Exhaust Gas Waste Heat Recovery and Utilization System in IC Engine

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1 IJIRST International Journal for Innovative Research in Science & Technology Volume 1 Issue 11 April 2015 ISSN (online): Exhaust Gas Waste Heat Recovery and Utilization System in IC Engine Alvin P Koshy Jeffin Easo Johnson Bijoy K Jose K Navaneeth Krishnan Bijeesh P Associate Professor Abstract Most of the heat energy released from the fuel of an internal combustion engine is wasted to the environment. This is a serious issue in this world of depleting fuels. So an effort is made to recover the heat wasted from the exhaust gas of an internal combustion engine. If the heat wasted out through the exhaust gas is utilised, we can improve the efficiency of the engine to some extent. There are a lot of research works in the field of waste heat recovery systems. Many succeeded in their own methodologies. We hereby attempt to recover the waste heat from the exhaust gas and use the heat energy recovered to improve the efficiency of the internal combustion engine. For the same we studied the exhaust gas temperature of a four stroke diesel engine at various RPM. The exhaust gas temperature at 4000 RPM has got the maximum temperature. So a recovery system for a constant RPM of 4000 is designed. The recovery system consists of a shell and tube heat exchanger and a uniflow steam engine which is coupled to the main engine. The coupled steam engine improves the efficiency of the main engine by lowering the frictional power at the power stroke and idle stroke of the main engine. The initial cost of the system is high due to the additional recovery system. But in the long run the system proves to be profitable. Keywords: IC Engine, Exhaust Gas, Efficiency I. INTRODUCTION In this age of globalization there is a decreasing availability of fossil fuels. So there is a need of conserving it for the future generations. In normal IC engines, a major part of fuel energy is wasted through exhaust gas, cooling water and other losses. We know that a normal IC engine is only 30 to 40 %. This means that the rest of the 70 to 60 % of the heat is lost as waste to the environment. But we know from the basic law of thermodynamics we cannot tap 100% of the available energy. But if we synthesis a method to tap the lost heat from the sink and formulate a method to increase the efficiency of the IC engine, it would be worth for the future generation. We could tap this lost heat by many ways and utilized it for many purposes. In this project we used a heat exchanger to tap the heat. This heat is further used to increase the efficiency of the engine with the help of a steam. The steam engine cylinder used is considered as an extra cylinder which working together with the other cylinders of the engine whose efficiency is to be increased. The steam engine used gives additional power to the whole system. This additional power decreases the frictional power of the system thereby increasing the efficiency of the IC engine. II. METHODOLOGY The heat energy released to the exhaust gas in engines of various cubic capacities is analyzed. Engine suitable for this system is selected. The amount of heat in exhaust gas is calculated. Suitable heat exchanger type is selected. Numerical designing of heat exchanger is done. The different parts of the heat exchanger are modeled using CATIA. The volume of steam chamber required is calculated. The power developed from the steam chamber is calculated. The software analysis of the heat exchanger and the steam chamber are done using ANSYS. All rights reserved by 392

2 The main work procedure consists of the following steps: 1) Engine selection. 2) Waste heat calculation. 3) Selection of heat exchanger. 4) Design and analysis of heat exchanger. 5) Design and analysis of steam cylinder. 6) Calculation of power developed from recovered heat III. MAIN WORK PROCEDURE Fig. 1: Schematic Representation of the System A. Engine Selection: Field analysis and literature study on different engines of various cubic capacity from 150cc to 1500cc were conducted. We studied the temperature of exhaust gas from these engines and found that the temperature is too low for low capacity engines. C in engines of higher capacities. Also, the mass flow rate of the exhaust is higher in large engines. Finally we selected 1573cc diesel engine. Engine specification: Engine type : inline 4 cylinder Bore : 75mm Stroke : 89mm Displacement : 1573cc Compression ratio : 18 Rated power : 80bhp@4000rpm We also checked the exhaust gas temperature from the engine when it is working under various rpm, i.e. from 1000rpm to 4000 rpm. Here we also found that the temperature is high when the engine speed is 4000 rpm. Table-1: Exhaust Gas Properties at Various Engine Speeds ITEM CONTENT Engine Speed(rpm) Engine Power (kw) Exhaust temperature(k) Exhaust mass flow rate(g/s) B. Heat Content of Exhaust Gas: We measured the temperature of the exhaust gas from the engine at 4000rpm. We obtained the mass flow rate of exhaust gas at this rpm as 0.108kg/sec. The specific heat capacity of exhaust gas is 1.185kJ/kgK. So heat duty of exhaust gas at 4000rpm is calculated as: Q max = ṁ ex c pex T = 0.108*1.185*(737-30) = 90.4kW Where, ṁ ex = mass flow rate of exhaust gas c p = specific heat T = temperature difference= inlet temperature of exhaust inlet Temperature of working fluid All rights reserved by 393

