HOMOGENEOUS CHARGE COMPRESSION IGNITIONCOMBUSTION WITH DIMETHYL ETHER(EFFECT OF STRATIFIED FUEL CONCENTRATION)

摘要

Although homogeneous charge compression ignition (HCCI) engines areexpected to have both higher thermal efficiency and lower nitrogen oxides (Nox) emissions,they have problems about high hydrocarbon (HC) and carbon monoxide (CO), high rates ofheat release, and difficulty of control of auto-ignition. The combustion process in the HCCIengine is due to auto-ignition of an unburned mixture. The occurrence of auto-ignition isdependent on the temperature and pressure histories of the unburned mixture. In order tocontrol the auto-ignition in HCCI engine, the reaction mechanism of auto-ignition is neededto understand. Moreover, the controllable equivalence ratio range is narrow because ofknocking and misfiring. Stratified charge compression ignition (SCCI) is one of the solutionsin order to control the ignition timing with various stratified fuel concentration in the cylinder.Dimethyl ether (DME) is a promising alternative fuel suitable for compression ignitionengines. DME engines have the potential to solve air pollution problems caused by diesel sootand Nox. This is due to its oxygen content and absence of carbon-carbon bonds. DME showsvery strong low-temperature kinetic reactions in HCCI. A study of HCCI fueled with DMEmay provide useful information on the low-temperature kinetic reactions in HCCI operationof other fuels. The oxidation of DME has been examined at room temperature and pressure ina number of laboratory studies. In order to understand DME oxidation, experimental kineticstudy of DME combustion in engines should be investigated and DME combustion in anHCCI engine should be studied.The purpose of this research is to investigate the auto-ignition characteristics of stratifiedcharge compression ignition (SCCI) engine fueled with dimethyl ether (DME). The singlecylinder engine with a transparent piston was used. The influences of equivalence ratio, intaketemperature and engine speed on characteristics of auto-ignition were investigated. Spectrumanalyses of chemiluminescence using spectroscopy were carried out. Three main conclusionswere drawn from this study. 1) The hot-flame reaction progresses homogeneously in HCCI,while the inclination of flame appears in SCCI. 2) Inhomogeneity of fuel concentrationdistribution can extend auto-ignition region into lower intake temperature and equivalenceratio. 3) Emitting lights from HCHO according to Emeléous’s cool flame bands appear at lowtemperature reaction under both the HCCI and SCCI operation.