Combustion Process Of Natural Gas Research Articles

The chemical kinetic and heating effects decoupling of pilot diesel in a diesel ignited natural gas engine under various pilot diesel injection timing

The diesel ignited natural gas engine suffers from low load low thermal efficiency and high load knocking problems. The solution to these problems requires control of the combustion process. The combustion of pilot diesel plays an important role in the natural gas combustion process. The combustion of pilot diesel not only provides heat for the natural gas combustion process (heating effect), but also provides highly intermediate chemicals for the chemical reaction of natural gas (chemical kinetic effect). However, the mechanism of this effect under various pilot diesel injection timing is unclear. To decouple the heating effect and chemical kinetic effect of pilot diesel, a detailed study was conducted by numerical simulation combined with chemical inertness method. A 6-cylinder turbocharged intercooler diesel/natural gas dual fuel heavy-duty engine was used in this study, and the pilot diesel injection timing was controlled over a very wide range. The result shows that the chemical kinetic effect of pilot diesel increases while the heating effect shows the opposite trend with the advance of injection timing. When the fuel injection timing is 40° CABTDC, the pilot diesel chemical kinetic effect begins to exceed 50%. This may serve as judging the start timing of RCCI combustion mode. The low concentration and wide distribution of pilot diesel at the beginning of natural gas combustion is the leading reason for the increase of chemical kinetic effect. When the fuel injection timing is advanced, the high concentration area and distribution of highly active intermediate CH2O show an increasing trend, while the high-temperature area decreases and the low-temperature area gradually increases. There is a strong correlation between strong chemical kinetic effect and low-temperature combustion.

Experimental and kinetic modeling study on the oxidation and laminar combustion characteristics of natural gas

The oxidation process in the flow tube reactor and the laminar combustion process in the constant volume combustion bomb of natural gas (0.9 methane/0.07 ethane/0.03 propane, mole fraction) were experimental tested. Furthermore, a reduced reaction mechanism (including 40 species and 189 reactions) of natural gas was developed based on the Aramco 2.0 mechanism by combining the path sensitivity analysis, rate of production analysis, reaction path analysis and the decoupling method. The results show that, in the oxidation process of natural gas, with the equivalence ratio increasing, the starting and ending temperatures for oxidation reaction of natural gas are increased, the reaction temperatures corresponding to CO generation and consumption are higher, and the amount of NO production is decreased. In the the laminar combustion process of natural gas, with the initial temperature and oxygen content increasing or the initial pressure, CO2 and H2O contents decreasing, the laminar flame speed is increased. Through comparing with the calculated results by the Aramco 2.0 mechanism and the corresponding test data, the reduced reaction mechanism can well predict the oxidation, ignition delay and laminar combustion characteristics of natural gas under various conditions.

Calculation and analysis of the flamelet library for numerical modelling of the non-premixed combustion of natural gas in a pilot burner

The flamelet modelling concept has been employed for numerical simulation of the non-premixed combustion of natural gas in a pilot burner of novel type. This prospective laboratory-scale burner device is featured by axial supply of high-speed jet of flue gases, while the fuel (natural gas) and the oxidizer (air) are supplied radially and separately inside the burner chamber. With the use of chemical kinetics mechanism for natural gas (62 species, 398 reactions) the flamelet library has been generated, from its analysis the flame quenching has been determined at the scalar dissipation rate limit of 42 (1/s). From this library the lookup-table of thermochemical solution has been pre-calculated with the presumed beta-function pdf averaging. On this basis the numerical simulation of aerodynamics, heat transfer and the natural gas combustion processes, including soot formation and its effect on radiative heat transfer, has been performed in the considered pilot burner run at the thermal load of 8.8 kW and air excess coefficient of 0.85 (inside the burner body). The distributions of gas species are presented. The predicted NOx emission in exhaust gases is 48.8 mg/m3 for the studied burner regime.