3 This is the maximum heat that can be transferred from exhaust gas to the cooling fluid. Exhaust Gas Waste Heat Recovery and Utilization System in IC Engine C. Heat Exchanger Selection: Since we have to run a steam engine which works with the pressure of the steam, it should be critically noted that the heat exchanger selected should be on with minimum pressure drop. Also, the function of our heat exchanger is to transfer the heat from the exhaust gas to the working fluid, and the working fluid has to be vaporized and superheated when coming out from the heat exchanger. Based on the requirements, we studied the characteristics of the available types of heat exchangers and found out that horizontal shell and tube heat exchanger with counter flow arrangement is the best suited one for our application. D. Design Considerations: The working is fed to the heat exchanger at a pressure of 10bar and the heat exchanger designed should provide steam at the outlet of shell with pressure drops within allowable limit. The exhaust gas is fed to the tube at a pressure of 5bar. Designing of the heat exchanger is usually done on the basis of certain assumptions. There is no heat transfer between the fluid streams and the outside environment. There are no leakages from the fluid streams to each other or to the environment. No heat is generated or lost via chemical or nuclear reactions, mechanical work or other means. There is no heat conduction along the length of the heat transfer surface, only in the direction of the normal of the surface. Fluid flow rates are equally distributed throughout the whole cross-sectional areas of flow. Where temperature distribution transverse to the flow direction is relevant, any fluid flow can be considered either completely mixed or completely unmixed. Properties of fluids are constant inside the heat exchanger. Overall heat transfer coefficient is a constant at all locations of the heat exchanger. Initial assumption that overall heat transfer coefficient U = 150 W/m 2. Negligible fouling resistance occur in the heat exchanger E. Designing Procedure: The process of sizing a heat exchanger will inevitably be an iterative one. To calculate the area one has to have at least an estimate of U, once an area is calculated on the basis of the estimate (or guess), the geometry of the heat exchanger will be known so that a better estimate of U can be calculated, leading to a better estimate of the area, therefore some change in geometry, requiring a new value of U to be calculated, and so on. Processes taking place in heat exchanger: Heating working fluid from 30 to Vaporization of the working fluid at Superheating of the working fluid to 205. Since these stages occur - Calculation of mass flow rate of working fluid: We know the maximum heat transferred from the working fluid. We also know the processes happening to the working fluid. So the flow rate of working fluid can be calculated by the following steps. To increase temp of WF Q 1 = ṁ wf c pwf T = ṁ wf 4.18 ( ) = ṁ wf To vaporize Q 2 = ṁ wf h fg = ṁ wf To superheat Q 3 = ṁ wf c pwf T = ṁ wf ( ) = ṁ wf Q max = Q 1 + Q 2 + Q = ṁ wf ( ) = ṁ wf ṁ wf = kg/sec 1) ε- NTU Method: The -NTU method of heat exchanger analysis is based on three dimensionless parameters: the heat exchanger effectiveness, ratio of heat capacity rates of the fluid streams CR, and number of transfer units NTU. is a function of heat duty and/or outlet temperatures and NTU a function of heat transfer area. Functions correlating the three dimensionless parameters to each other exist for a variety of flow arrangements. Use of the -NTU method starts by solving two of the dimensionless parameters from what is known about the situation, and then using the correct -NTU relationship to find the third. From that value and definition All rights reserved by 394

4 of the third dimensionless parameter one then solves what needs to be determined: for example the required heat transfer area from NTU in a sizing problem, or fluid outlet temperatures from in a rating problem. Find out the mass flow rate of working Finding out the temperature of exhaust gas after each phase Finding out the value of heat capacity ratio R; Based on the value of R from standard graph between ε - NTU, take values of NTU for maximum effectiveness. Take estimated value of U for shell and tube heat exchanger for doing initial iteration Calculate the area required Fix standard tube and shell diameters Find out the number of tubes required Fix the number of tubes as specified by s standards Assume single pass and find out the velocity and Reynolds number for exhaust flow Table-2: Heat Exchanger Design Specifications PROPERTY VALUE Effectiveness 76.3 Total heat exchange area 18.27m 2 Tube pitch 1 inch square pitch Tube inner diameter 12.2mm Tube outer diameter 19.1mm Shell inner diameter mm No of tubes 150 No of passes 6 No of baffles 11 IV. MODELLING OF HEAT EXCHANGER Parts of the heat exchanger is designed and made using CATIA. The major parts of heat exchanger are: Tube Shell Front end head Rear end head Tube Plate Fig. 2: Front End Head Fig. 3: Rear End Head Fig. 4: Shell Fig. 5: Tube Plate All rights reserved by 395

5 Fig. 6: Tube Fig. 7: Tubes Assembled in Tube Plate Fig. 8 Fully Assembled Heat Exchanger V. ANALYSIS OF HEAT EXCHANGER COMPONENTS Fig. 9: Stress Distribution in Front End Head Fig. 10: Deformation in shell All rights reserved by 396

