in SI engine configurations. For this study, three different fuels (Methane, Propane, Iso-octane) were studied, but at different air-fuel lean mixture conditions, to present almost equivalent laminar flame speeds and thermo-dynamical properties at ignition timing condition. Besides those mixtures present different Lewis numbers which are relevant parameters to describe flame-stretch interactions. Mie-scattering tomography was then performed in an optical Spark Ignition (S.I.) engine. Using a high speed camera, flame propagation images were acquired through the piston. Thermodynamic analyses based on in-cylinder pressure traces were performed to estimate in-cylinder temperature and burnt mass fraction during the engine cycle. From the determination of flame areas, the global flame stretch and an equivalent propagation speed have been then defined and estimated. Results prove that mixtures have the same ranking in terms of flame stretch sensitivities as in the laminar regime. Probability density functions of flame curvature are centered on 0.05 mm−1 for the three mixtures whereas differences are observed on the global wrinkling. Finally the impact of the Lewis number on the Burned Mass Fraction curved was studied thus showing a linear relationship between crank angle corresponding to 5 and 10 % of burned mass fraction and the Lewis number.
Brequigny, Pierre, Halter, Fabien, Mounaïm-Rousselle, Christine, Moreau, Bruno, Dubois, Thomas
The Effect of the Induction of Nitrogen Oxides on Natural Gas HCCI Combustion2014-01-269710/13/2014
The main aim of this study is to investigate the effect of NO and NO2 on the combustion characteristics such as pressure development and combustion phasing in natural gas HCCI engine. A secondary aim is to demonstrate a method of obtaining a significant sensitizing effect on methane oxidation reaction from small amounts of NOx. Experiments were conducted using a rapid compression-expansion machine that was constructed from a single-cylinder diesel engine. First, the sensitizing effect of NO and NO2 on the HCCI combustion of natural gas was investigated in a case where NOx was uniformly mixed into a charge. Obtained results show that the auto-ignition timing is significantly advanced and an acute heat release is promoted by adding either NO or NO2. Second, the effect of non-uniform mixing of NOx into an air-fuel mixture was investigated according to our expectation that the existence of local spots with high NOx concentrations can assist auto-ignition more effectively than the same amount of NOx homogeneously distributed. Obtained results show that when NO and air-fuel mixture are individually inducted into a cylinder, by retarding the NO induction timing to suppress the progress of mixing, combustion phasing is advanced and higher combustion pressure is obtained with keeping the inducted NO amount constant.
Kawasaki, Kiyoshi, Kubo, Soichiro, Yamane, Koji, Kondo, Chihiro
Kinetic Reduced Model of Methane Combustion in an IC Engine2014-01-258010/13/2014
The simulation of combustion in the internal combustion engines (ICE) is very important for an accurate prediction of engine performance and pollutant formation. These engines simulation help to gain a better understanding of the coupling between the various physical and chemical processes. The objective of the present paper is to study turbulent combustion in IC engine. A lagrangian eulerian model coupled with presumed pdf is used to study the problems of chemical kinetics (and), while the k-ε model is used for the modeling of the turbulence. We got the reduced mechanism through the reduction of detailed mechanism of the methane (GRI 3.0) combustion by using the Principal Component Analyses (PCAF). It is considered the first point for the application of the Computational Singular Perturbation method (CSP). We used this method (CSP) to reduce the detailed mechanism of the methane that is already reduced by PCAF to a mechanism containing 9-Steps. The validation of this reduced mechanism has been made by the comparison between the results of the reduced and detailed mechanisms of methane GRI 3.0; this comparison for major species, pollutants species and temperature at high pressure and lean mixture. The results of computations with the present model are compared with the experimental and simulation GRI 3.0. These comparisons between the modeling and the experiments show a good agreement for emission pollutant, major species, pressure, and temperature. We, also, studied the effect of operating conditions such as equivalent ratio and crank angle rotation on the formation of pollutants emissions. This parametric study showed the sensitivity of variations in operating parameters of the engine on the prediction of emissions pollutant (CO, NO, CO2 and HC), the pressure and temperature in the combustion chamber; which has a positive point of the model elaborated.
