Abstract
The main purpose of this research is to analyze the performance of an evaporator for the organic Rankine cycle (ORC) system and discuss the influence of the evaporator on the operating characteristics of diesel engine. A simulation model of fin-and-tube evaporator of the ORC system is established by using Fluent software. Then, the flow and heat transfer characteristics of the exhaust at the evaporator shell side are obtained, and then the performance of the fin-and-tube evaporator of the ORC system is analyzed based on the field synergy principle. The field synergy angle (β) is the intersection angle between the velocity vector and the temperature gradient. When the absolute values of velocity and temperature gradient are constant and β < 90°, heat transfer enhancement can be achieved with the decrease of the β. When the absolute values of velocity and temperature gradient are constant and β >90°, heat transfer enhancement can be achieved with the increase of the β. Subsequently, the influence of the evaporator of the ORC system on diesel engine performance is studied. A simulation model of the diesel engine is built by using GT–Power software under various operating conditions, and the variation tendency of engine power, torque, and brake specific fuel consumption (BSFC) are obtained. The variation tendency of the power output and BSFC of diesel engine–ORC combined system are obtained when the evaporation pressure ranges from 1.0 MPa to 3.5 MPa. Results show that the field synergy effect for the areas among the tube bundles of the evaporator main body and the field synergy effect for the areas among the fins on the windward side are satisfactory. However, the field synergy effect in the areas among the fins on the leeward side is weak. As a result of the pressure drop caused by the evaporator of the ORC system, the diesel engine power and torque decreases slightly, whereas the BSFC increases slightly with the increase of exhaust back pressure. With the increase of engine speed, power loss, torque loss, and BSFC increment increase gradually, where the most significant change is less than 1%. Compared with the diesel engine itself, the maximum increase of power output of the diesel engine–ORC combined system is 6.5% and the maximum decrease of BSFC is 6.1%.
Highlights
Car ownership increases rapidly with economic development
The results showed that the organic Rankine cycle system produced 5.5 MW of electricity with no additional fuel consumption and near-zero emissions
The results showed that the simulation results that selected the SST k-ω and RNG k-ε model were closer to the experimental results
Summary
Car ownership increases rapidly with economic development. The growing number of cars in use will raise energy consumption and cause serious environmental pollution. The transformation and utilization of the waste heat of engine exhaust gas is an effective way to improve the efficiency of the engine and reduce fuel consumption and pollutant emissions. Organic Rankine cycle (ORC) is an effective waste heat recovery method that has been widely applied in many domains, such as steel industry [3], cement industry [4], solar-powered plant [5], biomass cogeneration plant [6], internal combustion engine and so on. Uusitalo et al [7] studied the potential for electricity production from the waste heat of large reciprocating engines with the ORC process technology, which is beneficial for increasing the efficiency of the engine power plant. The results showed that the organic Rankine cycle system produced 5.5 MW of electricity with no additional fuel consumption and near-zero emissions. The organic Rankine cycle improved the overall energy efficiency by 28%
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