| Homogeneous Charged Compression Ignition (HCCI) combustion is one of the popular research topics of internal combustion engine technology. Aromatic compounds exist widely in today's commercial gasoline fuels and diesel fuels. Many papers have been published on aromatic effect on conventional, (diesel engine and gasoline engine), combustion behavior and emission characteristics. Most previous experimental studies on HCCI combustion used non-aromatic, Primary Reference Fuel (PRF) for testing. Benzene is the simplest aromatic species and is chosen to represent the general fuel aromatic content in this study. Tested fuels are divided into two groups, blending Research Octane Number (RON) 20 and blending RON60. The tests are conducted on a Co-operative Fuel Research (CFR) engine equipped with a port injector, a data acquisition (DAQ) system and an exhaust sampling system. Samples of exhaust gas are gathered, diluted with N2, stored in steel canisters and analyzed to provide detailed hydrocarbon speciation. It is found that aromatic content tends to push the engine operating condition toward the rich side, thus enabling higher maximum Indicated Mean Effective Pressure (IMEP) output with more fuel per engine cycle. It is found that the benzene content increase results in retarded ignition timing, lowered cylinder peak pressure, lowered Low Temperature Heat Release (LTHR) rate and High Temperature Heat Release (HTHR) rate. It is also found that aromatic increase does not affect the three main elements of engine emissions in most of the engine operating conditions. It is found that the benzene proportion in the THC emissions is about twice its content in the fuel, implying that benzene is more difficult to oxidize than iso-octane in the HCCI engine conditions. |
