End Gas Research Articles

Resource Misgovernance and the Contradictions of Gas Flaring in Nigeria: A Theoretical Conversation

Nigeria remains Africa’s largest energy producer and at the same time possesses one of the highest gas flaring rates in the continent. Gas flaring in the Niger Delta region, estimated at 75% of the entire gas produced in Nigeria, highlights the environmental abuse posed by resource extraction, and exposes the failure of successive governments to eliminate the threat it portends to human survival in the oil region. The federal government formally declared gas flaring illegal since 1984, but multinational oil companies continue to treat compliance as a matter of convenience and not of necessity. Despite persistent protests against environmental degradation by the oil-producing communities, the refusal of the oil companies to end gas flaring and complicity of the government remained sources of concern. In the light of these, the study examines the crux of the gas flaring imbroglio, assesses the cost–benefits of gas flaring, and explores how gas emissions to the atmosphere have threatened human existence and ecological sustainability in the Niger Delta oil region. The study reiterates the urgency to enforce a zero-gas-flaring policy in Nigerian oil communities.

A phenomenological model of knock intensity in spark-ignition engines

In experimental calibration of mass production spark-ignition (SI) engines, knocking cycles are usually determined by a specified threshold of knock intensity (KI). In engine cycle simulation, however, modeling of knock is usually limited to prediction of knock onset (i.e. auto-ignition of end gas), or merely simple parameters such as unburned mass fraction (UMF) for KI are taken into account, causing considerable deviation from actuality. The objective of this study is to develop a phenomenological KI model to improve predictability of engine cycle simulation. The experiments with a turbocharged 1.5L gasoline engine operated by spark sweeps around knock limits over a wide speed range are conducted to generate the data base for the model formulation and evaluation. With assumption of lognormal distribution of KI in consecutive cycles, a knock factor (KF) based on the likelihood ratio is proposed as a criterion for definition of knocking cycles. The model developed in the previous study, which includes the cylinder pressure, end gas temperature, exhaust gas recirculation (EGR) ratio and excess air ratio as variables, is used to predict the knock onset. With in-depth analysis of the physics influencing knock intensity, the energy density and heat release rate (HRR) in hot spots are identified to play critical roles in determination of knock intensity. The heat release rate is related to the end gas temperature, pressure, EGR ratio and excess air ratio, while the energy density is determined by the amount of fresh charge in the cylinder and the charge volume at knock onset. Thus, the correlation of the two factors, including the HRR factor α and the energy density factor β, is formulated to develop the predictive model of knock intensity YKI. Finally, the newly developed KI model is evaluated through comparison with other KI models, and better performance in terms of prediction of knock intensity is obtained.

Numerical study on transition of hydrogen/air flame triggered by auto-ignition under effect of pressure wave in an enclosed space

End gas auto-ignition and transition of flame front are considered as the main causes of severe pressure oscillation in spark-ignition engines, which is one of the major features of knock and super-knock. The knowledge of characteristics of auto-ignition, flame front development, propagation of pressure wave and relations between them, still needs to be maintained. In this study, flame front transition induced by pressure wave and auto-ignition are investigated using one-dimensional simulation with detailed chemistry in an enclosed space Calculation cases with different initial thermodynamic conditions are investigated. Mass fraction of OH is employed as indicator of auto-ignition progress under variable conditions caused by pressure wave. Different propagation modes of flame front, including subsonic deflagration, detonation and supersonic deflagration, are developed under the effects of both pressure wave and auto-ignition. Results show that mass fraction of OH could successfully reflect auto-ignition progress, thus indicating occurrence and sequence of auto-ignition at different locations. Transitions from deflagration to detonation and detonation to supersonic deflagration are found to be triggered by sequential auto-ignition with different gradient of auto-ignition progress ahead of flame front induced by pressure wave.

Knock characteristics analysis of a supercharged spark Ignition engine using three grades of fuels

The power output of a spark ignition engine could be improved by boosting the intake pressure and compression ratio; however the applications of these are limited by knock in engines. This study examined the knocking behaviours of three commercially available fuels for spark ignition engines operated at engine intake pressures of 1.6 and 2.0 bar. The pressure data for the fuels tested were grouped into three: the fast cycle, medium cycle and slow cycles. Knock intensities from the pressure data were processed with Fast Fourier Transform (FFT) and band pass filtering techniques. The results showed that the knocking cycles occurred only in the fast and medium cycles. These results supported the view that auto-ignition of end-gases was due to compression from the high speed propagating flames. FTiR spectrums showed that the presence of aromatics was responsible for the better anti-knock quality exhibited by E5 and ULG 98 over PRF 95. Keywords: End gas, Fuel, FTiR , Knock, Spark Ignition Engine, Supercharging, Pressure.

