Browse Topic: Exhaust pipes

Items (135)
Find
Relevance of Exhaust Aftertreatment System Degradation for EU7 Gasoline Engine Applications2020-01-03824/14/2020
Exhaust aftertreatment systems must function sufficiently over the full useful life of a vehicle. In Europe this is currently defined as 160.000 km. With the introduction of Euro 7 it is expected that the required mileage will be extended to 240.000 km. This will then be consistent with the US legislation. In order to quantify the emission impact of exhaust system degradation, an Euro 7 exhaust aftertreatment system is aged by different accelerated approaches: application of the Standard Bench Cycle, the ZDAKW cycle, a novel ash loading method and borderline aging. The results depict the impact of oil ash on the oxygen storage capacity. For tailpipe emissions, the maximum peak temperatures are the dominant aging factor. The cold start performance is effected by both, thermal degradation and ash accumulation. An evaluation of this emission increase requires appropriate benchmarks. For this purpose, an analysis of the emission impacts of ambient temperatures, driving modes and particulate filter regenerations follows. The comparison shows the severe impact of very low ambient conditions. Considering the high statistical relevance of catalyst degradation however, full useful life optimization requires special attention for Euro 7 gasoline engine applications.
Sterlepper, Stefan, Claßen, Johannes, Pischinger, Stefan, Görgen, Michael, Cox, Jim, Nijs, Martin, Scharf, Johannes
Experimental Study of Acoustic and Thermal Performance of Sound Absorbers with Microperforated Aluminum Foil2019-01-15806/5/2019
Aluminum foil applied to the surface of sound absorbing materials has broad application in the automotive industry. A foil layer offers thermal insulation for components close to exhaust pipes, turbo chargers, and other heat sources in the engine compartment and underbody. It can also add physical protection for acoustic parts in water-splash or stone-impingement areas of the vehicle exterior. It is known that adding impermeable plain foil will impact the sound absorption negatively, so Microperforated Aluminum Foil (MPAF) is widely used to counteract this effect. Acoustic characteristics of MPAF can be modeled analytically, but deviation of perforation size and shape, variation of hole density, material compression, and adhesive applied to the back of the foil for the molding process can impact the acoustic and thermal insulation performance. Because we cannot rely on analytical tools to generate accurate performance of these materials in a production environment, this paper will focus on the acoustic and thermal experimental characterization of these materials. Studies were conducted on flat test samples which have commonly used MPAF applied to the top surface. Results are presented showing the effects of the hole perforation size and density on the acoustic and thermal performance. Results are compared with sound absorbers with other facing materials. Conclusions from this investigation provide guidance for the selection of MPAF during the sound absorber development.
Yin, Gang Glenn, Parrett, Alan, Salazar Prieto, Felipe G., Roggenkamp, Timothy J.
Development and Experimental Validation of a Control Oriented Model of a Catalytic DPF2019-01-09854/2/2019
1 The wall-flow Diesel Particulate Filter (DPF) is currently the most common after-treatment system used to meet the particulate emissions regulations for automotive engines. Today’s technology shows the best balance between filtration efficiency and back-pressure in the engine exhaust pipe. During the accumulation phase the pressure drop across the filter increases, thus requiring periodic regeneration of the DPF through after and post fuel injection strategies. This paper deals with the development of a control oriented model of a catalytic silicon carbide (SiC) wall flow DPFs with CuFe2O4 loading for automotive Diesel engines. The model is intended to be used for the real-time management of the regeneration process, depending on back-pressure and thermal state. In order to ensure suitable computational demand and to realize emissions control and fuel economy objectives, the 0-D model has been developed with the aim of investigating the essential behavior of the system, such as the chemical kinetic of filtered soot oxidation, the thermal and backpressure dynamics along accumulation and regeneration processes. Parameters identification and model validation have been performed vs. experimental data measured on the engine test bench at the exhaust of a EURO 5 light-duty Diesel engine, in different operating conditions. During the accumulation process, engine speed, load and rail pressure are controlled to ensure several levels of trapped soot; on the other hand, the injections pattern, which directly affects the DPF inlet temperature, is handled during regeneration tests. The results show that the model simulates the thermal dynamics and the pressure drop across the filter with good accuracy.
D'Aniello, Federica, Rossomando, Bruno, Arsie, Ivan, Pianese, Cesare
Agglomeration and Nucleation of Non-Volatile Particles in a Particle Grouping Exhaust Pipe of a Euro VI Heavy-Duty Diesel Engine2019-01-00441/15/2019
The possibility of non-volatile particle agglomeration in engine exhaust was experimentally examined in a Euro VI heavy duty engine using a variable cross section agglomeration pipe, insulated and double walled for minimal thermophoresis. The agglomeration pipe was located between the turbocharger and the exhaust treatment devices. Sampling was made across the pipe and along the centre-line of the agglomeration pipe. The performance of the agglomeration pipe was compared with an equivalent insulated straight pipe. The non-volatile total particle number and size distribution were investigated. Particle number measurements were conducted according to the guidelines from the Particle Measurement Programme. The Engine was fuelled with commercially available low sulphur S10 diesel. Experiments conducted in heavy duty engine relevant operating points were done to sweep the effect of (i) Mass flow rate in the exhaust (ii) Temperature in the exhaust and (iii) Engine speed and thus exhaust pressure pulsation frequencies in the exhaust. The test matrix included eleven operating points at steady-state. The results show that, using the agglomeration pipe, neither significant non-volatile particle reduction nor noticeable change in particle size distribution could be proven. In the current study, nucleation of non-volatile particles could not be observed along the straight pipe. Furthermore, it was found that the variable cross-section agglomeration pipe and straight pipe showed similar results in the total particle number and particle size distribution with respect to non-volatile particles.
K, Arun Prasath, Stenlaas, Ola, Bernemyr, Hanna, Erlandsson, Anders
Water Load Determination Approach in Two Wheeler Exhaust System2018-32-007510/30/2018
Future emission norms in India (BS6) necessitates the 2 wheeler industry to work towards emission optimization measures. Engine operation at stoichiometric Air-Fuel Ratio (AFR) would result in a good performance, durability and least emissions. To keep the AFR close to stoichiometric condition, an Oxygen sensor is placed in the exhaust system, which detects if air-fuel mixture is rich (λ<1) or lean (λ>1) and provides feedback to fuel injection system for suitable fuel control. O2 sensor has a ceramic element, which needs to be heated to a working temperature for its functioning. The ceramic element would break (thermal shock) if water in liquid form comes in contact with it when the element is hot. To counter this, oxygen sensor is either fully heated only when all the water in the exhaust system is evaporated, which results in delayed closed loop control, or is capable to withstand higher amount of water in the exhaust system by for example being applied with thermal shock protection and a protective tube. It’s a challenge to control the HC emissions during first 100 seconds of engine start, as the catalyst is not functioning during this duration. Also, the system runs in open loop for first 50 seconds, as the lambda sensor is not functioning. Hence, determining the amount of water present in exhaust and having a protective layer for lambda sensor against water would enable early start of sensor functioning. The present paper explains an approach to determine the maximum water droplet size and water flow rate using a special Liquid sensor mounted in the exhaust pipe. Test cases are defined at various engine and exhaust gas temperatures to determine an appropriate set up and methodology for measurement on a 2Wheeler. The test cases are repeated on various 2wheelers available in the Indian market and influence of different exhaust configurations, mounting location of the Lambda sensor are analysed. The information of water droplet size and water flow rate are driving factors for the design and application of lambda sensor. With thermal shock protection over lambda sensor a full heater voltage can be applied to sensor even before all the water has evaporated in the exhaust system. An early sensor readiness results in a quick closed loop control of the fuel mixture thus reducing emissions.
Meena, Ranjana Kumari, Krusch, Andrea, Meister, Konrad, Holzknecht, Christopher
Nonlinear Acoustic Analysis of Loudspeakers in the Exhaust Dynamic Sound Technology2018-01-15596/13/2018
An ongoing trend among automotive exhaust suppliers is the application of loudspeakers in their systems to tailor the exhaust sound to the customers’ needs. In addition to it, undesirable engine order noise can be cancelled by a closed loop control system. Due to the high sound pressure from the engine, the loudspeaker is often required to run at its power maximum. A higher input power eventually causes a nonlinear behavior, resulting in undesirable sound pressure level or harmonic distortion. Thus, the understanding of nonlinear behavior of loudspeakers and the recognition of dominant effects are required. This paper presents the main nonlinearities of loudspeakers and the comparison of theories on linear and non-linear loudspeaker models. For validation of the model, one loudspeaker enclosure and one typical exhaust system with a loudspeaker have been calculated. Ultimately it was found that a nonlinear loudspeaker model would be essential for a precise tuning of active exhaust sound systems.
