Decoupled control of combustion timing and work output in residual-affected HCCI engines

Homogeneous charge compression ignition (HCCI) is a promising low temperature combustion strategy for internal combustion engines. However, when HCCI is achieved with variable valve actuation (VVA) the lack of a direct combustion initiator and cycle-to-cycle dynamics complicate control of the process. This work outlines a strategy for the simultaneous control of both in-cylinder pressure and combustion timing through the use of an approximately decoupled timing/pressure controller. The decoupling is achieved by controlling peak pressure and combustion timing on separate time scales with different VVA-induced control inputs, inducted gas composition and effective compression ratio, respectively. The paper also details how the strategy can be extended to handle decoupled timing/work output control. Experimental results show that in-cylinder pressure or work output can be controlled on a cycle-to-cycle basis, while combustion timing is slowly varied.