Fuel-air Mixture Research Articles

Premixed combustion of producer gas in a cyclonic flow combustion chamber under varying number of burners

ABSTRACT Producer gas derived from biomass gasification can be used as an alternative to fossil fuel for generating power. Low heating value and high CO content are main obstacles for using it via a combustion process, leading to require a special combustor design to achieve its efficient burning. This study aims to investigate premixed combustion characteristics of producer gas in a cyclonic flow combustion chamber under varying from single to four burners using 3D computational fluid dynamics simulation. Combustion process is operated at fixed thermal power input of about 90 kW with respect to injection of air-fuel mixture at the ambient condition. A 17 species skeletal reaction scheme with 73 chemical reversible reactions is used for chemical interactions. The numerical result is well agreed with the experimental data. Through all studied results it could be concluded that the peak combustion temperature, which is higher than 1600 K, is obtained for the case of multiple burners, except for the single burner case. The lowest CO formation is obtained for the case of four burners, which is approximately 243 ppm while lowest NO formation is obtained for the single burner case, which is approximately 17 ppm.

Development of effective methods and means of normalizing the atmosphere of working zones of open-cast mines

The search for technical solutions for effective air exchange in the space of deep open-cast mines. Since intensive air exchange is necessary to remove and disperse harmful impurities from the open-cast mines, improvement can be achieved mainly by intensifying natural air exchange based on phase transformations of liquids in the lower atmosphere of the working zones of the open-cast mines by creating a positive or negative temperature gradient. New technical solutions are considered that provide support for the sanitary-hygienic parameters of the atmosphere of the deep open-cast mines at the normative level. The formation of an ascending gas stream by a cascade explosion of a fuel-air mixture has the greatest efficiency. The proposed method allows for the implementation of a pulsed ventilation mode with a power of the outgoing air flow of more than 1010 W with a blasting fuel mass of 30 tons. It has been established by analytical and experimental studies that it is advisable to use pulsed fine irrigation systems to intensify air exchange in a deep open-cast mines, using the double effect, ventilating gaseous working zones and cleaning them from harmful substances with the help of a fine aerosol freely floating in space. It is also advisable to use such facilities to reduce peak loads on emissions of harmful substances from the open-cast mines into the environment and to normalize the composition of the atmosphere of the deep open-cast mines. Significant peak emissions of harmful impurities in open-cast mines include mass explosions and situations involving the creation of internal inversion zones. In a computational experiment, there are two water guns: big gun (the water jet range is 200 m, water volume per one cycle is 1000 dm3) and small gun(the water jet range is 100 m, water volume per one cycle is 200 dm3). The results of the experiment indicate greater efficiency in the use of a large water gun for airing the lower horizons of the deep open-cast mines. The use of pulsed fine irrigation systems will allow for carrying out internal technological work at a depth of more than 500 meters using a motorized ore delivery system to transfer points of cyclic-flow technology.

The scavenging timing of pre-chamber on the performance of a natural gas engine

The pre-chamber ignition system scavenged with natural gas can effectively improve the in-cylinder combustion process and extend the lean-burn limit of natural gas engines. The scavenging process affects the flow field and fuel-air mixture concentration distribution in the pre-chamber and affects the combustion process in the pre-chamber as well as the ignition process in the main chamber. This has a significant influence on the performance of natural gas engines. It is supposed that the ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing affects the combustion process in the pre-chamber. To verify this suppose, an independent injection system for injecting natural gas into the pre-chamber is designed and experiments are carried out on a single-cylinder natural gas engine. The ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing is adjusted by changing the injection start angle of the scavenging process. The combustion process in the pre-chamber and the main chamber are analyzed using the in-cylinder pressures. The results indicate that, with the delay of the injection start angle, the ratio of natural gas remaining in the mixture inside the pre-chamber at the ignition timing increases, the combustion process in the pre-chamber is enhanced, the maximum pressure difference between two chambers increases and appears earlier. The energy of the hot jets and the penetration of the jets increase, which enhances the combustion process in the main chamber.

