valve needed

[john_carroll]

I need suggestions for an appropriate, available and affordable valve to bypass some fuel from the distributor block in a port injected CIS system.  The object is to manage the mixture control of an aircraft engine.  The CIS system is from Airflow Performace and much like the old Bendix systems.  This injection system is used because it is not dependent on electrical power.  The main pump is mechanical.  The pressure is set at 25 psi, so the distributor block pressure will always see <25.

With the system I am building, the manual mixture control will always be able to override the electronic control, again relieving the system of ultimate reliance on electrical power.  We electronically spark one plug per cylinder and let a magneto continue to operate the other for the same reason.

The challenge is to find a valve that operates much like an injector so that a PWM signal can slightly modify the injector pressure.  Other than power requirements, the flow rating of the valve is not critical,the flow can be controlled with an orifice. The valve needs to pass a maximum of 2 gallons of fuel per hour, so if the duty cycle is maintained at 30% for cruise, a valve rated at 7 gph and capable of following a signal from 4 to 8 ms wide repeated as often as every 25 ms would be perfect.  Is this in the range of injector performance?  Perhaps I could simply inject back into the fuel system, using an off the shelf injector but the fittings and hardware would likely require a lot of machine work.

Perhaps a better alternative is to set the manual mixture control slightly lean and then inject a small amount of additional fuel into the induction system just past the throttle body with a conventional injector.  Will the available devices operate at such low pressure? Is the hookup hardware available for a single isolated injector used in this fashion?

I agree this is a simplistic approach, but it avoids modifying the existing hardware.  Your thoughts?

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John Carroll
jac at wavecom.net
 08/30/97 00:33:59