摘要
柴油机进气道结构是决定气缸内空气量及其涡流强度重要因素,直接影响柴油机混合气形成和燃烧,从而影响柴油机的动力性、经济性和排放性能。本文应用CFD三维数值模拟和气道稳流试验对某柴油机螺旋进气道流动性能进行了研究,具体内容如下：
采用逆向工程技术测量气道外形,得到气道外形的数值化模型,然后在Pro/E软件上实现了气道的三维实体造型；应用CFD软件进行了稳流试验条件下的气道—气门—气缸内流场的模拟试验；通过网格的优化、湍流模型的选择、壁面的处理使得模拟试验和稳流试验结果达到一定的精度,保证了模拟计算的正确性。
模拟得到试验的验证后,详细分析了气道流动的速度场、压力场分布情况,为气道结构优化和开发提供了理论依据和指导方向；结合CFD模拟提供的进气道流动微观详细信息分析了气道流量系数和涡流比随气门升程变化趋势的原因。
研究了螺旋进气道不同结构参数对其流动的影响规律,结合CFD模拟提供的气道流场信息,对该进气道提出了调整引导管和蜗壳连接处的位置来进一步提高流量系数的实用性修改方案,修改方案的模拟试验表明：修改后的气道模型平均流量系数提高了7.3%。
本文采用气道稳流试验和CFD模拟相结合的方法,实现了对柴油机螺旋进气道改进优化的快速化,这一方法同样适用于其它发动机气道的设计开发中。
The structure of the intake port of diesel engine is an important factor to affect the amount and the strength swirl of fresh air in cylinder, has direct influence on the air fuel mixing and combustion. So it affects the power, economic performance and the emissions. The steady flow test and the CFD 3D numerical simulation were employed to study the helical intake port of a diesel engine in this paper. The main content are as following:
The technology of reverse engineering was applied to acquire the model date of helical intake port of the diesel engine. And the 3D geometric solid model of the port was built by Pro/E. Then the numerical simulation of the flow field in port-valve-cylinder under the condition of steady testing was done by 3D CFD software. By optimizing grid quality, choosing suitable turbulence model and cliff treatment, the results between simulation test and steady flow test had good agreement. It guaranteed the correctness of the simulation.
After simulation was verified, field distribution of the flow field in port was analyzed. It provided theoretical basis and guidance to optimize the structure of port. The flow information of the port provided by CFD was used to analyze how the flow coefficient and the swirl ratio vary with different valve lift in this paper.
The port performances with different structure parameters were studied. With the help of flow characteristic and information provided by CFD, a modification plan by adjusting the position of the connection between guiding tube and spiral to further improve flow coefficient, was put forward. The result of simulation tests of modification plan showed that: the flow coefficient of modified model has been improved by 7.3%.
The methods of steady flow test and CFD numerical simulation were used to study the helical intake port of a diesel engine, provided a fast way for optimization and design of the port in this paper. They are also could be used in other intake port design process.
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