Ultralight aviation is based on piston engines requiring both performance and reliability. An important aspect is also the require-ments for the installation of such an engine on an airframe, ...especially its heat emission. This is firstly because of the need to ensure proper engine cooling and secondly because composite elements of the airframe skin are not exposed to excessive overheating. For this purpose, bench tests of the temperature distribution of the exhaust system of ROTAX 912 engine were carried out. Measurements were taken at 6 points of the exhaust system, where the temperature of the exhaust gases and exhaust pipes were measured. The tests covered a wide range of engine operation. The paper presents the temperature distribution at selected points in relation to the engine speed and load.
To understand the jet flow characteristics of turbofan separate exhaust system, a parametric design method based on the initial Class Shape Transformation function was developed. HBPR and UHBPR ...turbofan separate exhaust systems were designed. Furthermore, the jet flow characteristics of the HBPR turbofan exhaust system under take-off condition with zero angle of attack were studied based on numerical simulation. The jet flow characteristics of the HBPR and UHBPR turbofan exhaust system under take-off condition with high angle of attack were also simulated. The effects of angle of attack and bypass ratio on the jet flow characteristics were investigated and the related flow mechanisms were analyzed. Results show that the axisymmetric plumes of the HBPR turbofan exhaust system are distributed around the engine axis under take-off condition with zero angle of attack. With the plug wake as the center, the core flow, the fan/core shear layer, the fan flow, the fan/free stream shear layer and the free stream are wrapped around the plug wake from inside out. Vortexes appear in the lee area at the back of the cowl and jet flow under take-off condition with high angle of attack. These vortexes cause cross sectional secondary flow and expose the high-velocity core flow to the low-velocity free stream. The contact area and velocity gradient in the mixing region among the free stream, fan flow and core flow increase. Therefore, the mixture among jet flow and free stream strengthens. So the high-velocity region, the high-vorticity region, and the high turbulence kinetic energy region shorten by 55.1%, 47.7% and 50.9% respectively. The vorticity values and turbulence kinetic energy level peak on the upper side of the exhaust plumes increase by about 30% and 87% respectively. Relative to these parameters from the HBPR turbofan exhaust system, the jet velocity peak value of UHBPR turbofan decreases by 5.5% under take-off condition with high angle of attack. The vorticity values and turbulence kinetic energy level reduce due to decreased velocity gradient in shear layers downstream of the nozzle exit plane. The turbulence kinetic energy level peak on the upper side of the exhaust plumes decreases by 29.3%. The reasons are that the contact area between high-velocity core flow and the free stream decreases due to thicker fan flow and the velocity gradient in the core flow and free stream mixing region decreases because of the lower core flow velocity.
This paper deals with analysis of the vehicle exhaust system quality and its influence on the results of measuring exhaust emissions of the Otto and Diesel motor vehicles. Results of eco-tests ...obtained from correct and faulty vehicle exhaust systems were compared to conclude that damages caused by corrosion had significant influence on the pass rate of vehicles at eco-test. Referring to vehicles with the Otto engine, damages in the exhaust system increase the oxygen level, which results in the increased λ factor and in failure at the eco-test. On the contrary, vehicles with the damaged Diesel engine exhaust system allow the gas to leak through the damage, so the measurement of blackening is lower, i.e. the eco-test result is better than that of the exhaust system without damage.
•Combination of experiments and MVEM to study effects of back pressure on marine engine performance.•Method applying smoke limit and thermal overload to define ceiling of acceptable back ...pressures.•Two different turbocharging technologies and valve overlaps to tackle 1mWC of back pressure.
After-treatment technologies are adopted in automobiles and ships to meet strict emission regulations, which increase exhaust back pressure. Furthermore, underwater exhaust systems are employed on board ships to save space, and reduce noise and pollution on working decks. However, water at exhaust outlet creates a flow resistance for the exhaust gases, which adds to the back pressure. High back pressure reduces the operating limits of an engine, increases fuel consumption, and can lead to exhaust smoke. While the effects of back pressure were recognized earlier, there is a lack of experimentally validated research on the performance limits of a turbocharged, marine diesel engine against high back pressure for the entire operating window. The focus of this research is to provide a comprehensive understanding of back pressure effects on marine diesel engine performance, and to identify limits of acceptable back pressure along with methods to tackle high back pressure.
