DESIGN OF EXHAUST MANIFOLD TO IMPROVE PERFORMANCE OF IC ENGINE- A REVIEW

Transcription

1 International Journal of Recent Innovation in Engineering and Research Scientific Journal Impact Factor by SJIF e- ISSN: DESIGN OF EXHAUST MANIFOLD TO IMPROVE PERFORMANCE OF IC ENGINE- A REVIEW Sachin G. Chaudhari 1, Prof.P.N.Borse 2 and P.S.Nikam 3 1 M.E. student, SGDCOE, Jalgaon.(MS),India. 2 Asso. Professor, Mechanical Engg. SGDCOE, Jalgaon.(MS),India. 3 Trainee at Hindusthan Aeronautics Limited Nasik Division (MS),India. Abstract- In internal combustion engines, exhaust system plays a vital role in the improvement of the combustion efficiency. A good conditioned exhaust manifold increase the performance of the engine. This paper is focused on reducing the backpressure in the exhaust manifold to increase the combustion efficiency using experimental analysis and CFD analysis. Exhaust manifolds collects the exhaust gases from the engine cylinders and discharge to the atmosphere through the exhaust system. The engine efficiency, combustion characteristics would depend upon how the exhaust gases were removed from the cylinder. The design of an exhaust manifold for the internal combustion engine depends on many parameters such as exhaust back pressure, velocity of exhaust gases etc. Keywords - Backpressure, CFD analysis, Exhaust Manifold, Internal Combustion Engine. I. INTRODUCTION The exhaust system of an IC engine has a significant influence on the global engine operation. Among the different component of the system the exhaust System has a paramount relevance on the gas exchange process. Though the intake system is dominant on the cylinder filling process, the exhaust system is able to influence the gas exchange process in several aspects, like the piston work during the exhaust stroke, the short-circuit of fresh charge from the intake into the exhaust and even the filling of the cylinder. In this sense, the most influential boundary condition imposed by the system is the pressure at the valve and especially the instantaneous pressure evolution. The mean backpressure is determined mainly by the singular elements, such as the turbine, the catalytic converter and the silencer. The instantaneous pressure evolution imposed by the system at the exhaust valve depends essentially on the layout and dimensions of the pipes, therefore an adequate design of the system geometry can improve the engine power and efficiency, and reduce the emissions of pollutants. Exhaust system design parameters are 1) Minimum possible resistance in runners. 2) Properly design of System geometry to reduce the pressure drop. 3) Eliminate the unnecessary turbulence & eddies in the System. II. PROBLEM DEFINITION Traditional manifold optimization has been based on tests on Exhaust Manifold. This trial & error method can be effective but is very expensive & time consuming. Beside this method cannot provide any information about the actual flow structure inside the manifold. This vital information can be obtained using 3-D CFD analysis. The design engineers can study the flow structures & understand whether a particular manifold performs correctly or not. The steady state analysis was performed in ANSYS Fluent, from this we can get the flow structure, pressure drop etc. higher the pressure drop higher will be the back pressure and there is power loss due to back pressure since piston has to overcome this pressure. So ultimate goal is to reduce the pressure drop in the manifold and make the necessary geometry changes. III. PROPOSED METHODOLOGY The objective of present work is to development of four strokes IC Engine exhaust manifold. CFD analysis results are validated by experimental results. After modification of geometry, pressure drops are calculated for each geometry. The geometry is found, which gives least pressure drop. rights Reserved Page 41