About the possibility of using natural gas as a fuel on agricultural tractors

AIMS: Evaluation of the effectiveness of converting diesel engines used in agricultural self-propelled vehicles to fully or partially natural gas (methane) fueled engines.
 METHOD: Is analytical.
 RESULTS: In agriculture up to 25% of operating expenses are fuel costs. However, the only number of the concomitant objective and subjective factors allow us to estimate expedience and efficiency of converting diesel engines used in agricultural self-propelled vehicles for full or partial supply of natural gas (methane). On the one hand, the price of an equivalent amount (in terms of work performance) of natural gas is more than 2 times lower than the price of diesel fuel. At the same time, natural gas is the most environmentally friendly hydrocar-bon fuel. But, on the other hand, the underdeveloped refueling infrastructure is obvious, and the environmental friendliness of natural gas itself is not a guarantee of the environmental friendliness of the engine itself. Also, the safety of gas equipment operation under high pressure is an important matter.
 CONCLUSIONS: Firstly, the use of natural gas instead of diesel fuel requires taking into account the difference in the physicochemical characteristics of these fuels, which determines both the requirements for the organization of the working process and the advantages and disadvantages of such replacement. Secondly, the combustion process of natural gas, compared to diesel fuel, is characterized by in-creased formation of water leading to more intensive watering of lubricating oil, although it re-duces carbon dioxide emission into the atmosphere. Safety of natural gas equipment operation plays an important role, and first of all, it is concern of cylinders that are filled at pressure of 20.025.0 MPa.

An investigation of thermal radiation from laminar diffusion flames in a tri-coflow burner with central oxygen

In natural gas combustion processes, oxygen-enriched combustion is often used to improve heat transfer and thermal efficiency. In this investigation, a triple-port burner is employed to investigate the effect of oxygen enrichment on thermal radiation when introducing oxygen into the center of a normal coflow diffusion flame, while maintaining an outer coflow of air. Two fuels are investigated: methane, being the primary constituent of natural gas and having a low propensity for soot formation, and ethylene, which acts as a reference fuel with a much higher propensity for soot formation. The flow rates of air in the outer annulus and fuel in the inner annulus are held constant, while the flow rate of oxygen in the central tube is systematically increased. Total radiation, which is converted to radiation loss fraction, is measured using a wide-angle radiometer. Soot volume fraction and soot temperature are measured using two-color ratio pyrometry with a digital camera.For low flow rates of central oxygen when an inner oxygen-fuel flame is apparent, the thermal radiation is increased due to an increase in soot concentration. At these low flow rates, thermal radiation is increased by 20% for methane and 26% for ethylene, as compared to a normal coflow flame without central oxygen. The increase in radiation from these flames results in a decreasing, or relatively constant soot temperature in the soot laden region as the increased soot concentration radiates heat from the flame, even though gas temperatures upstream near the central oxygen flame are quite high. For relatively high flow rates of central oxygen, radiation from the tri-coflow methane flame increases by up to 31% compared to a normal coflow flame, while radiation from the ethylene flame monotonically decreases. For both fuels, when oxygen flow rates are high, soot concentration decreases (due to a change in flame shape and enhanced oxidation rates) and soot temperature increases. Product gases are the dominant emitters of radiation in the methane flames studied. Soot is the dominant radiant emitter in the ethylene flames until high flow rates of central oxygen reduce the soot concentration, such that high temperature product gases take over as the dominant radiant emitters. Overall, low flow rates of central oxygen can increase thermal radiation from the coflow methane flame by 20% due to increased soot concentration, and high flow rates of central oxygen can increase thermal radiation by 31% due to increased gas temperatures. However, the methane flames with central oxygen still emit at least 41% less radiation than the coflow ethylene flame. These results indicate that when considering the effect of oxygen enrichment on thermal radiation, the change in overall flame (gas and soot) emissivity can be just as important as the change in temperature.

Impacts of the horizontal swirl and axial tumble on the turbulent kinetic energy and combustion process of a natural gas engine