In this work, a pulse turbocharged, medium speed, diesel engine was tested at different loads and engine speeds; against different values of static back pressure. Additionally, mean value model simulations could be validated and were used to compare the performance of a pulse and constant pressure turbocharged engine against high back pressures of 1meter water-column (mWC), and for two different values of valve overlap.
Using the validated simulation model, the conceptual basis for the engine smoke limit as well as for thermal overloading is investigated. A methodology applying the conceptual basis to define boundaries of acceptable back pressures has been presented in this paper. A combination of pulse turbocharger systems and small valve overlap showed to significantly improve back pressure handling capabilities of engines.
The present study focuses on the design and performance analysis of an exhaust system for an over-under turbine based combined cycle (TBCC) operating at Mach 0–6. The computational fluid dynamics ...(CFD) approach is employed to obtain the flowfield and performance of the exhaust system. The single expansion ramp nozzle (SERN) considering geometric constraints at the cruise condition is designed by a new method based on maximum thrust theory, and the initial expansion angle on the cowl is set at 0.37 rad. The lower cowl is sliding as well as rotating around a fixed point to satisfy the adjustment requirement of the high-speed flowpath, and shifting the location of the fixed point forward has a positive effect on the performance of the exhaust system. In order to eliminate the adjustment interaction between the low-speed and high-speed flowpaths and decreases the expansion ratio of the low-speed flowpath, the splitter location is shifted backward, and the optimal location and top contour angle of the splitter are set to 220 mm and 20°, respectively. The flowfield structure is relatively simple at the separate operation, while it is obviously complex at the parallel operation, with the flow interaction between the turbine exhaust jet and rocket ejector plume. With the increase in the flight Mach number, the axial thrust coefficient is increased rapidly at the separate operation of the turbine, while it increases firstly and then decreases at the parallel operation. For the separate operation of the high-speed flowpath, the axial thrust coefficient maintains above 0.96 and also increases firstly and then decreases gradually as the increase in the flight Mach number.
The present study focuses on the unsteady mode transition process of an over-under TBCC exhaust system. The method of characteristics is applied to design the over-under TBCC exhaust system according ...to the entrance parameters of the turbine nozzle and ramjet nozzle at the design point. The dynamic mesh is adopted to adjust to the update of the computational domain, and the unsteady numerical method is employed to simulate the dynamic flowfield of the exhaust system during the mode transition process. The results show that the flowfield structure and the performance vary greatly during the mode transition. Owing to the interaction between the turbine exhaust jet and ramjet plume, the flowfiled in the turbine nozzle is affected by the ramjet exhaust jet considerably. The axial thrust of the turbine nozzle decreases, while that of the ramjet nozzle increases gradually during the mode transition, but the total axial thrust of the entire exhaust system varies smoothly. Both the axial thrust coefficient and pitching moment of the exhaust system increase along with the open of the ramjet nozzle, while the result for the lift is contrary. However, the axial thrust coefficient, lift and pitching moment all decrease rapidly with the shutdown of the turbine nozzle, and the decreases in axial thrust coefficient, lift and pitching moment are 1.04%, 67.15% and 80.92%, respectively. Besides, two sudden change of the axial thrust coefficient exist at the beginning and end of the motion of the splitter plate.
•The unsteady mode transition process for an over-under TBCC exhaust system is investigated.•The unsteady flowfield of the exhaust system during the mode transition process is analysis.•The performance variance of the exhaust system during the mode transition process is discussed.