Ait Msaad, Abdelouahad, Mahdaoui, Mustapha, Affad, Elhoussin, Mouqallid, Mhamed
Experimental Investigation on the Performance and Exhaust Emission of Biogas-Diesel Dual-Fuel Combustion in a CI Engine2014-01-268910/13/2014
The crude oil depletion, as well as aspects related to environmental pollution and global warming has caused researchers to seek alternative fuels. Biogas is one of the most attractive available fuels. It is of great interest both economically and ecologically. However, it faces problems that may compromise its industrial use. The dual-fuel engines have been investigated as a technique for the recovery of these gases and finding solutions to these problems. In the present work, performance and emissions of a direct injection diesel engine were first evaluated in conventional mode and dual fuel mode. The effect of biogas composition, based on methane content, is then examined. Also, dual fuel operation with regard to knock is investigated. The results show that, up to 95% of engine full load, the brake thermal efficiency (BTE) is lower in dual fuel mode. In terms of the specific consumption, although at high load the gap is much less, it is more significant in case of dual fuel mode. This is justified by the low energy content of biogas in comparison with diesel fuel. In addition, the particulate emissions are drastically reduced compared to conventional diesel operating mode. Thus, the biogas can be used in the dual fuel engines with very attractive performance. Regarding the effect of the biogas composition, the results showed that a biogas with 70% of methane offers the best performance compared to biogas fuels with 50, 60 and 80% of methane content. On the other hand, biogas fuels showed good resistance to knocking since measured torque at the occurrence of knock onset is higher than the maximum torque recorded for conventional diesel. This resistance is even higher when the percentage of carbon dioxide is higher.
Lounici, Mohand Said, Loubar, Khaled, Tazerout, Mohand, Balistrou, Mourad, Tarabet, Lyes
Effect of Additives on Combustion Characteristics of a Natural Gas Fueled HCCI Engine2014-01-266210/13/2014
Homogeneous Charge Compression Ignition (HCCI) is among the new generation of combustion modes which can be applied to internal combustion engines. It is currently the topic of numerous studies in various fields. Due to its operating process, HCCI ensures a good efficiency, similar to that of compression ignition (CI) engines, and low particulate and nitric oxide (NOx) emissions. However, before promoting the use of this kind of engine, several challenges must be addressed, in particular controlling the combustion. Recent work showed that the combustion phasing can be controlled using low concentrations of ozone, an oxidizing chemical species. As ozone generators become increasingly compact, the integration of this kind of device in passenger cars can be considered. The present study investigates the effect of ozone on the combustion of different fuel mixtures. The engine was fuelled with various blends: a 95%methane/5%propane mixture and three different methane/hydrogen mixtures. The engine parameters and pollutant emissions were analyzed as a function of ozone seeding in several cases: by degrading the intake pressure, by degrading the intake temperature, and by varying the volume fraction in the blend composition to obtain a fuel that auto-ignites less readily. Overall, experimental results showed that ozone improves and advances the combustion of all the fuels considered. Lastly, computations were conducted using a simple constant volume model to study fuel oxidation in the presence of ozone. Results showed that ozone quickly oxidizes the fuel and is therefore a good combustion promoter.
Masurier, Jean-Baptiste, Foucher, Fabrice, Dayma, Guillaume, Dagaut, Philippe
The Analysis of Energy Conversion Efficiency in SI Engines for Selected Gaseous Fuels2014-01-269210/13/2014
The analysis of the overall performance of the engine powered by selected gaseous fuels has been presented in this paper. Primary objective of the research was to determine the influence of fuel type on efficiency of energy conversion in the tested engine. The scope of the research featured: application low-carbon fuels, use of DME as a renewable fuel in blends with LPG. The use of low-carbon gaseous fuels gives the opportunity to reduce exhaust gases emissions. The basic assumption in the presented research was the use of gaseous fuels, for which the main component is methane. The main problem taken into consideration was excessive duration of the combustion process, which is one of the causes of the engine overall efficiency reduction when running on gaseous fuels. This issue becomes even more important due to the lower heating value of natural gas (methane) when compared to conventional fuels. One of possible solutions is the use of fuel blends, e.g. methane-enriched hydrogen as an activator of the combustion process [18]. Authors have chosen in this case eight methane/hydrogen blends, with various hydrogen shares (by volume): 0% (pure methane), 5%, 10%, 15%, 20%, 30%, 40% and 50%. Another interesting alternative considered by authors was dimethyl ether (DME). Due to its properties, it is recently becoming a more popular fuel. The high cetane number (about 55) allows its easy application for diesel engines propulsion additionally featuring low sooting propensity. Considering that other DME properties are very similar to those of petroleum based hydrocarbon gases, it is possible to effectively use it in the SI engines. One of DME applications presented by authors is a fuel blend based on LPG. The research program provided the use of fuel blends featuring DME mass fraction varying from 0 to 26%. The research project allowed the verification of simulation studies carried on the basis of mathematical model, with the real data from a 4 cylinders 1600cm3 SI engine. This made it possible to conduct a precise analysis of combustion process for all the tested fuels. The relationships between various components of energy balance in the tested engine have also been interpreted.