Detonability of fuel–air mixtures

A new experimental method for evaluating the detonability of fuel–air mixtures (FAMs) based on measuring the deflagration-to-detonation (DDT) run-up distance and/or time in a standard pulse detonation tube (SDT) is used to rank gaseous premixed and non-premixed FAMs by their detonability under substantially identical thermodynamic and gasdynamic conditions. In the experiments, FAMs based on hydrogen, acetylene, ethylene, propylene, propane–butane, n-pentane, and natural gas of various compositions, as well as FAMs based on the gaseous pyrolysis products of polypropylene (PP), are used: from extremely fuel-lean to extremely fuel-rich at normal temperatures and pressures. The concept of equivalent FAMs exhibiting the same or similar detonability under the same conditions is proposed. Equivalent FAMs can be used for predictive physical modeling of detonation processes involving FAMs of other fuels. The ranking of FAMs in terms of their relative detonability allows choosing a propylene FAM for physical modeling of the operation process in the PP-fueled solid-fuel ramjets operating on detonative combustion.

Smoothed particle hydrodynamics modeling of fuel drop impact on a heated surface at atmospheric and elevated pressures.

The outcomes of fuel drop impact on heated walls will affect the fuel-air mixture distribution and the subsequent combustion and emissions in internal combustion engines. Existing numerical models for drop-wall interactions are mainly validated for conditions at atmospheric pressures. In this work, a numerical method, based on smoothed particle hydrodynamics, was developed to simulate the drop impact on a heated wall at high pressures. The effects of high temperature and high pressure on the evaporation of the drop were considered. The impact regimes under various wall temperatures and ambient pressures were identified, including deposit, contact splash, film splash, and rebound. Numerical predictions were validated by experimental observations. The present method predicted the increase in the critical temperature above which the drop would rebound as the ambient pressure increased. For example, for n-heptane drop impact on a 200 °C wall at We=50, the drop rebounds at 1 bar but deposits at 20 bars ambient pressure. The present method is able to capture the shift in the Leidenfrost point with the change in ambient pressure. The ability to predict such effects of the ambient pressure on drop-wall interactions is important in simulating spray impingement at realistic engine conditions.

Proper interpretation and overall accuracy of laminar flame speed measurements of single- and multi-component liquid fuels

Low-vapor pressure liquid fuels, particularly kerosene-based fuels, are notoriously difficult to use in precision laboratory-scale flame experiments. This difficulty could result in several sources of uncertainty when preparing fuel-air mixtures for laminar flame speed experiments in constant-volume vessels. To accurately measure the experimental uncertainties in a spherical, laminar flame, n-decane, a component of several popular kerosene-based surrogate fuels was utilized in a methodical study to elucidate and minimize the primary sources of error and to determine a realistic, overall measurement uncertainty. This careful study allowed for isolated analysis of the overall behavior of the fuel (such as whether or not the fuel is condensing) and the accuracy of the instrumentation used. The results show that for the single-component liquid fuel, equivalence ratio could be accurately measured to within φ=±0.03 and flame speed to within 2.79 cm/s. One of the primary sources of discrepancy and confusion when presenting and comparing laminar flame speed data of complex, liquid fuel mixtures is the identification of the average fuel molecule. This seemingly trivial detail is actually a very important property of the fuel because it leads to the determination of φ, which is commonly used as the independent variable of laminar flame speed plots. However, when reported at all, the uncertainty in the average molecular weight of these fuels is on the order of 15%. Because of this large uncertainty, φ is shown to not be the most useful parameter for comparing different data sets. Rather, fuel mole fraction, XFUEL, is much more useful as it describes the overall amount of fuel in the mixture, and plotting laminar flame speeds as a function of XFUEL results in better agreement amongst different data sets from the literature for Jet-A.

