Inlet Exhaust Research Articles

Using CFD to model the distortion of pollutant concentration signal at exhaust lines

The present study introduces a method for generating the distortion of species concentration signals within exhaust lines, employing Computational Fluid Dynamics (CFD) modelling instead of experimental techniques. Understanding distortion is important when e.g. tailpipe pollutant signals need to be correlated to engine operation patterns and related correction models need to be built. The approach was initially applied on a typical exhaust line geometry of a car, demonstrating the ability of CFD modelling to simulate the CO2 signal distortion from engine out to tailpipe, and was validated against laboratory measurements. Comparisons for variable operating points, between simulations and experiments, presented a good agreement with a deviation of up to 0.04 s in the time required for the signal to reach 50 % of its final output value (t50), and of up to 0.1 s in the rise time (t90-10). The methodology was applied to a vehicular exhaust line comprising tubing and buffer volumes, simulating catalysts or mufflers. This investigation aimed to identify the parameters that influence the distortion of CO2, revealing that inlet exhaust gas velocity can significantly impact CO2 distortion. Inlet temperature variations of ± 50 K produce a negligible deviation in t50 of ± 0.01 s for low inlet velocities and of ± 0.001 s for high inlet velocities. CFD is a useful tool to characterize pollutants signal generation within exhaust line configurations not limited to cars. Such a technique can be used to any mobile or stationary combustion system to study species concentration distortions caused by the individual components.

Effects of Performance and Normalized Parameters on Various Materials Based Multistage Thermoelectric Generator

Abstract Multi-staging and variable cross section greatly improve the performance of thermoelectric generators. Hence, the present theoretical study analyzes a multi-stage-variable-shaped thermoelectric generator (MVS-TEG) for a combination of dissimilar materials. Effects on voltage, power, conversion efficiency, normalized constraints (voltage, power, and conversion efficiency), and second law efficiency with a row number, exhaust inlet temperature, and the coolant flowrate have been investigated. Results reveal that the row number is the most critical input parameter followed by exhaust inlet temperature and coolant flowrate. Also, the work gives optimum values of rows for voltage and power as Nx = 19 for MVS TEG-1, MVS TEG-3, and MVS TEG-4 while Nx = 18 for MVS TEG-2. The exhaust inlet temperature variation increases the voltage and power output by 54–59% and by 53–58% respectively. The coolant flow variation has a greater impact on the conversion efficiency and the average improvement in the efficiency is about 9.23% in the present study. The second law efficiency decreases with the increase in all the input parameters.

Improvement of flow field uniformity and temperature field in gasoline engine catalytic converter

The uneven temperature field, flow field, and internal low temperature of the catalytic converter can cause substrate thermal deformation and catalytic ability decrease, which is not conducive to the service life of catalytic converter and control of automotive pollutants emission. A novel substrate structure with uniformly changes cell density and a new heater of three layers diffuser with optimized flow field uniformity are proposed. Their application in catalytic converter can effectively improve the above problems. Firstly, physical and mathematical models of the new catalytic converter were established, and the accuracy was verified by experiments. Next, the flow characteristics and catalytic performance was analyzed. Finally, the effects of different parameters on catalytic performance and temperature were analyzed. The results show that: (1) Compared with traditional catalytic converter, gas uniformity and NO conversion efficiency of the new catalytic converter are increased by 0.0885% and 13.66%, respectively, improving flow field uniformity and NO conversion. (2) The NO conversion efficiency increases and then decreases with adding of electric power, exhaust inlet temperature and exhaust inlet velocity; substrate temperature increases with adding of electric power and exhaust inlet temperature, but decreases with increase of exhaust velocity. During heating time, the NO conversion efficiency and substrate temperature first increase and then tend to stabilize. After heating is stopped, the NO conversion efficiency and substrate temperature will decrease. (3) The field synergy theory shows that synergy angle cosβ tends to − 1 with increase of electric power, which means convective heat transfer effect inside substrate becomes worse. (4) The grey relational analysis shows that exhaust inlet temperature is a key factor affecting the new catalytic converter performance.