Kim, Hoi-Jeon, Schultz, Bernhard
The Measures of Improving Power Generation Stability for Harvesting Automobile Exhaust Energy2018-01-13674/3/2018
The automobile exhaust energy can be recovered by the thermoelectric module generator(TEG). Owing to the complex urban traffic, the exhaust gas’s temperature fluctuations are resulted, which means the unstable hot-end temperature of the TEG. By installing solid heat capacity material(SHCM) to the area between the outer wall of the exhaust pipe and the TEG, it is possible to appropriately reduce the temperature fluctuation, but there is still a fluctuation of the TEG’s power output. Then by adding voltage filter circuit (VFC) after the TEG, the power output stability can be improved. This research uses SHCM and VFC to improve the stability of the exhaust gas generation. Firstly, the three-dimensional heat transfer model of the exhaust pipe thermoelectric power generation system is established. The heat capacity materials with low thermal resistance and high heat capacity were selected as the research object based on previous research. Secondly, the fluctuation relationship of the exhaust temperature over time is established. Then, the effect of the VFC without SHCM method, the effect of the SHCM without VFC method and the effect of the SHCM with VFC method on the TEG power generation stability is analyzed. The results show that, by installing SHCM before TEG, TEG hot-side temperature fluctuations can be reduced, while TEG power generation stability is improved. By adding VFC after TEG, the voltage through VFC tends to be stable and can be better used by vehicle’s circuit load. By adding SHCM and VFC simultaneously, the power generation stability of the exhaust gas power generation system can be significantly improved. SHCM storages the heat energy of exhaust gas, which makes TEG produce more electrical energy. But, VFC consumed some power generated by TEG. This shows that the VFC regulator needs consuming energy to stable voltage output, so that TEG net power generation has declined.
Wang, Zongsong, Tan, Gangfeng, Xiao, Longjie, Huang, Miaohua, Yu, Houyu, Wang, Yishi, Quan, Jiakang, Huang, Shiping
High-Performance Rear- and Mid-Engine Vehicle Exhaust System Temperatures2018-01-14364/3/2018
Hot surface ignition of combustible material is a known cause of vehicle fires. Although the detailed mechanisms of hot surface ignition are highly complex, the surface temperature is known to play a crucial role in this process. There has been limited previous work in the literature on this topic, much of which has focused on engine or exhaust system surface temperatures of the most common types of passenger vehicles. Also, much of this work was done in an unrepeatable manner and suffered from measurement technique induced errors. The focus of the present work is on repeatable and low measurement technique induced error temperature measurements of exhaust system surface temperatures of rear- and mid-engine sports cars. Temperature measurements were made at several points along the exhaust systems of vehicles both with and without turbo chargers on a 5-mile oval track. The exhaust system surface temperatures were examined under conditions of transient acceleration and steady-state driving for vehicle speeds of up to 125 mph (201 km/h). Finally, the effect of engine rotation speed for a constant vehicle speed on exhaust surface temperature was examined. It was found that the exhaust temperatures of rear- and mid-engine sports cars have maximum surface temperatures that are within the range of temperatures reported in literature for passenger vehicles in the range of speeds for which comparison data exists. It was also found that increased engine rotation speed for a constant vehicle speed results in increased surface temperatures for all measured locations.
Papageorge, Michael, Colwell, Jeff
Feasibility Analysis of a Non-Intrusive Exhaust Energy Recovery System Based on the Use of Thermoelectrics2018-01-07804/3/2018
This paper presents a feasibility analysis of the use of a thermoelectric generator for the design of a non-intrusive exhaust energy recovery system. The energy recovery system is intended to be used on a light duty vehicle with naturally aspirated internal combustion engine. The non-intrusive characteristic is proposed as an exploratory work with the aim to develop an aftermarket system. The energy source for the system is the exhaust pipe wasted heat. The analysis includes as design variables the number of thermoelectric modules and their location along the exhaust system. The characteristics under analysis are fuel consumption and payload. A numerical model is developed and used to investigate the possible design scenarios. This model is composed by three sub-models. The sub models are mean value engine model, exhaust heat transfer model, and vehicle longitudinal dynamics model. Three driving cycles are used: two standard driving cycles and a real driving cycle. Two commercial technologies were evaluated, but showed negative impact on fuel consumption. Therefore, a third technology, a state of the art technology was considered with the objective to explore possible future capabilities of a high efficiency device. From the feasibility analysis, a fuel consumption reduction potential of 14% is identified for the best case scenario and 10.7% on average. In addition, the highest performance technology showed 0.8% fuel consumption reduction in the best case and 0.67% on average. From the results obtained, it was concluded that the non-intrusive thermoelectric generator is not feasible for the scenarios studied. However, state of the art technology shows capability to reach the potential fuel consumption reduction under certain vehicle operation conditions. Recommendations are given with the aim to attain higher fuel consumption reduction, refinement of models and achieve a feasible system.
Gomez Herrera, Jorge David, Munoz, Luis
An Investigation of the Transient DPF Pressure Drop under Cold Start Conditions in Diesel Engines2017-01-237210/8/2017
To monitor emission-related components/systems and to evaluate the presence of malfunctioning or failures that can affect emissions, current diesel engine regulations require the use of on-board diagnostics (OBD). For diesel particulate filters (DPF), the pressure drop across the DPF is monitored by the OBD as the pressure drop is approximately linear related to the soot mass deposited in a filter. However, sudden acceleration may cause a sudden decrease in DPF pressure drop under cold start conditions. This appears to be caused by water that has condensed in the exhaust pipe, but no detailed mechanism for this decrease has been established. The present study developed an experimental apparatus that reproduces rapid increases of the exhaust gas flow under cold start conditions and enables independent control of the amount of water as well as the gas flow rate supplied to the DPF. The results show that the sudden decrease in the DPF pressure drop is caused by the water in the developed system used here. Observations of the soot cake layers in the DPF show that the decrease in the DPF pressure drop is caused by peeling-off and separation of the soot cake layer from the walls of the DPF. An increase in the water flow rate thins the soot cake layer and decreases the DPF pressure drop. Further, numerical simulation using a DPF model developed by a research group at Waseda University was also performed, and the calculated DPF pressure drop captures the changes obtained by the experiments well.
Kobashi, Yoshimitsu, Oooka, Shun, Jiang, Lin, Goto, Jun, Ogawa, Hideyuki, Shibata, Gen
The Application of Solid Selective Catalytic Reduction on Heavy-Duty Diesel Engine2017-01-236410/8/2017
Urea SCR technology is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea SCR process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and reduces NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12°C. For preventing deposits formation, aqueous urea solution is hardly injected into exhaust gas stream at temperature below 200°C. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for control NOx emissions from heavy duty diesel engines. The solid SCR technology, using a solid metal ammine complex to store ammonia, can overcome the issues of urea SCR by dosing gaseous ammonia directly to the exhaust gas steam. In this paper, the applications of solid SCR for a CN-5 heavy duty diesel engine and a CN-4 heavy duty diesel vehicle was discussed based on engine bench tests and portable emission measurement system tests, a comparison study on NOx emission was performed with urea SCR during real world driving conditions. The results showed that the solid SCR technology could promote the deNOx performances more efficiently than urea SCR technology at low temperature conditions.
Li, Jiaqiang, Ge, Yunshan, He, Chao, Tan, Jianwei, Peng, Zihang, Li, Zidi, Chen, Wei, Wang, Shijie
DMADV Approach for Engineering Optimization and Quality - Application and Adaptability in Indian Automobile Industry2017-28-19307/10/2017
Indian Automobile Industry has started using Six Sigma for Vehicle Design and process improvement to compete with Global competition. This Paper describes how the Tools of Six Sigma shall be used as an Effective Tool for both redefining the Design and the Process Improvement. This Paper talks on the evolution of DMADV approach in Indian Automobile Industry compared to the related Trends in Other Manufacturing Sectors. The Author describes how the warranty failures in Commercial Segment Vehicle Category which was the selling talk for the Competition was addressed in Leading Indian Automobile OEM. As this Failure was adversely impacting customer satisfaction and no solution seemed forthcoming, top Management indicated to use a radically different approach to solve the problem within a years’ time. Among the different processes evaluated, DMADV six sigma approach brought in a creative approach to problem solving and improved systematic team work between the supplier, manufacturing function and R&D function, which were based in different demographic locations, with different work culture. This approach resulted in the goal of 10x warranty failures reduction being achieved within 10 months, besides monetary saving to the Organisation.
Jaswal, Anil Kumar, Chandrasekaran, Pradeep, Ramadoss, Surendran
Quantitative Analysis of Low Pressure-Driven Spray Mass Distribution and Liquid Entrainment for SCR Application through a Mechanical Patternator2017-01-09653/28/2017
The application of liquid aqueous Urea Solution (AUS) as reductant in SCR exhaust after-treatment systems is now a commonly accepted industry standard. Unfortunately, less acceptable are the associated difficulties caused by incomplete decomposition of the liquid, resulting in solid deposits which accumulate in the exhaust pipe downstream of the dosing components. The correct prediction of the spray pattern and, therefore, the spray impact on the walls is a key feature for the system optimization. A mechanical patternator, designed on the basis of CFD performance assessment, involving a Lagrangian representation of the dispersed liquid fully coupled with a 3D Eulerian description of the carrier phase, has been built and used to measure the spray mass distribution. The effect of the droplets generated from the interaction among spray, probes and contingent liquid film is taken into account in the geometrical definition of the shape and the position of the patternator, as well as the flow field modification. The whole simulation process is carried out with the open source finite volume platform OpenFOAM®. The investigation of the effect of a wide range of thermal and kinematic cross flow conditions on the behavior of a multi-hole pressure-driven injector for SCR applications has been performed in an engineless test bench at the Empa laboratories. Major focus is put on the evaluation of the complete spray footprint, which is collected with high spatial resolution to generate a reliable map of the conditions, aiming at avoiding the formation of permanent liquid film, which is undeniably the basis of solid deposit formation. A detailed parametric analysis of the liquid entrainment and of the impact location is reported to provide a concise description of the spray behavior.
