| With fuel prices rising and increasingly strict emissions regulations, high efficiency,energy saving and environmental protection has become the essential conditions of a newengine product development. Gasoline Direct Injection (GDI) engine has high power, goodfuel economy, low emissions and rapid response, so it’s main product in the future.Based on the8AYN10PFI engine,8AYT10GDI engine was designed. High tumbleratio port and piston with special designed top surface have been developed, the piston ringstructure, intake pipe parameter and cam lobe have been optimized, GDI system wasdesigned and turbocharger matching has been studied, and plateau performance, transientresponse character have been estimated. The bench test datas show that the power, fueleconomy and emissions meet expectation, and reached the international leading level.CFD simulation technology was used to study spray process, speed field, turbulentkinetic energy, air-fuel ratio distribution and temperature distribution of GDI engine.Revealed tumble feature from birth, development to be compressed and broken process incylinder. and find that stable flow field was formed in spark plug electrodes at ignitiontiming, flow velocity and turbulent kinetic energy were gradient distribution from spark plugelectrode to the wall of combustion chamber, and these distribution are conducive to stablecombustion and flame propagation, proved combustion system design of8AYT10isreasonable. The effects of different injectors to mixture uniformity, fuel concentration andfuel impingement wall were analyzed, the results show that the fuel impingement wall iseffected by injector scheme greatly. Scheme1injector assembly was reasonable for littlefuel impingement wall quantity. The effects of secondary injection to mixture formationprocess were studied in cylinder, and proposed the scheme that using secondary injectionstrategies to reduce spray penetration, decrease fuel impingement wall in GDI engine, andthis scheme was verified in cold start condition.GDI optical single-cylinder engine was designed for researching, and optical testingsystem was established, and it realized visualization of spray process in cylinder. Sprayshape, air motion and combustion chamber structure interaction rules were researched byusing optical single cylinder engine, and the results were compared with CFD calculation,the conclusion was that simulation results were right. Combustion flame propagation underdifferent conditions and soot formation were analysed, and found that through two times injection, the spray penetration can be decreased, and reducing soot formation at1650r/min,full load. Finally, integrated optical single cylinder engine results and CFD simulationresults, the scheme1injector was confirmed and set-100°CA ATDC as second injectiontimming at cold start condition. Optical single cylinder engine testing and CFD simulationtechnology were used in researching at the same time, and this was the first time. Thesimulation results were validated in experiment, and the CFD simulation can guide theexperiment further. Development schemes were more accurately by using this method, andimproved development efficiency, reduced development risks.Through GDI engine test bench, the effects of injection timing on combustioncharacteristics of GDI engine was studied. The results show that if injection timing was tooearly, fuel beam can impinge on piston and cause wet wall phenomenon, reducedtemperature of chamber wall, decreased mixture speed of air and fuel, and heat efficiencywas low. While if injection timing was too late, there was no enough time for air and fuelmixture, and uniformity was poor at ignition time, flame propagation speed was slow,thermal efficiency was decreased, and combustion stability was poor. Injection timing hasthe best time, and in the best injection timing, cumulative heat release rate and combustionduration of engine were short, and cyclic variation was low, torque was bigger, fuelconsumption was low, but the maximum combustion temperature was high, and NOxemission was high. Experiment of different injection pressure condition shows that ifinjection pressure was high, air and fuel mixture were fully and torque was high, fuelconsumption rate was low. High injection pressure reduced HC emission, but the effects6onCO and NOx emissions were smaller. VVT opening test show that, fuel consumption of theengine was reduced with increasing exhaust VVT opening, while for cyclic variation rate,the effect of exhaust VVT opening to cyclic variation was greater than intake VVT opening,but the cyclic variation rate can be controlled within3%.A fiber test system was built, and realizing visualization research of irregularcombustion in cylinder, The influence mechanism of conventional knock with engine loadand fuel injection timing were studied, and obtained the effective methods to control knock.Test results at low speed, high load showed that the flame propagation irregular less than40%of8AYT10engine, indicating that the engine has high anti-konck performance. Thepre-ignition and super knock were studied in GDI engine, researched distribution of timeand location when pre-ignition was occur, and proposed the strategy and detail methods forrestraining pre-ignition by secondary injection. The results at1500r/min, full load showthat there was no pre-ignition phenomenon in GDI engine after running3hours by using optimized secondary injection strategy, proved the methods were effective.Generation mechanism of NVH was analyzed in GDI engine, and the methods forreduce engine’s mechanical noise were proposed, such as decreasing gap between cylinderand piston, using bias piston pin, increasing diameter of the high pressure fuel pumpplunger, reducing injection rate and optimizing turbocharger etc. The methods to reduceengine’s combustion noise were proposed too, such as optimizing ignition advance angle,changing combustion mode and controlling fuel quality. All of these methods haveimportant guiding significance to improve NVH performance of GDI engine. |
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