Numerical Calculation of Wet Exhaust Gas Condensation in the Heat Exchanger

Based on the background of waste heat recovery of gas-fired boiler, this paper studied wet exhaust gas condensation heat transfer using numerical methods. The calculated results indicated that with the exhaust gas Re number increases, heat flux, and Nu number gradually increase, while the Eu number decreases simultaneously. Besides, the variation trend of the Nu and Eu number gradually reduced with Re number increases. With inlet exhaust gas temperature increase, the Nu number increases, and the Eu number decreases. Meanwhile, Nu number and Eu number increases with the increase in wall temperature. On this basis, the empirical correlations for calculating Nu and Eu numbers are obtained, and the deviation between the calculated values and the numerical results is within ±8%. The conclusion of this study provides basis for heat exchanger design in wet exhaust gas waste heat recovery.

Experimental investigation of a new ammonium bicarbonate reactor induced with an electromagnetic heater

This work presents the experimental study conducted on a newly developed ammonium bicarbonate reactor for the purposes of carbon capturing and utilization. This reactor produces ammonium bicarbonate with the assistance of an industrial catalyst (such as steel) and an electromagnetic induction heater for enhancing the production of ammonium bicarbonate. The experimental setup is prepared to have three cases which are the baseline case, catalyst case, and induction heating case. These three cases are compared in terms of ammonium bicarbonate production by mass and the ratio of actual mass produced over their theoretical limits. The results of our present experiments show that the steel catalyst is proven to be an effective catalyst as it helps improve the production of ammonium bicarbonate by a factor of 1.56 when the inlet exhaust gases have 30% mol of carbon dioxide compared to the baseline case. In addition, the ammonium bicarbonate production improves by a factor of 2.56 when a steel catalyst and an induction heater are used together compared to the baseline case where the carbon dioxide composition entering the reactor is 80%mol. These results present the promising potential for implementing a cheap catalyst and an electromagnetic induction heater for the enhancement of carbon capture and utilization reactors.

A combined technique using phase change material and jet impingement heat transfer for the exhaust heat recovery applications – A numerical approach

Increasing the development of industries and automobiles requires developing a new system to recover exhaust heat emitted from these sources. Phase change materials are known for energy storage because of their latent heat properties. With this idea, a combined technique of phase change material (PCM) and jet impingement heat transfer is proposed where the exhaust gas acts as an impinging jet on storage with phase change material. The study is performed numerically with ANSYS Fluent. Initially, the study involves validating numerical setup for melting of PCM and Jet impingement heat transfer with benchmark experimental data. Later, both models are combined to study exhaust heat recovery. Parametric studies are performed by changing the materials, temperature, Reynolds number, spacing ratio (ratio of the height of the exhaust inlet from the impinging plate to the diameter of inlet), and orientation of the system. The parametric study reveals several important characteristics to be considered while choosing the material, such as conductivity and latent heat. The temperature study shows that the significance of the Reynolds number is reduced as the temperature is increased. By changing the spacing ratio from 2 to 6, the energy recovery is decreased by 23 %. However, changing the orientations of the system has shown a significant improvement on the energy recovery.

Study on Characteristics and Control Strategy of Diesel Particulate Filters Based on Engine Bench

The ignition temperature of a diesel oxidation catalyst (DOC) and the internal temperature-field distribution of the diesel particulate filter (DPF) during active regeneration are investigated during an engine bench test in this study. Based on the dropped to idle (DTI) test, a test method is developed to determine the safe regeneration temperature of the DPF. The results show that when the inlet temperature of the DOC is more than 240 °C, the DOC begins ignition and reaches the target temperature of 600 °C set for active regeneration of DPF; when the inlet exhaust temperature of the DOC is between 240 and 280 °C, a higher injection rate is required to reduce the secondary pollution of HC and thus make the DPF reach the set target temperature as soon as possible. The active regeneration process of the DPF is divided into three stages. During ignition, the temperature of the DPF inlet and outlet increases rapidly and successively. The internal and outlet temperatures of DPF during regeneration are approximately 50 °C higher than the inlet temperature. At the end of regeneration, the DPF inlet to outlet temperature drops rapidly. A feed-forward design and feedback algorithm are used to verify the change in the target regeneration temperature. The overshoot of the DPF control strategy was less than 3%, and the steady-state temperature control error was less than 20 °C. The results of this study provide a basis for the safe control of DPFs’ active regeneration temperatures.

