Experimental investigation on influence of EGR on combustion performance in SI Engine

In this research, the use of stoichiometric air-fuel mixture with exhaust gas recirculation (EGR) technique in sparkignition engine was experimentally investigated and its influence on main SI combustion parameters is shown. Experimental setup on which this research is performed consists of SI engine, AC Dyno, software for control of engine and dyno, and various measurement devices including the indicating equipment for SI engine. The research is performed by comparing the SI operation at specific load with and without EGR. In this analysis two comparisons are made: one with fixed spark timings and one with optimized spark timings. Introduction The future development of motor vehicles is oriented to environmental awareness in order to prevent global pollution. Greenhouse gases are proven to be one of the main reasons for global warming [1][2]. Therefore, the internal combustion engines are today designed so that they emit limited pollutants and CO2 emissions, while delivering the required performance. As CO2 emission is proportional to fuel consumption, the efficiency of IC engines is becoming one of the primary development targets [3]. On the other hand, one of the pollutants that is restricted by emission regulations and is produced in large amounts in SI engines is NOX. Although NOX is efficiently cleaned by a three way catalysts in SI engines exploration of pathways toward lower NOx production is still worthy especially if one considers running the engine in lean conditions. In [4] it has been shown that exhaust gas recirculation (EGR) is one of the most effective techniques for reducing engine out NOX emission in SI engines. Suppression of NOX formation is achieved by diluting the in cylinder mixture with EGR, by lowering the in-cylinder temperature through the increase of heat capacity in the incylinder mixture and by reducing oxygen concentration [6]. The reduction of fuel consumption of modern SI combustion engines is today obtained by several technologies: direct injection, combustion chamber optimization, turbocharging, etc. Turbocharging increases load and therefore reduces the ratio of friction losses, but at the same time increases the tendency to knock. In [5] it has been shown that cooled EGR can be employed for avoiding abnormal combustion, e.g. knock. This reduction of knock tendency is achieved by the combination of three effects: diluent effect, thermal effect and chemical effect [4]. The use of EGR for lowering fuel consumption was shown in [6] where the improvements from 6% at high speed up to 17% at low speed were presented. Similarly Potteau et al. [9] measured the reduction in BSFC up to 14% by use of EGR. Additionally they showed an exhaust gas temperature decrease up to 100°C. The use of EGR can also be employed for reducing throttling losses at part load as shown in [7]. Although there are some benefits of using EGR in SI there are also some shortcomings and limitations. The use of EGR decreases combustion stability and increases coefficient of variation of IMEP. Even though the use of EGR in SI has been researched [8] and there are some publications regarding its use, there is no comprehensive analysis of the EGR influence on SI combustion, performance and emissions. The purpose of this research is to make a step forward in the understanding of the EGR influence on SI combustion and consequently engine performance and emissions. This will be achieved by a comprehensive set of experimental results showing various influences of EGR and of methods of controlling the engine in conditions with elevated EGR settings for exploiting these benefits. The experimental work will be done at University of Zagreb, Faculty of Mechanical Engineering and Naval Architectures, Laboratory for Engines and Motor Vehicles on the experimental setup shown in