5-2-2 混合気温度が火炎伝播・エンドガス部の挙動およびノック発生に及ぼす影響(Session 5-2 燃焼・熱利用 2)

5-2-2 混合気温度が火炎伝播・エンドガス部の挙動およびノック発生に及ぼす影響(Session 5-2 燃焼・熱利用 2)

Executive Authority to Keep It in the Ground: An Administrative End to Oil and Gas Leasing on Federal Land

The United States maintains a federal program whereby private actors lease access to the federal mineral estate, including vast stores of fossil fuels. Issuing these leases to extractive industries means a considerable amount of otherwise-benign carbon is released into the atmosphere, which contributes significantly to global climate change. Environmental organizations have called on the executive branch to change this policy under a campaign called “Keep It in the Ground.” This article evaluates the executive branch’s authority to end onshore oil and gas leasing administratively, without action by Congress. I conclude that the Department of the Interior can terminate onshore oil and gas leasing under discretionary authority contained in the Mineral Leasing Act and the Federal Land Policy and Management Act. Based on this authority, the President, acting through the Interior Department, could create a national rule or set of rules, similar to the Forest Service’s 2001 Roadless Rule, ending oil and gas leasing nationwide. Only process, not substantive law, would limit the executive branch’s ability to stop the extraction of federal fossil fuels.

火花点火機関におけるエンドガス部での化学反応計算

火花点火機関におけるエンドガス部での化学反応計算

混合気希釈がノック強度に及ぼす影響（第2報 ノックを誘発しないエンドガス自着火条件）

混合気希釈がノック強度に及ぼす影響（第2報 ノックを誘発しないエンドガス自着火条件）

Development of a dynamic model and study of the dynamic characteristics of an end gas dynamic seal

A significant part of damages in end gas dynamic seals are caused by dangerous vibrations. To improve the reliability of these seals, it is necessary to develop adequate mathematical models and to perform integrated computational and experimental studies. In this article, the two-mass dynamic model for an end gas dynamic seal is considered, which is the most appropriate for practical cases. Theoretical and experimental analyses of the dynamic state of a seal have been performed. The scope of vibration amplitudes and frequencies has been determined for an end gas dynamic seal. The results can be used to design new seals and to implement seals in compressors with magnetic supports.

Direct numerical simulation of flame/spontaneous ignition interaction fueled with hydrogen under SACI engine conditions

In spark assisted homogeneous charge compression ignition (SACI) engines a premixed flame is first established; the propagating flame results in compression heating of the end gas and finally auto-ignition of the gas. Two dimensional direct numerical simulation (2D DNS) and one dimensional (1D) detailed simulations of flame/spontaneous ignition interaction in a lean hydrogen/air mixture under a constant volume enclosure relevant to SACI engine conditions are performed using detailed chemistry and detailed transport properties. In a 2D outward propagating spherical flame, thermal-diffusive instability is observed and once auto-ignition starts a low temperature region in the preheat zone of the flame is formed. Subsequently, the ignition in the preheat zone is suppressed. Then 1D flame/ignition interactions in H2/air, syngas/air and methane/air mixtures are studied using detailed numerical simulations. The results reveal that due to preferential diffusion of hydrogen, heat and mass transfer in the preheat zone inhibits the ignition process, yielding a slower reaction rate hence an even lower temperature in the region. It is shown further that the low temperature region is not affected by the domain size and one step chemistry but it will disappear at very low initial temperature conditions. This is due to the absence of auto-ignition under low temperature conditions.