The design of fuel dryer in palm oil processing industries by utilizing the heat product of boiler based on computational fluid dynamic

Incomplete combustion process from boiler in palm oil processing industry usually discharged into the air in the form of black smoke due to the high water contain in the fuel of the boiler which will pollute the air. With this problem the research was conducted of designing a simulation of fuel dryer to dry out the boiler fuel before it used by utilizing the exhaust heat of the combustion system in the boiler. The simulation design of the fuel dryer is based on computational fluid dynamic (CFD) with parameters control are air velocity and heat temperature of fuel dryer. The results obtained the distribution of air velocity in the dryer has a value range of 0-40 m/s with the highest velocity occurring when hot exhaust air enters the dryer while the temperature distribution inside the dryer has a value range of 90-270 °C with the highest temperature appearing around hot air inlet exhaust and the lowest temperature appears in the hot air outlet section of the dryer.

Investigation of displacement ventilation performance under various room configurations using computational fluid dynamics simulation

The performance of a ventilation system affects air quality, thermal comfort, and energy consumption in indoor environments. To evaluate the performance of displacement ventilation under various room configurations, steady Reynolds Averaged Navier–Stokes (RANS) Computational Fluid Dynamics (CFD) simulations were used. The CFD model was validated using measurements of a full-scale test room. The age of air concept was used to evaluate the ventilation performance regarding indoor air quality. The PD index was used to control the case studies for draft risk. Twelve cases with different configurations were systematically studied and compared with the reference case. The configurations included plan aspect ratio, exhaust opening position, inlet position and geometry, and internal heat gains. The results showed that the overall ventilation performance of a room is less sensitive to room configurations compared with local ventilation performance around the occupants. However, almost in all cases, the occupants were exposed to better-than-average air quality in most cases. The results also indicated that when internal heat gains are small, displacement ventilation should be used with caution. Practical application: Any HVAC system design is based on assumptions made for ventilation performance. Comprehensive knowledge of the influential factors is critical for an efficient design. Regarding the architecture and interior design, the architects are also involved in the ventilation systems since they have an axial role in decision making for room configuration, including but not limited to room geometry, the position of inlet and outlet air terminals, and heat/pollutant sources. Consequently, the impact of room configuration on ventilation performance is of practical importance in the architecture, engineering, and construction industry.

Performance enhancement of methanol reforming reactor through finned surfaces and diffused entry for on-board hydrogen generation

Hydrogen-rich combustion in engines helps in reducing pollutants significantly. But hydrogen usage on a moving vehicle is not getting large-scale user acceptance mainly due to its poor energy storage density resulting in shorter driving ranges. This storage issue led to the hunt for mediums that can efficiently produce on-board hydrogen. Methanol proves to be an efficient alcohol fuel for producing hydrogen through steam reforming reaction. The heat energy required for such endothermic reaction is obtained through exhaust engine waste energy and this process is collectively known as thermochemical recuperation. However, the conventional reactor used for this process faces a lot of problems in terms of efficiency and methanol conversion. In this study, an attempt has been made to improve the design of the reactor for on-board hydrogen generation using engine exhaust heat for addressing the challenges related to performance and hydrogen yield. For enhancing the heat transfer, a finned surface (straight & wavy) was introduced in the reactor which resulted in an increment in methanol conversion significantly. It was found that wavy fin improved the methanol conversion up to 96.8% at an exhaust inlet temperature of 673 K. Also, a diffusing inlet section was introduced to increase the residence time of reactant gases while passing through the catalyst zone. Under given inlet conditions, the methanol conversion for 6° diffuse inlet reactor goes up to 87.9% as compared to 75.4% for the conventional reactor.

