Design for Integration of a Compact Waste Energy Recovery ...

1 Copyright © 2014 by ASME

DESIGN FOR INTEGRATION OF A COMPACT WASTE ENERGY RECOVERY SYSTEM FOR AUTOMOBILE ENGINE EXHAUST GAS AND COOLANT

Mohammed S. Mayeed Department of Systems and Mechanical

Engineering, Southern Polytechnic State University

Marietta, Georgia, USA

S. Mostafa Ghiaasiaan Department of Mechanical Engineering,

Georgia Institute of Technology Atlanta, Georgia, USA

Thuyen Luong

Department of Systems and Mechanical Engineering,

Southern Polytechnic State University Marietta, Georgia, USA

Erhan Ilksoy Department of Systems and Mechanical

Engineering, Southern Polytechnic State University

Marietta, Georgia, USA

ABSTRACT In this study, key components of combined cycles

designed for waste energy recovery from automobile engines have been virtually designed for being light weight, small sized without compromising strengths, and based on integration with the existing components of an automobile. Originally a simulation was performed to examine the amount of waste energy that could be recovered and the consequential increase in the overall thermal efficiency through the use of Kalina, ethanol and steam cycles using Engineering Equation Solver software under typical engine operating conditions. It was found that steam cycle was better for recovering energy from the exhaust gas at the higher temperature range (689 C to 160 C) and Kalina cycle was better for recovering energy from the exhaust gas and the cooling water at the lower temperature range (122 C to 80 C) among the three cycles. It was found that using this combination of cycles about 5 kW of power could be extracted from the wasted energy. The next thing was to determine the amount of space, weight and design to incorporate a system of cycles like this with an automobile. The combined cycle generation, a process widely used in existing power plants, has become a viable option for automotive applications due to advances in materials science, nanotechnology, and MEMS (Micro-Electro Mechanical Systems) devices. Critical components of the best performing cycles have been designed using computer aided engineering

for the minimization of weight and space, and integration with the typical components of an automobile. INTRODUCTION

Fossil fuel consumption by human daily life and industrial production continues to increase and has caused many environmental problems; therefore, energy saving has been of great significance. In an industrial country, 30%-40% of the total energy consumption is caused by transportation. It is generally known that the maximum thermal efficiency of an automotive engine is rarely above 40%. It has been assumed that further improvements in the thermal efficiency through optimization of the combustion process have reached a technical limit [1]. In recent research aimed at improving automotive energy efficiency, specific trends have emerged. One trend involves the development of electric hybrid cars. Research on hybrid automobiles is actively being conducted by many automotive companies [2-9]. Another trend is the downsizing of the internal combustion engine, which is also considered to have great potential in improving the thermal efficiencies of engines [10-15]. A relatively new approach for improving the overall energy efficiency of vehicles is the implementation of the cogeneration concept [16-19]. It has been noted that energy loss in modern engines may reach approximately 60%. Therefore, recovering heat waste through an exhaust and cooling circuit seems to be a very effective way to improve the overall thermal efficiency.

Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014

November 14-20, 2014, Montreal, Quebec, Canada

IMECE2014-37309


Fig. 1 Steam cycle for high temp exhaust gas energy recovery

Fig. 2: Ethanol cycle for low temp coolant energy recovery.

a c

b Exhaust gas

While cogeneration systems have been successfully adopted in many power plants, there is a concern that such systems may be too large for use in automobiles. In a cogeneration system, waste energy may be recovered in three different ways: turbo compounding, thermo-electric conversion, or thermodynamic processing (e.g., the Rankine cycle) [20]. The Rankine steam cycle has exhibited better efficiency than both thermo-electric devices and turbo compounding, which utilizes the kinetic energy of the exhaust [21]. The combined cycle generation, a process widely used in existing power plants, has become a viable option for automotive applications due to advances in materials science, nanotechnology, and MEMS (Micro-Electro Mechanical Systems) devices. The waste heat generated from automotive engine exhaust and coolant is a feasible heat source for a combined cycle generation system, which is basically a combination of Rankine and Kalina cycles in the context of this study. A simulation was performed to examine the amount of waste energy that could be recovered and the consequential increase in the overall thermal efficiency through the use of combined cycle systems using Engineering Equation Solver software under typical engine operating conditions. However, there are numerous technical issues that need to be solved before the technology can be implemented in automobiles e.g. how a combined cycle can be installed in an automobile with its additional space and light weight requirements. A particular issue the study will address is the virtual realization or design of

key components of the designed combined cycles using computer aided engineering and analyses which is an economically viable alternative compared to expensive physical prototype designs and tests.