ABSTRACT Natural gas (NG) engines are restricted by slow combustion rates. An appropriate flow condition is considered to be the most promising way to improve the combustion rate of NG. In this study, decoupling analysis of the impacts of swirl and tumble on turbulent kinetic energy (TKE) and combustion process of a spark ignition (SI) NG engine was conducted by simulation. A 3D model was established and boundary conditions of the most economical operating point (1200 r/min, 100% load) were obtained through tests, and the rationality of the case was verified. Then, the flow field of the original engine was decoupled at the intake valve closing time to obtain the decoupled swirl field and the decoupled tumble field. Finally, the swirl field and the tumble field were amplified and applied to the SI NG engine. The results showed that high swirl or tumble can obtain high TKE, but the contribution mechanism of them to TKE is significantly different. According to the analysis of the spatial motion structure and energy conversion, the TKE in tumble field is much higher than that in swirl field with the same intensity. In addition, the impacts of swirl and tumble on the combustion process of the SI NG engine are both divided into two phases, and high swirl or tumble can obtain higher thermal efficiency. The combustion rate of NG first increased with the increase in initial flow field strength. When the swirl ratio at intake valve closing time (SR0) and the tumble ratio at intake valve closing time (TR0) exceeded 2.0 and 1.25, respectively, the combustion rate is kept in a fluctuating equilibrium state. At this time, the improvement of swirl and tumble on NG combustion process was brought into full play, the maximum indicated thermal efficiency reached 43.18% and 44.39%, respectively. Finally, the conclusion was drawn by comparing swirl and tumble in different aspects where high tumble shows greater potential in achieving super-high thermal efficiency.

Estimation of CO₂ emissions from petroleum refineries based on the total operable capacity for carbon capture applications

Carbon capture and storage processes are sought to play a major role in reducing carbon emissions from large point sources. Petroleum refineries, in particular, produce several streams that are CO2-rich, including fluidized catalytic cracking, steam methane reforming, and natural gas combustion processes that generate heat for refinery operations. Of these, stationary combustion processes account for nearly two-thirds of all CO2 generated within a refinery. In this work, a regression analysis was performed to correlate the size and power requirements for the combined capture, compression, and dehydration process dependent upon a refinery's operating capacity. Refinery capacity and CO2 generation data from 128 U.S. refineries were normalized, and a linear regression model was developed. A capture, compression, and dehydration process model was developed using Aspen HYSYS for delivery of CO2 (10–15 wt. % in steam) to pipeline specifications (500 ppm H2O, 15.2 MPa). Predicted CO2 emissions were 0.1 to 7.7 % of actual emissions, depending on whether a refinery had a low, medium, or high carbon emission/capacity ratio.

Influence of H2O on Oxygen Enriched Diffusion Combustion of Natural Gas

O2/H2O combustion technology, as the next generation of oxy-fuel combustion technology with great potential, can greatly increase the utilization rate of clean energy CH4. In this paper, the natural gas combustion process under 6 operating conditions of O2/H2O atmosphere and O2/FH2O atmosphere is numerically simulated. The horizontal analysis is carried out on the characteristics of H2O fraction, CO2 volume fraction and the amount of pollutants (NOx, carbon black), and in-depth exploration of the content of additive H2O and the influence of chemical action on the above characteristics. The research results show that the chemical effects of H2O have a negative effect on combustion temperature, and the physical effects are dominant. The chemical effects of H2O have a great impact on CO production and little effect on the production of CO when the proportion of H2O is 65-79%. The chemical effects of H2O inhibit the formation of NOx and carbon black when the proportion of H2O is within the range of 55-70%. The chemical effect has the greatest impact on the formation of dyes (NOx, carbon black) when the proportion of H2O is within the range of 65-70%.

Analytical Determination of Torch Characteristics of Rotary Kiln Burners

Fuel combustion processes play an important role when firing materials in rotary kilns. In this paper, we provide brief information on the design and operation principle of the burner with a combined combustion system that was developed specifically for the new rotary kiln for burning chamotte. The computer modeling results of the natural gas combustion process performed in the ANSYS software package are presented.

