Application and failure evaluation of ferritic stainless steels for automotive exhaust systems

In recent years, with attention paid to global environmental problems, there have been requirements for continuous improvement of automobile fuel economy and exhaust gas purification rate. The properties of the ferritic stainless steels （FSS） used to make automobile parts have been improved. This paper introduces the construction of automotive exhaust systems and describes their main failure behaviors and corrosion evaluation procedures.

Optimizing the Exhaust System of Marine Diesel Engines to Improve Low-speed Performances and Cylinder Working Conditions

Proper design of exhaust systems in marine high-power turbocharged diesel engines can contribute to improve the low-speed performance of these engines and make the working conditions of the cylinders more uniform.Here a high-power marine 16-cylinder V-type turbocharged diesel engine is simulated using the GT-Power software.The results reveal the differences induced by different exhaust system structures,such as an 8-cylinder-inpipe exhaust system with single/double superchargers and a 4-cylinder-in-pipe exhaust system with a single supercharger.After a comparative analysis,the 8-cylinder type with double superchargers is determined to be the optimal solution,and the structure of the exhaust system is further optimized.The simulations show that the optimized maximum exhaust temperature difference among cylinders is reduced by 66%.Finally,the simulation results and the optimized performance of the designed exhaust system are verified through experiments.

Influence of the Hook Position on the Vertical Vibrations of an Automobile Exhaust System:Application of the Robust Optimization Design

A robust optimization design method is proposed to investigate the influence of the hook position on the vertical vibration(bending)of an automobile exhaust system.A block diagram for the robustness analysis of the exhaust system is initially constructed from the major affecting factors.Secondly,the second-order inertia force is set as the vibration excitation source of the exhaust system and the displacement of four hooks of the exhaust system is selected as the variable factor.Then tests are carried out to investigate the resulting vertical bending considering four influencing factors and three levels of analysis.Finally,a variance analysis of the vertical bending is performed.The present study provides a set of guidelines to control the key factors affecting the vibration of vehicle exhaust systems while proposing an effective method to reduce vehicle vibration and improve noise analysis。

Design of Mechanical Smoke Exhaust System in Large Space of Convention Center

The volumetric flow rate of smoke generated from the fire in large space often reaches to hundreds of thousands CMH because of extended floor height and as it’s more difficult to isolate the smoke to the limited area, comparing to normal-scale building, design and operation of effective smoke control system for large space is more than important. In this study, with the analysis model for such a large space as exhibition hall or conference room in conventional center, design of mechanical smoke exhaust system was conducted based on currently-available design standard which was then followed by numerical analysis of the design using 3D numerical analysis method. For conference room at 2.0 MW heat release rate, 99,173 CMH flow rate is required, if smoke layer is maintained at 60% of the floor height and for exhibition hall at 8.8 MW with 80% of floor height, flow rate required is 219,802 CMH, which are incorporated into the design. In view of 3D numerical analysis, accuracy of the design according to algebraic expression is sufficient.

Jet Noise Reduction of Double-Mixing Exhaust System

A jet noise reduction technique by using the external chevron nozzle with lobed mixer in the double-mixing exhaust system is investigated under cold conditions.The computations of jet field and the experiments of noise field are conducted with scaled model of high-bypass-ratio turbofan engine mixing exhaust system composed of external chevron nozzle with lobed mixer.The computational results indicate that comparing with the baseline nozzle with lobed mixer,the external chevron nozzle with lobed mixer increases mixing of jet and ambient air near the nozzle exit.The experimental results show that the external chevron nozzle with lobed mixer has better jet noise reduction at low frequencies,and this reduction rises with the increase of chevron bend angle.The experimental results also show that the external chevron nozzle with lobed mixer has sound pressure level(SPL)increase which is not obvious at high frequencies.With chevron bend angle increasing,SPL has relatively marked increase at 60°(directivity angle measured from upstream jet axis)and little fluctuations at 90°and 150°.The external chevron nozzle with lobed mixer has overall sound pressure level(OASPL)reduction in varying degrees at 60°and 150°,but it has little OASPL increase at 90°.

