In order to study the influence of Miller cycle and exhaust gas recirculation(EGR) on combustion performance at the best fuel consumption point and high load

a 15L turbocharged direct injection gasoline engine with EGR system was changed from Otto cycle operation to Miller cycle operation by modifying its intake cam profile. Results show that in a comparative test of two different operating modes of Miller cycle and Otto cycle

the pumping loss from the Miller cycle operation is smaller than from the Otto cycle operation. However

as the load increases

the influence of the Miller cycle begins to decrease

causing the difference in pumping loss between the two cycles to gradually become smaller

which hinders the improvement of the Miller cycle thermal efficiency. In addition

the Miller cycle also reduces the end of compression temperature

increasing the combustion duration and exhaust temperature

which makes it difficult to improve the fuel economy at the best fuel consumption point. Moreover

this study also compares the effect of EGR on Miller cycle and Otto cycle. With the increase of EGR rate

the thermal efficiency of both cycles increases first and then decreases. However

the use of Miller cycle reduces the intake time and valve lift

and then greatly decrease the in cylinder tumble ratio and turbulent kinetic energy

thus retarding the angle of 50% mass fraction burned(MBF50) and extending the combustion duration

which makes its thermal efficiency and fuel economy lower than the Otto cycle operation at high load.