Abstract: In order to improve the performance of diesel fuel, polyisobutylene phenol Mannich base quaternary ammonium salt (HRPIBP-DMPA-QAS) was prepared, and its effects on diesel thermal efficiency and emission characteristics were studied. Firstly, polyisobutylene phenol (HRPIBP) was synthesized by the reaction of highly reactive polyisobutylene (HRPIB) with phenol, and then reacted with formaldehyde and N,N-dimethyl-1,3-propanediamine (DMPA) to prepare polyisobutylene phenol Mannich base (HRPIBP-DMPA). Finally HRPIBP-DMPA-QAS was prepared by reaction of HRPIBP-DMPA with 1-bromobutane. The synthesis conditions of HRPIBP and HRPIBP-DMPA were optimized. The optimum conditions of HRPIBP covered a reaction time of 4 h, a reaction temperature of 100 ℃, a molar ratio of boron trifluoride etherate to HRPIB equaling to 0.4 and a molar ratio of phenol to HRPIB equaling to 2. The optimum conditions of HRPIBP-DMPA covered a eaction time of 16 h, a reaction temperature of 110 ℃, and a molar ratio of HRPIBP, formaldehyde and DMPA equaling to 1.0:3.0:2.5. The evaluation results of engine bench test with diesel fuel samples containing HRPIBP-DMPA-QAS showed that the HRPIBP-DMPA-QAS addition of 1 500 mg/L could improve the effective thermal efficiency of diesel fuel and reduce the emission of NO_x, soot and CO. Compared with blank diesel fuel, the maximum reduction rate of NO_x and soot was 27.4% and 28.6%, respectively, which indicated that HRPIBP-DMPA-QAS had good application prospects.

Key words: diesel detergent, polyisobutylene, mannich base, quaternary ammonium salt, thermal efficiency, emission characteristics