Abnormal combustion phenomena with different fuels in a spark ignition engine with direct fuel injection

Characterizing abnormal combustion behavior of different fuels is of significant importance to explore the highest fuel economy and to improve the power density of modern spark ignited (SI) engines. Many experimental and numerical investigations have been reported in the literature for conventional pump fuels, whereas scientific findings for biofuels and gasoline-biofuel blends are less available. In the present study, special focus is set on the correlation of experimental investigations and corresponding auto-ignition theories. Therefore, the auto-ignition characteristics of biofuels and gasoline–biofuel mixtures for two different abnormal combustion phenomena (hot spot surface-ignition and gas phase auto-ignition under typical engine knock conditions) are studied using a direct injection spark ignition (DI–SI) single cylinder research engine featuring variable charge motion and a compression ratio of 11. The obtained results for all tested fuels are benchmarked against investigations using conventional E0RON95 fuel and isooctane as reference fuels. Additionally, kinetic investigations are performed to confirm the experimental results combined with auto-ignition theories. It could be shown via engine experiments with a controlled hot surface that the hot spot surface-ignition tendency is influenced by the chemical heat release rate of the fuel and the charge cooling effect due to the stoichiometric air requirement related heat of vaporization. Due to the increased enthalpy of vaporization with the applied (engine) configuration all gasoline–biofuel mixtures improve the hot spot surface-ignition propensity compared to the reference fuel EORON95 by 20–50K. The gas phase auto-ignition propensity decreases substantially with increasing ethanol content, revealing a boost pressure increase of at least 40–60% under conditions typically relevant for knocking combustion in the end gas. For the applied configuration and with direct fuel injection, the location of auto-ignition has the highest frequency near the spark plug for all investigated fuels. Often, the most critical point for auto-ignition is the center electrode or the gas space in its immediate proximity between the ceramic insulator and thread.

Application of a Gas–Liquid Mixing Pump in Biogas Purification and the Co-production of Nano Calcium Carbonate

CO2 removal is one of the key technological requirements in biogas purification. A technique using a gas–liquid mixing pump to capture CO2 and co-produce nano calcium carbonate was devised and tested in this work. The characteristic curves and CO2 absorption efficiency of the pump were investigated. The CO2 content of the end gas in all experiments was less than 2%, and the calcium carbonate samples showed that calcite was produced with a favorable particle size. A solution was proposed to deal with gas inlet blockage by preparing polyphenylene sulfide (PPS)–polytetrafluoroethylene (PTFE) coating. The coating had superhydrophobicity, self-cleaning ability, a unique microstructure, and good adhesion to the substrate. The gas inlet coated with PPS–PTFE could remain clean for at least 12 h, suggesting that the method used in this work was suitable. This work provides a novel approach for CO2 absorption and biogas purification.

The Effect of Humidity on the Knock Behavior in a Medium BMEP Lean-Burn High-Speed Gas Engine

The effects of air humidity on the knock characteristics of fuels are investigated in a lean-burn, high-speed medium BMEP engine fueled with a CH4 + 4.7 mole% C3H8 gas mixture. Experiments are carried out with humidity ratios ranging from 4.3 to 11 g H2O/kg dry air. The measured pressure profiles at non-knocking conditions are compared with calculated pressure profiles using a model that predicts the time-dependent in-cylinder conditions (P, T) in the test engine (“combustion phasing”). This model was extended to include the effects of humidity. The results show that the extended model accurately computes the in-cylinder pressure history when varying the water fraction in air. Increasing the water vapor content in air decreases the peak pressure and temperature significantly, which increases the measured Knock Limited Spark Timing (KLST); at 4.3 g H2O/kg dry air the KLST is 19 °CA BTDC while at 11 g H2O/kg dry air the KLST is 21 °CA BTDC for the same fuel. Excellent agreement is observed between the calculated knock resistance (using the Propane Knock Index, PKI) and the measured knock resistance (KLST) for the range in water content in air studied in this work. Since the effect of water on autoignition delay time is negligible, the observed increase in knock resistance of the fuel-air mixture is due a decrease in pressure and temperature of the end gas with increasing water content in as a result of changes in the mass burning rate, and thermophysical properties of the fuel-air mixture.