Nocivelli, Lorenzo, Montenegro, Gianluca, Onorati, Angelo, Curto, Francesco, Dimopoulos Eggenschwiler, Panayotis, Liao, Yujun, Vogel, Alexander
The TEG Hot-End Heat Capacity’s Effect on the Power Output Stability for Harvesting Automobile Exhaust Energy2017-01-01603/28/2017
While the car ownership increasing all over the world, the unutilized thermal energy in automobile exhaust system is gradually being realized and valued by researchers around the world for better driving energy efficiency. For the unexpected urban traffic, the frequent start and stop processes as well as the acceleration and deceleration lead to the temperature fluctuation of the exhaust gas, which means the unstable hot-end temperature of the thermoelectric module generator (TEG). By arranging the heat conduction oil circulation at the hot end, the hot-end temperature’s fluctuation of the TEG can be effectively reduced, at the expense of larger system size and additional energy supply for the circulation. This research improves the TEG hot-end temperature stability by installing solid heat capacity material(SHCM) to the area between the outer wall of the exhaust pipe and the TEG, which has the merits of simple structure, none energy consumption and light weight. Firstly, the exhaust temperature characteristics with various driving conditions are studied for the target engine. And then the candidate material and structure size of the heat capacity materials are determined according to the internal TEG thermal resistence and the heat transfer model from the exhaust gas to TEG hot-end. For various transient conditions, three materials’ specific heat capacity and thickness are considered for studying the TEG hot-end temperature stability and the average power output. The results show that the solid capacity material significantly improves the hot-end temperature’s stability of TEG but slightly reduces the average power. However, with the increase of the specific heat capacity, the high stability of the hot-end temperature and the decrease of the average power become less significant, and with the increase of the thickness, it becomes significant at a high degree.
Xiao, Longjie, He, Tianming, Tan, Gangfeng, Huang, Bo, Ping, Xianyao
Field Failure Resolution of a Tractor Engine Exhaust System Using Constrained Single Objective Optimization and Stochastic Analysis2017-26-02331/10/2017
The tractor engine related mounting brackets are very critical due to different aspects of vehicle performance, durability and noise. These mounting bracket have been designed as a framework to support engine external parts like muffler, exhaust tail pipe, alternator etc. Vibration and fatigue has been continuously a concern which may lead to structural failure and performance issues. Various such failures are faced regularly by automotive industry and finite element based analysis are used to resolve them. The resolution is done by playing with the component thicknesses, material, by providing additional support etc. However, due to large degree of uncertainty associated with the loading, boundary conditions, manufacturing, environmental effects; still there is some probability of failure. This paper focuses on a field failure issue of an exhaust system of a tractor and subsequent concern resolution. Multiple field failures like Under Hood Muffler (UHM) lug failure and UHM mounting bracket failure were reported during different tractor applications. A finite element model was generated; static, modal and force frequency response analyses were performed and the field failures were simulated. As there were multiple failure modes, a multi-constrained single objective optimization problem was formulated and an optimum solution was obtained. To start with, few key influencing design parameters were identified, design of experiments (DoE) were conducted, a transfer function was developed and finally an optimum solution was derived. To evaluate the robustness of optimum design under uncertainty of material properties, thicknesses, exhaust temperature; a stochastic analysis were performed to find out the probability of success. No probability of failure was observed for all the objectives.
Perumal, Solairaj, Kumar, Abhay, Mahajan, Arun, Redkar, Dinesh, Balakrishnan, Sureshkumar
Powertrain Mounted Exhaust System Failure Correlation and Methodology Development in CAE2017-26-02671/10/2017
Exhaust system is one of the complex automotive systems in terms of performance and strength prediction due to combination of transient mechanical and thermal loads acting on it simultaneously. Traditionally, most of automotive vehicles have exhaust systems with hot end mounted on engine and cold end mounted on chassis or BIW through hangers. A new powertrain mounted exhaust system was developed in-house. This exhaust system underwent validation and evaluation during development phase. Durability concerns were observed on exhaust system in Track test and gear shift durability test. This paper focuses on identifying the root cause of these concerns based on the failures observed during evaluation in Accelerated Durability (ADT) and gear shift durability (GSD) tests. Based on the architecture and packaging space challenges in vehicle, engine is mounted on two mounts and a roll restrictor. Muffler, which has higher inertia, is mounted at higher offset with respect to engine rolling axis. A new transient loadcase representative of gear shift durability test was developed. The misalignments due to tolerance stacking and process variability were measured on physical assembly at catalytic converter and muffler mountings and imposed in the analysis through appropriate enforced displacement constraints. These assembly preloads act as mean load for the exhaust system. Fatigue analysis was carried out for transient loadcase with assembly preloads and the results were correlated with failure data. A new design was proposed and evaluated based on this loadcase and it has cleared validation and evaluation phase without any concern. All new powertrain mounted exhaust systems will be evaluated and verified using this loadcase in early phase of program. The overall exercise has helped to improve the prediction and robustness of exhaust system analysis.
Mohapatra, Durga Prasad, Kangde, Suhas, Londhe, Abhijit, Srikanth, N N, Singh, Pravin
Investigation of Urea Derived Deposits Composition in SCR Systems2016-01-232710/17/2016
Ideally, complete decomposition of urea should produce only two products in active Selective Catalytic Reduction (SCR) systems: ammonia and carbon dioxide. In reality, urea decomposition reaction is a two-step process that includes the formation of ammonia and isocyanic acid as intermediate products via thermolysis. Being highly reactive, isocyanic acid can initiate the formation of larger molecular weight compounds such as cyanuric acid (CYN), biuret (BIU), melamine (MEL), ammeline (AML), ammelide (AMD), and dicyandimide (DICY). These compounds can be responsible for the formation of deposits on the walls of the decomposition reactor in urea SCR systems. Composition of these deposits varies with temperature exposure, and under certain conditions can create oligomers that are difficult to remove from exhaust pipes. Deposits can affect efficiency of the urea decomposition, and if large enough, can inhibit the exhaust flow and negatively impact ammonia distribution on the SCR catalyst. This paper presents results of investigation of the deposits collected at various gas temperatures for quantification of urea and by-products of urea thermal decomposition and for their trace elements. Urea related compounds, including oligomers and elemental composition of deposits collected from a urea decomposition reactor under various exhaust conditions, are compared in the paper.
Eakle, Scott, Kroll, Svitlana, Henry, Cary
Fast Exhaust Nephelometer (FEN): A New Instrument for Measuring Cycle-Resolved Engine Particulate Emission2016-01-232910/17/2016
Soot emissions from direct-injection engines are sensitive to the fuel-air mixing process, and may vary between combustion cycles due to turbulence and injector variability. Conventional exhaust emissions measurements cannot resolve inter- or intra-cycle variations in particle emissions, which can be important during transient engine operations where a few cycles can disproportionately affect the total exhaust soot. The Fast Exhaust Nephelometer (FEN) is introduced here to use light scattering to measure particulate matter concentration and size near the exhaust port of an engine with a time resolution of better than one millisecond. The FEN operates at atmospheric pressure, sampling near the engine exhaust port and uses a laser diode to illuminate a small measurement volume. The scattered light is focused on two amplified photodiodes. Proof-of-concept tests were conducted on a heavy-duty single-cylinder research engine using a Westport high-pressure direct-injection (HPDI) natural gas fuel system. For this engine, the particulate emissions are dominated by soot at high loads, as they would be for a conventional diesel engine. When tested on the diluted exhaust, the FEN shows a close linear correlation with a commercial light-scattering instrument (DustTrakTM DRX 8533). Undiluted PM measurements close to the exhaust port show a spike (several times the average) after the exhaust valve opens; the signal then drops to a plateau for the remainder of the cycle. The magnitudes of the peak and the plateau vary by a factor of two or more from cycle to cycle, depending on the engine operating mode. Analysis of the ratio of the forward-to-backward light scattering signal indicates the emission of larger particles soon after the opening of the exhaust valve. On average, the diameter of the freshly emitted soot aggregates sampled after the exhaust valve is smaller than the diluted soot. Particle coagulation in the exhaust pipes and surge tank may explain this. Using the ratio of signals at two angles, the mass concentration at the exhaust port can be adjusted according to the Rayleigh-Debye-Gans (RDG) light scattering theory, and brought closer to the average concentrations in the diluted exhaust.