Probabilistic modeling of forced ignition of alternative jet fuels

Fast and reliable high altitude re-ignition is a critical requirement for the development of alternative jet fuels (AJFs). To achieve stable combustion, a spark kernel needs to transit in a partially or fully extinguished flow to develop a flame front. Understanding the relight characteristics of the AJFs is complicated by the chaoticity of the turbulent flow and variations in the spark properties. The focus of this study is the prediction of such characteristics by high-fidelity simulations, with a specific focus on fuel composition effect on the ignition process. For this purpose, a previously developed computational framework is applied, which utilizes high-fidelity LES simulations, a hybrid tabulation approach for modeling forced ignition and detailed quantification of uncertainty resulting from initial and boundary conditions to predict ignition probability. The method is applied to two alternative fuels (named C1 and C5) and Jet-A fuel (named A2) under gaseous conditions. Results show that the mixing of kernel and fuel–air mixture is not affected by the ignition process, but chemistry effects strongly dominate ignition probability. In particular, C1 exhibits much lower ignition probability than the other two fuels, especially at lean operating conditions. More importantly, this behavior is contradictory to ignition delay experiments which predict longer delay times for C5 compared to C1. Comparisons with experiments show that the comprehensive modeling approach captures the ignition trends. Analysis of kernel trajectories in composition space shows that the variations are caused by the relative effects of kernel mixing, response to strain, and ignition properties of the fuel.

A novel method for comparing passenger car fleets and identifying high-chance gross emitting vehicles using kerbside remote sensing data

The quantification and comparison of NOX emission from in-situ car fleets, and identification of the highest emitters is an ongoing challenge. This challenge will become more important as new and increasingly complex emissions removal systems penetrate the market. We combine real-world data with new-to-the-field statistical methods to describe fleet-scale emissions behaviours and identify candidate gross-emitter vehicles.19,605 passenger cars were observed using a Remote Sensing Device across Aberdeen in 2015. Of these, 736 were Euro 6 Passenger Cars. The distribution of observed pollutant per unit of fuel burnt ratios for most fuel type and Euro standards followed an asymmetrical shape best characterised by the Gumbel distribution. The Gumbel distribution approach was not able to fully replicate the distribution of measurements of petrol or Euro 6 diesel cars due to the presence of a subset of high-emitting outliers, ranging from the 13th percentile for Euro 3 petrol to the 2nd percentile for Euro 6 petrol, with Euro 6 diesel having a 5th percentile outlier value. No outlier fraction was observed for pre-Euro 6 diesels.The off-model fractions resembled Gumbel distributed data and in some cases could be modelled as a separate distribution with the fleet behaving as a superposition of them. It is shown that VSP was not directly linked to this behaviour and it is hypothesised that it is caused by the emissions control systems operating sub-optimally. The reasons for sub-optimal operation are beyond the scope of this paper but may be linked to air-fuel mixture sensors, cold-start running and deterioration of the catalytic converter. Larger data-sets with more Euro 6 passenger cars are required to fully test this. Application of this methodology to larger data sets from more widely deployed remote sensing devices will allow observers to identify potentially problematic vehicles for further investigation into their emission control systems.

Calculation of the process of nitrogen oxides formation during combustion of methanol in the engine

The developed method is based on a two-zone model and allows calculating the pressure and temperature (fresh mixture and combustion products), cycle indicators, as well as the current concentration of nitrogen oxides (NO) in the combustion chamber as a function of the crank angle. It can be used to evaluate the influence of parameters such as the beginning and duration of combustion, the composition of the mixture, heat loss from the gas to the walls, compression ratio, etc. on indicator indicators and output. In this model, the cylinder charge during combustion is divided into two zones: the zone of unburned mixture and the zone of combustion products. It is assumed that the fuel-air (unburned) mixture before and during the combustion process is homogeneous. The zone of combustion products at each moment of the cycle has a uniform composition and temperature. The combustion process is calculated according to the specified fuel burn-out law, taking into account the dissociation of the combustion products. The equilibrium concentrations of individual combustion products necessary to account for dissociation (CO and H 2) and the formation of NO (O 2, H 2, O) are determined by approximating polynomials.

Analysis of the operation of the diesel engine on rapeseed oil

A comparative study of the working process of a rapeseed oil diesel engine for split fuel equipment and Common Rail equipment was carried out. The indicators of the working process, the parameters of heat emission and toxicity of the exhaust gases are given, the analysis of the indicator efficiency is carried out and the perspective of the use of the pilot portion in the fuel equipment of the Common Rail type is shown. One of the ways to improve the performance of diesel engines is to reduce the heterogeneity of the fuel-air mixture in the combustion chamber and the use of vegetable fuels, which include vegetable oils.

