Evaluation of MFB50 is very useful for combustion control, since it gives an evaluation of the combustion process effectiveness. Real-time monitoring its value enables to detect for example the kind of combustion that is taking place (useful for example for HCCI applications), or could provide important information to improve real-time combustion control. While it is possible to determine the position where the 50% of mass burned inside the cylinder is reached using an in-cylinder pressure sensor, this work proposes to obtain this information from the engine speed fluctuation measurement. In-cylinder pressure sensors in fact are still not so common for on-board applications, since their cost will constitute an important portion of the whole engine control system cost. Engine speed measurement is instead already performed in modern engine control systems and therefore being capable of obtaining MFB50 related information from this signal means obtaining it at approximately no additional costs. The MFB50 estimation procedure presented in this paper is based on the measurement of the engine speed fluctuations and it mainly consists in two separated steps. As a first step, a torsional behavior model of the powertrain configuration is developed. The engine-driveline torsional model enables to estimate the indicated torque frequency components, from the corresponding components of the instantaneous engine speed fluctuation. This estimation can be performed cycle by cycle and cylinder by cylinder. As a second step, the analysis of the relationship between MFB50 and the phase of the frequency components over an engine cycle allowed defining the final estimation algorithm that reconstructs the MFB50 starting from the instantaneous engine speed fluctuation analysis. The developed approach has been applied with success to a diesel engine mounted on-board a vehicle.

In modern Diesel engine control strategies the guideline is to perform an efficient combustion control, mainly due to the increasing request to reduce pollutant emissions. Innovative control algorithms for optimal combustion positioning require the on-board evaluation of a large number of quantities. In order to perform closed-loop combustion control, one of the most important parameters to estimate on-board is MFB50, i.e. the angular position in which 50% of fuel mass burned within an engine cycle is reached. Furthermore, MFB50 allows determining the kind of combustion that takes place in the combustion chamber, therefore knowing such quantity is crucial for newly developed low temperature combustion applications (such as HCCI, HCLI, distinguished by very low NOx emissions). The aim of this work is to develop a virtual combustion sensor, that provides MFB50 estimated value as a function of quantities that can be monitored real-time by the Electronic Control Unit (ECU).Modern technologies for Common Rail Multi-Jet Diesel engines allow designing injection patterns with many degrees of freedom, due to the large number of tunable injection parameters (such as rail pressure, start and duration of each injection….). First, this paper describes a model of the combustion process developed in order to evaluate the energy release within the cylinder. A zero-dimensional approach based on the Wiebe function has been chosen, because it allows obtaining a model which is accurate enough for the analysis at a low computational cost. Once the combustion model has been developed it can be used to determine MFB50. The second section of this paper describes the existing correlations between the injection parameters and the identified Wiebe parameters. These correlations can be used for heat release and MFB50 on board estimation.Experimental tests have been performed running a turbocharged Common Rail Multi-Jet Diesel engine (with up to 4 injections within the same engine cycle) in order to determine the accuracy of the methodology.The described approach allows evaluating MFB50 as a function of the injection parameters as well as other quantities that can be monitored real-time by the ECU. Additional sensors are not necessary for this methodology, therefore it requires no extra cost.

Due to increasingly stringent emission regulations and the need of more efficient powertrains, obtaining information about combustion process becomes a key factor. Low-cost in-cylinder pressure sensors are being developed, but they still present long-term reliability issues, and represent a considerable part of the engine management system cost. Research is being conducted in order to develop methodologies for extracting relevant combustion information using standard sensors already installed on-board. The present work introduces a methodology for combustion parameters estimation, through a control-oriented analysis of structure-borne sound. The paper also shows experimental results obtained applying the estimation methodology to different passenger car engines