Kheirkhah, Pooyan, Kirchen, Patrick, Rogak, Steven
Optimization of Muffler Acoustics Performance using DFSS Approach2016-01-12924/5/2016
Noise pollution is a major concern for global automotive industries which propels engineers to evolve new methods to meet passenger comfort and regulatory requirements. The main purpose of an exhaust system in an automotive vehicle is to allow the passage of non-hazardous gases to the atmosphere and reduce the noise generated due to the engine pulsations. The objective of this paper is to propose a Design for Six Sigma (DFSS) approach followed to optimize the muffler for better acoustic performance without compromising on back pressure. Conventionally, muffler design has been an iterative process. It involves repetitive testing to arrive at an optimum design. Muffler has to be designed for better acoustics performance and reduced back pressure which complicates the design process even more. A hybrid type muffler is the most commonly used muffler in automotive industry and it plays an important role in noise attenuation by using a combination of impedance mismatch and absorption techniques. In this paper a DFSS approach is developed in order to optimize a hybrid muffler design for a passenger car. DFSS approach has an input, output, control factors and the noise factors for the above problem. Exhaust gas mass flow rate at different engine rpm is the input and the tail pipe noise is the output for the analysis. All the design parameters which affects the output is considered as the control factors and the temperature of the exhaust gas is considered as the noise factor since it is not controlled by the design engineer. Commercial 1D simulation software GT-POWER® is used for this analysis. L18 orthogonal array is developed in order to capture the interactions of all controls factors, its levels and noise factor. Simulation is run for the L18 array for different engine rpm and results are plotted between engine rpm versus tail pipe noise. The tail pipe noises for the different design were studied and lowest one across different rpm is selected. Critical design parameter which affects the tail pipe noise is derived from this simulation. DFSS approach adopted in this paper has provided a better correlation of simulation results with test data. The optimized design shows better acoustic and back pressure performance than the original design. Deployment of advanced software and experimental methods leads to First Time Right product development by effectively reducing valuable design cycle time and can be further used in the field of research for future vehicle programs.
Dixit, Manish, Sundaram, V, Kumar S, Sathish
Performance Characteristics of an Ammonia-Water Absorption Refrigeration System Driven by Diesel Waste Exhaust Heat2016-01-06644/5/2016
The thermal performance of an ammonia-water-hydrogen absorption refrigeration system using the waste exhaust gases of an internal combustion diesel engine as energy source was investigated experimentally. An automotive engine was tested in a bench test dynamometer, with the absorption refrigeration system adapted to the exhaust pipe via a heat exchanger. The engine was tested for different torques (15 N.m, 30 N.m, and 45 N.m). The exhaust gas flow to the heat exchanger built on the generator was controlled manually using two control valves. The refrigerator reached a steady state temperature between 10 and 14.5°C about 3.5 hours after system start up, depending on engine load. The maximum coefficient of performance was 0.10 obtained for the controlled exhaust mass flow case at torque 30 Nm after 3hrs from system startup.
Hassaneen, Ahmed E., Aly, Wael I. A., Bedair, Gamal, Abdussalam, Mohammed
Thermal Stability Research of Vehicle Exhaust Waste-Heat Recovery System with Intermediate Medium2016-01-02284/5/2016
Vehicle exhaust waste-heat recovery with thermoelectric power generators can improve energy efficiency, as well as vehicle fuel economy. In the conventional structure, the hot-end of thermoelectric module is directly connected with the outer wall of the exhaust pipe, while the cold-end is connected with the water pipe’s outer wall of the vehicle engine cooling cycle. However, the variety of vehicle engine operating conditions leads to the instability of the hot-end temperature, which will reduce the generating efficiency of the thermoelectric modules and also shorten its service life. This research is on the basis of constructing a heat transfer oil circulation, and to study the action principles and implementation methods of it. In this circulation, the heat transfer oil, as the intermediate medium, absorbs the exhaust waste heat and transfers the heat to the hot-end of the thermoelectric module steadily, which stabilizes the hot-end temperature under various vehicle engine operating conditions. The final purpose of this circulation is to improve the power generation efficiency of the thermoelectric module and prolong its service life. Firstly, the temperature and flow characteristics of the vehicle exhaust under a specific engine working condition are studied. Secondly, the dynamic model of the oil-gas heat exchanger as well as the dynamic heat transfer model of the thermoelectric evaporation module is established. Then the effect law of the waste-heat recovery system with intermediate medium on the hot-end temperature stability under the driving conditions of city road and rural road are focused in this research. Finally, with the comparison of the conventional engine waste heat recovery system, the multiple-performance analysis and evaluation of the whole system are carried out. The result shows that the heat transfer oil circulation can lower the temperature gradient of thermoelectric modules’ hot-end greatly, and stabilize the power generation status of this system though the structure of this waste heat recovery system needs additional oil pump, tubes and other components, which will increase the cost and energy consumption of the whole system,. What’s more, the power generation efficiency of thermoelectric module is improved by 10%-15%, with its working life being prolonged as well.
Han, Mengzuo, Tan, Gangfeng, Guo, Xuexun, Zhan, Ruobing, An, Xuyang, Xue, Weiye, Kang, HongBo
A Novel Approach for Flow Simulation and Back Pressure Prediction of Cold End Exhaust System2016-28-02352/1/2016
The performance of any automotive engine depends not only upon its core engine parts but also on the effectiveness of the sub-systems attached to the engine, like the intake, fuel, engine cooling and exhaust systems. The exhaust system being a critical system of any automotive vehicle plays a responsible role of improving the ride quality of the vehicle and fuel economy. The effective design of exhaust system is critical in order to ensure the required exhaust gas is exited from the engine and at the same time the noise is attenuated. In this paper a novel approach is developed in order to characterize the flow through the cold end exhaust system and reduce the pressure drop to achieve desired performance. The exhaust system attenuates the noise from the engine without deteriorating the engine performance by ensuring an optimum value of exhaust back pressure. Exhaust back pressure is one of the crucial parameters that are always scrutinized by the automotive manufactures to ensure that the engine delivers a superior performance. The cold end of the exhaust system which consists of muffler and resonator contributes a major part in back pressure. GEM3D is used as a pre-processor for Muffler and Resonator modelling. Back pressure simulation is carried out using GT-POWER® tool. The discretization of muffler and resonator shell and pipes for element generation had played an important role in the proper prediction of back pressure and thereby reducing valuable design cycle time and cost. Detailed study is carried out with different shell and pipe discretization element size and shapes. Optimum combinations are derived based on the study which correlates well with the testing. A graph is plotted between flow rate vs pressure drop. This methodology can be used in system level simulation of Exhaust system with good accuracy. This approach shall be applied for future vehicle programs at the early stage of product development.
Dixit, Manish, Sundaram, V, Sathish Kumar, S.
Study of Pressure Losses of Unsteady Compressible Flows in Three- Way Junctions2015-24-23999/6/2015
The aim of this paper is to extend the evaluation of the accuracy of published 1-D pressure loss coefficients which are used in 1-D gas dynamics models, in unsteady compressible flows propagating in the exhaust pulses in manifolds. These pressure loss coefficients were derived from the conservation of linear momentum over finite control volumes based on assumptions including steady flow. The objectives of this work were to evaluate the accuracy of the pressure loss coefficients over the type of flows generated by engine-like pressure pulses propagating in a range of three-pipe junctions. The evaluation was performed by reference to results from unsteady, compressible, 3-D Reynolds-averaged computational fluid dynamic (CFD - open source software OpenFOAM) simulations. Two of the junction branches represented the exhaust pipes from two cylinders and the remaining was the outlet pipe. All pipes had a diameter of 25mm with length ratio 1:2 between inlet and outlet. Y junctions of 30° and 60° degrees and a T junction of 60° were tested with a blow-down 1.8bar isothermal pulse at 45Hz as the inlet boundary condition. The results have shown that the temporal pressure loss ‘signal’, as calculated between stations 5 diameters away of each of the junction ends, has also the shape of a pulse. The discrepancies observed with the 1D model occur at the beginning of the pulse and during the deceleration phase for all three geometries tested. For the Y30° discrepancies also occurred in the intermediate regions leading to less satisfactory results.
Nikita, Christina, Hardalupas, Yannis, Taylor, Alexander
Prediction of Airborne Sound Transmission into the Passenger Compartment2015-01-22666/15/2015
Several of the exterior noise sources existing around a vehicle can cause airborne noise issues at relatively low frequencies. SEA, traditionally used for airborne sound issues is not suitable for the frequency range of interest. Finite Element analysis has been used. Handling of the non-reflecting condition on the outer boundary of the exterior cavity is an issue. Recently, advances have been made in several commercially available codes, which made the analysis practical. Including the poro-elastic material model for foam-based carpets is also becoming practically possible. The purpose of the current study is to investigate the practical applications of those new developments against test data, and to estimate the feasibility of using these procedures in the vehicle development projects. Measurements were carried out in a new semi-anechoic chamber at Volvo Cars. These measurements involved 3 body objects - a Body-in-Blue (BIB) sedan, a Complete Vehicle (CV) sedan and a CV wagon. The measured BIB configurations included also the ones with individual carpets. Several microphones were used outside of the bodies in order to monitor the exterior sound field. A sound source was placed initially at the exhaust pipe position. Later, more positions for the sound source were used and measurements were extended to higher frequencies. The accuracy of predictions obtained with different modeling approaches is discussed. Practical aspects of running such CAE analyses are highlighted. The feasibility of application of CAE analysis in vehicle development projects for exterior source issues is assessed.
Pietrzyk, Andrzej
Advanced Spray Impingement Modelling for an Improved Prediction Accuracy of the Ammonia Homogenisation in SCR Systems2015-01-10544/14/2015
A fast preparation of the liquid urea water solution (UWS) is necessary to ensure high conversion rates in exhaust aftertreatment systems based on Selective Catalytic Reduction (SCR). Droplet wall interaction is of major importance during this process, in particular droplet breakup and the Leidenfrost effect. A deeper understanding of the underlying mechanisms is a basic requirement to calibrate CFD models in order to improve their prediction accuracy. This paper presents a detailed literature study and discussion about the major impact factors on droplet wall interaction. Measurements of the Leidenfrost temperature were conducted and the corresponding regimes classified based on optical observations. The pre- and post-impingement spray was analysed using the laser diffraction method. Further, the validity of spray initialisation based on measurements at room temperature was verified. The Leidenfrost effect, partial droplet evaporation, droplet breakup and evaporation at the catalyst are the crucial aspects of impingement modelling. Their implementation and calibration against measurement data is presented. Sensitivity studies of single impact factors were carried out based on two exhaust systems that are representative for the spectrum of typical automotive applications. A set of operating points was used that covers the whole range of typical operating conditions. Finally, a best practice setup was derived and validated with measured ammonia distributions. With the help of the presented numerical and experimental investigations the prediction accuracy of the simulated ammonia homogenisation could be significantly increased for inherently different exhaust pipe geometries.
