Research On Two-stage Charging System Matching And Performances Of Gasoline Engines

As the boost pressure level continuously increases, single stage turbochargingsystem is no longer to meet the boosting requirements of modern engines any more.Under this circumstance, two-stage charging system emerges, since it can effectivelyimproves the engine performance, acceleration and fuel economy as well as transientload-step response characteristic. This research is focused on the engine chargingsystem matching and performance comparison between a superturbo system and atwo-stage sequentially turbocharged system, and provides a new method for impovingthe low speed engine torque, transient load-step response characteristic as well as thefuel economy by comparing and analyzing with the traditional single-stageturbocharged gasoline engine.According to the actual structure sizes and dyno test data of the1.4L superturboengine, one-dimensional simulation software GT-Power is utilized to creat thesimulation model, with detailed description to the important submodules and parametersettings. The model is then calibrated and validated against experimental data, and thetwo sets of data match well, it indicates that the simulation model has high precision.Thus, the1.4L single-stage turbocharged gasoline engine simulation model is createdand calibrated.Then,the gear ratio, inlet control valve and wastegate control strategy are analyzedfor engine power, fuel economy, pumping loss, supercharger etc. The influence trendsof the three elements on the engine performance are summarized. According to therequirements and principle of the charging system matching as well as the goal of thetwo-stage turbocharging system, the BorgWarner KP35type compressor and KP31type turbine are selected, and the two-stage turbocharged engine model is establishedon the basis of superturbo engine simulation model.Then, through detailed study of engine knocking theory, a knocking module isdeveloped and utilized to optimize the spark timing of the two-stage turbochargedsystem to suppress the engine knock.Finally, based on the GT-Power simulation results,the low speed engine torque,transient load-step response characteristic as well as the fuel economy of the threetypes of charging systems under consideration are compared and analyzed with eachother. Results indicate that the superturbo and the two-stage sequential turbochargercould increase the1000r/min full load torque by62.80%and54.35%respectively， while the engine BSFC at4000r/min full load could also be reduced by as much as23.45%and22.71%respectively over the single-stage turbocharged baseline engine；Charging systems in the order of fastest to slowest transient load-step response are thesuperturbo, the two-stage sequential turbo and the single-stage turbo. The three typesof charging systems demonstrate the most obvious differences at the engine speed of1500r/min.