Numerical Simulation And Experiment Research On Lean Burn And NOx Emissions Purification On Gasoline Engine

Saving energy resource and protecting environment are two critical issues to realize consecutive development of human society. Development of internal combustion engines has to meet the demands of low fuel consumption and low emissions. Lean burn techniques in gasoline engines can both reduce fuel consumption effectively so as to reduce the emission of greenhouse gas-CO2 and lower the emissions of HC and CO significantly. However, the problem of the controlling NOx emissions at lean conditions is limiting the development of the lean burn gasoline engines. Therefore, the further studies on the lean burn and NOx emission control technologies are very important.Experiments were conducted on a YH465 gasoline engine. The flow characteristics of the inlet port in the cylinder head were tested on a steady flow test rig. The experiment results show that a rather strong tumble motion and a wake swirl motion both exist in the YH465 gasoline engine. Air motion combining fuel injection strategy can achieve lean burn. A one-dimensional engine numerical simulation program which was proved relatively exact through the test was implemented using AVL-boost software to study the lean burn.To satisfy the special requirements of lean burn technology and the emission control of gasoline engine, an electronic control system suitable for lean burn gasoline engine has been developed. This system can control injection and spark exactly to achieve lean burn. Using fuzzy parameter self-tuning PID controller, the fluctuation of the speed during the transitional time can be adjusted within the estimated and acceptable range.The economic and emission characteristics were simulated through analyzing the rate of the burned fuel on the engine simulation program. A best tumble ratio and a best swirl ratio were dug out through simulating the air motion in the cylinder of the impact of the lean burn. The methods to reduce NOx emissions were simulated, including increasing air-fuel ration, retarding spark timing, using rich-lean strategy and using exhaust gas recirculation(EGR). NOx emissions reduce obviously through all of these methods Experiments of the lean burn limits test were conducted on the test equipment. The limits of YH465 were 20.5～23,which saved fuel more than 10 percent. Experiments of reducing NOx emissions were examined increasing air-fuel ration combining three way catalyst strategy, rich-lean combining three way catalyst strategy and lean burn combining EGR strategy. The experiment results were consistent with the simulation results. The NOx emissions of the increasing air-fuel ration combining three way catalyst strategy were not completely to fit the emission low. The NOx emissions of the rich-lean combining three way catalyst strategy met the EuropeanⅡemission low. The NOx emissions of the lean burn combining EGR strategy were much lower than the content of the EuropeanⅡemission low, which met the EuropeanⅢemission low with the aftertreatment of the three way catalyst.