Flekiewicz, Marek, Kubica, Grzegorz, Flekiewicz, Bartosz
Lunar Organic Waste ReformerTBMG-199166/1/2014
The Lunar Organic Waste Reformer (LOWR) is a novel technology to convert organic wastes from human space exploration outposts into useful propellant constituents. The LOWR meets NASA’s Trash to Supply Gas (TtSG) objective under the Advanced Exploration Systems Logistics Reduction and Repurposing project by integrating steam reformation, methanation, and electrolysis to convert organic waste into methane and oxygen products. At reformer temperatures above 700 °C, oxygenated steam reacts with organic matter to produce a gas mixture largely composed of hydrogen, carbon monoxide, and carbon dioxide. After condensing and removing excess water, the reformer exhaust gases are fed to a catalytic Sabatier reactor where they are combined with supplemental hydrogen at 350 to 500 °C to produce methane and water. The methane product can be liquefied for storage.
Experimental and Modeling Study on Auto-Ignition of Methane/Hydrogen Blends at Elevated Pressures2014-01-13354/1/2014
Both experimental and simulated ignition delay times were obtained behind reflected shock waves for the diluted stoichiometric methane/hydrogen blends with hydrogen fractions of 20%, 60%, and 80%. Test temperatures are from 1000 K to 1820 K and pressures are from 0.5 to 2.0 MPa. Results showed that increase in hydrogen fraction can promotes significantly the ignition of methane due to higher activity of hydrogen. Pressure-dependence of auto-ignition was observed in three ignition regimes (methane chemistry dominating ignition, combined chemistry of methane and hydrogen dominating ignition and hydrogen chemistry dominating ignition). Kinetic model, NUIG Mech C5_49, was used and validated against current ignition data. It was found that NUIG Mech C5_49 can give a good prediction for all test mixtures. A fuel flux analysis was performed to explain the chemical interaction between methane and hydrogen.
Zhang, Yingjia
Negative Valve Overlap Reforming Chemistry in Low-Oxygen Environments2014-01-11884/1/2014
Fuel injection into the negative valve overlap (NVO) period is a common method for controlling combustion phasing in homogeneous charge compression ignition (HCCI) and other forms of advanced combustion. When fuel is injected into O2-deficient NVO conditions, a portion of the fuel can be converted to products containing significant levels of H2 and CO. Additionally, other short chain hydrocarbons are produced by means of thermal cracking, water-gas shift, and partial oxidation reactions. The present study experimentally investigates the fuel reforming chemistry that occurs during NVO. To this end, two very different experimental facilities are utilized and their results are compared. One facility is located at Oak Ridge National Laboratory, which uses a custom research engine cycle developed to isolate the NVO event from main combustion, allowing a steady stream of NVO reformate to be exhausted from the engine and chemically analyzed. The other experimental facility, located at Sandia National Laboratories, uses a dump valve to capture the exhaust from a single NVO event for analysis. Results from the two experiments are in excellent trend-wise agreement and indicate that the reforming process under low-O2 conditions produces substantial concentrations of H2, CO, methane, and other short-chain hydrocarbon species. The concentration of these species is found to be strongly dependent on fuel injection timing and injected fuel type, with weaker dependencies on NVO duration and initial temperature, indicating that NVO reforming is kinetically limited. Further, NVO reforming does not require a large energy input from the engine, meaning that it is not thermodynamically expensive. The implications of these results on HCCI and other forms of combustion are discussed in detail.