Investigations of the Working Process in a Dual-Fuel Low-Emission Combustion Chamber for an FPSO Gas Turbine Engine

Abstract This investigation is devoted to an analysis of the working process in a dual-fuel low-emission combustion chamber for a floating vessel’s gas turbine. The low-emission gas turbine combustion chamber with partial pre-mixing of fuel and air inside the outer and inner radial-axial swirlers was chosen as the object of research. When modelling processes in a dual-flow low-emission gas turbine combustion chamber, a generalized method is used, based on the numerical solution of the system of conservation and transport equations for a multi-component chemically reactive turbulent system, taking into consideration nitrogen oxides formation. The Eddy-Dissipation-Concept model, which incorporates Arrhenius chemical kinetics in a turbulent flame, and the Discrete Phase Model describing the interfacial interaction are used in the investigation. The obtained results confirmed the possibility of organizing efficient combustion of distillate liquid fuel in a low-emission gas turbine combustion chamber operating on the principle of partial preliminary formation of a fuel-air mixture. Comparison of four methods of liquid fuel supply to the channels of radial-axial swirlers (centrifugal, axial, combined, and radial) revealed the advantages of the radial supply method, which are manifested in a decrease in the overall temperature field non-uniformity at the outlet and a decrease in nitrogen oxides emissions. The calculated concentrations of nitrogen oxides and carbon monoxide at the flame tube outlet for the radial method of fuel supply are 32 and 9.1 ppm, respectively. The results can be useful for further modification and improvement of the characteristics of dual-fuel gas turbine combustion chambers operating with both gaseous and liquid fuels.

Alternative fuel engine duty cycle

In developing promising systems for reducing the toxicity of ICE emissions, special attention is paid to suppressing the formation of toxic components directly in the engine’s working chamber. This primarily relates to nitrogen oxides. The method is of particular interest when using aqueous solutions of ethanol as fuel. Therefore, the study of the ignition and combustion capabilities of various fuels includes the study of the prospects for using water-saturated air-fuel mixtures in a multi-fuel operating cycle to reduce the emission of nitrogen oxides. It is assumed that the formation of shock and detonation waves as a result of self-ignition in local foci is acceptable if they propagate attenuate to a level that does not pose a danger to the engine design and does not impair its effective performance.

Study of Flame Stabilization Behavior in Supersonic Gaseous Fuel Jets

The results of numerical and experimental studies of the processes of mixture formation of a supersonic under-expanded gaseous methane jet with incident flow are presented in relation to the issues of gas-dynamic flame stabilization in straight-flow combustion chamber of gas turbine engine. The study shows the possibility of forming the combustible compositions of the air-fuel mixture in the combustion zone without additional air supply to the stabilizing jet.

RESEARCH OF FUEL/AIR MIXING CONDITIONS INFLUENCE IN UPRATING OF OPPOSED-PISTON TWO-STROKE DIESEL ENGINE

The article analyzes fuel/air mixture formation and ways to increase the fuel combustion efficiency in a highly-forced 2-stroke boxer diesel engines.An increase in liter capacity requires appropriate increase in cyclic fuel supply, which must be efficiently burned in the limited space of the combustion chamber. As it is known, it is at full and timely combustion of fuel that economy and efficient operation of a heating machine are achieved and the formation of a fuel-air mixture is an important condition for ensuring a quality combustion process. To study the influence of individual design parameters on the working process, we used mathematical modeling of the working process using the DIESEL-RK software package, which belongs to the class of thermodynamic programs, as well as the program of visualization of the process of fuel jets movement. The assessment of factors influencing the two-stroke diesel engine indicators was carried out on the basis of fuel distribution by zones (illustrations are given) and on the basis of the results of injection and heat generation calculation. Such factors as a change (increase) in the cyclic feed at a fixed value of the coefficient α, the change in the vortex ratio (the fuel injection direction depends on the intensity and rotation direction of the air vortex), fuel supply start angle, change in the fuel supply duration, change in the fuel distribution in the combustion chamber volume (by changing the spatial orientation of the nozzle openings of the atomizer and their diameter) have been reviewed.The nature of the change in the fuel distribution, the fuel jet deformation in the combustion chamber of a diesel engine and the possibility of reducing the contact the core of jet with the combustion chamber and increasing the fuel evaporation zone volume with a reduction in fuel delivery time are established in research result. The results obtained are a prerequisite for the development of technical solutions to ensure a new level of forcing and increase the fuel efficiency of a two-stroke diesel engine and development of recommendations for improving combustion efficiency.

