Torque based estimation of diesel engine combustion phasing

Licentiate thesis, 2009

Demands on increased efficiency and reduced emission levels introduce new challenges for the design of modern diesel engines. In order to fulfill these demands, diesel engines of today are becoming more and more complex. This escalating complexity not only applies to the engine itself, but also to its control system. As a result, the interest in closed-loop combustion control is growing since it offers more accurate and robust control while requiring less calibration effort than an open-loop control system. This thesis deals with estimation of diesel engine combustion phasing, based on measurements of the crankshaft torque. The purpose is to investigate whether or not a crankshaft integrated torque sensor can provide information about the combustion phasing in a diesel engine and hence enable the control of this combustion property in closed-loop. The proposed method has previously been implemented for combustion phasing control in a gasoline engine and is in this work adapted to suit the principally different and more complex combustion process in a diesel engine. The first part of the studied method consists of separating the measured torque signal into cylinder individual torque contributions. These contributions are then used, together with a combustion model, in order to estimate combustion phasing. Both of these steps are presented and analyzed in this thesis. Based on measurement data, the results indicate that a crankshaft torque sensor is a viable source of information for closed-loop diesel engine combustion phasing control.