2 results for the different geometry are validated by experimental results with the help of test rig and suitable instrumentation IV. EFFECTS OF BACK PRESSURE Backpressure usually refers to the pressure exerted on a moving fluid by obstructions against its direction of flow. The average pressure in the exhaust pipe during the exhaust stroke is called the mean exhaust pressure and the atmospheric pressure is called the ambient pressure. The difference between these two pressures is defined as backpressure. IC engine causes emissions in the environment; some of them are harmful for human being. Exhaust systems including catalytic converter, muffler and resonator in engine reduce the engine emissions. Increase in exhaust back pressure decreases nitric oxide, due to the increased exhaust gas remaining in the cylinder, as has also been demonstrated by others. Hydrocarbon emissions are also reduced as exhaust back pressure is increased. Long term application of the system causes significant effect on engine performance and emissions. Particulate matter and other exhaust product adhere with flow passage of exhaust systems and the passage is reduced and backpressure is building up on the engine. The performance and emissions of a IC engine can control by backpressure. Excessive backpressure in the exhaust system create excessive heat, lower engine power and fuel penalty in the engine cylinder, that may cause damage of the engine parts and poor performance. The amount of power loss depends on many factors, but a good rule-of-thumb is that one inch (25.4 mm) of mercury backpressure causes about 1.0% loss of maximum engine power. Hence, backpressure can be used up to a certain level to improve the engine performance and reduce emissions. An experimental investigation was performed at RUET, Bangladesh to obtain the allowable level of backpressure for which, there is no significant change in engine performance and fuel penalty. Its effect on exhaust emissions including odour was also investigated. Backpressure is one of the common problem associated with the exhaust manifold. The literature review reveals that the lots of work have been done for the improvement of the exhaust manifold in order to improve the working of the engine. CFD method reduces the cost of manufacturing and production time. Literature review shows that lots of exhaust manifold study have been done using the CFD technique. Some of the literature review are as follows. V. LITERATURE REVIEW Mohd Sajid Ahmed has designed five models using the computer aided drawing software. The five models are analyzed using commercial CFD tool. The models are prepared and discretized using CFD-Grid generation tool. In the model 1 shape of the inlet has been modified from straight inlet to convergent inlet, In model 2 outlet of exhaust manifold is modified from converging outlet to divergent-straight-convergent outlet, In model 3 the divergence length of the outlet is increased and convergence length is decreased, In model 4 the divergence length of the outlet is decreased and the convergence length is increased, In model 5 the divergent area and convergent area of the outlet are kept equal and straight area is decreased. In his work, different exhaust manifolds are analyzed with the help of commercial CAE software and flow of exhaust is observed and velocity and pressure distribution along the length of exhaust manifold is obtained through simulation. Five different models designed and results were analyzed through CFD Post processing. The use of different shapes of exhaust manifold helps in easy flow of exhaust. And he conclude that, Model 5 facilitates easy flow of exhaust without recirculation and low backpressure at the exhaust outlet in comparisons with all other models. Turbulence kinetic energy is almost zero in the model 5 and hence the exhaust flows easily. Velocity at the outlet of model 5 is more and hence the backpressure reduces considerably. The optimum design for a exhaust manifold is Model 5 with bar back pressure and outlet velocity 12.5m/s. Available Online at : Page 42

