In the conceptual design stage of a 2.0 L turbocharged gasoline engine for a commercial vehicle

one-dimensional thermodynamic calculation was carried out using GT-Power software and the influence was studied of the Miller cycle technology and low-pressure exhaust gas recirculation (EGR) technology on the fuel economy. The simulation results show that both long Miller cycle and short Miller cycle have the optimal VVT angles for the fuel economy. At medium-high-speed region

the fuel economy of the short Miller cycle is better

because in the long Miller cycle

the reversal of air flow in cylinder is not possible due to high mass flow and velocity

and the Miller effect is reduced. In addition

the long Miller cycle has two pumping processes

resulting in more pumping loss than the short Miller cycle. At low-speed region

the fuel economy of the long Miller cycle is better because the boost pressure of the short Miller cycle is higher

resulting in more pumping loss than the long Miller cycle. For this gasoline engine

the short Miller cycle has obvious advantages. The low-pressure EGR technology can decrease the maximum temperature in cylinder and reduce knock tendency

hence crank angle of 50% mass fraction burned(CA50) being advanced properly to optimize the fuel economy. Furthermore

the increase of the total amount of EGR and fresh air also leads to an increase in cylinder peak pressure

contributing to a better fuel economy. In different operating conditions

the maximum temperature in cylinder decreases with the growth of the EGR rate. Therefore

within a certain range

the higher the EGR rate

the better the fuel economy and the lower the turbine inlet temperature. However

in the meantime more cooling power is required by the EGR cooler. As a result

the short Miller cycle technology is applied for the engine combustion development process

and the recommended EGR rate is 8%. In order to verify the simulation results

the engine performance test was carried out

and the experimental results are in good agreement with the simulation results.