Управление параметрами газовых горелок отражательных печей горения при плавлении никельсодержащего сырья

The purpose of the reserch is to develop and justify the principles of the energy model of an industrial reverberatory furnace taking into account chemical composition and properties of natural gas, which is widely used as a fuel in metallurgical processes to ensure the efficient operation of open gas furnaces in the production of crude Nickel. Сombustion of natural gas in the burners of the gas brands GGSB-1.4 and GGSB-2,2 (of medium pressure with the heat capacity of 1.4 MW, gas flow rate of 140 m 3 /h and connecting gas pressure before the burner of not more than 40 kPa, nominal gas pressure before the burner of not more than 20 kPa) always results in the production of carbon dioxide and soot, which have an adverse effect on the process flow. High content of hydrogen and carbon in the gas changes the thermal balance of the process of crude Nickel smelting. To study the combustion process of natural gas of different composition taking place in the burners of medium pressure the computer program STANJAN is used with the application of the wet gas-based flowmeter OPTISONIC 7300 for pressure measurement. The flowmeter confirmed the stable operation of the device when the liquid content in the gas is up to 1% of the gas volume. The amount of waste flue gases is measured using MRU Delta 65-3 gas analyzers, which identify the total amount of gases (O 2 , CO, NO), temperature, pressure (vacuum), as well as calculate the content of CO 2 and plant efficiency. The value of the maximum temperature of combustion products and their ratio to the excess values in the balance during the entire heating of the air is obtained. The dependencies for industrial burner automation process optimization while minimizing energy losses and emission of harmful substances are determined. Conducted research allows to reveal the negative effect of excess air on the maximum temperature of melting products and the positive effect of air preheating at this temperature. When the air with the temperature of 50°C (instead of 25°C) arrives to the burner the temperature of flame rises, which increases the heat added to the load and reduces the energy consumption of the process. Excess air and product temperature in a thermal process based on natural gas combustion are the primary factors in the determination of environmental and energy aspects of the process.

Combustion process decoupling of a diesel/natural gas dual-fuel engine at low loads

The combustion process of diesel/natural gas dual-fuel engine is complicated. In order to decouple the combustion process of natural gas (NG) and diesel, a wide range of the NG from zero to 75%, by increasing the NG flow rate at a constant air and diesel consumption rate were studied. A detailed analysis based on heat release rate data has been carried out to better understand the effect and underlying mechanism of the two fuel combustion processes. A method of calculating the ratio of heat release from NG combustion to the total heat release through comparing the heat release rate data between dual-fuel mode at different NG quantities and original diesel mode was proposed. The tested engine is a 6-cylinder turbocharged intercooler dual-fuel engine. Several combustion parameters, including in-cylinder pressure, in-cylinder temperature and heat release rate, were analyzed under 1335 rpm, 10% load (A10) condition and 1335 rpm, 25% load (A25) condition. The results show that the heat release rate curves have only one peak firstly, then transform into two peaks, and change into a quasi-single peak at last with the increase of NG quantities under A10 condition when Tinj is 7°CA BTDC. The maximum ratio of heat release from combustion by NG around diesel spray to the total heat release is 25.4% and the premixed combustion of diesel occupies the main combustion process, the maximum ratio of heat release from combustion by flame propagation of NG to the total heat release is 75.4% (PES is 73%) and the combustion of NG is the main part of the combustion process. A similar discussion under A25 condition when Tinj is 7°CA BTDC and about advancing and retarding Tinj under A10 condition was conducted.

Modelling of the combustion velocity in UIT-85 on sustainable alternative gas fuel

The flame propagation velocity is one of the determining parameters characterizing the intensity of combustion process in the cylinder of an engine with spark ignition. Strengthening of requirements for toxicity and efficiency of the ICE contributes to gradual transition to sustainable alternative fuels, which include the mixture of natural gas with hydrogen. Currently, studies of conditions and regularities of combustion of this fuel to improve efficiency of its application are carried out in many countries.Therefore, the work is devoted to modeling the average propagation velocities of natural gas flame front laced with hydrogen to 15% by weight of the fuel, and determining the possibility of assessing the heat release characteristics on the average velocities of the flame front propagation in the primary and secondary phases of combustion.Experimental studies, conducted the on single cylinder universal installation UIT-85, showed the presence of relationship of the heat release characteristics with the parameters of the flame front propagation. Based on the analysis of experimental data, the empirical dependences for determination of average velocities of flame front propagation in the first and main phases of combustion, taking into account the change in various parameters of engine operation with spark ignition, were obtained.The obtained results allow to determine the characteristics of heat dissipation and to assess the impact of addition of hydrogen to the natural gas combustion process, that is needed to identify ways of improvement of the combustion process efficiency, including when you change the throttling parameters.