ОПТИМІЗАЦІЯ КОНСТРУКЦІЇ ФАКЕЛЬНОГО ЗАПАЛЬНИКА ГТД ЧИСЕЛЬНИМ МЕТОДОМ

Solved the problem of gas-turbine engine combustion chamber flame igniter efficiency increasing by increasing the flame temperature via optimizing the body design. To determine the influence of the igniter body various geometric parameters, affecting the formation and combustion of the fuel-air mixture, a parametric model was developed. This model together with the developed project in the ANSYS Workbench software package made it possible to automate the modeling process. The influence of the geometric parameters of the igniter body and external factors on the average flame temperature has been studied via a numerical model of the stationary combustion process of the air-fuel mixture formed inside the igniter of the combustion chamber of a gas turbine engine by evaporation and spraying particles of aviation kerosene in the air stream. The adequacy of the numerical simulation results was confirmed by the implementation of a series of full-scale experiments using the Fisher criterion.The uniformity of temperature and adequacy of the average temperature estimation algorithm was established using the correlation analysis of the results of measured temperature at various points of the flame. To determine the degree and nature of their influence, sequentially screening (fractional), as well as full-factor experiments with varying factors at two and three levels were implemented. Based on the results of the analysis of variance, the most statistically significant factors were selected. A regression dependence was established that relates the diameter of the air inlet orifice and the air pressure drop to the flame temperature. A qualitative and quantitative assessment of the influence of the considered factors on the process of formation of a hot air mixture and its combustion has been performed. The optimal values of the geometric parameters of the igniter body and its operating conditions are determined under which the maximum flame temperature at the stationary combustion stage is ensured. Relationships between design features, igniter operation mode, and the temperature of the flame are established. This allows expanding the range of stable ignition of gas turbine engine combustion chambers in accordance with the design of the igniter, the starting fuel supply mode, and the air pressure drop.

Modeling detonation limits for arbitrary non-uniform concentration distributions in fuel–air mixtures

In most scenarios where detonations in fuel–air mixtures can present a hazard, such as in industrial accidents, or where they can be used for practical purposes, like detonative propulsion applications, the mixture is essentially non-uniform. For industrial accidents, it is important to understand what fraction of the mixture can detonate in order to limit the consequences of an explosion event by ensuring proper separation distances to critical facilities and personnel. For propulsion applications, mixture non-uniformities directly affect the performance of the device by limiting the detonable portion of the mixture. While it is known that detonation limits depend on mixture composition, geometry, and concentration gradients, these limits have only been defined for either uniform mixtures, or for detonation propagation in the direction of a smooth concentration gradient. In this study, a model is developed to generalize these classic detonation limits to consider arbitrary concentration distributions and is compared with experimental data for detonation propagation in non-uniform mixtures. The model is then applied to representative concentration distributions corresponding to two practical examples, a high-pressure hydrogen jet and a large-scale vapor cloud explosion (VCE). For both distributions, the model illustrates how a non-uniform mixture composition significantly limits the detonable portion of the flammable mixture created by a realistic release.

Development of a turbulent burning velocity model based on flame stretch concept for SI engines

According to the US Energy Information Administration, fossil fuels will remain the main source of energy for transportation over the next decades and thus the combustion of these fuels remains an important concern.This research studied the flame propagation under engine in-cylinder conditions and developed a correlation for turbulent burning velocity based on the global flame stretch concept. To study the impact of engine operation on flame stretch, two speeds, two loads, and three fuel-air mixtures were investigated. The flame front was determined by processing images of the flame natural luminosity.A turbulent burning velocity model was developed using dimensional analysis. The model showed that the turbulent burning velocity decreased due to flame stretching. Higher engine speeds increased the turbulent burning velocity by increasing the turbulent intensity, yet a tradeoff between the flame stretch and the turbulent burning velocity due to higher engine speed was observed. In cases where the flame distortion was very high, the flame stretch may cancel out any benefits of a large enflamed area.Incorporating the flame stretch into the burning velocity model and coupling the developed model with GT-Power simulation software revealed that the stretch may result in a 35% reduction in turbulent burning velocity.

