二甲醚和甲醇双直喷喷雾燃烧特性的光学研究

Optical Study of Dual Direct Injection Spray of Dimethyl Ether and Methanol and Combustion Characteristics

为明晰高压喷射条件下二甲醚和甲醇双直喷的喷雾形态和火焰发展特性,通过高温高压定容燃烧弹,利用高速相机基于纹影法,对比研究了甲醇和二甲醚双直喷的喷雾燃烧特性。实验中,喷射压力设置为60、80、100 MPa,环境背压设置为0.2、4 MPa,环境温度分别为500、800 K。背压为0.2 MPa时,二甲醚的气相和液相贯穿距以及喷雾投影面积小于甲醇;背压为4 MPa时情况相反。但是,二甲醚液相喷雾贯穿距和喷雾面积所占的比例在同工况下均小于甲醇,即两种背压条件下二甲醚的雾化效果均比甲醇的好。随着喷射压力的增加,双直喷喷雾的火焰浮起长度增加,喷射压力为100 MPa时的火焰浮起长度较60 MPa时增加约26.42%,着火延迟期变长,KL因子的总和减少了44.05%;随着二甲醚喷射延时的增加,两种喷雾碰撞后形成的双直喷喷雾发展变快,喷雾面积先变小后变大,燃烧火焰的着火延迟期变长。相比于同步喷射,二甲醚延迟1 ms喷射时火焰浮起长度增加8.34%,KL因子的总和下降26.12%。研究表明,增加喷射压力和二甲醚喷射延时对于优化二甲醚、甲醇双燃料发动机的喷雾与燃烧特性具有重要的促进作用。

In order to clarify the spray morphology and flame development characteristics of dimethyl ether(DME)and methanol dual direct injection under high injection pressure conditions,the spray and combustion characteristics of methanol and DME are compared and studied based on the schlieren method by using high-speed camera and high-temperature and high-pressure constant volume bomb.In the experiment,the injection pressure is set to 60 MPa,80 MPa and 100 MPa,the ambient pressure is set to 0.2 MPa and 4 MPa,and the ambient temperature is 500 K and 800 K,respectively.The results show that under 0.2 MPa ambient pressure,the gas phase and liquid phase penetration distance and the spray projection area of DME are smaller than those of methanol,while the result is on the contrary under 4 MPa ambient pressure,but the proportion of DME liquid phase spray penetration distance and spray area are less than those of methanol under the same working conditions,that is,the atomization effect of DME is better than that of methanol under the two ambient pressure conditions.With the increase of injection pressure,the flame floating length of dual direct injection spray increases,and the flame floating length under 100 MPa injection pressure increases by about 26.42%compared with 60 MPa,the ignition delay period becomes longer,and the sum of KL decreases by 44.05%.With the increase of the DME injection delay time,the development of dual direct injection spray formed by the collision of the two sprays becomes faster,the spray area becomes smaller first and then larger,and the ignition delay period becomes longer,the flame floating length increases by about 8.34%.Compared with synchronous injection condition,DME injection with a delay of 1 ms has the lower soot formation and 26.12%higher KL formation.It is indicated that increasing the injection pressure and delaying the injection time of DME are beneficial to optimize the injection and combustion of DME and methanol dual fuel engine.