Premixing Chamber Research Articles

The Effect of Combustion Phase According to the Premixed Ethanol Ratio Based on the Same Total Lower Heating Value on the Formation and Oxidation of Exhaust Emissions in a Reactivity-Controlled Compression Ignition Engine

A compression ignition engine generates power by using the auto-ignition characteristics of fuel injected into the cylinder. Although it has high fuel efficiency, it discharges a lot of exhaust emissions such as NOX and PM. Therefore, there is much ongoing research aiming to reduce the exhaust emissions by using the technologies applied in this regard, such as PCCI, HCCI, etc. However, these methods still discharge large exhaust emissions. The RCCI method, which combines the spark ignition method and compression ignition method, is attracting attention. So, in this work, the objective of this study is to numerically investigate the effect of combustion phase according to the premixed ethanol ratio based on the same total heating value in-cylinder by changing the initial air composition on the formation and oxidation of exhaust emissions in the RCCI engine. The heating value of the premixed ethanol ratio varied from 0% to 40% based on the same total lower heating value in-cylinder in steps of 10%. It was assumed that the ethanol introduced into the cylinder through the premixing chamber was evaporated, and the initial air composition in the cylinder was changed and set. It was revealed that when the premixed ratio based on the same total lower heating value was increased, the introduced fuel amount into the crevice volume with advancing the start of energizing timing was decreased, which increased the peak cylinder pressure. In addition, the ignition delay was also longer due to the low cylinder temperature by the evaporation latent heat of the ethanol, which reduced the compression loss, so the IMEP value was increased. The rich equivalence ratio had a narrow distribution in the cylinder, which caused a reduction in cylinder temperature, so the NO formation amount was reduced. The ISCO value increased the increase in premixed ethanol ratio based on the same total lower heating value in-cylinder because the flame propagation of ethanol by combustion of diesel did not work well, and the CO formed by combustion was slowly oxidized due to the cylinder’s low temperature as a result of the evaporation latent heat of ethanol. From these results, the optimal operating conditions for simultaneously reducing the exhaust emissions and improving the combustion performance were judged such that the start of energizing timing was BTDC 23 deg, and the premixed ethanol ratio based on the same total lower heating value in-cylinder was 40%.

The determination of the features of the process of mixture formation of hydrogen burner

The use of hydrogen fuel as an alternative source of individual heat supply is a rather promising direction in the development of thermal energy. However, due to the physical properties of hydrogen and the peculiarities of its combustion, several problems arise for the practical use of hydrogen heat generators. Such problems include ensuring flare stability and large emissions of thermal nitrogen oxides (NOX). For stable operation of the hydrogen burner, safe operation, and reduction of nitrogen oxide emissions when burning hydrogen, first, it is necessary to ensure high-quality pre-mixing with air. This work presents the first stage of research into the operation of a hydrogen burner for heat production in the Flow Simulation module of the SolidWorks software environment. For volume flow rates of air and hydrogen corresponding to capacities of 1, 1.5 and 2 kW and air excess coefficient α=1.6. The given design makes it possible to ensure uniform mixture formation (the volume fraction of hydrogen is approximately 18.5 % at the outlet cross-section of the burner and the speed at the outlet of the burner is 5.4, 8.1, and 10.8 m/s, respectively. The burner is a nozzle with a short premixing chamber First, hydrogen is supplied for mixing into the air flow through symmetrically located holes. After that, a vortex is created, which ensures high-quality mixing of gases with a short length of the burner, as well as a uniform distribution of velocity at the exit. The obtained results allow to proceed to the next stage – the study of hydrogen combustion processes in the combustion chamber of the contact heat generator, which would ensure the formation of a stable flame and low NOX emissions. In addition, this design can be used in the development of hydrogen burners for heating boilers to meet the needs of private homes and small businesses

Simulation study of key cross-sectional area dimensions of CO2 ejector on performance

