Based on a common-rail diesel engine equipped with two-stage turbocharger system

a one-dimensional thermodynamic model was established to study the effects of different valve secondary opening strategies (intake valve re-opening

exhaust valve re-opening as well as intake and exhaust valves re-opening) on engine combustion

NOx emissions and energy distribution. The results show that

at the same valve lift

with the advances of the intake valve re-opening timing and exhaust valve re-opening timing

and with the increase of interval between the timings of the intake valve re-opening and exhaust valve re-opening

the pressure in the cylinder and peak heat release rate increases

the crank angle corresponding to 50% of total heat release (CA50) advances

and the brake thermal efficiency

combustion temperature as well as NOx emissions increases. At the same valve re-opening timing

the influence of increasing valve lift on the engine performance and emissions increases. The comparison of the different valve re-opening strategies shows that the re-opening of both intake and exhaust valves has the greatest impact on the CA50

exhaust energy loss

brake thermal efficiency and NOx emissions

while the exhaust valve re-opening strategy has the least impact. The trade-off between the brake specific fuel consumption (BSFC) and NOx emissions can be better improved by the intake valve re opening strategy with the intake valve lift being 2.4 mm and the re-opening timing 30 degrees after bottom dead center.