COMPUTATIONAL METHODS In this study Kalina, ethanol and steam cycles have been considered to recover waste energy from the internal combustion engine exhaust gas and cooling water or coolant. Engineering Equation Solver (EES) software of F-Chart

Software, LLC. has been used to code all these cycles and then the cycles have been compared with respect to thermal efficiency and amount of generated work for a particular flow rate of the source (source of energy) fluid. EES is a general equation-solving program that can numerically solve thousands of coupled non-linear algebraic and differential equations. A major feature of EES is the high accuracy thermodynamic and transport property database that is provided for hundreds of substances in a manner that allows it to be used with the equation solving capability.

The state of the art flow simulation software SolidWorks Flow Simulation 2013 has been used to perform internal flow analysis on all the SolidWorks (Dassault Systèmes SolidWorks Corp.) CAD generated heat exchanger design models. The SolidWorks Flow Simulation (Dassault Systèmes SolidWorks Corp.) which is a computational fluid dynamics (CFD) simulation software uses full Navier Stokes equations that govern the motion of fluids. There are a number of bench-mark internal flow analyses performed using SolidWorks Flow Simulation software [22] with reasonable accuracy.

Finite element thermal stress analysis was performed using SolidWorks Simulation software. The temperature profiles were taken from the flow simulations, put on the structures of the heat exchangers, and stresses, strains and factors of safety were

calculated. The minimum factors of safety were the critical issues in terms of structural integrity and were based on maximum von-Mises stress failure criteria.

Real wall boundary condition with heat conduction in solids has been used at the heat exchanger walls. Mesh verification in flow analysis has been performed by increasing mesh density about twice the original density and no significant variation in the temperature profiles has been observed. In flow analysis steady state solution is considered based on the residuals of all the velocity components, pressure, and temperature showing very


Fig. 3: Kalina cycle for low temp coolant energy recovery

s [kJ/kg-K]

T [C

]

low and constant values. Moreover, mesh convergence has been

confirmed in all stress and deformation calculations using finite element thermal stress analysis.

RESULTS AND DISCUSSION A study has been carried out using Kalina, ethanol and steam cycles to recover waste energy from the internal combustion engine exhaust gas and cooling water or coolant. Engineering Equation Solver software was used to design and compare all these cycles. The first cycle designed was a steam cycle (Fig. 1) to extract waste heat from the exhaust gas at 689 C from a typical internal combustion engine of an automobile (gasoline driven). It was found that steam cycle was suitable for recovering energy from the exhaust gas at the higher temperature range (689 C to 160 C). The typical mass flow rate of exhaust gas in automobile engines vary from 0.035 kg/s to 0.1 kg/s as mentioned in Kumar et al. [23]. It can be observed from Table 1 that for an exhaust gas mass flow rate of 0.035 kg/s, the net amount of extracted work was about 4.03 kW with an overall thermal efficiency of the cycle of approximately 19%. Table 1 Steam Cycle for High Temp Exhaust Gas Energy Recovery

