Evaluation of SI-HCCI-SI mode-switching using conventional actuation on a CNG engine
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Abstract
Homogeneous Charge Compression Ignition (HCCI) operation is desirable for its high thermal efficiency and low emissions of NOx and particulates. Difficulty with cold starting and maximum achievable speed/load highlight the desire for mode-switching to traditional spark ignition (SI) operation.
Mode-switching between SI and HCCI is investigated using only actuation of throttle, CNG injector pulse width, and CNG injection timing on a single cylinder CFR engine. Open-loop control achieves a one cycle mode-switch between two adjustable IMEP levels. Sequences are repeatable as demonstrated by 10 mode-switches with the same inputs. Performance is evaluated using a developed mode-switch performance criterion (MSPC) by considering duration between steady-states of operation, smoothness of IMEP, and knock based on maximum rate of pressure rise. Comparing the results with subjective analysis (the current standard) reveals good correlation. Throughout development, mode-switching performance is shown to improve by a factor of 60.