Study On Low-Temperature Combustion Characteristics Of A Homogeneous Charge Compression Ignition Engine Fuelled With N-Butanol-Gasoline Blends

Homogeneous charge compression ignition (HCCI) combustion can effectivelyimprove the fuel economy of conventional gasoline engines and reduce their oxides ofnitrogen emissions at part loads. Bio-butanol, known as n-butanol, is a promisingalternative fuel of internal combustion engines. The combination of n-butanol andHCCI engine can reduce the dependence of vehicle on fossil energy to a certain extentand improve the thermal efficiencies of gasoline engines. Therefore, it is necessary todo research related to its application. The combustion and emission characteristicswere conducted on a single cylinder engine when different n-butanol-gasoline blendswere fuelled and different dilution ways were used for n-butanol, respectively.Moreover, several intermediate combustion products during low-temperatureoxidation processes in the cylinder for n-butanol and iso-octane was investigatedthrough gas sampling method and their chemical reaction pathways were deducedbased on simulation. Results show that,For the HCCI engine fuelled with n-butanol-gasoline blends operated at fixedvalve timings and lifts, with the increase of n-butanol volume fraction，ignition timingadvances, combustion duration shortens while indicated mean effective pressure(IMEP) decreases and the maximum rate of pressure rise increases.For the n-butanol HCCI engine at stoichiometry, the maximum rate of pressurerise can be effectively reduced by residual gas dilution through earlier exhaust valveclosing timing. The increase of excess air ratio, called air dilution, can also reduce themaximum rate of pressure rise. However, the decrease in IMEP in the former is larger.By combining air dilution with residual gas dilution, ignition timing is delayed and itsmaximum rate of pressure rise is lowered. In the meantime, indicated thermalefficiencies increase at fixed IMEPs.Differences in molecular structure for n-butanol and iso-octane lead to differentreaction pathways and intermediates during low-temperature oxidation. For n-butanol,the formation and consumption of C2H4, C3H6and C2H2is earlier and occur at lowerin-cylinder temperature as compared to iso-octane.Simulation results show that HO2radical and H2O2have dominant role inlow-temperature oxidation of n-butanol and iso-octane. H-atom abstraction from n-butanol, especially the H-atom abstraction at α carbon atom position, has significanteffect on the autoignition of n-butanol.55.3%of ethylene (C2H4) is formed byH-atom abstraction from the α carbon atom during the low-temperature oxidation ofn-butanol. Propene (C3H6) is the main intermediate and66.8%of C3H6is formedthrough the decomposition of iC4H9radical during the low-temperature oxidation ofiso-octane.