| The experimental studies on coal liquefactions which can be used as a vehiclealternative energy were conducted. The difference of physical and chemical propertiesbetween two kinds of coal liquefactions and Euro IV diesel fuel (DF) was analyzed.The study on spray characteristics was conducted on a constant-volume bomb. Asingle cylinder engine which was refitted by a six-cylinder diesel engine was used tothe combustion and emission characteristics experiment study. The main researchcontents and results are listed as follows:1) In the terms of the physical and chemical properties:The density of DDCL (diesel of direct coal liquefaction) is5.27%higher than thatof DF, whereas it is7.36%lower for F-T fuel compared with the DF. The cetanenumber (CN) of DDCL and F-T fuel is12.72%lower and approximately40%higherthan that of DF, respectively. The calorific value is only0.79%lower for DDCLcompared with the DF, whereas it is1.89%higher for F-T fuel compared with the DF.The distillation temperatures are lower for the two types of coal liquefaction fuelscompared with the DF. The two types of coal liquefaction fuels contain extremely lowlevels of aromatic hydrocarbons and sulfur. In addition, the two types of coalliquefaction fuels were mixed to conduct the experiments of spray, combustion andemission.2) In the terms of the spray characteristics:The spray penetration is longer for DDCL compared with DF, whereas it isinsignificantly different for the F-T fuel compared with DF. The spray angle is slightlylarger for the F-T fuel and DDCL compared with DF. Although there are somedifferences in the terms of the spray characteristics, the differences are within a smallrange. For the mixed fuel (DDCL: F-T fuel=3:1), the spray penetration is slightlylonger than that of DF, whereas the mixed fuel is similar to DF in terms of the sprayangle. With the increment of injection pressure and orifice diameter, the spraypenetration and spray angle increase. With the improvement of ambient density, thespray penetration decreases，while the spray angle increases.3) In the terms of the combustion characteristics:Under low load (5bar IMEP), DDCL shows a longer ignition delay and more heatrelease in premixed combustion and a higher maximum rate of pressure rise with a later corresponding crank angle. The combustion characteristic of F-T fuelperformance just is the opposite of DDCL. Under high loads (10-15bar IMEP), theyshow insignificant differences in the combustion processes. Changing the injectiontiming cannot make the combustion characteristics of two types of coal liquefactionssimilar to those of DF, but mixing the two types of coal liquefactions in a certainproportion can. For the mixed fuel (DDCL: F-T fuel=3:1), the spray and combustioncharacteristics are similar to those of DF.4) In the terms of the emission characteristics:The NOx emission is slightly lower for F-T fuel compare with DF at low load,while it is slightly higher for DDCL compare with DF. The Soot emissions of the twokinds of coal liquefactions are all lower than those of DF, which Soot emissions ofF-T fuel and DDCL decrease by37.31%and19.2%respectively. The four kindsemissions of mixed fuel are all lower than DF. The HC emissions of F-T fuel are13.14%lower than those of DF. The HC emission of DDCL is higher than those ofDF at low load, while it is basically at the same level at medium load and evenslightly lower than those of DF at high load. The CO emissions of F-T fuel are11.19%lower than those of DF. The CO emissions of DDCL are all higher than those of DF atthe tested load (11.03%on average). However, with the load increasing, the emissionsof HC and CO of coal liquefactions are gradually closed to those of DF. In terms ofunregulated emissions, the two liquefaction fuels show insignificant differencecompared with the DF at very low levels. |
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