进气门晚关机构对高增压柴油机排放与热效率的影响

摘要

以某重型柴油机为研究对象，在低速中等负荷工况，通过对比进气门晚关机构开闭两种状态对两级增压系统匹配关系的影响，分析其对柴油机排放和热效率的影响。研究表明，喷油定时（上止点后－2．5°～8．5°）和EGR率（0％～21％）恒定时，使用进气门晚关（IVCA ）机构后 HC排放降低，有效热效率下降。当喷油定时不变， BNOxdif与 BCOdif随着EGR率的增加而减少；当EGR率保持恒定时，随着喷油定时增加，BCOdif呈现先增加后减小的趋势，拐点在4．5°～6．5°（ATDC）之间；同时，开启IVCA机构后，EGR率在15．29％～21．16％，喷油定时在－2．5°～8．5°（ATDC）范围内，Bsootdif均小于0。在保证喷油定时恒定时，EGR率越大，Bsootdif越小。当量比在0．42～0．52范围内，保持喷油策略不变，使用IVCA机构致使进气流量减少，若当量比在原状态的基础上增加超过0．07，即可克服由于流量减少导致柴油机缸内平均温度和燃烧持续期增加对NOx 生成的负面影响。%For a heavy‐duty diesel engine ,the influences of opening and closing status of intake valve late closing actuator on turbocharging match were compared at medium load and low speed and its influences on the emission and thermal efficiency of diesel engine were analyzed .The results showed that the emission of HC and the effective thermal efficiency decreased when the intake valve late closing actuator worked and the fuel injection timing and the EGR rate kept unchanged in the range of -2 .5°‐8 .5°(ATDC) and 0%‐21% respectively .Moreover ,the value of BNOxdif and BCOdif decreased with the increase of EGR rate when the fuel injection timing kept unchanged and the value of BCOdif first increased and then decreased in the range of 4 .5°‐6 .5°(AT‐DC) with the increase of fuel injection timing when the EGR rate kept unchanged .In addition ,the value of Bsootdif was less than 0 when the EGR rate and the injection timing were in the range of 15 .29%‐21 .16% and -2 .5°‐8 .5°(ATDC) respectively .The value of Bsootdif also decreased with the increase of EGR rate when the fuel injection timing kept unchanged .It was also found that the intake valve late closing actuator could lead to the reduction of intake air mass flow when the equivalent ratio was a‐mong the range of 0 .42‐0 .52 and the same injection strategy was used .The increase of more than 0 .07 for equivalent ratio would offset the negative influence of NOx emission brought by the in‐cylinder temperature increasing and combustion duration prolonging because of the intake air reduction .