3 The minimum backpressure and higher exhaust velocities are achieved by using exhaust manifolds with reducers, thus also reducing emissions. Paulduray Seeni Kannan, in his experimental work he was supplemented by a comprehensive theoretical analysis that included a detailed simulation code of design and optimization of the engine, which is specially developed, taking into account the engine performance. GT-Power6.2 computer simulation techniques were adopted not only to gain an indepth understanding of the one dimensional unsteady flow character that occurs during the scavenging and exhaust processes, but also for development of the Y-section exhaust system so as to enhance engine volumetric efficiency over a wider speed range. The higher volumetric efficiency obtained with the Y-section exhaust manifold could allow a substantial enhancement of brake mean effective pressure in the low and medium speed range, with a significant improvement. Comparison and careful observation of the experimental and theoretical results facilitate to investigate the phenomenon further, proving insight into many interesting aspects of mass flow rates and valve lift when the engine operating conditions are concerned. Peter Hield,The Ricardo Wave engine modelling software has been used to examine the effect of increased back pressure on a turbocharged diesel engine. Steady state and varying back pressure are considered. The results show that high back pressure has a significant adverse effect on the operation and reliability of the engine. The response to fluctuating back pressure is strongly nonlinear, and depends on the amplitude and period of the fluctuations. For a constant output load, the exhaust gas temperature increases significantly with increasing back pressure, leading to reduced engine reliability. Due to the speed control strategy used on this engine, speed fluctuations are an unavoidable consequence of imposed back pressure fluctuations.in his study he found that, As the back pressure increases, the engine must work harder to pump the gases out of the cylinder against the higher pressure. The pressure ratios across the turbocharger compressor and turbine decrease, reducing the mass flow of air through these components and thus the air available to the engine. At the same time, the fuel flow must increase to provide the extra power necessary to overcome the increased pumping losses while maintaining a constant brake power output. As a result the brake specific fuel consumption increases above that for an engine operating in atmospheric conditions. The response of the engine to dynamic back pressure variations is strongly non-linear, and depends on the engine speed, the load torque, the mean back pressure and the amplitude and period of the fluctuations. The majority of the non-linear effects are due to the turbocharger. The compressor and turbine operating points describe distorted ellipses approximately centred on the steady state operating point. This is due to the inertia of the rotor. The shapes of the orbits follow the shapes of the compressor and turbine maps, and the distortion becomes increasingly pronounced as the amplitude of the fluctuations increases. The engine speed governor responds to changes in engine speed and adjusts the fuel flow to maintain constant speed. However, it has a finite response time, and is only able to adjust the fuel flow after a change in speed has occurred. As a result, with this engine control strategy, fluctuations in engine speed are an inevitable consequence of fluctuations in the back pressure. The exhaust gas temperature increases significantly with increasing back pressure due to the increased power required (to overcome the additional pumping work) and the reduced air flow. In addition, imposed back pressure fluctuations cause large exhaust temperature fluctuations, which further increases the maximum temperature and also induces thermal cycling. These effects lead to increased wear and reduced reliability, and can cause thermal failures. Ricardo Wave provides a powerful tool for investigating the behaviour of engines under varying back pressure conditions, and the software also has the capability to model engine control systems, allowing the development of control strategies to mitigate the effects of the varying back pressure. However, an experimental program is required to provide validation of the model before the results obtained can be relied on. Twinkle Panchal, Research work on designing of exhaust system design based on heat transfer computation had performed in According to their research the exhaust gas flow in the Available Online at : Page 43

4 exhaust system is unsteady and compressible. The flow condition at each location is described by three independent parameters, namely velocity, density and back pressure. The following exhaust system design parameters they had optimized to get appropriate flow. Exhaust manifold material, thickness and insulation Exhaust manifold and downpipe design (geometry) Position of catalytic converter in gasoline engines Position of particulate trap in Diesel engines Research on optimal design of automobile exhaust system had done in The newly designed exhaust manifold shows lower back pressure which ultimately results better performance of the engine. They concluded that by reducing the angle of bend pipes, the back pressure reduced so that the exhaust gases removed easily from the engine cylinder and thus gave better breathing capability to the engine. The Effect of Exhaust Manifold Design on the Motorcycle Gasoline Engine Combustion Characteristics was examined. They had proved that the engine s volumetric efficiency can directly affect the engine s output and the emission levels. This research was done to modify the intake and exhaust manifold to understand the pipe boundary layer effects on the air s resistance entering the engine and the engine performance. These improved designed of intake and exhaust manifold resulted in good volumetric efficiency and lower back pressure. They concluded that the back pressure in the exhaust pipe can severely affect the intake flow characteristics. The research on optimization of exhaust system parameters for fuel economy improvement of small gasoline engine was done in The effects of exhaust pipe length and exhaust valve timing on the fuel economy performance of small gasoline engine were investigated based on thermodynamic cycle simulation. The calculation results demonstrated that the exhaust pipe length and exhaust valve timing exert great influences on the engine efficiency, mean pressure loss for gas exchange and indicated specific fuel consumption. Jae Ung Cho,In his study, the following results are obtained through the analyses of the thermal stress and the flow in cases of two forms of turbo diesel engine exhaust manifolds. 1) Model 1 shows the largest deformation of mm at the curved part of the entrance where the exhaust gas of cylinder enters. Model 2 shows the largest deformation of mm, at the same part. 2) At the equivalent thermal stress levels of model 1and mode 2, at the inner entrance of flange, jointed with the manifold and the entrance through which the exhaust gas of each engine's cylinder enters, the highest stress levels of MPa in model 1 and MPa in model 2 at the same part was shown. 3) The difference of velocity at the entrance and the exit are 14,993m/s in model 1 and m/s in model 2. The pressure drop of model 1 was 500Pa and of model 2 was 700Pa. 4) By the analysis result of thermal stress, model 1 showed smaller deformation, less thermal stress, and less pressure difference than model 2, the manifold of model 1 has more superior performance than that of model 2. 5) If these analysis results are applied to the manifolds with the turbo diesel engine to be designed later, it is thought that the products with the improved thermal characteristics, structural durability and engine performance can be developed. Xiaomao Zhang, Low flow resistance of exhaust port benefit exhaust gas scavenges from the cylinder which can decrease pump loss and fuel consumption. Available Online at : Page 44

