Cylinder Deactivation Strategies to Stabilize High Stratification Gasoline Compression Ignition Down to Idle

Gasoline compression ignition (GCI) is a family of combustion strategies that can be used to achieve low emissions and fuel consumption in medium- and heavy-duty applications while taking advantage of projected cost advantages of gasoline over diesel fuel in the future. In particular, high fuel stratification GCI (HFS-GCI) has been shown to have CDC-like thermal efficiency and combustion control by utilizing near-TDC injection timings to achieve a principally mixing-controlled combustion event. The stability of HFS-GCI combustion at low loads has been shown to be the principal challenge to its implementation in production applications and in this study, a novel class of cylinder deactivation strategies to achieve stable HFS-GCI combustion down to no-load (0 kW brake power) is proposed and studied. 1D simulations were carried out in GT-POWER and coupled experiments were carried out in a single-cylinder medium-duty test cell with an on-road 87AKI gasoline fuel. The effects of deactivation, alongside the effects of load, combustion phasing, and valve closure were thoroughly examined. Deactivation-based strategies were found to be successful in extending the low-load limit of the engine down to 0 kW of brake power. Valving action was seen to be important at no-load conditions; flow of air through the nonoperational cylinders was found to provide additional enthalpy to the turbocharger, which increased boost pressure, further stabilizing the combustion. However, the importance of the valving action was seen to reduce as load was increased; in fact, the additional pumping loss incurred by permitting airflow through the nonoperational cylinders was found to reduce the thermal efficiency and worsen the fuel consumption. An optimum between stability, thermal efficiency, and fuel consumption was realized through the use of cylinder deactivation strategies at all the conditions considered, offering a promising, near-term pathway to the use of gasoline-like fuels in diesel engines.