The mathematical model of kitchen smoke exhaust system in high-rise residential buildings considering the Influence of Stack effect

In high-rise buildings with large indoor and outdoor temperature difference,neglecting the effect of stack effect in smoke exhaust shafts may cause calculation error of the fluid network model.In this paper,the mathematical model of kitchen smoke exhaust system considering the influence of stack effect was put forward and it can be inserted different range hood sub-models.Compared with the results of six working conditions of the model without considering the stack effect,the error of the proposed model were reduced by 7.6%,4.3%,4.1%,2.8%,2.4%,and 2.1%.While the indoor and outdoor temperature difference varies from−5℃ to 49℃,the effect of stack effect on the pressure in the flue and the flow rate for each user was studied for six operating rates s.The results show that under the combined effect of stack effect and flue resistance,the static pressure of the kitchen smoke exhaust system showed a low-high-low distribution,and the maximum static pressure in the flue moved toward the bottom with the increase of temperature difference.User flow rates exhibit a low-high-low-high distribution,with an increased flow rate in the bottom users and the largest flow rate in the top users.

Infrared radiation simulation of exhaust system by coupling FVM with narrow band k-distribution

A three-dimensional infrared radiation code for exhaust system was developed by the finite volume method coupled with narrow band k-distribution in non-gray absorbing-emitting media.The final infrared signature had considered the atmosphere effect,and the simulation values were favorably consistent with testing ones.The results indicate that the relative errors considering the effect of atmosphere compared with that of the contrary condition reduce by 31%,it shows that when simulating the infrared radiation of the target which is received by the infrared detectors,even the calculation band is in atmospheric windows 3～5 μm,the effect of atmospheric transmission on infrared signature of the target should not be neglected.

Calculation of Wall Temperature for Aircraft Exhaust System with Considering Gas Radiation Heat Transfer

The coupled numerical simulation of flow field, solid temperature field, species concentration field and gas radiation transfer/ energy field based on statistical narrow-band correlated-k （SNBCK） model, is employed to accurately predict aerothermodynamic characteristic of aircraft exhaust system. A series of methods to increase computational efficiency and descend computational resources make it possible to finish the calculation in PC. The parameters of narrow-band model are evaluated by HITEMP line-by-line database. Three examples have proved the accuracy of using these methods to solve flow heat transfer coupled problem and radiation transfer/energy equation, which are the calculation of temperature distribution of water-cooling nozzle in rocket engine, the calculation of carbon dioxide absorptivity at 4.3 micron band, and the gas radiation heat transfer evaluation of the cylindrical furnace. Finally, the inner flaps temperature distribution of ejecting nozzle with floating outer flaps is computed, under high-altitude, high-speed and afterburning conditions. Two completely different air-inlet schemes of ejecting channel almost achieve the same effect in cooling inner flaps.

Design and optimization of exhaust gas aftertreatment system for a heavy-duty diesel engine

Diesel engines meeting the latest emission regulations must be equipped with exhaust gas aftertreatment system,including diesel oxidation catalysts(DOC),diesel particulate filters(DPF),and selective catalytic reduction(SCR).However,before the final integration of the aftertreatment system(DOC+DPF+SCR)and the diesel engine,a reasonable structural optimization of the catalytic converters and a large number of bench calibration tests must be completed,involving large costs and long development cycles.The design and optimization of the exhaust gas aftertreatment system for a heavy-duty diesel engine was proposed in this paper.Firstly,one-dimensional(1D)and threedimensional(3D)computational models of the exhaust gas aftertreatment system accounting for the structural parameters of the catalytic converters were established.Then based on the calibrated models,the effects of the converter’s structural parameters on their main performance indicators,including the conversion of various exhaust pollutants and the temperatures and pressure drops of the converters,were studied.Finally,the optimal design scheme was obtained.The temperature distribution of the solid substrates and pressure distributions of the catalytic converters were studied based on the 3D model.The method proposed in this paper has guiding significance for the optimization of diesel engine aftertreatment systems.

