Simulation Study On Homogeneous Charge Compression Ignition Engine Fueled With Ethanol

Energy source and environment protection are main problems that confronted to the humankind .As the development of society, the amount of automobile increase and automobile not only become the main energy consumption source but also the largest emission pollution resource.As a developing country, the conflict between energy source and environmental protection should be resolved to keep the country harmonious and sustainable development.The researchers in the internal combustion engine business should find new combustion form with higher thermal efficiency and corresponding alternative fuels.Homogeneous charge compression ignition (HCCI) is a new combustion mode, which is different from combustion in spark ignition (SI) and compression ignition (CI) engine. CoMPared to the traditional SI and CI combustion, HCCI has the advantage of higher thermal efficiency with extra-low PM and NOx emission. The new combustion concept has become one of the hottest topic all over the world and many conclusions obtained from experiments and simulation have been made.CHEMKIN was used to study the chemical kinetics process of ethanol combustion, a comprehensive analysis was performed through reaction flow analysis and rates of product analysis rates of reactions analysis.And the ethanol HCCI combustion simulation On the basic of ethanol's chemical kinetics process study, a computational study on ethanol HCCI combustion simulation based on these analysis was carried out further.The thermal data used in this study was published by Lawrence Livermore national laboratory, and the chemical kinetics mechanism based on Lawrence Livermore national laboratory's data is assembled using reaction sub-mechanism of hydrogen, methane, ethylene, aether, propane and so on. In order to predict NOX emissions, extended Zeldovich mechanism was used in the ethanol oxidation mechanism. Gas Ar is added into the mixture to model the atmosphere as true as possible. At last, the compiled ethanol oxidation mechanism consists of 62 species and 395 cell reactions. The ethanol oxidation mechanism coupled with 0-D single zone HCCI model can successful predict CO emission and the NOX prediction precision hasbeen improved greatly.It's find out that:1. The combustion process of ethanol can be divided into three stages: solicitation stage of reaction chain and accumulation stage of active radicel and ignition and combustion stage.At the first stage, the reaction chains are induced and a little heat is released.At the second stage, the produce rates of active atom and radicel are faster than the consumption rates and the a lots of energy was released, which result in in-cylinder pressure and temperature rise. The oxidation of ethanol and aldehyde are used to dominantly to energy release.At the third stage, all kinds of reactions'rate are very fast and the oxidation of aldehyde and CO as well as produce HO2 release much heat fully at this stage.The temperature is determined by those reactions: R23.OH+OH(+m)=H2O2(+m),R155.C₂H₅OH+HO2=CH3CHOH+H2O2 and R2. O+OH=O2+H and so on. Under the HCCI combustion model, ethanol is mainly consumed by three ways: C₂H₅OH + OH→products; C₂H₅OH+O→products; C₂H₅OH+CH3→products.2. 0-D HCCI combustion model coupled with ethanol chemical kinetic mechanism was used to simulate the ethanol HCCI cobustion.In this paper, the affects of combustion boundary conditions on l HCCI combustion has been studied. The investigation results show that: when engine speed and air/fuel equivalence ratio were kept constant, as the intake charge temperature risesm, the peak in-cylinder pressure and temperature rise, the CO emission decreases and NOX emission increases.When engine speed and intake charge temperature keep constant, as the air/fuel equivalence ratio increase, the peak in-cylinder pressure and temperature decrease. At big air/fuel equivalence ratio condition, there happened partial combustion and CO emission increase and NOX decrease.And at small air/fuel equivalence ratio condition, join EGR can avoid knock combustion, but as EGR rate increased to a quantity the in-cylinder pressure and temperature are decreased and CO emission increase and NOX decrease.3. The affects of air/fuel equivalence ratio and exhaust gas recirculation (EGR) ratio on HCCI combustion had been studied and the ethanol HCCIoperation region indicated by EGR ratio and air/fuel equivalence ratio had been defined.The ethanol HCCI operation region is enclosed by knock combustion limited line and partial combustion limited line and misfire limited line.The results show that the ethanol HCCI combustion can be achieved without EGR when the air/fuel equivalence ratio is between 3.2 and 8.5. when the air/fuel equivalence ratio is small than 3.2, the EGR should be added to dilute the mixture in order to realize HCCI combustion in order to realize HCCI combustion and the maximum EGR ratio is up to 52%.4. Partial performances in the HCCI operation region was studied, and the MAPs of ignition timing, combustion duration, indicated mean effective pressure ,NOX emissions and CO emission were obtained.In the HCCI operation region, the ignition timing retards as EGR rate increase. The combustion duration mainly depends on the air/fuel equivalence ratio when the EGR rate is low and as the EGR rate increase the combustion duration more depends on EGR rate. The affects of EGR on indicated mean effective pressure is big. The indicated thermal efficiency near the knocking limitation line is more higher than the value of near the partial burning limitation line and misfire limitation line, the maximal value up to 40%. And the emissions of CO, it is high near the partial burning limitation line and misfire limitation line and the NOX emission is high near knocking limitation line, and at other region is low.