Pr. Ratio

Mass Flow Rate of the Exhaust Gas

Mass Flow Rate of Water

Net Work

Thermal Efficiency of the Cycle

kg/s kg/s kW 40/5 0.035 0.00675 4.029 0.186

Table 2 Kalina Cycle for Low Temp Cooling Water Energy Recovery

Pr. Ratio

Mass Flow Rate of Coolant

Mass Flow Rate of Ammonia and Water Mixture

Net Work


kg/s kg/s kW

35/6.5 1 0.195 21.59 0.128

Table 3 Ethanol Cycle for Low Temp Cooling Water Energy Recovery Pr. Ratio

Mass Flow Rate of Coolant

Mass Flow Rate of Ethanol

Net Work


kg/s kg/s kW 3/1 1 0.231 13.35 0.0632

Table 4 Kalina Cycle for Low Temp Cooling Water and Exhaust Gas Energy Recovery

Pr. Ratio

Mass Flow Rate of Coolant and Exhaust Gas

Mass Flow Rate of Ammonia and Water Mixture

Net Work,


kg/s kg/s kW 35/6.5 0.035+0.035 0.008403 1.048 0.1338

As the steam cycle cannot be feasible under 160 C, an ethanol cycle and a Kalina cycle have been designed as shown in Figs. 2 and 3 respectively to extract waste heat energy at a lower temperature range (122 C to 80 C). The results from the Kalina cycle code developed in Engineering Equation Solver have been compared with the results in Ogriseck [24] and found to have obtained excellent comparison. Tables 2 and 3 show the results of using Kalina and ethanol cycles respectively to extract heat energy from the coolant with a mass flow rate of 1 kg/s at a lower temperature range. Kalina cycle shows about twice the amount of net extracted work and higher overall thermal efficiency of the cycle compared to those of the ethanol cycle. Kalina cycle was used for recovering energy from the cooling water only (Fig. 3 and Table 2), and also used for recovering energy from the cooling water and the exhaust gas at the same time (Fig. 4 and Table 4). The latter case shows higher net amount of work and overall thermal efficiency of the cycle. Therefore, Kalina cycle has been applied to extract energy from

the coolant and the exhaust gas at the same time at a realistic mass flow rate of 0.035 kg/s and the net amount of extracted work is 1.05 kW with an overall thermal efficiency of the cycle of approximately 13.4%. It is conclusive from the generated

Fig. 4: Kalina cycle for low temp coolant and exhaust gas energy recovery

s [kJ/kg-K]

T [C

]


(b) (a)

Fig. 5: A schematic diagram of a typical steam or organic Rankine cycle

Fig. 6: A schematic diagram of a typical Kalina cycle

Fig. 7: Schematic diagrams of the evaporator for the steam cycle for high temp exhaust gas energy recovery

Fig. 8 Temperature profiles in the exhaust gas and water sides of (a) the water evaporator; and (b) the vapor evaporator.

(a)

(b)

results that a steam cycle should be at the higher temperature range and a Kalina cycle should be at the lower temperature range to maximize the energy extraction. In this combination of cycles the total net amount of extracted work is 5.08 kW under a mass flow rate of 0.035 kg/s which is the lowest level of mass flow rate in the typical exhaust gas mass flow rate range from 0.035 kg/s to 0.1 kg/s. As can be seen from these thermodynamic cycles, several key components such as evaporators, condensers, turbines, pumps, separators, mixers etc. are needed to be designed for application in automobiles (Figs. 5 and 6). The most difficult challenge of this project is to design light weight and miniaturized versions of these key components of the thermodynamic cycles. First the steam cycle evaporator design requirements have been summarized from Table 1, and Fig. 7 is showing a schematic of the evaporator of the steam cycle that is extracting heat from the exhaust gas at the highest temperature of 962 K which denotes the steam cycle shown in Fig. 1. Then computer aided engineering was used to design the evaporator using the state of the art commercial software SolidWorks Flow Simulation. Again the most critical objectives of designing all the key components of the thermodynamic cycles are to have these components light weight, compact and miniaturized. Therefore conventional heat exchanger i.e. evaporator or condenser

designs will most certainly not fit the purpose and an emphasis has been given to design these components using mini-channel


Fig. 9 A typical evaporator section showing multiple mini-channels stacked side by side with alternative rows of exhaust gas and water or vapor, and using pin fins.

plate heat exchanger concepts which can provide higher surface area to volume ratio. First the evaporator or the boiler of the steam cycle has been considered to be designed in 3D in SolidWorks. Then SolidWorks Flow simulation has been used to design the evaporator of the steam cycle. It should be mentioned that this steam cycle and thereby its evaporator is the most critical component in the size determination because it extracts about 80% of the total extracted energy from the exhaust gas if using a combined cycle. The entire evaporator has been divided into three parts: (a) the water evaporator; (b) the vapor evaporator; and (c) the phase changing evaporator as shown in Fig. 1. Using simple heat balance the water evaporator part should theoretically heat up water from 426 K to its saturation temperature of 523 K at a constant pressure of 40 bar and at the same time cool down exhaust gas from 560 K to 491 K. Similarly the vapor evaporator part should heat up vapor from the saturation temperature of 523 K to about 952 K at a constant pressure of 40 bar and in the process cools down exhaust gas from 962 K to 802 K. The phase changing evaporator will convert water to steam at the saturation temperature of about 523 K at a constant pressure of 40 bar which will bring down the exhaust gas temperature from 802 K to about 560 K.

