汽油直喷发动机燃烧特性分析

Study on Combustion Characteristics of Gasoline Direct Injection Engine

通过试验研究了2.0L汽油直喷(GDI)发动机在中、低转速和部分负荷下的燃烧特性,并与进气道喷射(PFI)发动机的燃烧特性进行了对比,同时分析了滚流比对GDI燃烧特性的影响.结果表明:在转速为2000r/min、平均有效压力为0.2MPa的工况下,GDI发动机的燃烧速度要低于PFI发动机的;发动机在中、低转速工况下,提高气道滚流比可以增强缸内气流运动强度,提高混合气的燃烧速度;当发动机转速达到3000r/min时,高滚流比会引起燃烧过程恶化.进气道翻板的应用可以提高低转速发动机的气流运动速度,加快缸内混合气的燃烧,改善低转速发动机的热效率.在转速为2000r/min、平均有效压力为0.2MPa工况下的计算流体力学分析结果显示,进气道翻板的关闭会增强缸内气流运动强度,提高可燃混合气分布的均匀性.

The combustion characteristics of a 2.0 L gasoline direct injection （GDI） engine were studied at the engine＇s medium and low speeds and part load operation conditions,and compared with that of PFI engine. The effects of port tumble ratio on GDI engine＇s combustion characteristics were also analyzed. The results show that,with the same engine compression ratio and operation condition of 2 000 r/min,0.2 MPa brake mean efficient pressure,the combustion velocity of GDI engine is slower than that of PFI engine. At the engine＇s medium and low speeds,increasing inlet port tumble ratio can enhance airflow intensity and combustion velocity. However,when engine speed increases to 3 000 r/min,big tumble ratio deteriorates combustion in cylinder. The flap added to the inlet port can increase the air flow velocity and the combustion process of the fuel air mixture at engine low speed conditions,so that improve the engine＇s low speed thermal efficiency. The CFD results of 2 000 r/min,0.2 MPa BMEP condition show that closing the inlet flap can intensify the in cylinder air flow and increase the uniformity of fuel air mixture.