In this paper, based on the homogeneous equilibrium model, the effects of nozzle inlet cross-sectional area, nozzle throat cross-sectional area, pre-mixing chamber cross-sectional area, mixing chamber cross-sectional area, and diffusion chamber outlet cross-sectional area on the performance of the ejector of a CO2 transcritical refrigeration system are analyzed by using Ansys Fluent. The simulation results show that the primary flow rate of the ejector is sensitive only to the nozzle throat cross-sectional area, while the entrainment ratio is strongly influenced by the nozzle throat and the mixing chamber cross-sectional area, and there is an optimum value. The nozzle inlet cross-sectional area has no significant effect on the performance of the ejector. The pre-mixing and diffusion chamber outlet cross-sectional areas do not have a significant effect on the performance within a limited range, but deviating too much from the optimum value can also lead to degradation of ejector performance.

PSIV-26 Development of a Controlled Exposure Particulate and Oxidative Radical Mask for Causality Experiments Investigating Smoke Exposure on Livestock Animals

Abstract Understanding and mapping the specific effects of smoke inhalation on cattle performance provides strategic insights for producers and policy makers to better prepare or adjust when faced with sporadic or even seasonal reductions in air quality. As of now, no current studies have attempted to investigate the effects of seasonal fires on performance and health adequately in livestock while addressing obvious confounding effects, controlling exposure, and examining fuel for differential oxidative radicals and particulate smoke. Herein, we propose the design of the first cost-effective controlled system for investigating smoke, particulate matter, and varied oxidative radicals through a pre-mixing chamber. The mask main body is constructed from 8” nominal diameter schedule 40 PVC pipe. The endcap was designed in an online CAD software to provide an interface for standard 2 ⅞” bulkhead fittings and was produced via additive manufacturing (3D printing). A silicone SCUBA neck seal was used to line the face orifice and is the component that directly contacts the animal’s nose and mouth. A neoprene rubber sheet and an insulation hose were used as padding under the silicone seal to help maintain an airtight connection and animal comfort when the mask is worn. Bulkhead fittings used provide 1 ½” female national pipe thread connection to allow for modular connection of inlet and outlet hoses, check valves for airflow isolation, filters, or any number of connections can be made via these gasket sealed fittings, making this platform extremely adaptable. In its shown configuration, 3D printed adapters were made to attach 4” suction hose to 2” socket union joints for quick connect/disconnect functionality. An inlet and outlet gas/smoke flow regulator are attached to a mixing chamber where particulate and chemical composition sensors are utilized to deliver the desired composition of smoke delivered to the animals. Negative pressure fans and pumps regulate the flow to the animals and are utilized for exposure of smoke in time-specific intervals. An additional fully 3D printed version enables the mask design to be lower in weight through regulation of the density of the internal matrix, and after an initial investment in the equipment also represents a cost-efficient approach to generating multiple masks. Understanding the effects of particulate and reactive oxidative molecules on livestock health and performance requires the study of a controlled exposure, the system presented herein represents a viable and cheap alternative for bettering a mechanistic model and understanding of the effects of smoke on animal health and performance. Ultimately, the proposed mask paired with currently available sensors permit for the controlled exposure of smoke particulate with different chemical compositions for accurate evaluation of prolonged exposure effects on livestock.

Combustion characteristics of a dual-mode ramjet engine with a supersonic aerodynamic ramp injector

The combustion characteristics of a liquid-hydrocarbon-fueled dual-mode ramjet combustor with a new injector, including a cavity-type flame holder, were investigated under inflow conditions of M 1.8, total pressure of 590 kPa, and total temperature of 930 K. The newly proposed injector uses various injection methods, such as an aerodynamic ramp, pre-mixing chamber, barbotage gas, and supersonic nozzle. The aerodynamic ramp injection method consists of four injectors with inclination angles of 40° and 80° and toe-in angles of 30° and 60°. This was adopted to increase the penetration height of the fuel while minimizing the total pressure loss. A pre-mixing chamber with a barbotage gas injection device was employed to enhance atomization and fuel–air mixing. In addition, a contoured Mach 3 supersonic nozzle was used to obtain a higher momentum through acceleration. For performance comparison, a combustor with a pre-mixing chamber and barbotage gas was used in the same manner, but injected by a cylindrical nozzle with a 15-degree of transverse angle. The ignition was initiated by a torch ignitor installed on the cavity floor with hydrogen pilot fuel. Once combustion stabilized, only the main liquid fuel was supplied. The Mach number was calculated using quasi-one-dimensional analysis based on the measured wall pressures and inlet conditions. The results showed that the model combustor with two types of injectors operated in the ramjet mode, which was subsonic near the flame holder and supersonic at the exit of the combustor. At the combustor outlet, the total pressure according to the equivalence ratio of 0.25 to 0.56, the newly proposed injector case showed a higher pressure level, steep increase, and more uniform pressure distribution than the baseline injector from the measurement result of the pitot pressure rake at the combustor exit.