Techno-economic feasibility assessment of a diesel exhaust heat recovery system to preheat mine intake air in remote cold climate regions

Underground mines in Arctic and Subarctic regions require the preheating of mine intake air during winter.The cold fresh air of those remote areas can be as severe as
40℃ and commonly needs to be heated to around+3℃.This extensive amount of heating is usually provided by employing large-size air heaters,fueled by diesel,propane,natural gas,or heavy oil,leading to high energy costs and large carbon footprints.At the same time,the thermal energy content of a diesel generator sets(gen-sets)exhaust is known to be one-third of the total heating value of its combusted fuel.Exhaust heat recovery from diesel gen-sets is a growing technology that seeks to mitigate the energy costs by capturing and redirecting this commonly rejected exhaust heat to other applications such as space heating or pre-heating of the mine intake air.The present study investigated the possibility of employing a simple system based on off-theshelf heat exchanger technology,which can recover the waste heat from the exhaust of the power generation units(diesel gen-sets)in an off-grid,cold,remote mine in Canada for heating of the mine intake air.Data from a real mine was used for the analysis along with environmental data of three different location-scenarios with distinct climates.After developing a thermodynamic model,the heat savings were calculated,and an economic feasibility evaluation was performed.The proposed system was found highly viable with annual savings of up to C$6.7 million and capable enough to provide an average of around 75%of the heating demand for mine intake air,leading to a payback period of about eleven months or less for all scenarios.Deployment of seasonal thermal energy storage has also been recommended to mitigate the mismatch between supply and demand,mainly in summertime,possibly allowing the system to eliminate fuel costs for intake air heating.

Simulation of Gas-Fired Triple-Effect LiBr/Water Absorption Cooling System with Exhaust Heat Recovery Generator

An exhaust heat recovery generator is proposed to be integrated with conventional gas-fired triple-effect LiBr/water absorption cooling cycles to improve system energy efficiency. As a case study, simulation of the novel cycle based on promising parallel flow with cooling capacity of 1 150 kW is carried out under various heat recovery generator vapor production ratios ranging from 0 to 3.5%. The life cycle saving economic analysis, for which the annual gas conservation is estimated with Bin method, is employed to prove the worthiness of extra expenditure. Results show that the optimum gas saving revenue is obtained at 2.8% heat recovery generator vapor production ratio with 42 kW exhaust heat recovered, and the system energy efficiency is improved from 1.78 to 1.83. The initial investment of exchanger can be paid back within 7 years and 9 000 CNY of gas saving revenue will be achieved over the 15-year life cycle of the machine. This technology can be easily implemented and present desirable economic effects, which is feasible to the development of triple-effect absorption cycles.

Effect of floor level slit exhaust ventilation system on distribution of house dust

Based on the fact that the house dust usually falls on the ground, the floor level slit exhaust ventilation system including inlet located at the ceiling and outlet of slit exhaust installed at comer between wall and floor was considered. Experiments and simulations were performed to investigate the flow and diffusion fields that are affected by this floor level slit exhaust ventilation system. The characteristics of airflow with experiments and computation fluid dynamics （CFD） are generally similar except airflow at the location of impinging flow and the location right below the inlet. Riboflavin particles were used as the house dust. For the spatial distribution of riboflavin particles in the ventilation system before operation, due to the influence of gravity, different sizes of particles show smooth decay curve. After floor level slit exhaust ventilation system is operated, the decay rate of the particles becomes faster than that after the ventilation system is powered on, and the particles with diameter of 0.5-3.0 μm in the experimental data and calculated values show good agreement.

