Analysis of vehicle exhaust waste heat recovery potential using a Rankine cycle (original) (raw)
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International Journal for Research in Applied Science & Engineering Technology, 2021
A combined dual-stage waste heat recovery system integrated to an internal combustion engine is studied. The system consists of high-temperature steam Rankine cycle (SRC) and a low-temperature organic Rankine cycle (ORC), both combined to recover the waste heat of the engine exhaust gases and engine coolant. In the ORC, organic working fluids R245fa, R600 and R601a are selected for analysis and sub-critical cycle adopted. For the comparative study of the selected working fluids, energy and exergy analysis are conducted based on the engine data, pre-set parameters and mathematic model with net-output power, utilization rate, thermal efficiency and exergy efficiency as the objective functions for optimization. I. INTRODUCTION Internal combustion engines (ICE), that converts energy from heat to work, has vast applications in road vehicles, marine transport, and power plants. In ICE, all the energy released during combustion of the fuel cannot be converted into useful work because of some thermodynamic limitations. About two-thirds of the total fuel combustion heat in automotive ICEs is wasted by the exhaust gases and engine coolant, resulting in energy waste and emission problem [1],[2],[3]. Recovering the waste energy could greatly improve the engine fuel efficiency and reduce environmental pollution. As energy crisis and environment pollution are increasingly severe, many technologies have been proposed to save energy and reduce emission in the field of ICE. Among these technologies, organic Rankine cycle (ORC) is an effective one because of its flexibility, economy and good thermal performance [4],[5]. Organic Rankine cycle (ORC) is seen as a high-effective way to recover the low-medium temperature heat (80 o C to 300 o C), such as biomass, solar, geothermal, and industry reject heat [6]. ORC has been also used in heat recovery systems of ICE [7]-[11]. These systems mainly use single-stage heat recovery. In ICE the waste heat released are at different temperatures, that is, exhaust gas temperature is high (450-600 o C) while coolant temperature is low (80-85 o C). Therefore, matching of the exhaust and coolant with organic working fluid is a problem. In single-stage systems and the engine coolant was usually used as the preheating heat source, resulting in little utilization of the engine coolant waste heat. There are also issues of decomposition of organic working fluid and unsafe direct heat exchange with high temperature waste heat. To solve these problems an integrated dual-stage is proposed, one to recover the high-temperature exhaust waste heat and the other to recover the heat from the low-temperature coolant. The high-temperature stage uses steam Rankine cycle (SRC) with water as the working fluid to recover the heat from exhaust gases; the low-temperature stage uses an organic Rankine cycle (ORC) with an organic working fluid to recover the heat from engine coolant; and both the stages being integrated. In this study, ORC working fluids R245fa, R600 and R601a are selected for the system's comparative analysis. For the selected working fluids, energy and exergy analysis are conducted based on the engine data, pre-set parameters and mathematic model with net-output power, utilization rate, thermal efficiency and exergy efficiency as the objective functions for optimization. The evaporator pressure, condenser pressure and mass flow rate are taken to be the decision variables.
A Study of Exhaust Waste Heat Recovery in Internal Combustion Engines
IOP Conference Series: Materials Science and Engineering, 2019
This research presents an investigation of an energy recovery solution from exhaust gases in internal combustion based on the heat exchange to distil fresh water from the sea water. Consequently, an optimization of the flow field design of the heat exchanger was performed using the commercial computational fluid dynamics (CFD) software. The result of this research showed that the energy recovery performance of the exchanger strictly depends on the engine load, which can reach a value of approximately 33% at the full load condition of the research engine. These results might forecast a future application of the optimized exchanger's flowfield design in automotive waste heat recovery in order to improve the internal combustion engine efficiency.
IOP conference series, 2016
Compression ignition engines transform approximately 40% of the fuel energy into power available at the crankshaft, while the rest part of the fuel energy is lost as coolant, exhaust gases and other waste heat. An organic Rankine cycle (ORC) can be used to recover this waste heat. In this paper, the characteristics of a system combining a compression ignition engine with an ORC which recover the waste heat from the exhaust gases are analyzed. The performance map of the diesel engine is measured on an engine test bench and the heat quantities wasted by the exhaust gases are calculated over the engine's entire operating region. Based on this data, the working parameters of ORC are defined, and the performance of a combined engine-ORC system is evaluated across this entire region. The results show that the net power of ORC is 6.304kW at rated power point and a maximum of 10% reduction in brake specific fuel consumption can be achieved. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
There are a substantial amount of waste heat through exhaust gas and coolant of an internal combustion engine. Organic Rankine cycle is one of the opportunities in internal combustion engines waste heat recovery. In this study, two different configurations of organic Rankine cycle with the capability of simultaneous waste heat recovery from exhaust gas and coolant of a 12 liter diesel engine were introduced: Preheat configuration and two-stage. First, a parametric optimization process was performed for both configurations considering R-134a, R-123, and R-245fa as the cycle working fluids. The main objective in optimization process was maximization of the power generation and cycle thermal efficiency. Expander inlet pressure and preheating temperature were selected as design parameters. Finally, parameters like hybrid generated power and reduction of fuel consumption were studied for both configurations in different engine speeds and full engine load. It was observed that using R-123 as the working fluid, the best performance in both configurations was obtained and as a result the 11.73% and 13.56% reduction in fuel consumption for both preheat and two-stage configurations were found, respectively.
2018
Automobiles refrigeration systems are mainly vapor compression refrigeration systems, and they use high power which is taken directly from the engine. The use of these systems will increase fuel consumption, and this fuel consumption will increase up to 15%. By considering the importance of fuel saving, optimum use of fuel will be necessary. One of the effective ways, is the waste heat recovery from the engine exhaust gas. The purpose of this study is the thermodynamic analysis of a new cogeneration system based on internal combustion engine. In fact, the system will generate power using heat recovery from exhaust the engine, and then the power will be used to run the refrigeration system. The system is used in the actual operating modes of gasoline and diesel engines. Different refrigerants are used in the system. Results show that the system can generate required refrigeration capacities of both automobiles and buses. Furthermore, additional refrigeration capacities will also be available. R245fa and R600 refrigerants have better performances in the system. Maximum refrigeration capacity generated by the system is 20 kW when using gasoline engine exhaust gases waste heat recovery, and 130 kW when using diesel engine exhaust gases waste heat recovery.