6 Fig. 11: Strain in Font End Head Fig. 12: Stress Distribution in Shell Fig. 13: Stress Distribution in Tube From the above analysis done in ANSYS R15.0, we could understand that the maximum stress on the parts is much lesser than the yield strength of the material made. Hence the design is safe. The factor safety of shell cover = = The factor safety of shell = = 8.84 The factor of safety of the tube = = 4.79 From the above analysis we could clearly understand that the design safe with a very high factor of safety. VI. THEORETICAL ANALYSIS OF THE STEAM ENGINE A. Steam Engine Cylinder Design Assumptions: The cylinder is one of the main parts of the steam engine. The design of steam engine requires certain assumptions. The main assumption is that the working fluid cut off percentage. Another assumption is that the stroke length is fixed to obtain a particular bore for the steam engine. This is to provide the steam engine with the stroke length as that of the IC engine stroke length. So a stroke length of m is assumed for the steam engine. The cut off of the working fluid is at 50% of the cylinder volume. Thus with these assumptions we could determine the volume of the steam chamber required. All rights reserved by 397

7 B. Volume of the Steam Chamber: Volume flow rate of working fluid = volume flow rate of steam chamber cut off M ṁ= 32 3 / 3 D ρ = 4 52 / Hence volume flow rate of steam = Volume rate of steam chamber = = = = m 3 /sec Bore of steam chamber = 2 Exhaust Gas Waste Heat Recovery and Utilization System in IC Engine = *2 = m = 55.2 mm Volume of the cylinder = = = 213 cm 3 Hence the required volume of the steam engine cylinder is 213 cm 3 C. Cam Design: The cam profile is designed such that the cut off of the working fluid is at 50%. The lift of the valve is 4.5mm which is Fig. 14: Cam Follower Displacement Diagram Fig. 15: Cam Profile All rights reserved by 398

8 This is the required cam profile that is used to produce the required displacement of the valve. Exhaust Gas Waste Heat Recovery and Utilization System in IC Engine D. Theoretical Analysis of Steam Engine: The analysis is carried out on the assumption that the steam engine is having an efficiency of 15%. The assumption is on the basis that normal steam engine efficiency ranges from 10 to 20%. IC engine is operating0 at 4000 RPM and at full load. The gross power output from the steam chamber is calculated as follows. Recovered heat = kw Power output= 68.15*0.15 = kw Power loss due to pump = = kw = kw This is the power loss from pump. The gross power = = kw E. Strokes in Engine Cylinders: Table-2: Strokes in Engine Cylinders CYLINDER NUMBER STROKES 1 S C P E 2 E S C P 3 P E S C 4 C P E S 5 (Steam cylinder) E P E P Where, S = suction stroke C = compression stroke P = power stroke E = exhaust stroke F. Improvement in Engine Performance: 1) Variation in Thermal Efficiency: Thermal efficiency, of the IC engine = 37.3% But = We also know brake power = 80 kw (Mass of fuel/sec) Calorific value of diesel = kw New brake power = bp of IC engine + (bp of steam engine)/2 = = kw New = = = 38.19% Increase in thermal efficiency = % 2) Variation in Brake Specific Fuel Consumption: Brake specific fuel consumption, bsfc of the IC engine = 225 g/kwhr But, bsfc = Fuel consumption for unit time for 80 KW = g/hr The new bsfc = g/kwhr There is a decrease in bsfc = 5.28 g/kwhr VII. CONCLUSION This is a novel mechanism which improves the performance of the engine. The power of the engine increases from 80 kw at 4000 RPM to kw. The thermal efficiency increases from 37.3% to 38.19%.There is a decrease in the bsfc by 5.28 g/kwhr. The initial cost of the recovery mechanism is very high. But this becomes economic in long run. The analysis is carried All rights reserved by 399

9 out theoreticallybut there may be differences when it is experimentally analyzed. The low value of the recovered heat is due to the small engine that we took. The improvement in the performance of the engine is due to the fact that the power developed by the mechanism is utilized to decrease part of the frictional power of the engine. VIII. FUTURE SCOPE The recovery mechanism should be experimentally analyzed. An organic working fluid may be used in place of water. The experiment may be conducted in big engines which may be more effective than small engines. The experiment may be conducted at various RPM and loads. A recovery mechanism should be developed for engines working at various RPM and loads. ACKNOWLEDGEMENT The authors would like to acknowledge the support of Mechanical Engineering Department of Saintgits College of Engineering for conducting the present investigation REFERENCES [1] Jianqin Fu, Jingping Liu, Yanping Yang, Chengqin Ren, Guohui Zhu- A, Applied Energy, 2013, pp [2] J.S. Jadhao, D.G. Thombare- R I, Applied Energy, [3] Kiran K. KattaMyoungjin Kim- E -, Applied Energy, [4] Q.A Kern P [5] C P Kothandaraman, S Subramanyan H All rights reserved by 400