ANALYTICAL SOLUTION OF FILLING AND EXHAUSTING PROCESS IN PNEUMATIC SYSTEM

The filling and exhausting processes in a pneumatic system are involved with many factors, and numerical solutions of many partial differential equations are always adapted in the study of those processes, which have been proved to be troublesome and less intuitive. Analytical solutions based on loss-less tube model and average friction tube model are found respectively by using fluid net theory, and they fit the experimental results well. The research work shows that： Fluid net theory can be used to solve the analytical solution of filling and exhausting processes of pneumatic system, and the result of loss-less tube model is close to that of average friction model, so loss-less tube model is recommended since it is simpler, and the difference between filling time and exhausting time is determined by initial and final pressures, the volume of container and the section area of tube, and has nothing to do with the length of the tube.

Exhaustive entropy based SLM method for PAPR reduction of OFDM system

Orthogonal frequency division multiplexing(OFDM) is an attractive technology to provide immense improvement in wireless transmission capacity but high peak-to-average power ratio(PAPR) is a major drawback of OFDM system.Selected mapping(SLM) scheme has good performance for PAPR reduction.It requires the transmitting data to be multiplied by random phase sequences.However,the sequences are pseudo-random which will decrease the method effectiveness.Exhaustive entropy is introduced in this paper which can identify the strength of random phase sequences property.Then an exhaustive entropy based on SLM method is proposed.The scheme improves the effectiveness of random phase sequences by selecting the larger exhaustive entropy of them.The simulation results show that the PAPR reduction performance is better than that of conventional SLM through this method.

The Efficiency Analysis of the Exhaust Air Heat Pump System

This paper is based on long term parameter measurements of the exhaust air heat pumps (EAHP) system in a new built apartment building. The building was equipped with an exhaust air ventilation system and exhaust air heat pump for ventilation heat recover. The results of the measurements show that the COP of the EAHP is mainly related to the temperature graph of the heating system and the supply temperature of domestic hot water (DWH). During the measurement period some other impact factors, such as the quality of maintenance, the nighttime temperature graph of the heating system, the reduction of the exhaust air flows in case of low temperatures, mistakes in designing and low building quality, have also played a role. An analysis of energy consumption shows that in winter conditions the COP is about 3.0 and in the transition period about 3.3. The energy recovery value of the EAHP is 0.5.

Optimization and Evaluation of a Vehicular Exhaust Heat Recovery System

Exhaust waste heat recovery system based on organic Rankine cycle(ORC)has been considered as an effective method to achieve energy conservation and emissions reduction of engine.The performance of adiesel engine with an on-board ORC exhaust heat recovery system was evaluated through simulations in this study.The combined system was optimized through controlling the exhaust gas mass flow rate entering the ORC system.The models of the engine with ORC system were developed in GT-suite and Simulink environment.The validation results showed high accuracy of the models.The performance of the system recovering heat from different exhaust gas mass flow rates was evaluated.The comparative analysis of the performance between the optimized and un-optimized system was also presented.The results indicated that the exhaust gas mass flow rate had significant effects on the system performance.Integration with the onboard ORC system could effectively improve the engine power performance.The power output of the engineORC combined system with optimization had further improvement,and the maximum improvement could reach up to 1.16 kW.

System analysis based on the T cell exhaustion‑related genes identifies CD38 as a novel therapy target for ovarian cancer

Ovarian cancer(OV)is highly heterogeneous tumor with a very poor prognosis.Studies increasingly show that T cell exhaustion is prognostically relevant in OV.The aim of this study was to dissect the heterogeneity of T cell subclusters in OV through single cell transcriptomic analysis.The single RNA-sequencing(scRNA-seq)data of five OV patients were analyzed,and six major cell clusters were identified after threshold screening.Further clustering of T cell-associated clusters revealed four subtypes.Pathways related to oxidative phosphorylation,G2M checkpoint,JAK-STAT and MAPK signaling were significantly activated,while the p53 pathway was inhibited in the CD8+exhausted T cells.The standard marker genes of CD8+T cell exhaustion were screened to develop a T-cell related gene score(TRS)based on random forest plots in TCGA cohort.The patients with low TRS have better prognosis compared to the patients with high TRS in both TCGA and GEO.In addition,most genes included in the TRS showed significant differences in expression levels between the high-and low-risk groups.Immune cell infiltration was analyzed using the MCPcounter and xCell algorithms,which revealed significant differences between the two risk groups,indicating that the different prognoses may stem from the respective immune landscapes.In addition,CD38 knockdown in OV cell lines increased apoptosis and inhibited invasion in vitro.Finally,we performed a drug sensitivity analysis and identified six potential drug candidates for OV.To summarize,we identified the heterogeneity and clinical significance of T cell exhaustion in OV and built a superior prognostic model based on T cell exhaustion genes,which can contribute to the development of more precise and effective therapies.