Understanding the effect of external-EGR on anti-knock characteristics of various ethanol reference fuel with RON 100 by using rapid compression machine

In this study, the effect of external-exhaust-gas-recirculation (EGR) on anti-knock characteristics of ethanol reference fuels (ERFs) with research octane number (RON) 100 was analyzed by measuring the ignition delay of the simulated end gas from a representative spark ignition (SI) engine operation, i.e. ASTM RON test condition. An in-house SI engine model was used to derive temperature and pressure profiles of the end gas with and without external-EGR for various ERFs, and then the ignition delay was measured by using a rapid compression machine along the derived temperature-pressure paths. The effect of external-EGR on the ignition delay of the simulated end gas was divided into two effects affecting the auto-ignition behavior: composition effect and temperature effect, then each effect was evaluated separately. As a result, the composition effect by adding external-EGR was maximized when the fuel is ERF10. With a regression analysis, it was found that there is the correlation between the amount of composition effect and the amount of pre-heat release in the end gas during a flame propagation; therefore, it is understood that ERF10 shows the most sensitive composition effect due to its pre-heat release characteristic. On the other hand, ERF with higher ethanol content was more sensitive to temperature effect by external-EGR on the ignition delay. It is found out that the amount of temperature effect depends mainly on latent heat of fuel; therefore, high latent heat of ethanol in ERF leads to its being influenced more by temperature effect. Consequently, ERF10 has the highest external-EGR sensitivity in anti-knock behavior at RON test condition, and it is further discussed that the optimum ERF for external-EGR strategy could vary from ERF0 to ERF10 according to different engine operating conditions.

Effect of turbulent mixing on the end gas auto-ignition of n-heptane/air mixtures under IC engine-relevant conditions

The effect of turbulence on the end-gas auto-ignition (AI) of stoichiometric n-heptane/air mixtures under engine relevant conditions is numerically studied through a combined methodology of Large Eddy Simulation (LES) and one-dimensional stand-alone Linear Eddy Model (LEM). Similar end-gas auto-ignition process in super rapid compression machine experiments is first been qualitatively reproduced through LES. To further investigate the effect of small-scale turbulence-chemistry interaction on the end-gas auto-ignition in the near-wall region which consists of a core region and a boundary layer, 1-D LEM simulations are performed by extracting the thermal-chemical and turbulent parameters at top dead center from LES. The parametric study covers a range of representative fluctuation velocity values under engine-like conditions at two initial temperatures of 700K and 900K, which are below and within the Negative Temperature Coefficient regime respectively. It is generally found that, increased turbulence intensity delays AI formation and also reduces the kernel size at the onset of AI. At the initial temperature of 700K, intense turbulence can change the combustion mode of the end-gas following the initial spontaneous auto-ignition in the core region. Diffusive - reactive flame structures are observed and the kernel expansion is governed by turbulent flame propagation. At a high initial temperature of 900K, the formation of “cold” AI kernels is inhibited with increased turbulence intensity. A budget analysis reveals that the expansion processes of nascent kernels mainly are spontaneous ignitions and turbulence may enhance the local scalar mixing. However, turbulence won't change the nature of auto-ignition propagation wave driven dominantly by exothermicity during the end-gas combustion process.

Extension of PREMIER combustion operation range using split micro pilot fuel injection in a dual fuel natural gas compression ignition engine: A performance-based and visual investigation

The effects of split pilot fuel injection on engine performance and PREmixed Mixture Ignition in the End Gas Region (PREMIER) combustion characteristics were investigated in a single-cylinder dual-fuel natural gas engine ignited with diesel fuel. In particular, the effect of second spray timing on combustion mode was examined. PREMIER combustion was observed in a wider range of operating conditions with split injection strategy compared to single injection strategy. We determined that it was possible to both decelerate heat release and suppress knocking to PREMIER combustion, and accelerate heat release and promote normal combustion to PREMIER combustion, with suitable second injection timing. The maximum of thermal efficiency of PREMIER combustion operation with split injection was close to the results obtained with knocking operation. In-cylinder images showed that split injection strategy advances or retards the progress of combustion by controlling the size and rate of growth of flame kernels, depending on the timing of the second injection. The combustion progress is earlier when the pilot fuel delivered during the first injection autoignites during the second injection. Kernel growth and the final size were adversely affected when the second injection was initiated after pilot fuel autoignition.

