engleski

Experimental Investigation of Sources of Influence of Exhaust Gas Recirculation on the Spark Ignition Combustion

Modern internal combustion engines are designed so that they emit limited pollutants and low CO2 emissions, while delivering the required performance. Due to the requirements for more efficiency and lower emissions, modern SI engines are optimized for maximum efficiency which is usually close to the limit of the knock ignition. To enable further developments, knock avoiding strategies have to be further investigated. One of the methods to suppress knock is to lower the temperature of the end- gas, because engine knock occurs when the end- gas auto ignites. Cooled exhaust gas recirculation (EGR) has proven to be a promising way to reduce end-gas temperature. Furthermore, EGR described in this study, is shown as one of the most effective techniques for reducing engine out emission of nitrogen oxides (NOX) in SI engines. In this research the influence of the main sources of knock suppression by using EGR in the SI engine are characterised. The factors that influence knock suppression are flame propagation speed, chemical influence on auto ignition (CO2, H2O, dilution etc.) and end-gas temperature influence. The study is performed by comparison of the SI operation at specific load with and without EGR. Further on, experimental study is carried out for three cases. First case is normal operating condition of engine without the application of EGR. In the second case cooled EGR is applied and finally in the third case engine is operated with application of the EGR and higher intake air temperature obtained with air heater. Higher intake temperature is applied in order to equalize the maximum temperature of the end-gas obtained in first case (the case without EGR) in order to determine the temperature influence on knock suppression. Since for the given cases the amount of fuel supplied to the engine is supposed to be constant, the constant fresh intake charge is maintained by optimization of the intake pressure. Results presented in this study characterize how end-gas temperature influences the knock occurrence when cold EGR is applied. Furthermore, it describes one of the ways to reduce the knock occurrence in the engine cylinder by reducing end-gas temperatures. All tests are performed on an in- house developed experimental setup that uses a modified single cylinder diesel engine HATZ 1D81Z that was converted for running in SI operation.

SI Engine, EGR, CoV, Heat release, Experimental engine, Knock

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