Design of Manure Gas Exhaustion to Reduce Ammonia Concentrations in Loose-Housing Systems for Laying Hens

Uniformity of air flow in extraction openings in exhaust air channels for manure gas exhaustion is determined by the distribution of pressure. The areas required in extraction vents and in extraction ducts are determined by the uniformity of air flow desired along the duct and by the loss of pressure that can be accepted. The area ratio between the vents and the cross section of the exhaust air duct will have a strong influence on both uniformity of flow and loss of pressure. The following ventilation properties were studied： Uniformity of air flow; Variations in static pressure along a duct; Air velocity at different distances from the vents. The area ratio should be about 1 for uniform exhaustion. The studies showed that the relative variation in air velocity is independent of the level of the ventilation rate. The uniformity of the exhaust distance is influenced in about the same way by the area ratio as the air velocity in the exhaust vents. Thus, it is important that the area ratio is not too high if a good exhaust function should be guaranteed. The studies also demonstrated that the uniformity of the exhaust distance is independent of the ventilation flow rate. The exhaust ventilation range is, maximally 0.3 m from the vents. The static friction coefficient was on average 0.80.

Exhaust gas energy recovery system of pneumatic driving automotive engine

Almost the same quantity to net output work of energy has been carried out and wasted by exhaust gas in typical automotive engine. Recovering the energy from exhaust gas and converting to mechanical energy will dramatically increase the heat efficiency and decrease the fuel consumption. With the increasing demand of fuel conservation, exhaust gas energy recovery technologies have been a hot topic. At present, many researches have been focused on heating or cooling the cab, mechanical energy using and thermo-electronic converting. Unfortunately, the complicated transmission of mechanical energy using and the depressed efficiency of thermo-electronic converting restrict their widely applying. In this paper, a kind of exhaust gas energy recovery system of pneumatic driving automotive engine, in which highly compressed air acts as energy storing and converting carrier, has been established. Pneumatic driving motor can produce moderate speed and high torque output, which is compatible for engine using. The feasibility has been certificated by GT-Power simulation and laboratory testes. The technologies about increasing recovery efficiency have been discussed in detail. The results demonstrated that the in parallel exhaust gas energy recovery system, which is similar to the compound turbo-charger structure can recovery 8 to 10 percent of rated power output. At last, a comprehensive system, which includes Rankine cycle based power wheel cycle unit etc., has been introduced.

Acoustic Valve Integration in Exhaust Line Systems

In recent years the demand for the acoustic performance of exhaust systems has increased and will further increase in the future. The main drivers are new pass-by-noise regulation and new powertrain technologies paired with exhaust muffler volume, weight and costs constraints. In the following paper several application examples for Adaptive ValveTM （self-actuated in-pipe valve）, in-muffler valve and electric valve are shown and the related benefits on the system performance are assessed. It is shown that implementing a valve into an exhaust system has a significant influence on the NVH performance. The resulting backpressure penalties can be minimized using the right implementation strategy of the valves in the exhaust system. Hence the exhaust system has to be specifically designed for the integration of a valve. All three valve types have additional benefits to their standard application for overall noise reduction and muffler volume reduction, which are analyzed. The Adaptive ValveTM, for example, is often used on cars with long pipe routing and has the additional benefit of reducing pipe resonance in the system. Another example, the electric valve, can be coupled with vehicle communication networks and hence the flexibility in application is significantly increased.