Szybist, James P., Steeper, Richard R., Splitter, Derek, Kalaskar, Vickey B., Pihl, Josh, Daw, Charles
Combustion Modeling of Landfill Gas Fueled Spark Ignition Engine Performance2014-01-14714/1/2014
Landfill gas (LFG) is a waste-product resource composed primarily of methane and carbon dioxide that can be collected and used to produce power either by extracting the methane or using the landfill gas directly in an internal combustion engine in what amounts to a net-negative greenhouse gas emission process. The carbon dioxide component of LFG dilutes the fuel and absorbs some of the heat of combustion, but also suppresses knock. A model is developed, using KIVA-4 code, to simulate engine performance at various operating conditions and evaluate the benefits of methane purification and direct use of LFG as a fuel. It was found that landfill gas used directly at higher compression ratios than can be used for pure methane fuel produces higher fuel efficiency than can be achieved using pure methane. Furthermore the study has shown that the fuel efficiency of the engine can be achieved within 5% of that of pure methane fuel for landfill gas, diluted up to 1:1 with carbon dioxide by simply adjusting the spark timing of the engine. A model for combustion duration is also developed which can estimate the combustion duration in an internal-combustion engine for varying fuel compositions.
Swain, Daniel, Bade Shrestha, S O
Economics of Transportation Hydrocarbon Fuels and Environmental Regulations with Conceptual Solutions - Carbon-Neutral and Carbon-Negative Synfuels2014-01-19434/1/2014
Of all current proposals for sustainable transportation, the assumption is energy scarcity when there are economically favorable alternatives using existing technology. This paper explores the economics of a sustainable transportation energy pathway that provides carbon-neutral and carbon-negative synthetic fuel derived from seawater as the feedstock and power via Ocean Thermal Energy Cycle (OTEC). Seawater-based synthetic fuel is naturally carbon-neutral - different synthesis processes can yield hydrogen, methane, methanol and ethanol as well as gasoline, diesel or jet fuel - and is carbon-negative when combined with aquaculture. Methanol is favored as a fuel as it requires relatively lower capital investment; can be easily transported and stored; can be used as a feedstock to many chemical processes that currently rely on petrochemicals; and can be coproduced with or converted to dimethyl ether. This paper proposes a new process that for the first time marries OTEC-power and seawater-based-methanol synthetic fuel generation. The proposed process is optimized for highest product yield for a given capital investment, in that operating costs and therefore product costs are dominated by capital cost amortization. The methanol fuel produced by this process within the amortization period has a cost per unit of energy potentially comparable to petroleum-derived gasoline or diesel fuel and post-amortization to natural gas. The economics of this new process is compared to prior synthetic methanol processes proposed by Meyer Steinberg and William Avery.
Bucknell, John R.
Pt/Pd Bimetallic Catalyst with Improved Activity and Durability for Lean-Burn CNG Engines2013-01-259110/14/2013
Compressed natural gas (CNG) has been regarded as an alternative fuel for current fossil fuels such as gasoline and diesel. Recently the increasing interest in shale gas is drawing more attention to CNG vehicles of which number is expected to increase. Exhaust gas from CNG engines with lean combustion contains relatively low nitrogen oxides and particulate matters compared to conventional fossil fuel based engines. However, high amount of unburned methane, which has much higher greenhouse warming potential than CO2, limits the wide use of CNG for many applications. Even though Pd-based catalysts have been popularly studied in order to convert methane, their activity and durability have not been sufficient for practical applications to aftertreatment of lean burn CNG engines and the formation of a new Pd containing. In the present study, we developed an improved Pd-based catalyst for CNG engines by introducing Pt and promoters to enhance methane oxidation activity at low temperature and long term durability. Pt was more active to oxidize paraffinic hydrocarbons that comprise ∼10% of total hydrocarbons in exhaust gas from lean burn CNG engines. Exotherm resulting from the paraffinic hydrocarbon oxidation by Pt could promote the remaining methane oxidation by Pd. Furthermore, potential causes for the deactivation of Pd-based catalyst were investigated from the various points of Pd-sintering by high temperature exposure, PdO decomposition, sulfation and coking, and the formation of new Pd containing compound. Optimal use of support material for Pd/Pt and promoters to keep Pd stable were identified as key factors for the design of more active and durable catalyst.