Synergistic effect of adjustable ejector structure and operating parameters in solar-driven ejector refrigeration system

The ejector has a substantial impact on the performance of the solar-driven ejector refrigeration system. This work designs an adjustable ejector without disassembly and performs numerical modeling of the geometric model to enhance the ejector capacity to adapt to various operating conditions; the simulations dependability was also validated using experimental evidence. The findings indicate that within the given operating conditions, the adjustable ejector efficiency increased by an average of 82.4 %; the COP of the system increased by an average of 72.8 %. It is also found that the adjustable ejector has a saturation region, where the ejector performance rapidly declines as the nozzle exit position increases. Under the given operating conditions, the functional relationship between the optimal area ratio and nozzle exit position is obtained. By defining the operating condition coefficient (Γ), the function of the Γ and optimal area ratio is obtained, which provides the adjustable ejector control logic. From the energy perspective, the influence of structural changes on the vortex near the premixing chamber wall is analyzed, and the basic internal reasons for how structural alterations affect the ejector performance are initially revealed.

Atomization Characteristics of Low-Volatility Heavy Fuel for Low-Pressure Direct Injection Aviation Piston Engines

Abstract Due to safety and convenience, aviation heavy fuel (AHF) is quite suitable for use as an energy source in aviation piston engines for small aerial drones, although its atomization is an important issue. The purpose of this article is to present the atomization mechanism of AHF during low-pressure direct injection (LPDI) and the results of the investigation of the mixing process and flow state of fuel–air two-phase flows. In this study, experimental data were obtained for parameters of fuel spray, which verified the improved calculation model of LPDI that considered the primary atomization of AHF inside the premixing chamber. The influences of injection pressure, ambient pressure, and AHF temperature on the spray characteristics were compared and analyzed. Increasing the injection pressure reduced the spray cone angle and increased the spray area. The penetration distance increased, and the Sauter mean diameter (SMD) of the fuel droplets decreased. Increasing the ambient pressure had significant effects on penetration distance and SMD. The spray area decreased, and the spray cone angle showed small variations. Increasing the AHF temperature had small effects on the penetration distance, and the SMD obviously decreased with increasing fuel temperature. The spray cone angle increased slightly, and the spray area decreased. The results showed that low-volatility AHF for safe and stable engine combustion could be achieved with air-assisted LPDI. In addition, the efficient atomization of AHF can be effectively implemented through the combined adjustment of injection control and physical and chemical parameters.

A comparative study for the effect of different premixed charge ratios with conventional diesel engines on the performance, emissions, and vibrations of the engine block.

Exploratory research of partially premixed charge compression ignition (PCCI) in conjunction with direct fuel injection was done. A single-cylinder commercial diesel engine was used. In this work, the evaluation of the engine vibrations, pollution, efficiency, and combustion properties has been performed on a PCCI diesel-fueled engine. A part of the fuel was converted into vapor inside the intake manifold by using an innovative premixing chamber with an electronic fuel injector. At the same time, the main fuel quantity was injected directly inside the engine cylinder before the top dead center (TDC) to control the engine phasing. A unique approach based on the fast Fourier transform (FFT) of the cylinder vibration data was applied for combustion vibrations and acoustic investigation. To further clarify their relationship, the influence of combustion characteristics on acoustic and vibrations metrics was investigated. The results demonstrate that combustion noise remains a crucial issue for adopting this novel combustion approach in the automotive industry. The studies revealed that partial premixing reduces nitrogen oxide (NOX) pollutants significantly. This is thought to be the outcome of the PCCI combustion, which occurs before the typical mixing controlled phase, lowering regional gas temperatures. The experiment findings also revealed that partial premixing has an intrinsic tradeoff between NOX emissions and inefficient combustion products (carbon monoxide (CO) and unburned hydrocarbons (UHCs)). It was also shown that incomplete combustion and non-optimized spontaneously igniting of the premixed charge resulted in a minor reduction in combustion efficiency (CE).

