Combined effects of electric supercharger and LP-EGR on performance of turbocharged engine

LP-EGR and turbocharging can improve thermal efficiency, but its specific mechanism needs to be further studied from the energy conversion. The fast response characteristic of electric supercharger can make up for turbine lag. The effect of electric supercharger on the steady state and transient characteristics of a LP-EGR turbocharged engine are investigated. Under the condition of 1500 r·min−1 and 14 bar, the electric supercharger can increase the EGR rate from 5% to 30%. The introduction of exhaust gas can increase the intake volume and reduce the pumping losses. The increase of turbocharger power indicates the reduction of exhaust energy losses. The decrease of combustion temperature optimizes the combustion phase, increases the constant volume degree of combustion and reduces the heat transfer losses. The application of EGR improves the fuel economy by 5%. For emission, low temperature combustion and low oxygen content reduce NOx emission by 80%. Incomplete combustion losses increase THC emission. CO emission is related to excess-air coefficient, so it is basically unchanged. The electric supercharger can speed up the establishment of the intake manifold pressure. The power transient response time is shortened by 72%. The advance of torque platform improves the power performance of engine at low speed. •The effects of E-booster and LP-EGR on turbocharged engine are investigated.•A complete theoretical analysis of energy conversion is carried out.•Electric supercharger mainly improves the EGR rate at low speed and high load.•Fuel economy is improved by reducing heat, exhaust and mechanical losses.•Engine transient response is improved with the adoption of electric supercharger.