During the high temperature maintenance of excavator, have you ever encountered the black smoke produced by diesel engine?

分析了挖掘机维修过程中产生黑烟的因素。

The factors of producing black smoke in the maintenance process of excavator are analyzed.

(1)压缩力不足:气门、活塞环和气缸套磨损，造成压缩压力不足，压缩压力和温度低于标准，燃料燃烧条件恶化，容易产生烟尘；

(1) Insufficient compression force: valve, piston ring and cylinder liner wear, resulting in insufficient compression pressure, compression pressure and temperature below the standard, fuel combustion conditions deteriorated, easy to produce smoke and dust;

(2)燃烧室形状和体积的变化:由于制造质量和长期使用，燃烧室的技术条件降低，压缩间隙的变化也会改变燃烧室的形状和体积，从而影响燃料和空气的混合质量，并使燃烧条件恶化。如果活塞反向安装，会影响喷油器、燃烧室和进气道的匹配工作，不会形成良好的混合气，会发生不完全燃烧。

(2) Change of combustion chamber shape and volume: due to manufacturing quality and long-term use, the technical conditions of combustion chamber are reduced, and the change of compression gap will also change the shape and volume of combustion chamber, thus affecting the mixing quality of fuel and air, and worsening the combustion conditions. If the piston is installed in the opposite direction, the matching work of injector, combustion chamber and intake port will be affected, and good mixture will not be formed, and incomplete combustion will occur.

(3)喷油器工作不良:喷油器工作不良主要表现在三个方面:一是喷油器质量差；第二，喷油器压力不足。第三，注射器滴水。在这三种情况下，燃料不能与气缸中的空气完全混合，因此不能完全燃烧。此外，如果选定的喷油器与原发动机不匹配，也会导致发动机冒烟。

(3) Poor working of fuel injector: the poor working performance of fuel injector is mainly manifested in three aspects: first, poor quality of fuel injector; second, insufficient pressure of fuel injector. Third, the syringe drips. In these three cases, the fuel cannot be completely mixed with the air in the cylinder, so it can not be completely burned. In addition, if the selected injector does not match the original engine, the engine will also smoke.

(4)供油过多，供油过多，导致混合气浓度高，燃烧不完全；

(4) If the fuel supply is too much, the mixture concentration is high and the combustion is incomplete;

(5)提前角不当:①供油提前角过大:在直喷式柴油机中，当其他参数不变时，适当增加喷油正时可以减少排气烟度。随着燃料喷射时间的增加和点火延迟时间的延长，在所有喷射燃料的火焰上升之前进行预混，以增加预混气体的量，加速燃烧速度，并且燃烧可以提前完成，因此快速燃烧形成的碳颗粒将在高温下停留更长的时间，这有利于烟灰的氧化和消失。然而，由于缸内压力和温度较低，过早喷射不利于燃料蒸发和混合，导致烟雾排放。同时，由于预混合燃料的量大大增加了粗柴油的量，燃烧噪音增加并导致更大的机械负荷。(2)供油提前角过小:当燃油喷射到后期时，在气缸内形成燃油的燃烧部分已为时过晚，混合气在气缸内被分离或排出，从而产生一些物质和燃气，与排气管内的废气一起通过热解和燃烧排出。

(5) In direct injection diesel engine, when other parameters remain unchanged, properly increasing injection timing can reduce exhaust smoke. With the increase of fuel injection time and ignition delay time, premixing is carried out before the flame of all injected fuels rises to increase the amount of premixed gas and accelerate the combustion speed. Moreover, the combustion can be completed ahead of time. Therefore, the carbon particles formed by rapid combustion will stay at high temperature for a longer time, which is conducive to the oxidation and disappearance of soot. However, due to the low pressure and temperature in the cylinder, premature injection is not conducive to fuel evaporation and mixing, resulting in smoke emission. At the same time, because the amount of premixed fuel greatly increases the amount of crude diesel, combustion noise increases and leads to greater mechanical load. (2) The fuel supply advance angle is too small: when the fuel injection to the later stage, it is too late to form the combustion part of the fuel in the cylinder, and the mixture is separated or discharged in the cylinder, so as to produce some substances and gas, which are discharged together with the exhaust gas in the exhaust pipe through pyrolysis and combustion.