Geometric model of a lobed mixing exhaust system is created and its flow field is simulated by using the steady Reynolds Averaged Navier-Stokes (RANS) equations under the condition of different core ...flow inlet swirl angles. According to the numerical simulation results, due to the guidance effect of the lobe parallel side wall, the structure and vorticity of streamwise vortices change little near the lobe exit with inlet swirl angle, and it is the same with the thermal mixing efficiency. As the flow develops, although the inlet swirl angle has limited influence on the streamwise vorticity, it greatly affects the structure of streamwise vortices. It causes the thermal mixing efficiency to increase with the swirl angle. As for the total pressure recovery coefficient, it falls slightly when the inlet swirl strengthens. At the nozzle exit, the total pressure recovery coefficient of CFISA = 30° model is 0.5% lower than CFISA = 0° model. Moreover, as the inlet swirl strengthens, the thrust fall of lobed mixing exhaust system gradually accelerates, especially when the inlet swirl angle is over 15°.
RESUMO Neste trabalho, analisou-se a eficiência de um sistema de exaustão de material particulado em um processo real de eletrofusão. Particularmente, realizaram-se análises de distribuição ...granulométrica em diferentes estágios do processo. Utilizando os dados da análise granulométrica, avaliou-se a eficiência do ciclone comparando-a com a eficiência de projeto - adicionalmente, a eficiência do ciclone foi também calculada com base no balanço de massa de todo o processo. Apesar de algumas medidas tomadas pela empresa a fim de melhorar a eficiência do sistema de exaustão, resultados indicam eficiência do ciclone da ordem de 50%, e perda de material particulado para atmosfera da ordem de 1 t a cada batelada do processo. Neste trabalho, apresentam-se detalhadamente as etapas da análise de eficiência do sistema de exaustão, particularmente do ciclone, e a proposta de redimensionamento do ciclone.
ABSTRACT In this work, we analyzed the performance of a particulate matter exhaust system of a real electrofusion production process. Particularly, we performed particle size distribution analysis at different stages of the process. Using particle size distribution data, cyclone operation efficiency was evaluated by comparing it with design efficiency - in addition, cyclone efficiency was also calculated based on the mass balance of the entire process. Despite some measures taken by the company in order to improve the exhaust system efficiency, results indicate cyclone efficiency of around 50%, and particulate matter loss to atmosphere of 1t at each batch of the process. This paper presented in detail the steps of the efficiency analysis of the exhaust system, particularly the cyclone, and the proposed cyclone resizing.
It is a relevant objective in thermal physics and in building reciprocating internal combustion engines (RICE) to obtain new information about the thermal-mechanical characteristics of both ...stationary and pulsating gas-flows in a complex gas-dynamic system. The article discusses the physical features of the gas dynamics and heat transfer of flows along the length of a gas-dynamic system typical for RICE exhaust systems. Both an experimental set-up and experimental techniques are described. An indirect method for determining the local heat transfer coefficient of gas-flows in pipe-lines with a constant temperature hot-wire anemometer is proposed. The regularities of changes in the instantaneous values of the flow rate and the local heat transfer coefficient in time for stationary and pulsating gas-flows in different elements of the gas-dynamic system are obtained. The regularities of the change in the turbulence number of stationary and pulsating gas-flows along the length of reciprocating internal combustion engines gas-dynamic systems are established (it is shown that the turbulence number for a pulsating gas-flow is 1.3-2.1 times higher than for a stationary flow). The regularities of changes in the heat transfer coefficient along the length of the engine?s gas-dynamic system for stationary and pulsating gas-flows were identified (it was established that the heat transfer coefficient for a stationary flow is 1.05-1.4 times higher than for a pulsating flow). Empirical equations are obtained to determine the turbulence number and heat transfer coefficient along the length of the gas-dynamic system.
This study aimed to evaluate the egress safety in nursing hospitals based on the capacity of the smoke exhaust system. To this end, the available safe egress time was calculated by analyzing changes ...in visibility, carbon monoxide, carbon dioxide, oxygen contents, and temperature depending on the fire duration. In addition, an egress simulation was performed using the number of workers (egress guides) and egress delay time as variables, and the required safe egress time was estimated. Based on the results, the egress safety of a prototype nursing hospital was evaluated. In this study, egress safety criteria to evaluate egress safety in a typical nursing hospital were presented, which are expressed in terms of normalized egress guides, the capacity ratio of the smoke exhaust system, and egress delay time. The proposed criteria can be used to evaluate the egress safety of typical nursing hospitals and to prepare complementary measures.
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