For all the three parts of the evaporator, plate heat exchangers have been used with plate and pin fins (diameter 3 mm and length 1.5 mm) with about 5 mm channel thickness. A plate heat exchanger with about 8 water/vapor channels sandwiched by exhaust gas channels at both sides (top and bottom) with pin fins is the most compact optimized design so far for both the water and vapor evaporators. The stacked channels are as shown in Fig. 9. Using this plate heat exchanger the water evaporator has generated temperature profiles for the water and exhaust gas as shown in Fig. 8(a) within an evaporator length of about 700 mm and both the fluids achieved temperatures close to the temperatures using simple heat balance equations. Similarly the vapor evaporator has generated temperature profiles for the vapor and exhaust gas as shown in Fig. 8(b) again within an evaporator length of about 700 mm. In this case

also the temperatures achieved in both the fluids are close to the theoretically calculated temperatures. In the phase changing evaporator surrogate water has been used with a higher specific heat to compensate for the latent heat of vaporization. Using a simple heat balance equation the value of the specific heat of the surrogate water is determined. Moreover, viscosity has been adjusted to keep the pressure drop from inlet to outlet similar to the calculated pressure drop during the phase change. The temperature profiles of both the surrogate water and the exhaust gas have been plotted in Fig. 10 over about 500 mm length of evaporator and the outlet temperatures of both the fluids are quite similar to those expected using a simple heat balance equation. As a mini-channel based evaporator is being designed to be installed along the exhaust gas pipeline from the auto mobile engine, back pressure due to the installed evaporator is calculated using flow simulations of exhaust gas through the exhaust pipe with and without the evaporator installed. From the difference of the pressure drops with and without the evaporator the back pressure due to the evaporator is calculated to be less than 1.5 psi which is similar to the back pressure created by a catalytic converter. After this, temperature profiles are taken from the thermal flow simulations and thermal stress analysis is performed to observe the stress, strain and factor of safety distribution on all the evaporator parts. The minimum factors of safety of 2.5, 8.5 and 11 are found in the vapor evaporator, the phase changing evaporator and the water evaporator respectively using copper as the structural material. It should be mentioned that these factors of safety ensure the structural integrity of all the evaporator parts using high temperatures and temperature gradients over their local thin wall structures that help high heat transfer.

Fig. 10 Temperature profiles in the exhaust gas and surrogate water sides of the phase changing evaporator.


This high temperature steam cycle evaporator is the most important and the largest key component of the power cycles being designed in this study as it is expected to extract about 80% of the waste energy through exchange of heat between the exhaust gas and the water. The estimated size of the steam cycle evaporator is about 1900 mm x 105 mm x 40 mm with an exhaust gas mass flow rate of 0.1 kg/s which is a typical maximum mass flow rate of exhaust gas in a modern day automobile. The compressor of this cycle would be an additional radiator which could be designed along with the current radiator. Although we are still left with the designs of the steam turbine and the pump, however these components should not occupy much of a space. Therefore, the overall size of a compact power station over an automobile does not seem unreasonable according to this study. Moreover, further optimization of the designs with respect to compactness is very much possible especially enhancing heat transfer using nano/micro scale technologies.