Kim, Joonwoo, Kim, Eunseok, Han, JaeUk, Han, Hyun Sik
Experimental Evaluation of a Novel High Frequency Ignition System Using a Flow-Reactor Set-up2013-01-256410/14/2013
Using diluted methane/air mixtures in internal combustion engines has a potential of reducing emissions and increasing efficiency. However, the ignition systems used today show difficulties igniting lean mixtures. For this purpose a new high frequency (HF) ignition system using pulse generators and a resonance circuit to achieve a controlled number of sparks during a controlled period of time has been developed. A first prototype of this high frequency system has been tested in a flow-reactor and compared to a conventional ignition system. Results show that the high frequency system improves the flame development under lean conditions compared to the conventional system. Higher frequencies have higher capability of igniting lean mixtures than lower frequencies. Lower spark frequencies were found to travel faster across the electrodes than high frequencies and also compared to the conventional system. High pressure and high flow rates affected the lean limit of all ignition strategies, but especially high spark frequencies had difficulties igniting the charge under high pressures, due to the resonant frequency changing with pressure. The high frequency system was also limited in the amount of available voltage. However, this will be improved with further development of the ignition system.
Dahlstrom, Jessica, Schönborn, Alessandro, Tunestal, Per, Johansson, Bengt
Reduction of Methane Slip from Gas Engines by O 2 Concentration Control using Gas Permeation Membrane2013-01-261810/14/2013
With progression of so-called shale gas revolution, gas engines are expected as a strong substitute for diesel engines in marine fields, where strict emission regulations have been recently introduced. Thanks to the sulphur-free and low-carbon features of natural gas, gas engines emit much less CO2 and particulate matter than marine diesels burning heavy fuel oil. The premixed lean-burn gas engines, however, suffer two massive flaws. One is abnormal combustion called knocking and the other is a methane slip, which substantially means the unburned methane emitted into exhaust ports. One of the methane slip sources is thought to be flame quenching inside dead volumes around a combustion chamber or inside a boundary layer near a cylinder wall. Only supportive measures like cutdown of crevice volume have been conducted against the unburned methane. The present study proposes novel and essential methane slip reduction for the first time using a gas permeation membrane, of which permeability to oxygen molecules excels the one to nitrogen molecules. The membrane inserted between a main compressor and a charge cooler helps to form uneven oxygen gradient inside a combustion chamber. After the feasibility check of the complicated charging system based on a one-dimensional engine simulator, the potential of the methane slip reduction is successfully examined through CFD simulation with detailed chemical analysis.
Tajima, Hiroshi, Tsuru, Daisuke
Characterization of CH 4 and CH 4 /H 2 Mixtures Combustion in a Small Displacement Optical Engine2013-01-08524/8/2013
In the last years, even more attention was paid to the alternative fuels which can allow both reducing the fuel consumption and the pollutant emissions. Among gaseous fuels, methane is considered one of the most interesting in terms of engine application. It represents an immediate advantage over other hydrocarbon fuels leading to lower CO₂ emissions; if compared to gasoline, CH₄ has wider flammable limits and better anti-knock properties, but lower flame speed. The addition of H₂ to CH₄ can improve the already good qualities of methane and compensate its weak points. In this paper a comparison was carried out between CH₄ and different CH₄/H₂ mixtures. The measurements were carried out in an optically accessible small single-cylinder, Port Fuel Injection spark ignition (PFI SI), four-stroke engine. It was equipped with the cylinder head of a commercial 250 cc motorcycle engine representative of the most popular two-wheel vehicles in Europe. Optical measurements were performed to analyze the combustion process with high spatial and temporal resolution. In particular, optical techniques based on 2D-digital imaging were used to follow the flame propagation in the combustion chamber. UV-visible spectroscopy allows detecting the chemical markers of combustion process such as the radicals OH* and CH*. The exhaust emissions were characterized by means of gaseous analyzers. The measurements were performed under steady state conditions at different engine speed in order to evaluate the interaction of turbulence with the kernel and the interaction with the local flame. All the results highlight the combustion promotion due to the hydrogen addition.
Catapano, Francesco, Di Iorio, Silvana, Sementa, Paolo, Vaglieco, Bianca Maria
A Multi-Dimensional CFD-Chemical Kinetics Approach in Detection and Reduction of Knocking Combustion in Diesel-Natural Gas Dual-Fuel Engines Using Local Heat Release Analysis2013-01-08654/8/2013
Dual-fuel diesel-natural gas (NG) engine exhibits higher power density and lower specific emissions compared to dedicated diesel engines. However, high intake temperatures, high compression ratios, combined with high engine loads may lead to engine knock. This is potentially a limiting factor on engine downsizing and getting higher power. In the present study, the combustion process under knocking conditions has been investigated in a dual-fuel diesel-NG engine. A comprehensive multi-dimensional simulation framework was generated by integrating the CHEMKIN chemistry solver into the KIVA-3V code. A detailed chemical kinetics mechanism was used for n-heptane and methane as diesel and NG surrogates. Combination of detailed chemical kinetics and detailed fluid dynamics calculation enabled the model to take into account the characteristics of most pronounced knock type in dual-fuel engines, so called end-gas knock. Within the CFD computational domain, eight regions that are the representatives of the dual-fuel heat release patterns have been selected to extract local properties. Using local knock identification factors, end-gas knock was observed in abnormal combustion cases. A new Knock Intensity factor (K.I) was introduced based on local heat release rate. Using developed knock prediction method, results showed knock could be mitigated by using EGR. Moreover, effect of premixed methane equivalence ratio on knocking combustion was investigated.