Smith, Henrik, Zöchbauer, Markus, Lauer, Thomas
Influence of Linear and Parabolic Elements in Structural Rigidity of Converter Mounting Brackets2015-01-13264/14/2015
Generation of discretization with prescribed element sizes are adapted to the geometry. From the rules of thumb, for a complicated geometry it is important to select the reasonable element order, shapes and size for accurate results. In order to that, this paper describes the influence of elemental algorithm of the catalytic converter mounting brackets. Brackets are main source of mounting of various systems mainly intake and exhaust in the engine. In hot end exhaust system, a bracket design plays a vital role because it has to withstand heavy structural vibrations without isolation combined with thermal loads. Bracket design and stiffness determines the whole catalytic converter system's rigidity. So, here discretization of converter brackets by linear and parabolic elements is studied with different elements types and compared. The study shows disparity in the structural accuracies of the brackets in each of elemental orders respect to the element shapes i.e. in the stiffness and resonance frequencies. For an optimized proposal it is significant to predict the accurate resonances along with desired stiffness target in less time consumption. To accomplish these, a detailed perspective is given for selection of elemental orders and shapes.
Rajadurai, Sivanandi, Mani, Guru Prasad, Raja, Kavin, Mohan, Sundaravadivelu
The Predictive Simulation of Exhaust Pipe Narrow-band Noise2015-01-13294/14/2015
A method of predictive simulation of flow-induced noise using computational fluid dynamics has been developed. The goal for the developed method was application in the vehicle development process, and the target of the research was therefore set as balancing the realization of a practical level of predictive accuracy and a practical computation time. In order to simulate flow-induced noise, it is necessary to compute detailed eddy flows and changes in the density of the air. In the research discussed in this paper, the occurrence or non-occurrence of flow-induced noise was predicted by conducting unsteady compressible flow calculation using large eddy simulation, a type of turbulence model. The target flow-induced noise for prediction was narrow-band noise, a type of noise in which sound increases in specific frequency ranges. Assuming the area of generation of flow-induced noise to be the exhaust pipe, including the complex shape of the muffler, predictive accuracy was verified under conditions that modeled measurements in steady-state flow test equipment. In order to reduce computation time while maintaining predictive accuracy, calculation methods were combined and computation times compared. This made it possible to reduce computation time by 61% against that in the initial stage of development of the method. In addition, a study utilizing multiple exhaust pipe shapes indicated that a correlation existed between the number of computation cells and computation time. The developed method has made it possible to predict the occurrence of narrow-band noise within a practical computation time.
Kanai, Katsutomo, Katsuyama, Hideki
Simulation Study of Divided Exhaust Period for a Regulated Two-stage Downsized SI Engine2014-01-255010/13/2014
The Divided Exhaust Period (DEP) concept is an approach which has been proved to significantly reduce the averaged back pressure of turbocharged engines whilst still improving its combustion phasing. The standard layout of the DEP system comprises of two separately-functioned exhaust valves with one valve feeding the blow-down pulse to the turbine whilst the other valve targeting the scavenging behaviour by bypassing the turbine. Via combining the characteristics of both turbocharged engines and naturally aspirated engines, this method can provide large BSFC improvement. The DEP concept has only been applied to single-stage turbocharged engines so far. However, it in its basic form is in no way restricted to a single-stage system. This paper, for the first time, will apply DEP concept to a regulated two-stage (R2S) downsized SI engine. By controlling the timing of the exhaust valves separately to feed the exhaust mass flow to the high-pressure turbine or the low-pressure turbine or the exhaust pipe, it is anticipated that such system could achieve even better breathing characteristics than the standard one-stage turbocharged engine. The simulation was carried out on a heavily downsized R2S turbocharged SI engine model. As the major objective of this project is to explore the gas exchange process for the DEP-based R2S downsized engine, the knock model in the system is ignored. The results showed that PMEP is significantly improved over the entire engine speed and BSFC was decreased by up to 3% with minimum modification of the original system. The system also showed the potential benefit for knock sensitivity and it is considered that by adding the knock model, there will be some more BSFC improvement.
Hu, Bo, Brace, Chris, Akehurst, Sam, Copeland, Colin, Turner, J.W.G.
Cold-end Temperature Control Method for the Engine Exhaust Heat Thermoelectric Module2014-01-23439/30/2014
To make full use of engine exhaust heat and further improve the utilization of the energy efficiency of the heavy truck, thermoelectric module is used to contribute to thermoelectric power generation. The hot-end temperature of the module varies with the engine operating condition because it is connected with the exhaust pipe. The cold-end of the thermoelectric module is mainly cooled by engine cooling system. Increasing the temperature difference between the hot-end and cold-end of the thermoelectric module is a good way to improve the thermoelectric conversion efficiency. For the poor controllability of the hot-end temperature of the thermoelectric module, this study puts forward by lowering the cold-end temperature of the thermoelectric module so as to ensure the improvement of the thermoelectric conversion efficiency. The cooling circle for the cold-end of the thermoelectric module which is independent of the engine cooling system is built. The nucleate boiling flow is adopted to strengthen the heat transfer from the thermoelectric module cold side to the cooling water. The boiling temperature of the cooling water is reduced by setting the vacuum degree of the cooling system so that the phase transition occurs in the reasonable temperature range and the heat removal capacity from the cold-end of the thermoelectric module could be enhanced. Consequently, the cold side of the thermoelectric module is decreased and the temperature stability could be effectively achieved..
Bai, Manfei, Tan, Gangfeng, Deng, Yadong, Wang, Wenying, Yan, Hui
Scope of Fe-ZSM5 Zeolite Based Urea-SCR with Fish Oil Bio-Diesel Fuel in Compressed Ignition Engine2014-01-15414/1/2014
The present consumption rates and heavy dependence on fossil fuels pose a humongous threat to the environment. The increased pollution in urban areas is already causing serious sociological, ecological and economic implications. The issue of energy security led governments and researchers to look for alternate means of renewable and environment friendly fuels. Biodiesel has been one of the promising, and economically viable alternatives. The biodiesels are reported to cause reduction in CO, HC and PM emissions. However, NOx emissions are increased in case of biodiesel in CI engine. Therefore, a Urea-SCR over Fe-ZSM5 honeycomb substrate (400cpsi) zeolite catalyst after treatment system is an effective technology to reduce emissions for biodiesel applications. Exhaust gases pass through the catalyst and reactions take place along its surface, consequently converting NOx into nitrogen and H2O. This conversion compliments the functioning of fish oil biodiesel in reducing the overall emissions. Taking a lead from this, the present study focuses on evaluation of performance and emission characteristics of a medium capacity diesel engine on blends of fish oil biodiesel and diesel employing Urea-SCR. The relationship of urea injection distance from the SCR catalyst in the exhaust pipe is also studied. Fish oil was trans-esterified with methyl alcohol to produce methyl ester. B20 blend of biodiesel was used since it balances the property differences with conventional diesel e.g. performance, emission benefits and cost. Further, B20 blend can be used in automotive engines with no major modification. To produce Urea injection in the exhaust pipe, a solution of urea (32.5%w/w) with water was sprayed using electronic injectors. Fe-ZSM5, honeycomb structure substrate (400cpsi) was used as the SCR catalyst. Fe-ZSM5 was used due to its high activity in the working temperature regime of the current paper. The fuel, F20 and diesel, were tested in CI engine, one at a time, with and, without Urea-SCR. The distance of Urea injection in the exhaust pipe was also varied and related performance and emissions were studied in each case. The results showed that the use of F20 with SCR reduces NOx as compared to the absence of SCR, without compromising on the thermal efficiency and other emissions. Also the greater distance of injection from the SCR unit has been found to be beneficial for NOx reduction.
Sharma, Shubham, Kumar, Naveen, Jain, Sambhav, Kumar, Sidhant
Study of an EGR System for Downsizing Turbocharged Gasoline Engine to Improve Fuel Economy2014-01-11994/1/2014
This paper presents a study of a cooled exhaust gas recirculation (EGR) system applied to a turbocharged gasoline engine for improving fuel economy. The use of a higher compression ratio and further engine downsizing have been examined in recent years as ways of improving the fuel efficiency of turbocharged gasoline engines. It is particularly important to improve fuel economy under high load conditions, especially in the turbocharged region. The key points for improving fuel economy in this region are to suppress knocking, reduce the exhaust temperature and increase the specific heat ratio. There are several varieties of cooled EGR systems such as low-pressure loop EGR (LP-EGR), high-pressure loop EGR (HP-EGR) and other systems. The LP-EGR system was chosen for the following reasons. It is possible to supply sufficient EGR under a comparatively highly turbocharged condition at low engine speed. It is important for knocking suppression to remove nitrogen oxides (NOx) from the EGR gas, which means using EGR gas from the catalyst downstream. On the other hand, the lower differential pressure and longer EGR route that characterize the LP-EGR system make it necessary to apply more sophisticated EGR rate control. EGR flow is generated by the differential pressure at the EGR valve, which varies according to the air flow rate, so the EGR rate can be maintained with a constant EGR valve opening. Although this principle is usable only in a steady-state condition, we have developed a new compensation control that can maintain the EGR rate even under transient conditions by estimating the pressure delay at the point in the exhaust pipe where the EGR gas is extracted. Test results showed that fuel economy was improved by as much as 5% with LP-EGR under a turbocharged condition, and the exhaust temperature was also reduced.