Exergetic Analysis of Triple-Level Pressure Combined Power Plant with Supplementary Firing

AbstractThis work presents a thermodynamic analysis of a triple-level pressure combined power plant with supplementary firing. The supplementary firing is a technological development for improving and increasing the output power of a combined-cycle (CC) power plant. In Mexico, there is a plant operating with this configuration, which generates a net power of 1,170 MW, with a power ratio of the gas turbine (GT) to the steam turbine (ST) of 1.35∶1. This plant is composed of four combined-cycle units with supplementary firing, each providing an output power of 292.5 MW. The energetic and exergetic analyses of the combined cycle with and without supplementary firing are pursued, taking into account the combustion process of natural gas and humid air. These analyses are also carried out for the heat recovery steam generator, considering the waste gases of the gas turbine and of the supplementary firing as the energy sources. The obtained results are fuel, steam, and humid air flows; excess of air; gas and stea...

Thermodynamic investigation of different natural gas combustion processes on the basis of a heavy-duty engine

The main challenges in engine development are the compliance to the stringent and constantly tightened emission limits and the reduction in the CO2 release. Natural gas as fuel offers one possible way of CO2 reduction. Several research projects on gas engine investigations of different engine size are executed at the Institute of Internal Combustion Engines and Thermodynamics at the TU Graz. In one of these projects, a single-cylinder-research-engine was derived from a heavy-duty Diesel engine. This single-cylinder-research-engine was then adapted for the combustion of natural gas and equipped with a spark ignition system for the underlying investigations. Different cylinder head and piston configurations were tested for the evaluation of charge motion, combustion chamber geometry and compression ratio, which was varied from 11.8 to 16.5. The engine displacement of the single-cylinder-research-engine of 2 dm3 represents a typical heavy-duty size. Four different combustion concepts of natural gas were realized and analysed, namely, spark ignition compressed natural gas stoichiometric, spark ignition compressed natural gas lean burn, Diesel pilot ignition compressed natural gas lean burn and Diesel pilot ignition compressed natural gas/H2-mixture lean burn. For the compressed natural gas/H2 gas mixture, it is also referred to as hythane. These concepts were compared concerning thermodynamic behaviour and emissions. Therefore, a part load point and a high load point were chosen for evaluation, since these are of special interest for heavy-duty emissions legislation. The focus of the investigation is put on a thermodynamic loss analysis, which allows the subdivision of losses starting at the ideal engine. The losses of a natural gas engine show significant differences to those of a Diesel engine, which are taken as reference. As requirement for the combustion concepts, the fulfilment of the emissions legislation EURO VI under the consideration of realistic conversion rates of an exhaust aftertreatment system had to be guaranteed. Additionally, sufficiently stable combustion was required. The engine efficiency was then optimized under these boundaries. For the investigation of the Diesel pilot ignition concept, five parameters were defined for variation which are air–fuel ratio, exhaust gas recirculation-rate, mass fraction burnt 50% hythane proportion and the hythane composition.

Improving high resolution emission inventories with local proxies and urban eddy covariance flux measurements

Emission inventories are the fundamental official data on atmospheric emissions of pollutants and greenhouse gases at a variety of spatial and temporal scales worldwide. This study makes use of direct CO2 emission measurements made with the eddy covariance technique over a completely urbanized area, with no confounding effect of vegetation, where emissions are mostly controlled by natural gas combustion processes and road traffic. Objectives are: i) to validate top-down spatially and temporally disaggregated emission inventories at yearly, monthly, weekly and hourly time scales; ii) to quantify the improvement achieved in official inventories when replacing built-in temporal disaggregation proxies with customized proxies based on local data of road traffic and natural gas consumption. We demonstrate that the overall performance of official inventory at yearly scale is rather good with an emission of 3.08 g CO2 m−2 h−1 against a measured emission of 3.21 ± 0.12 g CO2 m−2 h−1. When temporally disaggregating annual emissions, the agreement between inventory and observations always significantly improves when using local proxies, by 47% (from 0.70 to 0.37 g CO2 m−2 h−1 RMSE) at monthly scale, by 26% (from 0.58 to 0.43 g CO2 m−2 h−1 RMSE) at weekly scale, and by 32% (from 1.26 to 0.85 g CO2 m−2 h−1 RMSE), at hourly scale. The validity of this analysis goes beyond CO2 since the temporal proxies used by the inventories mimic the intensity of specific emission processes, therefore species emitted in the same processes as CO2, would benefit from the improved parameterization of temporal proxies shown here. These results indicate that effort should be put into developing improved temporal proxies based on local rather than national scale data, that can better mimic site dependent behaviors.

