Fuel injection System

Design

Final Design

Valve Selection and Constraints

            In order to have the best possible control over the spray a fast acting valve must be chosen.  It is the opening and the closing of the valve that determines how much JP-10 is sprayed into the test chamber.  The valve will begin the test run in the closed position, and then is asked to come fully open as quickly as possible and then close as quickly as possible to stop the flow.  Since the time period when the valve is not fully closed nor fully open has a different flow rate then the fully open state it is preferable to have the fastest acting valve possible.  During the opening and closing time the flow rate will be much lower than the fully open flow rate.  This lower flow rate will relate directly to a lower pressure in the nozzle area producing larger, slower droplets which must be taken into account for the experiment.

            One valve that meets the pressure, fluid characteristic, and speed requirements is the Omega-Flo SV-501-240VAC.  This is a fast acting solenoid valve with ½ inch NPT fittings, a 7/16 inch diameter orifice  (at fully opened state), and a maximum water pressure of 355 psi.  The maximum pressures for this valve were determined using water which is more dense then JP-10.  Thus, the maximum allowable system pressure of 200 psi gauge should not damage the valve.  The approximate opening time for this valve is between.02 and .04 seconds.  During closing the valve is pushing against the pressure of the flowing fluid which causes the closing times to climb to between .1 and .25 seconds.  The manufacturer (Omega Co.) quotes a cycling rate of 250 cycles per minute, which indicates that the valve can go from fully closed, to fully open, and back to fully closed in as fast as .24 seconds.  This speed will help to ensure that the experiments are as precise as possible.  The only real drawback of this valve is that it is set up to run off of a 240 Volt source, while most standard wall outlets, and many control systems, run off of a 115 Volt source.  Omega Co.’s website’s Adobe Acrobat file on the SV-500 series valves is present as Appendix A, Figure 1.