Takaki, Daisuke, Tsuchida, Hirofumi, Kobara, Tetsuya, Akagi, Mitsuhiro, Tsuyuki, Takeshi, Nagamine, Morihiro
Comparative Study on Performance and Emission Characteristics of Fish Oil Biodiesel and Mahua Oil Biodiesel Blend with Diesel and Diesel Fuel in a Medium Capacity Compression Ignition Employing Urea-SCR with Cu-ZSM52014-01-14994/1/2014
The present world scenario faces a serious threat from increasing dependence on fossil fuels. This has triggered the awareness to find alternative energy as their sustainable energy sources. Biodiesel as a cleaner renewable fuel may be considered as a good substitution for diesel fuel due to it being used in any compression ignition engine without any modification. The main advantages of using biodiesel are its renewability and better quality of exhaust gas emissions. In terms of emissions from biodiesel, the cause of concern continues to be the NOx emissions. Therefore, to compliment the functioning of biodiesels, Urea-SCR over Cu-ZSM5 catalyst is an effective option due to its ability to convert NOx into nitrogen and water. There has been increasing concerns that biodiesel feedstock may compete with food supply in the long term. The recent paper focuses on use of two non-edible oils mahua oil and fish oil (processed from waste produced by fish). The acid number of fish oil was found to be lower than mahua oil. Hence, the base catalyzed transesterification process was employed for production of fish oil methyl ester. On the other hand, mahua oil due to its higher free fatty acid content was esterified first and then, transesterified. B20 blend of biodiesels were used since it balances the property differences with conventional diesel e.g. performance, emission benefits and cost. Further, B20 blend can be used in automotive engines with no major modification. The present study focuses on the comparison of performance and emission characteristics of mahua oil biodiesel blends and fish oil biodiesel blends with diesel along with the employment of Urea-SCR as an exhaust treatment technology. The urea injection points have been varied along the exhaust pipe to study the dependence of distance between the engine exhaust and the SCR catalyst on the NOx emissions. The result shows the greater reduction of NOx for fish oil biodiesel and the brake thermal efficiency of fish oil biodiesel was found to be higher.
Sharma, Shubham, Gupta, Sahil, Kumar, Naveen, Kumar, Sidhant
1-D Simulation Study of Divided Exhaust Period for a Highly Downsized Turbocharged SI Engine - Scavenge Valve Optimization2014-01-16564/1/2014
Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine. While the scavenge valve feeding the latter portion of the exhaust gas directly into the low resistant exhaust pipe behaves similarly to valves in a naturally aspirated engine. By combining the characteristics of both turbocharged and naturally aspirated engines, high backpressure between the turbine inlet and the exhaust port is maintained in the blowdown phase while significant reduction of the backpressure could be achieved in the latter displacement phase. This is directly beneficial for pumping work and residual gas scavenging. Combustion phasing & stability and turbocharger efficiency could also benefit from such concept. This simulation study was carried out using a validated 1D model of a highly downsized SI engine. Two degrees of freedom including the lift and the duration of the scavenge valve were optimized to achieve minimum BSFC. The potential for higher attainable BMEP was also briefly investigated at low engine speed.
Hu, Bo, Akehurst, Sam, Brace, Chris, Copeland, Colin, Turner, James
Model Based Study of the Urea Injector's Effects on SCR of an 11 Liter Diesel Engine2014-01-15554/1/2014
Selective catalytic reduction (SCR) has become one of the primary technologies to reduce internal combustion engine (ICE) emission. The installation angle of urea injector plays an important role during the SCR process. The urea injector is often vertically mounted to the exhaust pipe for on road heavy duty truck because of its good performance and general packaging convenience, and this type of installation has been the focus of previous research. However, due to certain packaging constraints or responsiveness considerations, the injector is installed with an inclined acute angle to the exhaust pipe under some circumstance. To evaluate the underlying benefits and risks of this type of installation angle, a computational fluid dynamic (CFD) model based on the Renolds averaged Navier-Stokes (RANS) solver from AVL Fire is used to simulate the injection process of urea for an acute-angled 3-hole injector, through which, the urea spray's formation and motion, wallfilm accumulation and NH3 distribution uniformity characteristics are studied. Result shows that with an inclined injector, the sprays are blown off from the centerline of the pipe in different operating conditions that lead to an early spray impingement with pipe wall and a postponed evaporation time. An inverse gas flow region is also found near the mounting flange of the injector that entrains the wallfilm upward, accumulating thick wallfilm with high probability of crystallization that has been confirmed by previous vehicle malfunction report. In part II of this research, orthogonalization method is used to find out the optimized combination of inclination angle, circumferential angle and injector reach within the limited installation space of the vehicle. Three operating conditions are considered with different weight according to their working time on road. The orthogonalization experiment schemes are calculated by the CFD model and the optimized combination of installation parameters is found. Result shows that it can improve the injection process with both urea wallfilm area and response time reduced.
Sun, Wanyu, Wang, Shufen, Yan, Shanheng, Guo, Lei, Hou, Yuanjing
LES Multi-cycle Analysis of a High Performance GDI Engine2013-01-10804/8/2013
The paper reports the application of LES multi-cycle analysis for the characterization of cycle to cycle variability (hereafter CCV) of a highly downsized DISI engine for sport car applications. The analysis covers several subsequent engine cycles operating the engine at full load, peak power engine speed. Despite the chosen engine operation is usually considered relatively stable, relevant fluctuations were experimentally measured in terms of in-cylinder pressure evolution and combustion phasing. On one hand, despite the complex architecture of the V-8 engine, the origin of such CCV is considered to be poorly related to cyclic fluctuations of the gas-dynamics within the intake and exhaust pipes, since acquisitions of the instantaneous pressure traces at both the intake port entrance and exhaust port junction by fast-response pressure measurements over 250 subsequent engine cycles showed almost negligible differences in both amplitude and phasing compared to those within the cylinder. On the other hand, being the combustion affected by a complex chain of preceding factors (air admission during the intake stroke, variations in the residual gas fraction, generation of complex turbulent flow structures, fuel injection and dispersion in the combustion chamber and subsequent mixing, interaction between the spark discharge and the surrounding local flow pattern, etc.) a clear understanding of the actual origin of cyclic variability is far from being trivial. LES CFD simulations can therefore become a very powerful tool to help investigating the possible causes of such cyclic variations, since detailed analyses of both global and local parameters can be carried out on an almost unlimited set of available virtual measurements. In the first part of the paper, the modeling framework is presented and considerations on the adopted numerical strategy are presented, with particular emphasis on grid size, grid distribution and numerical parameters. Subsequently, LES results are analyzed and discussed in order to understand the cycle-to-cycle variations through the use of correlation coefficients between global/local flow variables in order to highlight the major causes of CCV and establish a possible hierarchy among the analyzed quantities. Finally, criticalities of the currently adopted approach and possible enhancements are briefly discussed at the end of the paper. The results presented in the paper clearly highlight the potential of the modeling methodology to help understanding the origin of CCV as well as to address possible engine optimizations to limit the cyclic dispersion.
Fontanesi, Stefano, Paltrinieri, Stefano, Tiberi, Alessandro, D'Adamo, Alessandro
Effect of Injection Parameters on Spray Characteristics of Urea-SCR System2013-01-10674/8/2013
Urea-SCR system is one of the after-treatment methods for diesel engines, which could effectively reduce the NOX emissions and enable diesel engines to meet increasingly stringent emission legislations. Within the urea-SCR system, characteristics of urea-solution spray, especially the distribution uniformity of spray droplets as well as gaseous NH₃ within the exhaust pipe, play an important role in the efficiency of catalytic reduction. In this paper, an SCR spray visualization test bench was set up. Urea-solution from a non-air-assist injector is injected into the steady stream of simulated exhaust gas flow. The transient characteristics of spray are recorded by high-speed photography. Specific spray characteristics in the original photographs, i.e., mixing distance and degree of uniformity are extracted. The influence of injection pressure and injection angle on spray characteristics are tested in different sets of experiments. Wall impingement on the inner surface of the pipe is also captured in several experiments and discussed. The experimental results reveal that: within a reasonable injection pressure range, the spray develops without impinging on the pipe wall. When the injection pressure becomes lower, the urea-solution droplet distribution shows better axial concentration uniformity. The mixing distance decreases as injection pressure decreases. Meanwhile, compared to the forward, i.e., downstream, direction of injection angle, reversing injection angle helps the spray atomize better with higher homogeneity. Injection parallel to the radial direction acquires the shortest mixing distance.