Experimental study on thermoelectric performance and power consumption characteristics of flat-plate thermoelectric generator

Thermoelectric generator can directly convert thermal energy into electrical energy, and applying it to recover waste heat from automobile exhaust is conducive to energy saving. In this paper, a thermoelectric generation experimental system is built, the power output performance and channel power consumption of the flat-plate thermoelectric power generation system under different exhaust gas flow rates are experimentally studied. The results show that when the exhaust flow rate is 40 Nm3/h and the exhaust inlet temperature is 400 °C, the maximum output power of the system is 26.8 W, and the maximum net output power is about 23.3 W. In addition, the exhaust flow rate is changed from 10 Nm3/h to 40 Nm3/h, and the proportion of power consumption in the hot air channel is changed from 1.91% to 12.85%, which has increased by more than six times.

Effect of ball-milling process in combination with the addition of carbide microparticles on the microstructure and wear resistance of a Co–Cr–W alloy prepared by powder metallurgy method

Co–Cr–W alloys were widely used in the inlet exhaust valve of aeroengine. However, the traditional manufacturing process of Co–Cr–W alloys can not meet the demand for higher comprehensive performance, and an optimum method needs to be developed. Herein, a Co–Cr–W alloy reinforced by exogenous carbides was prepared by the powder metallurgy method. Effect of ball-milling time on the microstructure and wear resistance of the alloy was investigated, and the formation mechanisms of the reinforcing phases were discussed. Results showed that with prolonging the ball-milling time, the uniformity of the reinforcing phases was improved, grain refinement was achieved, the hardness increased, a suitable bonding interface was formed between the matrix and reinforcing phases, and better wear resistance was thus achieved. However, when the ball-milling time increased from 60 h to 70 h, local segregation of the reinforcing phases occurred, the hardness decreased from 64 HRC to 60 HRC, and the friction coefficient increased from 0.53 to 0.58. Based on our experimental results, we proposed two formation mechanisms of the reinforcing phases (carbides): In-situ precipitation from the matrix and in situ autogenic reaction between the elements of the matrix and the added carbides (WC and Cr3C2 particles). Both mechanisms contributed to the formation of M23C6 and M6C carbides. Our results underscore the importance of added reinforcing phases and help to optimize the ball-milling process in preparing the Co–Cr–W alloys.

Simulation of Optimizing the Partial Load Performance of a Gas Turbine Combined Cycle Using Exhaust Heat Recuperation and Inlet Bleed Heating

Abstract This paper proposes a novel method to extend the operating range and improve the partial load efficiency of the gas turbine combined cycle (GTCC). The combination of exhaust heat recuperation and inlet bleed heating (IBH) was evaluated through a cycle simulation. The degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency. The recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature (TIT) were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. Both IBH and recuperation were effective in extending the operating range. The turndown ratio was predicted to decrease by approximately 10%p. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

A CFD Study on Flow Control of Ammonia Injection for Denitrification Processes of SCR Systems in Coal-Fired Power Plants

The selective catalytic reduction method is a useful method for the denitrification process of exhaust gas emitted from industrial facilities. The distribution of the ammonia–nitrogen oxide mixing ratio at the inlet of the catalyst layers is important in the denitrification process. In this study, a computational analysis technique was used to improve the uniformity of the NH3/NO molar ratio by controlling the flow rate of the ammonia injection nozzle according to the flow distribution of nitrogen oxides in the inlet exhaust gas of the denitrification facility. The application model was simplified to the two-dimensional array adopted from the existing selective catalytic reduction (SCR) process in the large-scaled coal-fired power plant. As the inlet conditions, four (4) types of flow pattern were simulated, i.e., parabolic, upper-skewed, lower-skewed, and random. The flow rate of the eight (8) nozzles installed in the ammonia injection grid was controlled by Design Xplorer as the optimization tool. In order to solve the two-dimensional steady, incompressible, and viscous flow fields, the commercial software named ANSYS Fluent was used with the κ-ε turbulence model. The root mean square of NH3/NO molar ratio at the inlet of the catalyst layer has been improved from 84.6% to 90.1% by controlling the flow rate of the ammonia injection nozzles. From the present numerical simulation, the operation guide could be drawn for the ammonia injection nozzles in SCR DeNOx facilities.