REFERENCES (1) Kim, K.-B., Choi, K.-W., and Lee, K.-H., 2012, “VIABLE COMBINED CYCLE DESIGN FOR AUTOMOTIVE APPLICATIONS,” International Journal of Automotive Technology, 13(3), pp. 401-407. (2) Kim, P. S., 2000, “Future cost estimation of hybrid electric vehicle using the learning curve,” SAE Paper No. 2000-05-0354. (3) Walters, J., Husted, H., and Rajashekara, K., 2001, “Comparative study of hybrid powertrain strategies,” SAE Paper No. 2001-01-2501. (4) Hirose, K., Abe, S., and Killmann, G., 2002, “Overview of current and future hybrid technology,” SAE Paper No. 2002-33-0016. (5) Liu, X., Kiallo, D., and Marchand, C., 2011, “Design methodology of hybrid electric vehicle energy sources: Application to fuel cell vehicles,” Int. J. Automotive Technology, 12(3), pp. 433−441. (6) Shin, D. H., Lee, B. H., Jeong, J. B., Song, H. S., and Kim, H. J., 2011, “Advanced hybrid energy storage system for mild hydrod electric vehicles,” Int. J. Automotive Technology, 12(1), pp. 125−130. (7) Suh, B., Frank, A., Chung, Y. J., Lee, E. Y., Chang, Y. H., and Han, S. B., 2011, “Powertrain system optimization for a heavy-duty hybrid electric bus,” Int. J. Automotive Technology 12(1), pp. 131−139. (8) Wang, B. H., and Luo, Y. G., 2011, “Application Study on a control strategy for a hybrid electric public bus,” Int. J. Automotive Technology, 12(1), pp. 141−147. (9) Kim, K. B., Choi, K. W., Lee, K. H., and Lee, K. S., 2010, “Active coolant control strategies in automotive engines,” Int. J. Automotive Technology, 11(6), pp. 767−772. (10) Hauet, B., and Maroger, Y., 2002, “Engine downsizing, a contribution to greenhouse effect reduction,” SAE Paper No. 2002-33-0003.

(11) Zaccardi, J. M., Pagot, A., Vangraefschepe, F., Dognin, C., and Mokhtari, S., 2009, “Optimal designing for a highly downsized gasoline engine,” SAE Paper No. 2009-01-1794. (12) Fraser, N., Blaxill, H., Lumsden, G., and Bassett, K., 2009, “Challenges for increased efficiency through gasoline engine downsizing,” SAE Paper No. 2009-01-1053. (13) Lee, B. H., Song, J. H., Chang, Y. J., and Jeon, C. H., 2010, “Effect of the number of fuel injector holes on characteristics of combustion and emissions in a diesel engine,” Int. J. Automotive Technology, 11(6), pp. 783−791. (14) Park, J., Lee, K. S., Song, S., and Chun, K. M., 2010, “Numerical study of a light-duty diesel engine with a dual-loop EGR system under frequent engine operating conditions using the DOE method,” Int. J. Automotive Technology, 11(5), pp. 617−623. (15) Liu, Y., Zhang, Y. T., Qiu, T., Ding, X., and Xiong, Q., 2010, “Optimization research for a high pressure common rail diesel engine based on simulation,” Int. J. Automotive Technology, 11(5), pp. 625−636. (16) Ringler, J., Seifert, M., Guyotot, V., and Hubner, W., 2009, “Rankine cycle for waste heat recovery of IC engines,” SAE Paper No. 2009-01-0174. (17) Freymann, R., Strobl, W., and Obieglo, A., 2005, “The turbosteamer: A system introducing the principle of cogeneration in automotive applications,” MTZ Conf., 0512008 69, pp. 20−27. (18) Endo, T., Kawajiri, S., Kojima, Y., Takahashi, K., Baba, T., Ibaraki, S., Takahashi, T., and Shinohara, M., 2007, “Study on maximizing exergy in automotive engines,” SAE Paper No. 2007-01-0257. (19) Kadota, M., and Yamamoto, K., 2008, “Advanced transient simulation on hybrid vehicle using Rankine cycle system,” SAE Paper No. 2008-01-0310. (20) Saqr, K. M., Mansour, M. K., and Musa, M. N., 2008, “Thermal design of automobile exhaust based thermoelectric generators: Objectives and challenges,” Int. J. Automotive Technology 9(2), pp. 155−160. (21) Ringler, J., Seifert, M., Guyotot, V. and Hubner, W., 2009, “Rankine cycle for waste heat recovery of IC engines,” SAE Paper No. 2009-01-0174. (22) Matsson, J. E., 2013, An Introduction to SolidWorks Flow Simulation 2013, SDC Publications. (23) Kumar, S, Heister, S. D., Xu, X, Salvador, J. R., and Meisner, G. P., 2013, “Thermoelectric Generators for Automotive Waste Heat Recovery Systems Part II: Parametric Evaluation and Topological Studies,” Journal of Electronic Materials. (24) Ogriseck, S., 2009, “Integration of Kalina cycle in a combined heat and power plant, a case study,” Applied Thermal Engineering, 29, pp. 2843-2848.

Design for Integration of a Compact Waste Energy Recovery ...

Documents

Transcript of Design for Integration of a Compact Waste Energy Recovery ...