Shi, Xian, Deng, Jun, Wu, Zhijun, Li, Liguang
In-Situ Real-Time Fuel Consumption Measurement Using Raw Exhaust Flow Meter and Zirconia AFR Sensor2013-01-10584/8/2013
Fuel efficiency is one of the most important parameters in advanced vehicles. Therefore, the measurement of fuel consumption in-situ and in real-time is obviously demanded in development and evaluation processes of new engines and vehicles. This paper describes a new concept for measuring fuel consumption in real-time, which utilizing raw exhaust gas flow rate and exhaust air-to-fuel ratio (AFR). The AFR is defined as the mass ratio of air and fuel supplied to the engine, and the mass flow rate of exhaust gas can be regarded as the summation of the mass flow rate of air and fuel. This means the fuel consumption can be calculated from exhaust flow rate and AFR. To realize in-situ, real-time measurement, we used an ultrasonic exhaust flow meter which can measure a wide flow range accurately with no pressure loss, and a fast response zirconia sensor which can be installed onto the exhaust pipe directly without any sampling system. This exhaust flow-AFR method has the advantage that the real-time fuel consumption can be easily obtained without delay time by these in-situ measuring devices which can be installed at the almost same location. Integrated fuel consumption by this method showed good correlations with conventional methods, i.e. the carbon balance method and the fuel flow method. Furthermore, in the transient tests including engine start and fuel cutting operation, it showed sufficient response for real-time analysis. The results suggest that this method has a significant potential for measuring fuel consumption in-situ and in real-time.
Akita, Masanobu, Nakamura, Hiroshi, Adachi, Masayuki
The Fluid Induced Vibration Analysis on an Integrated Exhaust Manifold2013-01-09374/8/2013
With its advantages on cost and performance, the integrated exhaust manifold (casting with the turbine) is being used on more vehicles by auto makers. Generally, when compared with the divided exhaust manifold, the integrated exhaust manifold stands for higher vibratory excitation from gas dynamics. In this paper, the gas dynamics excitation has been computed through the GD (gas dynamics) software GT-Power which calculates the exhaust pipe surface pressure, and CFD code Star-CCM+ which calculates the turbine blade force. And the response of manifold has been solved under this excitation. On the other hand, the mechanical excitation has been computed through the MBD (multi-body dynamics) platform AVL-Excite-PU, and the responses under the gas excitation plus the mechanical load have been studied in order to analyze the effects of the fluid excitation on an integrated manifold. The results show that the pressure fluctuation has more energy input than blade force, but both of them are negligible to the exhaust manifold vibration.
Deng, BangLin, Liu, Jingping, Feng, Renhua, Zhang, Daming
Investigations on the Tail-Pipe Emissions of Commercial Engines with Advanced One-Dimensional Simulation Methods2013-01-11174/8/2013
Current commercial vehicles' engines are complex systems with multiple degrees of freedom. In conjunction with current emissions regulations manufacturers are forced to combine highly developed engines with complex aftertreatment systems. A comprehensive simulation model including the engine and aftertreatment system has been set up in order to study and optimize the overall system. The model uses a phenomenological spray combustion model to predict fuel consumption and NO emissions. In addition physical models for the material temperatures and the reaction kinetics were generated for the aftertreatment system. Steady state and transient measurements were used to calibrate the engine as well as the aftertreatment model. The aim for a system-level optimization was a reduction of fuel consumption while meeting emission standards. Different parameters influencing the overall process of engine and aftertreatment have been chosen for optimization with parameter variations and the DoE method. Different configurations regarding length and insulation of the exhaust pipes have been studied and the best possible solution for reduction of NOx emissions has been evaluated. EGR temperature directly influences the engine process. The influence of EGR temperature on the overall process has been evaluated and the potential of reduced EGR temperature could be shown. Another important factor for the reduction of NOx is the volume of the catalyst brick which has been varied and optimized together with engine operating parameters using the neural-network-based model. Finally, reduced fuel consumption could be found taking into account emission restrictions.
Forsthuber, Friedrich, Krenek, Thorsten, Marinitsch, Franz, Lauer, Thomas, Weiss, Joachim, Raup, Markus, Schatzberger, Thorolf
Design Optimization of an Emissions Sample Probe Using a 3D Computational Fluid Dynamics Tool2013-01-15714/8/2013
Emissions sample probes are widely used in engine and vehicle emissions development testing. Tailpipe bag summary data is used for certification, but the time-resolved (or modal) emissions data at various points along the exhaust system is extremely important in the emission control technology development process. Exhaust gas samples need to be collected at various locations along the exhaust aftertreatment system. Typically, a tube with a small diameter is inserted inside the exhaust pipe to avoid any significant effect on flow distribution. The emissions test equipment draws a gas sample from the exhaust stream at a constant volumetric flow rate (typically around 10 SLPM). The sample probe tube delivers exhaust gas from the exhaust pipe to emissions test equipment through multiple holes on the surface of tube. There can be multiple rows of holes at different axial planes along the length of the sample probe as well as multiple holes on a given axial plane of the sample probe. In a traditional sample probe design, there are multiple planes of holes along the length and several holes evenly distributed on a given plane with a constant hole size. It was observed that the exhaust gas sample composition detected utilizing a traditional sample probe design may not accurately represent the gas composition in the exhaust system especially for samples taken from a larger diameter exhaust pipe. In this study, a systematic numerical investigation was conducted to characterize the mass flow distribution for different emissions sample probe designs used in 3.5\mi and 8\mi exhaust pipe applications. First, the numerical investigation focused on the effects of the number of holes in each axial plane (or row along the circumference on the tube surface) and on the number of rows of holes (along the tube length). Next, the effect of location and orientation of the sample holes, as well as exhaust mass flow rate effects were studied. Then, the effect of sample hole size on sample mass flow rate distribution along the length of the emissions sample tube was investigated. In the end, the sample hole sizes were optimized for both 3.5\mi and 8\mi diameter exhaust pipe applications. Numerical results showed significant improvement in the mass flow rate distribution as the number of holes on a given axial plane in an emissions sample probe tube was reduced from 3 holes to 1. An improvement in the mass flow rate distribution was also found when the number of rows along a column was reduced. Additionally, for a longer sample probe tube in a large diameter exhaust pipe (8\mi), sample probe tube diameter also plays an important role in achieving uniform mass flow rate distribution.
Zhang, Xiaogang, Tennison, Paul, Yi, Jianwen, William, Ruona
Determining Soot Distribution in the Vehicle Exhaust Downstream of a Faulty Diesel Particulate Filter2013-01-15624/8/2013
New emissions certification requirements for medium duty vehicles (MDV) meeting chassis dynamometer regulations in the 8,500 lb to 14,000 lb weight classes as well as heavy duty (HD) engine dynamometer certified applications in both the under 14,000 lb and over 14,000 lb weight classes employing large diameter exhaust pipes (up to 4″) have created new exhaust stream sampling concerns. Current On-Board-Diagnostic (OBD) dyno certified particulate matter (PM) requirements were/are 7x the standard for 2010-2012 applications with a planned phase in down to 3x the standard by 2017. Chassis certified applications undergo a similar reduction down to 1.75x the standard for 2017 model year (MY) applications. Failure detection of a Diesel Particulate Filter (DPF) at these low detection limits facilitates the need for a particulate matter sensor. With the active sensing elements of the particulate matter (PM) sensors extending less than ½″ into a 4″ ID exhaust pipe, the question arises of where to locate the PM sensor to ensure it sees a properly mixed exhaust stream. Packaging and warranty requirements dictate the sensors be located near the outlet of the DPF cone, but generic fluid dynamics requirements dictate ten tube diameters after the outlet of the DPF cone. Experiments were conducted at the Ford Motor Company's Vehicle Emissions Research Laboratory on a medium duty vehicle (chassis certified application) with a diesel engine and an aftertreatment system containing a diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) catalyst, and a diesel particulate filter (DPF) utilizing both artificial and induced actual DPF faults. Several downstream DPF axial locations were selected at distances between 5 times and 18 times the diameter of the exhaust pipe from the DPF outlet. Real time PM measurements were performed at multiple sample points of each axial location (soot plane) to map out the PM distribution in the exhaust pipe. As part of this series of experiments a few DPF failures initiated during drop-to-idle (DTI) DPF regeneration were monitored with PM instrumentation. Additionally, Computational Fluid Dynamics (CFD) analyses were performed to predict mixing efficiency of the PM at each of the axial locations of the exhaust system. Both experimental and computational data will be presented.
Tennison, Paul, Szente, Joseph, Loos, Michael, Korniski, Thomas, Zhang, Xiaogang
Design of Durable Vanadium - SCR Catalyst Systems for Heavy - Duty Diesel Applications2013-26-00491/9/2013
The emission regulations for mobile applications become stricter in Euro-IV to Euro-VI levels. Carbon monoxide and hydrocarbon can be removed by efficient Diesel Oxidation Catalysts (DOC) but Particulate Matter (PM) and NOx are more demanding requiring the use of active methods (urea-SCR and DPF) which will be world-wide implemented in the 2010's. Durable, coated V-SCR catalysts are based on stabilized raw materials and tailored preparation methods. Coated V2O5/TiO2-WO3 catalysts (ceramic 300/400 cpsi and metallic 500/600 cpsi) were evaluated by laboratory and engine bench experiments. Traditional V-SCR catalysts are durable up to about 600°C and have a high efficiency at 300°C-500°C. SCR activities were tailored to be higher also at 200°C-300°C or 500°C-600°C. The use of thermal stabilizers or the vanadium loading variation enabled the changes in operation window and stability. The stabilized V-SCR catalyst kept the SCR activity also after ageing at 600°C-650°C when the reference lost partly the activity. NOx conversions (DOC+SCR, 300 cpsi ceramic) without NH3 slip were above 95% in steady engine points (250°C-530°C, 19.000-51.000 h−1). DOC with a low Pt loading (25 g/cft) was efficient to reach target NO2 promotion (>30% NO2 at 250°C-300°C) needed at low temperatures. The promotion by hydrolysis catalysts on SCR was demonstrated by full and partial flow designs. The development for hydrolysis catalyst coating resulted in lower HNCO formation and better SCR selectivity. The NOx conversions with defined NH3 slip (<10-20 ppm) by catalyst volumes and controlled urea dosing were used for dosing strategy design over the life-time (>500.000 km) of the system. The target NOx conversion (80%-95%) has a crucial effect on required catalyst volumes and dosing strategy marginal, which principles were analyzed based on urea-dosing experiments.