5 "Fig"1. Geometry of Conception and Optimization Exhaust Port. The steady state flow test shows that the flow coefficient of the conception exhaust port locates medium level and the resistance can decrease through the optimization design. Figure shows the geometry difference of conception and optimization exhaust ports. The shape of optimization exhaust port is smoother than the conception exhaust port. The port test results shown as Figure 6 indicate that the flow coefficient of the optimization port increase 10% or so in comparison with the conception port at typical exhaust valve lift that is equal to 0.35 minimum exhaust valve inner seat diameters. Atul A. Patil, has studied that increase in inlet cone angle increases the pressure of the flow which leads to reduce the recirculation zones. Experimental setup of the diffuser with different angles i.e.22.5, 45, 90 degree is design and fabricated. With the help of C.I. engine test rig and suitable instrumentation different parameters pressure, temperature, mass of exhaust gases is determined. The exhaust gases from an optimal sized engine currently used, to convert available Kinetic energy and enthalpy of exhaust gases into the pressure energy for useful after treatment of exhaust gases. This pressure is being used and sent through diffuser which reduces the back pressure. Installation of the EDS III increases the brake thermal efficiency and decreases the backpressure. VI. CONCLUSION This work has presented a powerful method to evaluate exhaust system performance. Traditional method of analysis by experiments is time consuming and expensive. Also it does not give the flow structure. CFD simulation is a powerful method to give flow structure, pressure variation in the flow domain. CFD results are experimentally validated for analysis. From the results of it we are getting the flow structure. According to these results geometry is modified. Analysis is carried out on each modified geometry. The geometry, which gives minimum pressure drop and hence minimum backpressure and increased velocity, is the necessary geometry. REFERENCES [1] Atul A. Patil, Experimental Verification And CFD Analysis Of Single Cylinder Four Strokes C.I. Engine Exhaust System, Pratibha: International Journal Of Science, Spirituality, Business And Technology (IJSSBT), Vol. 3, No. 1, Dec [2] Mohd Sajid Ahmed, Design And Analysis Of A Multi-Cylinder Four Stroke SI Engine Exhaust Manifold Using CFD Technique, Volume: 02 Issue: 09 Dec-2015 [3] Twinkle Panchal, Effect of Exhaust Back Pressure on Exhaust Emissions by Altering Exhaust Manifold Position, International Journal of Emerging Research in Management &Technology ISSN: (Volume-3, Issue-11). [4] Peter Hield, The Effect of Back Pressure on the Operation of a Diesel Engine, Maritime Platforms Division DSTO Defence Science and Technology Organisation 506, Lorimer St Fishermans Bend, Victoria 3207 Australia. [5] Paulduray Seeni Kannan, Design strategy for six-cylinder stationary diesel engine Exhaustsystems,STROJN ICKY CASOPIS, 59, 2008, ˇC. 1 [6] Jae Ung Cho,A, Study on Flow Analysis of the Exhaust Manifold for Automobile, International Journal of Applied Engineering Research ISSN Volume 11. Available Online at : Page 45

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