The Research To The Influential Factors Of Diesel Engine Helical Inlet Flow Characteristics

The design of the intake ports of an internal combustion engine plays an important role in modern low emission engines. The port design determines the volumetric efficiency and in-cylinder charge motion thus influence performance of combustion systems. In small bore DI (direct injection) diesel engines, which have a very short duration for the mixture formation and combustion, it requires strong swirl to quicken mixing of air and fuel. Large-bore diesel engines have relatively low swirl, so more fresh air can flow into the cylinder. It is known that, for a certain diesel engine, the swirl should be controlled at an optimum level, and volumetric efficiency should be as high as possible. The combination of CAD and CFD is an effective way to realize this goal. Therefore, contrapose a one-cylinder diesel engine, joint use3D modeling, numerical simulation and steady test to study the influence of factors on flow characteristic of helical intake port.(1) Create parameterized models of helical intake portCreate parameterized models of helical intake port using UG NX software and forward design method. Using spiral lines to control the helical part, NURBS to control the straight part and bridge curve to realize connection. Virtual assemble the intake port with exhaust port, intake and exhaust valves, cylinder and combustion chamber. Then steady state simulation was carried out using AVL FIRE to calculate flow coefficient, at different valve lifts. Analyze flow state inside the intake port and the cylinder. Calculating model was validated by steady state flow rig experiment.(2) Study effect factors on intake port flow characteristicsStudy the effect of different parameters on flow characteristics of intake port using steady numerical simulation. The results show that, flow coefficient firstly increase and then decrease with the increasing of spiral terminate angle; it increases with the increasing of minimum cross section by modifying the outer contour; the variation trend of swirl ratio is basically reverse. Offset distance has great effect on uniformity and backflow of airstream. The max flow coefficient is0.6418and the minimum value is0.59; the max SR is1.755and the minimum value is0.85. Intake-port’s movement up and down in cylinder-head has the greatest effect on flow characteristic and the inclination is the least.(3) Transient simulation of in-cylinder flow during intake and compression stroke The intake-compress stroke is calculated using transient simulation; attain the relation of pressure and TKE in cylinder with crank angle and the distribution of streamline and velocity fields. Study in details the whole process of vortex’s generation and development. The research shows that, during intake process pressures both in cylinder and in port first reduce and then increase. At the end of intake stroke, pressure in cylinder is slightly lower than local atmospheric pressure. During compression process, in-cylinder pressure arises constantly and rate of pressure-rise increases. At the end of compression stroke, vortex take up the whole in-cylinder space and it is good for mixing of air and fuel.