Maghbouli, Amin, Shafee, Sina, Khoshbakhti Saray, Rahim, Yang, Wenming, Hosseini, Vahid, An, Hui
Development of a Sulfur Tolerant PGM Based Zeolite Catalyst for Methane Oxidation and Low Temperature Hydrocarbon Trapping2013-01-05314/8/2013
With forthcoming 2014 EPA GHG legislation capping methane emissions at 0.10 g/bhp-hr for heavy-duty engines, development of a thermally stable and sulfur-tolerant methane oxidation catalyst becomes more critical. This is particularly true for natural gas-powered engines where methane slip is a significant contributor in the emissions and sulfur is present as a constituent of odorants used in CNG. Scientists at Clariant have recently developed a novel process for manufacturing a PGM containing zeolite that is both thermally stable and resistant to sulfur poisoning. Methane oxidation catalysts typically require temperatures in excess of 400°C to achieve light-off and are often sensitive to exposure to sulfur. The PGM zeolite catalyst has shown remarkable activity at low temperatures and a resistance to sulfur poisoning. Tests have shown that even after exposure to heavy concentrations of sulfur, the catalyst has little change in activity. In addition to methane oxidation, this catalyst has shown excellent hydrocarbon storage and oxidation activity at low temperatures. These properties allow this new material to be used in applications where cold-start emissions control is particularly important.
Guliaeff, Alexander, Wanninger, Klaus, Klose, Frank, Maletz, Gerd, Tissler, Arno
Impact of Supplemental Natural Gas on Engine Efficiency, Performance, and Emissions2013-01-08474/8/2013
In this study, the performance and emissions of a 4 cylinder 2.5L light-duty diesel engine with methane fumigation in the intake air manifold is studied to simulate a dual fuel conversion kit. Because the engine control unit is optimized to work with only the diesel injection into the cylinder, the addition of methane to the intake disrupts this optimization. The energy from the diesel fuel is replaced with that from the methane by holding the engine load and speed constant as methane is added to the intake air. The pilot injection is fixed and the main injection is varied in increments over 12 crank angle degrees at these conditions to determine the timing that reduces each of the emissions while maintaining combustion performance as measured by the brake thermal efficiency. It is shown that with higher substitution the unburned hydrocarbon (UHC) emissions can increase by up to twenty times. The NOx emissions decrease for all engine conditions, up to 53%. The thermal efficiency of the engine is highest with the most advanced injection timing for high load conditions; however, the tradeoff is an increase in CO emissions by up to 23% and up to two and a half times the NOx emissions. As a result, it is observed that by altering the injection timing, optimum performance can be achieved taking into consideration all of the tradeoffs when methane is added to the intake air.
Maxey, Claire, Kalaskar, Vickey, Kang, Dongil, Boehman, Andre
Detecting Methane From Leaking Pipelines and as Greenhouse Gas in the AtmosphereTBMG-1483410/1/2012
Laser remote sensing measurements of trace gases from orbit can provide unprecedented information about important planetary science and answer critical questions about planetary atmospheres. Methane (CH4) is the second most important anthropogenically produced greenhouse gas. Though its atmospheric abundance is much less than that of CO2 (1.78 ppm vs. 380 ppm), it has much larger greenhouse heating potential. CH4 also contributes to pollution in the lower atmosphere through chemical reactions, leading to ozone production. Atmospheric CH4 concentrations have been increasing as a result of increased fossil fuel production, rice farming, livestock, and landfills. Natural sources of CH4 include wetlands, wild fires, and termites, and perhaps other unknown sources. Important sinks for CH4 include non-saturated soils and oxidation by hydroxyl radicals in the atmosphere.
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