Syngas as a Reburning Fuel for Natural Gas Combustion

Abstract The paper aims to confirm the syngas application as a reburning fuel to reduce e.g. NO emission during natural gas combustion. The main aim of this modelling work was to predict pollutants generated in the exhaust gases and to indicate the influence of the syngas on the natural gas combustion process. The effect of residence time of fuel-air mixture was also been performed. Calculations were made with CHEMIKN-PRO for reburning process using syngas. The boundary conditions of the reburning process were based on experimental investigations. The addition of 5, 10, 15 and 19% of reburning fuel into natural gas combustion was studied. The effects of 0.001 to 10 s of residence time and the addition of 5, 10, and 15% of syngas on combustion products were determined. The performed numerical tests confirmed that co-combustion of the natural gas with syngas (obtained from sewage sludge gasification) in the reburning process is an efficient method of NOx reduction by c.a. 50%. Syngas produced from sewage sludge can be utilised as a reburning fuel.

Numerical comparative analysis of the combustion process in an engine powered by CNG

This paper contains the analysis of Compressible Natural Gas combustion process in engine dedicated to diesel oil. The analysis was performed on the basis of the numerical results of two systems for methane dosing. The first simulation considers the CNG delivery into the suction manifold, and subsequent production of air-fuel mixture as well as separate combustion model of a homogenous mixture. The second simulation comprises a numerical application of the fuel injection directly into the combustion chamber. Therefore it is also a simulation of a combustion process. Among the numerical results conducted with the aid of Computational Fluid Dynamics the following parameters were selected for the combustion qualitative evaluation in terms of mechanical, heat and flow properties: fields of pressure and temperature, mass fraction of the fuel and turbulence intensity. All test were conducted on the engine adopted to be fed with CNG.

Numerical simulation of a tubular solar reactor for methane cracking

This study addresses the solar thermal cracking of methane for the co-production of hydrogen and carbon black as a medium to avoid CO 2 emissions from natural gas combustion processes. The objective of this work is to numerically simulate the transport processes of momentum heat and mass in an indirect heating solar reactor, which is fed with an argon-methane mixture. The reactor is composed of a cubic cavity receiver, which absorbs concentrated solar irradiation through a quartz window and a graphite reaction tube is settled vertically inside this cavity. A series of numerical experiments were carried out in order to gain a better understanding of the interaction between the several transport phenomena taking place. The simulations showed that, in general, when the temperature of the reaction chamber is higher than 2000 K, the methane conversion is practically 100%. To validate our simulation results we compared them with available experimental data obtaining good agreement. Moreover, our results clearly evidence that most of the reaction takes place at the bottom of the reactor, which is the zone with the highest temperature profiles. Therefore, we propose modifications in the reactor design to increase conversion. The results of this work can thus serve to improve design and control of solar reactors for light hydrocarbons.

A thermodynamic analysis of the environmental indicators of natural gas combustion processes

Environmental indicators of the natural gas combustion process are studied using the model of extreme intermediate states developed at the Melent’ev Institute of Power Engineering Systems. Technological factors responsible for generation of polycyclic aromatic hydrocarbons and hydrogen cyanide are revealed. Measures for reducing the amounts of polycyclic aromatic hydrocarbons, hydrogen cyanide, nitrogen oxide, and other pollutants emitted from boilers are developed.

Indicated Mean Effective Pressure Oscillations in a Natural Gas Combustion Engine

Fluctuations in a combustion process of natural gas in the internal spark ignition engine have been investigated. We measured pressure of the cyclic combustion and expressed its cyclic oscillations in terms of indicated mean effective pressure per cycle. By applying the statistical and multifractal analysis to the corresponding time series we show the considerable changes in engine dynamics for a different equivalence ratio decreases from 0.781 to very lean conditions.