Abstract
Keywords - Homogeneous Charge Compression Ignition, Dimethyl Ether, Multi-Stage Heat Release, Stratified Fuel Concentration, Spectrum Analysis of Chemiluminescence
Abstract - Although homogeneous charge compression ignition (HCCI) engines are expected 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 of heat release, and difficulty of control of auto-ignition. The combustion process in the HCCI engine is due to auto-ignition of an unburned mixture. The occurrence of auto-ignition is dependent on the temperature and pressure histories of the unburned mixture. In order to control the auto-ignition in HCCI engine, the reaction mechanism of auto-ignition is needed to understand. Moreover, the controllable equivalence ratio range is narrow because of knocking and misfiring. Stratified charge compression ignition (SCCI) is one of the solutions in 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 ignition engines. DME engines have the potential to solve air pollution problems caused by diesel soot and NOx. This is due to its oxygen content and absence of carbon-carbon bonds. DME shows very strong low-temperature kinetic reactions in HCCI. A study of HCCI fueled with DME may provide useful information on the low-temperature kinetic reactions in HCCI operation of other fuels. The oxidation of DME has been examined at room temperature and pressure in a number of laboratory studies. In order to understand DME oxidation, experimental kinetic study of DME combustion in engines should be investigated and DME combustion in an HCCI engine should be studied.
The purpose of this research is to investigate the auto-ignition characteristics of stratified charge compression ignition (SCCI) engine fueled with dimethyl ether (DME). The single cylinder engine with a transparent piston was used. The influences of equivalence ratio, intake temperature and engine speed on characteristics of auto-ignition were investigated. Spectrum analyses of chemiluminescence using spectroscopy were carried out. Three main conclusions were 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 concentration distribution can extend auto-ignition region into lower intake temperature and equivalence ratio. 3) Emitting lights from HCHO according to Emeléouss cool flame bands appear at low temperature reaction under both the HCCI and SCCI operation.