Experimental investigation of R744 transcritical flow and mixing in the two-phase ejector

In this work, the laboratory test rig for visualisation of the CO2 ejector is shortly presented. The internal flow structures in the premixing chamber and expansion cone are visualised using two different measurement arrangements, i.e. Particle Image Velocimetry (PIV) system and high-speed camera system. Both systems allow to determine some characteristic features of the R744 flows and propose some important quantities (i.e. expansion and mixing angles) describing expansion and mixing processes. Potentials of those preliminary results for field validation data are also pointed out.

Effect of novel fuel vaporiser technology on engine characteristics of partially premixed charge compression ignition (PCCI) engine with toroidal combustion chamber

Partially pre-mixed charge compression ignition (PCCI) and combustion chamber geometry are significant factors that improve the potential of compression ignition engines and the sustainable effect on the environment. The considerable decline in brake thermal efficiency in PCCI has always been a point of halt in the progress of this technology. The toroidal combustion chamber (TCC) has proved its effectiveness in enhancing the performance characteristics of a conventional engine. The primary aim of this experiment is to improve the engine characteristics for PCCI mode when it operates with a TCC piston bowl geometry and compare the behavior with the conventional direct injection (DI) technology. A novel fuel vaporiser technology is developed and retrofitted in a single-cylinder DI diesel engine in this work. A comparative study on the effect of combustion chamber geometry (hemispherical and toroidal) on engine characteristics was performed and the engine setup was operated in conventional and PCCI mode. The PCCI mode was tested by using fuel vapour induction in intake manifold via the fuel vaporizer unit. Liquid diesel fuel was heated up to its vaporization temperature and sent to the intake manifold, wherein fresh air was mixed with vaporized fuel, forming an external mixture that enters the combustion chamber. The different vapour induction rates (2 ml/min and 4 ml/min) were used to understand the changes in combustion behavior. Compared to conventional, the PCCI mode proved its worth in limiting NOx emission with 7 g/kW-h reduction at 4 ml/min vapour induction rate with HCC at moderate engine load. Diesel vapour induction rate of 2 ml/min along with TCC piston resulted in improved engine characteristics with a marginal decrement in BTE by 1.2%, significant decrease of NOx by 5 g/kW-h at moderate engine load. Moreover, at full engine load, the PCCI anomaly is observed as the rate of pressure rise (ROPR) surpasses the conventional by 2 bar/deg for 2 ml/min induction rate with HCC, thereby favouring conditions for engine knock. Overall, the brake thermal efficiency limitations in PCCI can be countered by TCC piston bowl geometry; however, the PCCI usage is limited to a specific vapour flow rate and engine load range.

Numerical Investigation on the Performance of Two-Throat Nozzle Ejectors with Different Mixing Chamber Structural Parameters

In this study, the effects of the mixing chamber diameter (Dm), mixing chamber length (Lm) and pre-mixing chamber converging angle (θpm) were numerically investigated for a two-throat nozzle ejector to be utilized in a CO2 refrigeration cycle. The developed simulated method was validated by actual experimental data of a CO2 ejector in heat pump water heater system from the published literature. The main results revealed that the two-throat nozzle ejectors can obtain better performance with Dm in the range of 8–9 mm, Lm in the range of 64–82 mm and θpm at approximately 60°, respectively. Deviation from its optimal value could lead to a poor operational performance. Therefore, the mixing chamber structural parameters should be designed at the scope around its optimal value to guarantee the two-throat nozzle ejector performance. The following research can be developed around the two-throat nozzle geometries to strengthen the ejector performance.

