Effects Of The Exhaust Gas Dilution And Variable Tumble Ratio On The Combustion And Emissions Characteristics Of A Direct Injection Gasoline Engine At Part Load

An investigation of exhaust gas dilution and tumble ratio on combustion andemissions characteristics of a1.8L gasoline engine at part load is presented. Anexternal exhaust gas recycling system is introduced, providing homogeneous mixedgas and reaching the maximum EGR ratio of30%. Tumble ratio is changed bycontrolling the flap in the intake manifold, which can provide the tumble ratio from1.646to6.167.The results show that: with the combustion phase delayed gradually, the fuelconsumption rate firstly decreases, and then increases. The maximum combustionpressure in-cylinder decreases as the combustion phase delayed. With the increase ofEGR ratio, the maximum combustion pressure at the same combustion phaseincreases gradually. As the Tumble ratio increased, the maximum combustionpressure increases at all conditions. Maximum pressure rise rate gradually reduceswith the combustion phase delayed, and increases significantly with the tumble ratioincreased. In the region of lower fuel consumption rate, the maximum pressure riserate can be maintained below0.3MPa/°CA. With the combustion phase delayed, thecycle by cycle coefficient of variation decreases firstly, and then increases. In theregion of a lower fuel consumption rate, the cycle by cycle coefficient of variation canbe maintained at about2%. As the tumble ratio increased, the cycle by cyclecoefficient of variation improves obviously, and the maximum EGR ratio can beextended.At part load, the introduction of exhaust gas dilution can improve the fuel economyeffectively. As the EGR ratio increased, the fuel consumption can be reduced. But toomuch exhaust gas will cause increase of fuel consumption. When EGR ratio is lessthan20%, increasing the tumble ratio has little effect on fuel consumption. When theEGR ratio is higher than20%, the combustion gets deteriorate. Higher tumble ratiohas more significant impact on airflow movement and combustion, the fuelatomization improves compared to low tumble ratio, and the fuel consumptionreduces. Increasing tumble ratio allows increasing the airflow motion in cylinder, themixture turbulent kinetic energy increases, the flame propagation speed gets muchfaster. The maximum explosion pressure and pressure rise rate can be increased. The ignition delay and total combustion period increase as the EGR ratio increased.Increasing the tumble ratio can significantly shorten the flame development durationand total combustion period, resulting in improved combustion efficiency. When theEGR ratio is higher than20%, the cycle by cycle coefficient of variation begins to risesharply. Increasing the tumble ratio can lower cycle by cycle coefficient of variation,thus the EGR ratio limit extended. With the EGR ratio increased, HC emissionsslightly increase, NOx emissions drops significantly, with CO emissions shows somevolatility. With the tumble ratio increased, CO emissions reduced, NOx and HCemissions increased.