CAJ | 학술논문

柴油机多段燃油喷射可用来优化缸内燃烧以实现排放净化的目标。该文采用两段预喷和一段主喷组合的多段燃油喷射进行混合燃料D10（90%柴油+10%碳酸二甲酯）燃烧过程的研究。通过预喷相位可调但3段喷油之间相位间隔恒定、主喷持续时间可调但第1、2段预喷持续时间固定的喷油策略，实现在目标工况下精确的放热中心COHR（center of heat release）。当调整多段燃油喷射策略实现目标COHR以等步长推移时，柴油机的燃烧过程呈现如下特点：各工况的着火时刻均处于第2段预喷和主喷之间；从喷油时刻至着火时刻所经历的曲轴转角越来越小；着火时刻至放热中心所占用的曲轴转角则越来越大；缸内燃烧压力峰值出现位置与放热中心位置较为接近，相对缸内峰值压力出现位置，COHR不断后移且相距更远。与柴油相比，D10的滞燃期更长，其最大压升率也更高。由于易汽化的碳酸二甲酯促进了燃料混合及后续燃烧，从着火时刻到10%放热率及90%放热率对应时刻所占用曲轴转角均变小，说明碳酸二甲酯的加入有助燃烧的迅速进行。基于COHR为表征的燃烧特性分析，为碳酸二甲酯/柴油混合燃料的应用、多段燃油喷射调控燃烧过程及排放控制理论提供指导。
시유궤다단연유분사가용래우화항내연소이실현배방정화적목표。해문채용량단예분화일단주분조합적다단연유분사진행혼합연료D10（90%시유+10%탄산이갑지）연소과정적연구。통과예분상위가조단3단분유지간상위간격항정、주분지속시간가조단제1、2단예분지속시간고정적분유책략，실현재목표공황하정학적방열중심COHR（center of heat release）。당조정다단연유분사책략실현목표COHR이등보장추이시，시유궤적연소과정정현여하특점：각공황적착화시각균처우제2단예분화주분지간；종분유시각지착화시각소경력적곡축전각월래월소；착화시각지방열중심소점용적곡축전각칙월래월대；항내연소압력봉치출현위치여방열중심위치교위접근，상대항내봉치압력출현위치，COHR불단후이차상거경원。여시유상비，D10적체연기경장，기최대압승솔야경고。유우역기화적탄산이갑지촉진료연료혼합급후속연소，종착화시각도10%방열솔급90%방열솔대응시각소점용곡축전각균변소，설명탄산이갑지적가입유조연소적신속진행。기우COHR위표정적연소특성분석，위탄산이갑지/시유혼합연료적응용、다단연유분사조공연소과정급배방공제이론제공지도。
In order to achieve the target of emission purification within the aspect of combustion optimizing in a cylinder, as well as the partial replacement of fossil fuels, a study on the combustion process of dimethyl carbonate (DMC)-diesel fuel blend was carried off. A fuel blend D10 (10%DMC and 90%diesel by volume) was chosen as the test fuel. The experiments were conducted on a single-cylinder research engine originated from a Daimler Benz OM646 2.2 litre common rail direct injection four-cylinder in-line diesel engine. As for the research engine, the indicated mean effective pressure pmi was adopted as the baseline for assessment of engine performance. A given load at 1900 r/min was chosen as the engine operating mode. According to the first law of thermodynamics, the heat release rate can be presented in real-time by the IndiCom software. The exact position in the crank angle of the center of heat release (COHR, 50% of the total heat release) can be figured out by interpolation. It was a key parameter to describe the combustion process of the engine. Through a fuel injection strategy characterized by an adjustable first pre-injection phase but constant phase intervals between the three injections and adjustable main injection duration but fixed durations of first pre-injection and second pre-injection, the accurate COHR target at a steady working mode can be implemented. Therefore five modes with an even interval of COHR, under the same engine speed and pmi, were inspected. As for D10 fuel, to compensate for its energy density falling, the rail pressure of D10 was 3 MPa higher than that of a diesel. While using D10 fuel, two schemes were considered. One was to keep the injection parameters of fuel system unchanged. The other was to slightly adjust the injection parameters, thus the COHR can be precisely accorded with the original diesel engine. When multiple injection strategy was adjusted to achieve the exact COHR which was delayed in constant step, the features of the combustion process of a diesel engine were analyzed. The ignition for each operating mode occurred between the second pilot injection and the main injection. For every two adjacent modes varying with COHR, the crank angle intervals of the fuel injection timings as well as center of heat release and the location of heat release peak were almost identical. With the increase of COHR, the duration in crank angle taken from injection timing to ignition became shorter, while the duration in the crank angle taken from ignition to the center of the heat release became longer. As compared with the location of a peak pressure in-cylinder, the COHR would be moved backward far away. As for D10 fuel, because the easy vaporization of dimethyl carbonate promoting the mixing of fuel and air and combustion, both crank angle intervals, from the ignition to 10%of heat release and from ignition to 90%of heat release, were shorter, which indicated that the added dimethyl carbonate could help to promote the combustion process. These analyses of combustion features based on COHR will provide a fundamental guidance for the application of dimethyl carbonate/diesel blends, multiple injections regulating the combustion process, and emission control theory.