A comparative study to evaluate the effects of pre-chamber jet ignition for engine characteristics and emission formations at high speed

The pre-chamber ignition technology is a good solution that can make spark-ignition engines gradually more efficient. The novelty of the study is the testing of the pre-chamber jet ignition according to detailed air-fuel mixture range and fuel injection rates by combustion chambers. The main points in using this pre-chamber jet ignition were to observe the effect of reducing fuel consumption and emission formation. The tests were carried out for 0.80–1.80 lambda ranges and the pre-chamber injection/main chamber injection mass ratio ranges. A commercial RON 98 fuel was used at two ignition modes in tests for 5000 rpm high engine speed. At the pre-chamber jet ignition usage, the in-cylinder pressure for 1.00 lambda is overall 1.78% and 19.89% higher than the 0.80 lambda and the 1.80 lambda. The brake specific fuel consumption is about 8.67% lower than the spark-plug ignition usage at 0.80–1.20 lambda range. The HC formation is overall 8.12% lower than the spark-plug usage. The NOx formation for the spark-plug ignition is approximately 53.97% higher than the pre-chamber jet ignition usage as the temperature in-cylinder is high. The pre-chamber jet ignition was led to a much shorter flame development time and better combustion stability than the spark-plug.

Combustion Engine Test Bed System Identification Under the Presence of Cyclic Disturbances

In this article, a new approach for combustion engine test bed system identification is presented. Modern engine test beds are used to reduce development time by utilizing them for hardware-in-the-loop tests. For highly accurate and close-to-reality tests, model-based controllers are deployed, which rely on precise models of the test bed. Hereby, the main challenge is the unknown, cyclic disturbance of the engine due to compression and combustion of the air-fuel mixture. These disturbances also occur when the throttle is kept at zero and have a big impact on the measurements. Therefore, parameter estimation is strongly impeded. A method for dealing with these disturbances and embed them into the identification procedure in a two-step fashion is presented in this contribution. Further advantages of this new approach are that a physical model is obtained, but prior knowledge of parameters is not necessary. Moreover, disassembling of the test bed to perform separate parameter estimation is not needed and hence, the time consumption of the procedure is kept low. Experimental results on a 4-cylinder diesel engine test bed prove the feasibility and effectiveness of the proposed concepts.

Numerical analysis of flame stabilization for a steady premixed jet in vitiated coflow

Premixed staged combustion in gas-turbine combustors, where a premixed fuel–air mixture is injected into a hot vitiated environment, has promise for better emission control. In these hot environments that occur at high engine pressure, the flames may stabilize by a combination of autoignition and premixed flame propagation. In this work, a laminar and steady premixed jet in vitiated coflow was studied numerically to examine the stability behavior of such flames that are impacted by both autoignition and flame propagation. Simulations with detailed chemistry were used with boundary conditions matching previous experiments to understand the stability mechanisms. At the conditions studied, the laminar flame was lifted, with the region of highest heat release rates occurring downstream of the jet exit. However, non-zero heat release rates an order-of-magnitude below the maximum value were observed continuously to the jet exit. An energy budget analysis was conducted along streamlines through different portions of the flame. Streamlines flowing through relatively low heat release rate regions near the burner exit were only influenced by mixing between the jet and vitiated coflow. Streamlines which flowed through higher heat release rates in the lifted flame were influenced by heat transfer from both the coflow and the existing flame, leading to heat-transfer assisted propagating premixed-flame behavior. Species budgets analyzed in the low- and high-heat release regions of the flames were also used to characterize autoignition locations. The species budget through autoignition regions showed clear markers such as high CH2O concentrations present ahead of high heat release rates. The streamlines through premixed propagation regions of the flame also had high CH2O concentrations upstream of the high heat release region, but the species budget shows this is due to mixing from autoignition regions as opposed to reactions occurring on the streamline ahead of the flame. Thus, caution must be taken when using CH2O as a marker for autoignition in such flames with mixed stabilization modes.