Numerical investigation on the effect of second throat diameter on two-throat nozzle ejector

The employment of two-phase ejectors in the CO2 refrigeration systems is widely developed recently. Due to the lack reports on the two-throat nozzle ejectors, the performance of CO2 two-throat nozzle ejector varied with different second throat diameter (D t ) was numerically investigated under different primary pressures (P p ). The accuracy of established numerical simulation model was confirmed with the assistance of experimental data summarized in the literature. The simulated results show that the two-throat nozzle ejector performance corresponding to entrainment ratio (Er) is of better stability with relatively bigger D t under different working conditions. Next, the axial static pressure corresponding to bigger D t is lower than that of smaller one at pre-mixing chamber. And the secondary flow velocity of bigger D t is accelerated better as compared to that of smaller one.

Effect of preheating in premixed charge compression ignition engine using various fuels – an experimental investigation

This experimental work explains and compares the effect of preheating in Premixed Charge Compression Ignition technique(PCCI) by using three different fuels such as diesel, citronella oil – diesel blend (B20), cedarwood oil – diesel blend (B20). This experiment have been carried in a single cylinder diesel engine by incorporating a premixing chamber with port fuel injector in the intake port, and placing the preheater before to prechamber near to the surge tank in the intake manifold, the injector , preheater is controlled through ardino micro controller Experiments results showed that there is an increase in brake thermal efficiency with citronella oil – diesel blend (B20), cedarwood oil – diesel blend (B20), and also there is a simultaneous decrease in hydrocarbon (HC) and carbon monoxide (CO) emissions due the preheating effect. The performance results indicated that there is a drop in volumetric efficiency due do preheating effect of the premixed fuels, penalting in increased fuel consumption. NOx is lower for diesel fuel since it contains lower oxygen molecule than citronella, cedarwood diesel blends. So Neat diesel has the lower emission characteristics than the other premixed fuels in PCCI technique. And the effect of fuel distribution inside the premixing chamber is shown by using ANSYS-FLUENT.

On effects of shape, aspect ratio and position of obstacle on the mixing enhancement in micromixer with hexagonal-shaped chambers

AbstractThe micromixer geometry presented consists of T-type micromixer with premixing chamber, hexagonal shaped chambers and obstacles. In order to observe influences of obstacle shape, aspect ratio and position, simulations are carried out for two types of obstacle shapes viz. rectangular and triangular for the Reynold number in the range from 0.1 to 75. Flow and mixing dynamics are studied to investigate the effect of geometric modifications for identifying the mixing mechanisms. The effect of obstacle shape, aspect ratio and position is investigated using the performance characteristics viz. mixing index and pressure drop quantitatively. Both the micromixers demonstrate different mixing mechanisms, including transverse flow, vortices and chaotic advection due to split and recombination action. The mixing performance is diffusion dominated below Re < 5 and it is advection dominated beyond Re > 5. At Re ≥ 20, the mixing index observed is 0.80 in all the micromixer design configurations.

Effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustor

This numerical study investigated the effects of the fresh mixture temperature on thermoacoustic instabilities in a lean premixed swirl-stabilized combustion chamber by utilizing high-fidelity, fully compressible large eddy simulations. At low fresh mixture temperatures, the side recirculation zone stabilized the premixed flame on the boundary of the burner rim, while the central part of the flame was detached from the burner due to the inability of the central recirculation zone to assist in flame stabilization. However, the central recirculation zone became stable enough to stabilize the central portion of the flame near the burner rim as the fresh mixture temperature increased. Moreover, the coherencies and penetration depths of the coherent structures and precessing vortex cores in the combustor increased with the fresh mixture temperature. Analyses showed that the limit cycle instabilities that occurred at low fresh mixture temperatures resulted from coupling between heat release fluctuations and the first tangential acoustic mode of the combustor. However, as the fresh mixture temperature increased, a combustor dynamics transition occurred, through which the coupling between heat release and pressure fluctuations shifted toward the mixed tangential and radial acoustical modes of the combustor. During this mode transition, limit cycle oscillations were replaced by burst oscillations. The results revealed that recirculation zones are the key features that trigger thermoacoustic instabilities at low fresh mixture temperatures, while coherent structures and precessing vortex cores are the main combustion instability drivers at high fresh mixture temperatures.

