Abstract: In a heavy duty diesel engine equipped with regulated two-stage turbocharging system, the impacts of different turbocharge bypass valve opening on fuel consumption and emission are explored. Results show that, at low speed, opening the bypass valve helps to reduce NO_x emission, but in large load it causes the deterioration of the fuel economy. At high speed and low load, increasing the opening of the bypass valve helps to reduce pumping loss, the maximal drop in fuel consumption can reach 7.6%. While in middle and large load, due the effect of the interaction between pumping loss and indicated thermal efficiency, opening the bypass valve can reduce NO_x emission without worsening the fuel economy premise. At different speeds and low load condition increasing the opening of bypass valve, or at middle and large load condition closing or reducing the opening of the bypass valve can achieve the best fuel economy, without obvious deterioration of NO_x emission that the smoke emission is less than 4%. Under the optimal control strategy of turbocharged diesel engine, compared with the original single-stage turbocharged engine prototype, two-stage turbocharging in low speed has the advantage of high fuel economy.

Key words: power machinery and engineering, two stage turbocharged diesel engine, bypass valve, zoning control