Abstract
The limited load range is one of the issues of homogeneous charge compression ignition (HCCI) combustion. The authors have previously experimented using an engine equipped with an Electromagnetic VVT and charge boost from a mechanical supercharger. As a result, we confirmed that it is possible to increase the higher load operational range while keeping low NOx emission. However, the loss associated with the mechanical supercharger increases brake specific fuel consumption (BSFC). A turbocharger is not suitable because it cannot create the required charge boost effect at low and medium load because the exhaust energy is low at that condition. Therefore we have devised "Inter-Cylinder exhaust gas recirculation (EGR) Boost System" which enables charge boost HCCI operation by making use of the dynamic exhaust blow-down effect (pressure wave) and have confirmed its effectiveness in expanding the HCCI operational range.
The Inter-Cylinder EGR Boost System enabled HCCI combustion at higher loads up to IMEP 650kPa at an engine speed of 1500rpm (which cannot be achieved by "Internal EGR" through negative valve overlap because of knocking) while keeping low NOx emissions (at less than or equal to 1/100 that from spark ignition combustion). We confirm that this is because the boost system increases the amount of in-cylinder gas and therefore results in a larger heat capacity of the charge than does negative valve overlap, while keeping the compression TDC temperature at the value required for auto-ignition. As a result, it is possible to cover the Japanese 10-15 mode using HCCI by a combination of Inter-Cylinder EGR Boost, Internal EGR by negative valve overlap and direct injection during negative valve overlap, the latter improving the low load limit.
Keywords: HCCI, charge, boost, EGR, blow down