Application of adaptive control to reduce cyclic dispersion near the lean limit in a small-scale, natural gas genset

Predictive feedback control is applied to achieve moderate reductions in cyclic dispersion in a two-cylinder, four-stroke Kohler Command 25 genset which was modified to include port fuel injection and to operate at lean conditions on natural gas. Observations of the combustion dynamics were used to define a desired target point for control and to predict future combustion events that may stray from the target point. Two methods for obtaining the predictions of future combustion events were presented. In the first method, the recent history of cycle heat release was used to construct an adaptive, low-order map that relates the current-cycle heat release to the next-cycle heat release. The second method uses symbolic analysis to determine the relative frequency of successive-cycle combustion events and predict the most probable successor to the current cycle. A moderate reduction in cycle-to-cycle variation near the lean limit was observed. Similarities in behavior existed in various spark-ignition engines suggesting that a similar strategy could be successfully applied to large-scale reciprocating engines. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).