Study On Numerical Simulation Based Concept Design Method Of Engine Performances From The Fundemental Relationships And General Trends

There are tremendous amount of design and operation parameters which impactthe performances of an internal combustion engine. The amount of variables are stillincreasing everyday with the continuous introduction of new technologies. That makesthe concept study of a new engine a lengthy and costy process due to the amount ofparameters to be optimized. On the other hand, the traditional way of concept studyis based on a trial-and-error manner of engine dyno. tests, however such tests are notpossible before the engine hardware is developed. Thus several rounds of designmodifications to dyno tests to design modifications are usually required before all thedesign and operational parameters are optimized. Due to the enormous cases to bestudied, this process could still take a lot of time even taking a numercal simulationbased approach. On the other hand, the reliability and accuracy of the simulationstudies can not be guaranteed if the engineer is not experienced enough on how tosetup the boundary conditions and how to analyze the results. This research proposes anew numerical simulation based concept design method of engine performance basedon the fundamental relationships and general trends between the performance, designas well as operational parameters.This method is aimed at improving the effiency andaccuracy of a forward engine concept design.Firstly，the engines tested and the engine performance benchmarking method areintroduced. This process is to generate the raw data in order to establish therelationship between the performance with the design and opertational parameters.Then the fumdmental relationships and general trends between the engineperformance with the design and operational papameters are established via sorting，generalizing, summarizing and analyzing the experimental data. Based on this, theengine performances development targets could be broken up into the major design andoperational parameters according to the general trends summarized, also the range ofvalues and the variation directions of the major influencing parameters are obtainedfrom the summarized formulas and tables. The secondary infleuncing factors could betransplanted from other similar engines based on the similarity principle. In this way,the number of variables to be optimized, and the range of variations of the majorvariables, are significantly reduced and the time duration as well as the work effort forthe concept study will be significantly reduced. The results show that：the engine dynamic performance index has a good linearrelationship with inlet air density and charging coefficient；the pumping loss of thegasoline engine has a predictable relathionship the engine load and speed；combustionefficiency of the fuel depends very much on the excess air ratio；the10-90%burningduration is less influenced by the engine speed but more by engine load； thecombustion quality parameter is mainly influence by the load；The50%burningposition is affected by engine knock sensitivity and is closely related to the enginespeed；the results incate a good linear relationship between heat to power conversionefficiency and50%burning position. By applying the general trends above， thenumber of parameters to be studied and the range of their value variations can besignificantly reduced, thus the time duration for the numerical simulation basedconcept design will be reduced. Also the accuracy of simulation calculations is ensuredbecause the most important boundary contions come from experiments.