Parametric Computational Studies of NOx Emission Reduction in Staged Combustion of Ideal Fuel-Air Mixtures1

This paper is the second of series of articles devoted to computational studies for optimization of the combustion of fuel-oxygen mixtures with combustion chamber exhaust temperatures of 1600°C or more while meeting pollution emission standards. Calculations of the combustion of ideally mixed fuel-air mixtures in a combustor consisting of two sequentially positioned (staged) combustion volumes, each with its own burner, are presented. The first burner is a traditional low-emission combustion chamber with combustion of a pre-mixed fuel-air mixture with a swirler and a pre-mixing chamber, and pilot and main burners. The second burner lies downstream in the flow and a fuel-air mixture with a different composition is fed into it through a special aperture; this mixture is burnt in a medium with reduced oxygen content and a high temperature. The distribution and composition of the fuel-air mixture feeds between the two burners are optimized to attain minimum NOx emissions for outlet temperatures of 1700°C. The optimum length of the second combustion volume is determined for complete burnup of the fuel with minimum concentrations of the oxides of nitrogen and carbon at its outlet. The results can be used to evaluate the minimum possible level of nitrogen oxide emissions attainable in the sequential combustion scheme for ideally mixed fuel-air mixtures.

Peculiarities of Mixture Formation and Ignition of the Fuel Mixture in the Metal Sprayer Chamber

The paper presents a device for spraying the low-melting metal coating, based on the rocket chamber operation principle. The design of the fuel nozzle, pre-mixing chamber, and radial combustion chamber is considered. The processes of electro-spark ignition of the fuel mixture and the flame front stabilization are described. The choice of the critical section area as a place of the coating material feeding in the high-temperature combustion products flow is substantiated.

Acoustic transfer function of a combustion system with premixing chamber

In this study we develop an analytic thermoacoustic model of a combustor for gas turbines. The combustor under consideration is composed of a premixing chamber, a nozzle, and a combustion chamber. Our thermoacoustic model is given as an acoustic transfer function from a heat release perturbation to a velocity perturbation at a flame location. It is shown that the resonance frequencies are functions of three turnaround periods of acoustic waves at each stage, and the area ratios between stages. The resonance modes can be well captured by calculating the poles of the acoustic transfer function, our analytic results show a good agreement with existing measurement data in the literature.

예혼합실을 갖는 연소-노즐 시스템의 음향장 해석

예혼합실을 갖는 연소-노즐 시스템의 음향장 해석

A multi-objective CFD optimization of liquid fuel spray injection in dry-low-emission gas-turbine combustors

The main goal of this research is to investigate the effects of fuel injection strategy on the performance of the premixing chamber of modern Dry-Low-Emission (DLE) Gas-Turbine (GT) combustors. Here, an Eulerian-Lagrangian model for multi-phase multi-component flows is evaluated and used to investigate the effects of different fuel spray design parameters, including the injection location, direction, mass-flow-rate partitioning, and flow Swirl number, on the performance of the premixing chamber. The analysis is enriched by multi-objective optimizations accounting for several goals, including the evaporation efficiency, mixture stratification, entropy generation, and flow recirculation. It is observed that the droplet breakup, spray-vortex interactions, and wall-wetting have significant influences on the performance objectives while the droplet residence time effect is minor. Among the design parameters, the injection location and direction have a profound impact on the droplet breakup which predominately controls the evaporation efficiency. In addition, the interactions between the spray and the two swirling vertices inside the chamber strongly affect the mixture stratification (uniformity), e.g. the location and direction of the injection should not be chosen such that a large proportion of fuel droplets are trapped in the shear layer between the two vortices (otherwise the evaporation efficiency drops significantly) or trapped in the strong outer swirling vortex (if large mixture non-uniformity should be avoided). Finally, the best designs meeting a series of targets, e.g. simultaneous perfect mixing and uniformity, etc., are introduced.