Closed-Loop Combustion Control

Abstract

Low temperature combustion (LTC) is an engine combustion mode that yields ultralow NO x and soot emission levels along with high fuel conversion efficiency. Typically, LTC engines use premixed fuel–air mixture, and combustion is mainly governed by chemical kinetics. The LTC strategies such as partially premixed combustion (PPC) and reactivity-controlled compression ignition (RCCI) have some level of direct control on combustion phasing due to direct injection of fuel in the engine cylinder. However, homogeneous charge compression ignition (HCCI) combustion strategy lacks the direct control on combustion phasing. In HCCI combustion, ignition timings are kinetically controlled and affected by pressure and temperature history of the charge in the engine cylinder (indirect control). Therefore, HCCI combustion requires the combustion feedback control for its very operation. The present chapter describes the closed-loop combustion control in LTC engines. First, the need of closed-loop combustion control and control variables are discussed. Then, combustion feedback sensors and combustion control actuators are described in detail. Typically, cylinder pressure sensor and ion current sensors are used for sensing of combustion phasing in HCCI combustion. The last section presents the combustion control methods and various controllers used in different LTC strategies such as HCCI, PPC and RCCI, for closed-loop combustion control.