Applying forced induction to bioethanol HCCI operation with residual gas trapping

With increasing interest in renewable fuels, bioethanol has been successfully used in conventional internal combustion engines. Its application in naturally aspirated homogeneous charge compression ignition (HCCI) engines, however, has shown a much reduced usable load range. The approach documented here applies forced induction to bioethanol HCCI operation on a gasoline type engine, in conjunction with residual gas trapping. This retains the much reduced external heating benefits associated with residual gas trapping. In the present work, the achievable engine load range is controlled by boost pressure, excess air ratio, and trapped residual gas amounts. A substantial increase in load range can be achieved, up to 7.5 bar indicated mean effective pressure (IMEP), while keeping NOx emissions up to 2 orders of magnitude lower than spark ignition (SI) operation. There is, however, a possible fuel penalty of up to 11% at the maximum achievable load.