Investigations of Operational and Optical Indexes of the Combustion Process for the Multiple Injection Different Strategies in CI-Type Model Engine J. Kaźmierowski 1 , I. Pielecha 1 , J. Czajka 1 , K. Wisłocki 1 , P. Borowski 1 1 Poznan University of Technology, Poland Abstract The paper discusses the results of research on the influence of the strategies of fuel dose division on the engine operational and optical indexes and the combustion process. The paper also contains an exhaust gas analysis conducted with the use of a Rapid Compression Machine. The recorded images related to the period from the onset of the injection to the beginning of the appearance of combustion spots have also been analyzed. The following have been varied: number of doses, size of doses, dwell times and excess air coefficient. The authors performed a comparative analysis of the thermodynamic indexes of the combustion process obtained from the indicator tracings.  Corresponding author: ireneusz.pielecha@put.poznan.pl Proceedings of the European Combustion Meeting 2013 Introduction Technological advancement in combustion systems of diesel engines triggers the need of fulfilling many contradictory requirements. Among those are such issues as maintenance of environmental standards in terms of the exhaust emissions with a simultaneous preservation of the thermodynamic properties of the combustion process and fuel consumption. The fulfillment of the above requirements requires appropriate strategies of fuel dose division. Earlier works of the authors were related to the issues of fuel injection [1–3] and fundamental research of the combustion of diesel fuel in compression ignition engines [4]. The currently conducted research joins the two issues in the aspect of the influence of diesel fuel dose division on the initial stages of self-ignition. Literature analysis related to the application of the latest solutions in fuel dose division indicates the following facts: a) Literature analysis [5] shows that the division of the injected fuel into two doses has a significant impact on the emission of HC and CO. In a situation when the first dose is greater than the second one an increase in the hydrocarbons and nitric oxides emission was observed at a simultaneous reduction of the emission of particulate matter. An increase in the pilot dose also resulted in an increase in the combustion noise level and the emission of NO x . These effects were reduced by extending of the injection dwell time. Similar effects were observed in research [6] when a small pilot fuel dose was applied. The investigations presented in [7, 8] also indicate a reduction of the emission of particulate matter; b) The results of the investigations presented in [8, 9] indicate an improvement in the fuel combustion and consequently a reduction of the fuel consumption through fuel dose division (as compared to a single fuel dose injection); c) From the investigations presented in [6] results the dependence of the NO x emission from the size of the first fuel dose: a large pilot fuel dose increases the homogeneity of the charge and a reduction of the NO x emission can be obtained through a delay of the injection of the main fuel dose. In a situation when the injection angle of the first fuel dose was increased by 20-25° a lower emission of HC and CO was observed; d) Literature analysis [5, 10] is related to an engine fitted with an exhaust recirculation system. During the engine operation less oxygen is supplied with the intake air and the fuel dose division results in better mixing of fuel and air inside the cylinder. Owing to the application of fuel dose division a drop in the emission of NO x and PM was obtained. e) The results of the investigations presented in [11] indicate that the application of 25% of the mass of the injected fuel in the final fuel dose may lead to a reduction of the emission of particulate matter. The authors’ own research based on the knowledge related to these aspects allowed an assessment of the combustion processes and its thermodynamic indexes in relation to the exhaust emissions. Optical investigations of the combustion processes constituted a supplement to the indicator research and allowed determining of the intensity of formation of the self-ignition spots (hot flames) depending on the applied fuel injection strategy. Specific Objectives The research related to the fuel dose division and its combustion was conducted with the use of a Rapid Compression Machine (RCM) – Fig. 1. The system parameters were precisely described in [3]. The information contained there indicates the possibility of reflecting of the real engine thermodynamic parameters of the self-ignition process in an RCM. A pneumatic actuation of the piston movement (the pressure of 5 MPa) allowed an obtainment of the compression pressure on the level of 4 MPa. The values of the compression pressure correspond to typical direct injection diesel engine pressures. The investigations of the combustion process (development of the self-ignition spots) were conducted using High Speed camera (Star 5 by LaVision). The footage was recorded with the filming rate of f = 5 kHz, which allowed obtaining images with the time shift of