Maunula, Teuvo, Viitanen, Arto, Kinnunen, Toni, Kanniainen, Kauko
Cord-Reinforced Composite Exhaust Hangers for Optimizing NVH, Durability and Positioning in Automotive Applications2012-01-08034/16/2012
In connecting an exhaust pipe system to the body of a vehicle, a compromise between a soft attachment for good noise, vibration and harshness (NVH) behavior and a rigid attachment for optimum exhaust system positioning and hanger life is necessary. Classical exhaust system hangers, made entirely of rubber, cannot meet these conflicting requirements. Technology using reinforcement cording and woven fabric scrim has been used in automotive tires for many years, and scrim-reinforced rubber has been used in coolant hoses, steering couplings (“rag joints”), simple exhaust pipe isolators/hangers and other components. The presented research has culminated in a new technology in exhaust system hanger solutions comprised of a composite elastomeric rubber material reinforced with laid-in directional polyester cording. This approach in exhaust system hanger design offers development engineers the possibility of providing anisotropic and tunable stiffness characteristics to meet NVH requirements while accommodating compact size, high strength and high durability for system positioning and hanger life requirements. These findings are illustrated with physical test and analytical results, including a vibrational movement analysis of an exhaust unit relative to the car body, as well as comparison of acoustic measurements made inside the passenger compartment. A stiffness comparison between classical rubber hangers and cord-reinforced composite hangers will be illustrated by means of quasi-static bench test results.
Reihle, Joachim, Steinmaier, Klaus, Hahn, Ernst, Parker, Donald
Use of Heat Reflective Coating for Vibration Insulation Rubber Parts in Automotive Applications2012-01-11824/16/2012
Vibration insulation rubber parts are used in automotive applications to meet noise, vibration, and harshness (NVH) requirements. Some of these parts are located in high heat areas in the engine bay or near the exhaust pipe. Often, the parts need to be protected from heat to reduce material degradation, decrease in NVH benefit, and part failure. A number of methods are used to lower the part temperature. Layout, material change, and part shielding are common methods. Each of these methods has its own positives and negatives. A heat reflective coating was developed for use on these parts to provide an additional option to lower the part temperature. The coating is applied to the surface of the rubber to protect against radiant heat. It can match the elongation of the substrate rubber without impacting durability or the static and dynamic properties. The use of a heat reflective coating provides a reduction of the rubber substrate surface temperature in a laboratory setting using radiant heat as well as during on-vehicle testing.
Baumbarger, Michael A.
Hydrotreated Vegetable Oil and Miller Timing in a Medium-Speed CI Engine2012-01-08624/16/2012
The objective of this paper is to analyse the performance and the combustion of a large-bore single-cylinder medium speed engine running with hydrotreated vegetable oil. This fuel has a paraffinic chemical structure and high Cetane number. These features enable achievement of complete and clean combustion with different engine setups. The main benefits are thus lower soot and nitrogen oxides emissions compared to diesel fuel. The facility used in this study is a research engine, where the conditions upstream the machine, the valve timing and the injection parameters are fully adjustable. In fact, the boundary conditions upstream and downstream the engine are freely controlled by a separated supply air plant and by a throttle valve, located at the end of the exhaust pipe. The injection system is common-rail: rail pressure, injection timing and duration are completely adjustable. The gas exchange system consists of electro-hydraulic actuators, used for controlling the intake and exhaust valve timing. Using the flexibility of the engine parameters, several configurations have been tested to realize different in-cylinder conditions before the combustion: the compression temperature and the exhaust fraction have been changed by modifying valve timing and boundary conditions. The in-cylinder compression pressure and the injection parameters have been kept unchanged. The results are promising and show the benefits of hydrotreated vegetable oil compared to diesel fuel. NOx emissions have been reduced almost by 50% running with hydrotreated vegetable oil and opportunely tuned valve timing. Among all the other values, fuel consumption and soot values do not increase appreciably.
Imperato, Matteo, Sarjovaara, Teemu, Larmi, Martti, Tilli, Aki
Development of Unified Exhaust System Supported by CAE Software Programs2010-36-047310/6/2010
In spite of the changes in vehicle performance, one of the current challenges is to get components applicable to different vehicles with no changes in the project. Simulations made with specific numerical programs enable this process of unifying components, for different platforms, to be applied to the exhaust system. The projects proposed, based on the results obtained with the simulation programs, were tested experimentally. It was proven that the results of the simulation proposals correlated to the experimental results. This ultimately provided simplification to the project, with gains in logistics and productivity. Besides the technological process involved, possibilities to reduce costs can also be considered.
de Oliveira, Anderson Ricardo, da Silva Moura, Marcio, da Silva de Amorim, Osmar, de Oliveira Silva, Ricardo
Steady-State and Transient Motor Vehicle Exhaust System Temperatures2009-01-00134/20/2009
One of the known causes of motor vehicle fires is hot surface ignition of combustible material that contacts engine exhaust system components. While ignition is a complicated phenomenon, the temperature of the surface is known to be an important parameter. However, little data is available in the literature concerning exhaust system temperatures, and much of this data is confounded by thermocouple attachment techniques and undocumented variations in driving conditions. In the present study, engine exhaust system temperature measurements were conducted using six test vehicles on a level, 2-mile oval test track at constant vehicle speeds ranging from 0 (idle) to 70 mph. By normalizing transient temperature curves with these steady-state temperatures along with ambient temperature, the rates at which the exhaust system components warm up and cool down are also compared. The effect of thermocouple mounting technique was evaluated by conducting identical testing with the thermocouples located at identical locations on the exhaust system but with two different mounting techniques, namely hose clamps and welding.
Colwell, Jeff D., Biswas, Kaushik
Waza (Skilled Craftsmanship) that Created RA272 Exhaust Pipe used in Formula 1 Race in 1960's2008-01-05474/14/2008
This study attempted to faithfully reproduce and scientifically analyze the process of formation of the exhaust pipe of the winning RA272 engine used in Formula One in the 1960's, using the waza (skills) employed in its fashioning, which have been handed down by its makers. This analysis showed that the manual bending method, used to create the RA272 exhaust pipe, which was filled with sand and bent while being flame-heated, without the use of figures or molds, was superior to the mechanical bending method of that time, from the standpoint of short-term period of production. We have determined that the pipe displays that the microstructure of the material remains stable, even at exhaust temperatures of 700°C to 900°C, and that useful information on the pipe's shape stability and mechanical strength has been provided.
Ueda, Koji, Takahashi, Ryuichi, Konno, Osamu
Application of Exhaust Pipe Restriction Technique to a Small Two-Stroke Engine2007-32-003210/30/2007
A simple method to reduce HC emissions caused by fuel short-circuiting in a two-stroke engine is to apply a certain restriction to the exhaust gas flow in the exhaust pipe. This technique, developed for motorcycles, vehicles and outboards, has been applied to a small off-road two-stroke engine with a constant speed operating condition. In order to assess the feasibility and effectiveness of this technique for the reduction of HC and CO emissions in such an engine, a butterfly valve was installed in the exhaust pipe next to the exhaust port. Based on test results using the butterfly valve, a cylindrical restrictor was developed to generate various restrictions to the gas flow in the exhaust pipe and consequently reduce the fuel short-circuiting. The effectiveness of the restrictor on emission reduction was further improved by leaner air/fuel mixture. The experimental results showed improved engine performance including the best 24% reduction of total weighted HC and 25% reduction of total weighted CO when the exhaust pipe restriction was 50%. Additionally, Mota, a two-stroke engine simulation program, was used to simulate the engine performance with reduced diameter of the exhaust pipe. The outcomes of this simulation support and explain the experimental results.
Watson, Finlay Llewyn, Hong, Guang
Analysis for suitability of Loop and Cross Scavenged System for Stratified Charged Engine2007-24-00649/16/2007
The results obtained with Loop & Cross scavenged systems reveal that during early charging period the scavenged through losses are more in loop scavenged system in comparison to cross scavenged and in later part both shows considerable improvement still the probability of trapping of charge in cross scavenged are higher. Therefore stratification of charge helps in reducing the loss of fuel in both the system. But in case of cross scavenged system due to better trapping characteristics throughout the scavenging process leads to improved combustion too. Cross scavenged system employed with dual intake system shows reduction in fuel of the order of 26% & 29.7% for 40% & 50% flow through AASL, whereas, loop scavenged system shows 12.85% & 14.4% for the same flow through AASL.
Berwal, A. K., Gupta, V. K., Saxena, Mukesh
Items per page:
1 – 50 of 135