عنوان مقاله [English]
Operating an engine with homogeneous charge compression ignition (HCCI) technique is a promising technique to lower NOx and PM emissions of engines while achieving high efficiency and lower fuel consumption. Nevertheless, applications for HCCI are still limited due to the absence of a definite means to control ignition timing and narrow operating region. A single cylinder diesel engine with compression ratio of 19.3 has been used for running in HCCI mode. The operating region in this study was defined based on λ and EGR. For fixed values of compression ratio, intake temperature and engine speed, demand for a particular engine output can be met by varying combinations of λ and EGR. All experimental tests have been done in intake temperature of 75oC, exhaust pressure of 137 kPa and engine speed of 1600 rpm. Amount of EGR varied from 0 to 41 percent in tests. The results indicated that EGR can expand the HCCI operating regions into part loads (imep = 5.4 bar). At any constant EGR line, HC and CO increased by increasing λ. general trend of lower HC and CO emissions at higher EGR rates is just because of the mixture quality that is near to stoichiometric at higher EGR fractions. EGR itself increased HC and CO emissions as it was expected.