Evaluation of energy-exergy performance and sustainability index of a DI engine integrated with designed electromechanical EGR cooling system
Galip Kaltakkıran, Halil İbrahim Akolaş, Kadir Bakirci
Abstract
Exhaust Gas Recirculation (EGR) system is a commonly used pretreatment technique to improve pollutant emissions from modern diesel engines. Recently, the EGR cooling strategy focuses on improving combustion stability, NO x emission and fuel consumption values by controlling oxygen dilution, in-cylinder and exhaust gas temperatures. However, there are not enough studies focusing on energy and exergy analysis to improve the deterioration caused by hot EGR gas in engine performance and energy distributions. Therefore, in this study, classical and electronically controlled external EGR cooling systems are designed. The present study investigates the effect of the various EGR rates and EGR out gas temperatures on classical/electromechanics EGR cooling systems in a DI diesel engine and reveals the effects of energy-exergy distributions on each other and the sustainability index (SI) perspective. The tests are performed with various EGR rates (5%, 10%, 15%) and EGR out gas temperatures (75 °C, 90 °C, 110 °C) at 1700 and 2000 rpm. At 1700 rpm test conditions, the highest thermal-exergetic efficiencies for low and high load are recorded at 15% EGR rate-75 °C EGR out gas temperature and 5% EGR rate-75 °C EGR out gas temperature, respectively. At 2000 rpm test conditions, the highest thermal-exergetic efficiencies for low and high load are achieved at 15% EGR rate-110 °C EGR out gas temperature and 5% EGR rate-90 °C EGR out gas temperature, respectively. The main findings show that the EGR rate rather than the EGR out gas temperature has a more dominant effect on the in-cylinder combustion performance and thermal-exergetic efficiency. While the increase in the EGR rate from 5% to 15% contributes positively to the thermal-exergetic efficiency and SI performance at low engine load, the opposite is observed at high load. The study recommends that the EGR rate and EGR out gas temperature should be chosen at the optimum level for the engine performance and energy efficiency.