Inquisition on the Combined Effects of Ambient Temperature and Relative Humidity on The Performance of a Uniform Speed Single Shaft Gas Turbine in Tropical Monsoon Climate, using GPAL

This paper investigates the combined effects of Ambient Temperature and Relative Humidity on the performance of a uniform speed single shaft Gas Turbine, sited in Tropical Monsoon climate. A single shaft gas turbine simulator (known as GPAL) from Gas path Analysis ltd was employed. The City of Portharcourt, Nigeria, was chosen to represent the tropical monsoon climate, with its climatic data of monthly ambient temperature and relative humidity obtained from Koppen. With parameters like speed, reference power, inlet and exhaust losses kept constant, the ambient temperature and relative humidity were continually varied according to their climatic values. Each time, the performance of the gas turbine was simulated and parameters such as; Efficiency, Turbine power and Net power output, Turbine inlet Temperature and Exhaust Gas Temperature, as well as Specific fuel consumption were monitored. The environmental impact of the gas turbine was equally assessed in terms of Carbon (IV) Oxide (CO2) emission in Tonnes/day and in Kg/MWhr, NOX emission and Carbon Monoxide (CO) emission. The results of the study indicate that it is most efficient and productive to operate the gas turbine in Portharcourt in the months of January and December whereas it is least efficient in the month of April. Whereas CO emission was relatively low and uniform throughout the year, the highest specific fuel consumption was recorded in April.

Effect of Injection Pressure on Performance and Emission Characteristics HCCI Engines

Homogeneous Charged Compression Ignition engine (HCCI) is a suitable replacement of conventional diesel engines as it provides higher thermal efficiency and low oxides of emission (NOx) and particulate emissions. In HCCI engine, direct controlling of ignition timing is not possible. But it can be controlled by varying the engine parameters such as fuel injection pressure, inlet air temperature and exhaust gas recirculation. In this study, HCCI engine is controlled with changing the injection pressure of the fuel and analysed for the effect of injection pressure of the fuel for emission and performance of Karanja methyl ester fuel. The experiments were conducted on HCCI engine with fuel injection pressures of 2 bar, 3 bar, 4 bar and 5 bar and the optimum fuel injection pressure is found out. The results show that, the brake thermal efficiency is increased when the injection pressure is increased due to better atomisation and fuel penetration and also resulted in low emissions (NOx, smoke) compared with diesel engine.

An Inquisition on the Combined Effects of Ambient Temperature and Relative Humidity on The Performance of a Uniform Speed Single Shaft Gas Turbine in Tropical Monsoon Climate, using GPAL

This paper investigates the combined effects of Ambient Temperature and Relative Humidity on the performance of a uniform speed single shaft Gas Turbine, sited in Tropical Monsoon climate. A single shaft gas turbine simulator (known as GPAL) from Gas path Analysis ltd was employed. The City of Portharcourt, Nigeria, was chosen to represent the tropical monsoon climate, with its climatic data of monthly ambient temperature and relative humidity obtained from Koppen. With parameters like speed, reference power, inlet and exhaust losses kept constant, the ambient temperature and relative humidity were continually varied according to their climatic values. Each time, the performance of the gas turbine was simulated and parameters such as; Efficiency, Turbine power and Net power output, Turbine inlet Temperature and Exhaust Gas Temperature, as well as Specific fuel consumption were monitored. The environmental impact of the gas turbine was equally assessed in terms of Carbon (IV) Oxide (CO2) emission in Tonnes/day and in Kg/MWhr, NOX emission and Carbon Monoxide (CO) emission. The results of the study indicate that it is most efficient and productive to operate the gas turbine in Portharcourt in the months of January and December whereas it is least efficient in the month of April. Whereas CO emission was relatively low and uniform throughout the year, the highest specific fuel consumption was recorded in April.

