Lean combustion stability of spark ignition engines

Literature shows that by controlling engines at extreme lean operating conditions (equivalence ratio <0.75) can reduce emissions by as much as 30% and also it improves the fuel efficiency by as much as 5∼10%. However, the engine exhibits significant cyclic dispersion in heat release, which causes engine instability and poor performance. Therefore, our objective is to minimize the cyclic dispersion in engine dynamics using a novel control scheme. The non-causal problem encountered during this controller design is overcome with a linear filter. The stability analysis of the closed-loop system is shown ensuring boundedness of all the signals. The controller can be extended to minimize engine emissions with high EGR levels, where similar complex cyclic dynamics are observed. Further, the proposed approach can be applied to a class of nonlinear systems, which have dynamic structure similar to that of the lean engine operation.