MASS FRACTION BURNED ANALYSIS

Common algorithms for mass fraction burned computations are presented and compared. Some potential problems of these calculations are also discussed. The comparison shows that the evaluation of polytropic indices, necessary for current procedure may lead to some ambiguity in MFB determination. An internal combustion engine gains its energy from the heat released during the combustion of the oxidizer-fuel mixture. Engine processes leading to the conversion of the chemical energy contained in the fuel are complex phenomena that occur in transient thermodynamic conditions and the reliable evaluation of these processes is the key to engine optimization and effective control - combustion processes inside the engine cylinder “dictate” engine power, efficiency and emissions. The optimization methods may be based on cylinder pressure feedback control. In-cylinder pressure changes are the crucial parameters - combustion descriptors - affecting performance, thermal efficiency and emission of spark-ignition engine. Standard engine control systems rely on calibration tables. Their values are taken from an analysis of an engine under fixed test conditions. The extensive review of advanced engine controls for modern SI engine prepared by Delphi & GM is given in [11]. According to the authors, cylinder-pressure-based feedback control has potential to optimize spark timing, A/F ratio and EGR for the best engine operation. It may also offer improved detection of knocking combustion and cylinder misfire. The overall long-term goal of contemporary scientific studies in the field of internal combustion engines is to develop a neural-network-based control system - artificial neural network which derives its name from the human brain with its capability of learning. Such a system should be better than present day controllers, both in terms of fuel efficiency and exhaust emission levels. The successful development of artificial neural network algorithms for nonlinear signal processing and control of SI engines is led by Isermann’s group of Darmstadt University of Technology. The energy conversion during a combustion cycle can be described by the Mass Fraction Burned (MFB) at a specific crank angle degree (CAD) and the MFB, in turn, can be used by feedback control systems. In IC engine, the MFB depends on engine geometry, engine speed, A/F, ignition angle, residual mass etc. Measuring and controlling the result can compensate many variables that affect the combustion process compensated on an individual cylinder basis.