1. Classification of Cylinder Heads and Valve Trains

1.7. Variable Swirl Intake Ports

LO 9-02: Describe the functions, construction, composition, types, and applications of diesel engine cylinder head assemblies.

 

Variable Swirl Intake Ports

Using either one or two intake valves and a port for each valve has the advantage of potentially increasing the air turbulence entering the cylinder. The shapes of the intake ports of most modern diesels are tangentially arranged with the cylinder head centerline. This offset of the intake valves where one is slightly behind the other, or placement of intake and exhaust valves in a diagonal pattern, is designed to impart a twisting or spinning motion to the air as it enters the cylinder. The purpose of twisting intake airflow through bends and curves in the port is to increase swirl-type air turbulence. This setup, called tangentially arranged intake valve ports , also uses uneven lengths for the intake ports (or intake runners), which further helps to spin the air entering the cylinders Figure 12.

   Fig09_12

FIGURE 09-12: A tangential or star-shaped arrangement of the intake valves turns the valve placement 45 degrees to the centerline of the cylinder head. The placement helps impart more turbulence to intake air entering the cylinders because it enters at an angle.

 

At low-speed operation, increasing intake air swirl enhances mixing of air and fuel to produce cleaner, less sooty combustion. At high-speed operation, airflow is maximized when the air can take a straighter and more direct pathway into the cylinder. To further improve air turbulence characteristics to match engine operating conditions, variable intake swirl valves, or air motion systems, are installed in the intake ports of most light- and medium-duty (MD) diesel engines. These devices operate to vary the amount of cylinder air swirl during low- and high-speed engine operation. On engines equipped with variable intake swirl systems, one of the two intake air ports have a flap- or butterfly-type throttle plate valve installed in the port opening Figure 13. At low speeds, the flap is closed or partially closed to allow air into a cylinder only through a port having a sharper bend or curve. The port shape will bend or impart a twisting airflow to most of the air entering the cylinder to increase air swirl. At higher speeds, the plate is deactivated, and airflow can enter through both intake ports and valves for maximum airflow.

  Technicians Tip  
  Variable intake swirl valve faults are a common occurrence on engines operating in stop-and-go urban driving conditions. In these driving conditions, excess soot can accumulate from high exhaust gas recirculation (EGR) flow through the intake system. Actuator motors operating the swirl valves eventually require too much torque to rotate the valves and can burn out Figure 14.  

 

  Fig09_13

FIGURE 09-13: A throttle plate in one of the intake runners will vary between open and closed to change the degree of air turbulence entering the cylinder.

   Fig09_14

FIGURE 09-14: The intake runners and swirl valves of this V6 engine are fouled with coolant from an EGR cooler leak that mixed with the normal soot loading in the intake system left by EGR gas.

  

 

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