Study On Working Process And Performance Of Large Cylinder Diameter Dual Ignition Motorcycle Gasoline Engine

In China,the energy demand is enormous,especially for the fossil resource.However,the domestic exploitation quantity of fossil energy is far away from the need.So,during recent years,the foreign-trade dependence of fossil fuel is large up to70%,resulting in the energy security issue.The transportation sector is the main consumption of fossil fuel,which takes up more than half of the total fossil fuel's consumption,due to the large vehicle numbers in China.On the other hand,the environment pollution in China is serious.And the motor vehicles contribute a lot to the main environmental pollutants?such as HC,CO,NO and PM?,especially in metropolises.Among the motor vehicles,motorcycles also have lots of contribution in environmental pollutants,because the pollutant's emission factor is higher for motorcycles due to the fact that,motorcycle's emission standard is behind by 2-3stages relative to four wheels automobiles.Therefore,improvement of in-cylinder working efficiency and aftertreatment level is the imperative research direction for motorcycle industry.Investigations on the applications of advanced combustion technologies?such as the lean burn and multi-ignition?in motorcycle engines are meaningful for technical promotion and energy conservation and emission reduction in the field of motorcycle industry.In the present study,the performances and the essential working processes?especially for the flame propagation?of a motorcycle engine are thoroughly investigated under wide operating conditions through multi methods.We try to explore the interaction between operating parameters and their influencing patterns,and figure out the best implementation models of new technologies.Firstly,through the steady-state engine bench experiments,the engine's working parameters and performance were measured,and the performances and working processes were analyzed.For air/fuel ratio,the results indicated that the in-cylinder thermal-work conversion is more complete when the air/fuel mixture changed from rich to lean,resulting in the lower engine fuel consumption rate;the HC and CO emissions are decreased with the relative air/fuel ratio;and the NO rises as the increasing of air/fuel ratio;and for the cycle-to-cycle variation,at lightly lean operation?for instance,at?=1.1?achieves the best behavior.The cycle-to-cycle variation will deteriorate at too rich or too lean operations.These explain that more efficient and clean working process of gasoline engine can be achieved by optimizing the air/fuel ratio.For the ignition mode factor,the results demonstrated that the best engine's power,lower fuel consumption rate and slight decrease of knocking tendency are brought by the synchronous twin-spark ignition mode.Besides,under twin-spark ignition operation,all the HC,CO and NO emissions are higher than those of single-spark ignition.Then the reasons were investigated through CFD.And we found that,under dual-ignition the post temperature is lower than that of single-ignition,this is not good for oxidation of HC and CO during post flame or exhaust stage.But,the peak temperature of twin-spark ignition is higher than that of single-spark ignition,resulting in higher NO formation,because the NO almost only depends on the highest temperature.This indicates that the interaction between ignition number,timing and chamber structure must be optimized carefully,such that the engine's best combination performance can be obtained.Secondly,the gasoline surrogate combustion mechanism was improved by improving the core H₂/O₂/C₁ sub-mechanism,and the CO/CO₂ prediction was improved during combustion.Based on this,the zero-dimension ChemKin in-cylinder reactor model was built?only including the high-pressure cycle?.Meanwhile,the full cycle working process model was calculated through CFD?coupling a reduced chemical kinetics?.Then,their results were compared to experimental data.And some important observations were achieved.The homogeneous ChemKin reactor model can not catch the crevice and hierarchical effects?it only represents the core hot zone within the cylinder?,resulting in the poor predictions of pollutants.While,for CFD even it couples a simplified kinetics mechanism,it can still well predict the processes of heat release and formations of pollutants.These findings point out the direction for the coupling between physical and chemical models in in-cylinder simulations.The advantages of these two simulations were used to analyze the in-cylinder working process,all the specific patterns of pollutants formations under various ignition modes were explained well.Further,the flame propagation and its limitation were explored under various ignition modes.And this would guide the coordinatation among the ignition,geometrical structure and fluid organization.At last the vehicle transient cycle test was performed,and the results were compared to that under steady-state operations.The THC and CO emissions are very high at cold start stage,the CO₂ emission is also high not due to the good combustion,but due to the absolutely high fuel consumption;besides,CO and CO₂ emissions at transient operations are higher than that at corresponding steady operations.NO emission increases with vehicle speed.The results illustrated that lower volume efficiency and deviation of ignition timing from steady calibration points?especially at rural and motorway driving?lead to the poor combustion at transient operations.The influences of air/fuel ratio and ignition mode on combustion characteristics and emissions of large bore dual-ignition motorcycle engine were analyzed systematically in the present work.And the deterioration mechanism of engines performances under transient operation were explored.These largely extended the research range of operating condition and parameters in motorcycle engine field.And we provided a good research method and theoretical illustration to improve the combustion and emissions performances of motorcycle engines.