Influence of the exhaust gas recirculation on the oxygen contents and its excess ratio in the engine combustion chamber

Exhaust gas recirculation (EGR) can be realized on the external or internal way. The main goal of EGR is to decrease the combustion temperature of the combustible mixture by increasing the relative heat capacity of the working medium. An additional effect is to reduce the oxygen content in the gas mixture flowing into the combustion chamber. To quantify the exhaust gas recirculation some descriptive parameters are defined, including: – exhaust gas recirculation rate R, – multiple of exhaust gas recirculation K, – relative exhaust gas recirculation W. The analysis concerns the effective oxygen excess ratio Oef in the combustible mixture and the so-called internal oxygen excess ratio Ow,, which additionally takes into account the supplied oxygen with the recirculation stream. It was found that with increasing of the exhaust gas recirculation degree systematically decreases the content of the oxygen [O2]d in the combustible mixture, while increases the oxygen excess ratio Oef observed in the exhaust gases. Changes of this all parameters influence the combustion coditions in the engine cylinder, and next the achieved specifaic work, energy efficiency and emission of the combustion engine. An advanced system with independent, early exhaust valve closing enables realization of an internal EGR. Effectiveness of internal recirculation is lower than the external recirculation.