Mixture preparation and combustion in a GDI engine under stoichiometric or lean charge: an experimental and numerical study on an optically accessible engine

In direct injection spark ignition (SI) engines, the spray dynamics and interaction with the surrounding air flow are recognised as strongly affecting mixture quality, combustion development and amount of pollutants released at the exhaust. Spray impact against walls has also to be considered since undesired deposition of liquid as wallfilm causes unburned hydrocarbons and soot formation, hence increased fuel consumption and even augmented cyclic dispersion.Present work aims at clarifying the dynamics of sprays generated by multi-hole high pressure injectors in the combustion chamber of a gasoline direct injection (GDI) engine, as well as to characterize the combustion development and pollutants formation under various injection modes. Stoichiometric and lean operations are both studied into detail through a combined experimental and numerical approach. Experiments are conducted on an optically accessible engine, whereas numerical simulations are made after the development and validation of a three-dimensional (3D) sub-model reproducing at the best the spray dynamics also in its impact over walls.Early injection is shown to anyway determine at spark timing slight inhomogeneity in the equivalence ratio distribution of the stoichiometric charge, which makes for the flame propagation being anyway not spherical, but such to exhibit a preferential direction towards the richest zone of the combustion chamber. This leads to the formation of a pocket in the end gases where the knocking phenomenon is likely to occur under some circumstances. Lean charge operation is instead discussed as injection pressure and spark timing are varied to highlight mechanisms of formation of the main pollutants and to define routes for the development of proper engine control strategies. A deep insight in the in-cylinder thermo-fluidynamic processes is achieved thanks to the here followed synergic experimental-numerical approach.

Experimental investigation on the knocking combustion characteristics of n-butanol gasoline blends in a DISI engine

n-Butanol is a very competitive alternative biofuel for spark ignition (SI) engines given its many advantages. Current researches are mainly concentrated on the overall combustion and emissions performance concerning the feasibility of n-butanol gasoline blends in SI engines. In this work, focus was given on the knocking combustion characteristics of operation with pure n-butanol as well as a blend fuel with 20% volume content of n-butanol (Bu20), which was investigated experimentally in a direct-injection spark ignition (DISI) single cylinder engine. Operation condition is fixed at a constant engine speed of 1500r/min, using three throttle openings with stoichiometric air–fuel ratio. Spark timing was swept to achieve different knocking levels. The results of n-butanol and Bu20 were benchmarked against those obtained by the research octane number (RON) 92 commercial gasoline. Compared with the baseline fuel gasoline, neat n-butanol shows better anti-knock ability with more advanced knock limited spark timing, whereas slightly deteriorative knock resistance can be found for Bu20. It is hypothesized Bu20 has higher end gas temperature due to its higher brake mean effective pressure (BMEP) and faster burning rate compared with gasoline, which indicates the knock tendency depends not only on the fuel octane number, but also on the factors that affect the end gas thermodynamic state. The heavier knock propensity of Bu20 is furthermore confirmed by its more advanced knock onset and higher peak oscillation pressure. Results of fast fourier transform (FFT) indicate the knocking oscillation frequencies are mainly determined by the combustion chamber resonance modes. Statistics probability distribution and cumulative distribution are applied to evaluate the knock intensity variation for each fuel.

Experimental observations of turbulent flame propagation effected by flame acceleration in the end gas of closed combustion chamber

In present study, a new designed constant volume combustion bomb (CVCB) equipped with an orifice plate and visualized by high speed schlieren photography has been employed to study the turbulent flame propagation effected by flame acceleration in the end gas region. The orifice plate is employed to achieve flame acceleration and obtain different turbulent flames at different equivalence ratios. We investigate the flame propagation speed, the formation mechanism of compression front, the influence of flame acceleration on the end-gas as well as the flame structure changes. The results show that the laminar flame can be accelerated and transferred to a wrinkled turbulent flame through the orifice plate significantly and there forms a clear compression front ahead of the turbulent flame. The flame propagation speed without orifice plate shows the trend of initial increase and consequence decrease in the confined space. Moreover, the turbulent flame propagation speed shows the significantly different trend and demonstrates the “M” shape evolution including the self-acceleration, unstable and deceleration process. Finally, the evolution of turbulent flame in the end gas of the confined chamber was described in detail with three stages: compression front formation, flame front distortion and reverse propagation.

定容燃焼容器を用いたノック発生過程の予混合火炎およびエンドガスの挙動に及ぼす火炎温度の影響の考察

定容燃焼容器を用いたノック発生過程の予混合火炎およびエンドガスの挙動に及ぼす火炎温度の影響の考察