Numeric Investigation of Gas Distribution in the Intake Manifold and Intake Ports of a Multi-Cylinder Diesel Engine Refined for Exhaust Gas Stratification

In-cylinder exhaust gas recirculation (EGR) stratification, generally achieved by supplying EGR asymmetrically into intake ports on a four-valve diesel engine, is sensitive to trapped exhaust gas in the intake manifold and intake ports that is caused by the continuous supply of EGR during the valve-close periods of the intake valves. The subject of this study is to evaluate the distribution of trapped exhaust gas in the diesel intake system using commercial Star-CD software (version 4.22.018). Numeric simulations of the intake flow of fresh air and recycled exhaust in the diesel intake system were initialized following previous experiments that were conducted on a reformed six-cylinder diesel engine by supplying CO2 instead of EGR to the tangential intake port alone to establish CO2 stratification in the first cylinder. The distributions of the intake CO2 in the intake manifold and intake ports under the conditions of 1330 r/min and 50% load with different mass flow rates of CO2 are discussed. This indicates that CO2 supplied to one intake port alone would escape to another intake port, which not only weakens the CO2 stratification by diminishing the mass fraction disparity of the CO2 between the two intake ports of cylinder 1, but also influences the total mass of CO2 in the cylinder. There is 4% CO2 by mass fraction in the intake port without CO2 supply under the condition that the CO2 mass flow rate is 5 kg/h during the intake process, and 10% CO2 under the condition of 50 kg/h.