A Case Study of the Supercritical CO2-Brayton Cycle at a Natural Gas Compression Station

Heat losses caused by the operation of compressor units are a key problem in the energy efficiency improvement of the natural gas compression station operation. Currently, waste heat recovery technologies are expensive and have low efficiency. One of these technologies is organic Rankine cycle (ORC) which is often analyzed in scientific works. In this paper, the authors decided to investigate another technology that allows for the usage of the exhaust waste energy—the supercritical Brayton cycle with CO2 (S-CO2). With a thermodynamic model development of S-CO2, the authors preformed a case study of the potential S-CO2 system at the gas compressor station with the reciprocating engines. By comparing the values of selected S-CO2 efficiency indicators with ORC efficiency indicators at the same natural gas compression station, the authors tried to determine which technology would be better to use at the considered installation. Investigations on parameter change impacts on the system operation (e.g., turbine inlet pressure or exhaust gas cooling temperatures) allowed to determine the direction for further analysis of the S-CO2 usage at the gas compressor station. When waste heat management is considered, priority should be given to its maximum recovery and cost-effectiveness.

Performance Study on Methanol Steam Reforming Rib Micro-Reactor with Waste Heat Recovery

Automobile exhaust heat recovery is considered to be an effective means to enhance fuel utilization. The catalytic production of hydrogen by methanol steam reforming is an attractive option for onboard mobile applications, due to its many advantages. However, the reformers of conventional packed bed type suffer from axial temperature gradients and cold spots resulting from severe limitations of mass and heat transfer. These disadvantages limit reformers to a low efficiency of catalyst utilization. A novel rib microreactor was designed for the hydrogen production from methanol steam reforming heated by automobile exhaust, and the effect of inlet exhaust and methanol steam on reactor performance was numerically analyzed in detail, with computational fluid dynamics. The results showed that the best operating parameters were the counter flow, water-to-alcohol (W/A) of 1.3, exhaust inlet velocity of 1.1 m/s, and exhaust inlet temperature of 773 K, when the inlet velocity and inlet temperature of the reactant were 0.1 m/s and 493 K, respectively. At this condition, a methanol conversion of 99.4% and thermal efficiency of 28% were achieved, together with a hydrogen content of 69.6%.

CFD Analysis of Swirl Effect in a Diesel Engine Using OpenFOAM

The combustion process is a basic activity performed by internal combustion engines in charge of release chemical energy from a fuel-air mixture and transforms them into mechanical energy to produce work. Principles of fluid mechanics and thermal sciences are applied in the analysis of the complex flows developed during internal combustion processes with the aim of maximizing work, improving energy efficiency, minimizing fuel consumption, and reducing pollutants caused by the heat released in combustion chambers. Computational Fluid Dynamics help analyzing the turbulent flow phenomena presents in inlet flow, compression, combustion, and exhaust flow processes and defining optimization models that describe and improve swirl and tumble flows in combustion chambers of internal combustion engines. The purpose of developing a numerical simulation is to characterize turbulent flows developed in the admission and cylinders of a diesel engine to study the complex and sudden changes in flow parameters in order to describe a combustion process. Therefore, this paper presents a description of the flow behavior in an engine combustion chamber through a virtual environment. RANS k - e turbulence model is computed with OpenFOAM CFD code in order to solve the system of partial differential equations that define the turbulent mixture flow and swirl effects of the flow over the engine combustion chamber. The results of this research have shown a good agreement between numerical and experimental methods; an error rate of 5 % has been reached by using the KEpsilon turbulence model.