Low response time solenoid valves

[MikeMM]

I'm working on a new type of engine I invented. In part of the engine cycle water is injected to cool the gasses and create a vaccum. I am planning to use a solenoid valve to control the spraying of water into the engine. The timing for this is extremely important. What I need is a solenoid valve where the time it takes for the plunger to open and close completely is very low (10 millisecond to do both would be the maximum that would be acceptable but faster would definately be better). The time it takes to energize the coil will also matter some but since I am designing the electronics to controll this I should be able to compensate for this by simply sending the signals to open the valve slightly in advance.

It needs to be able to pump about 10 to 15 gpm and I was planning to have the water be at about 100 psi or less although I am somewhat flexible on this stuff if there is a valve out there that has a good response time.

I have searched google and most of the vavles either don't state the response time, have slow ones, or have extremely low flow rates. If anybody knows of any valves that might meet my criteria that would be a huge help.

thanks,

Mike

 

[MikeMM]

I forgot to mention in case anybody is thinking of suggesting this. None of the existing electronic fuel injectors will work in this application and I think that I will be able to get a better response time and lower cost by using a water injection system I'm designing rather than try to design a custom electronic fuel injector myself.

 

[israelkk]

What is the pressure difference? How much is the pressure at the exit of the water from the valve? Is it atmospheric pressure? If so, according to my quick calculations the orifice in the valve is quite large (around 0.25" diameter) resulting in a plunger travel of ~0.06in. This is not a small solenoid. To my best knowledge it can be done depends on your current and voltage limitations. Valve heat may not be a problem if it will be far enough from the hot gases and the water can cool the valve internally.

Can you provide more data on the size limitations of the valve if any?

 

[MikeMM]

The pressure where the water is sprayed is going to be a little bit below atmospheric pressure. The size of the valve doesn't matter and it will be placed away from any hot gasses or parts. Although the water may in some cases be as hot as 150F or about 65C. There are really no voltage or amperage limitations. I will build the circuit to controll this to whatever solenoid will work best. At this point I am trying to prove the engine concept so I will worry about electricity consumption of the solenoid later.

 

[btrueblood]

The response time of solenoids will depend a lot on how they are driven electrically. Driving the voltage prior to opening to a level about 40 to 50% of the pull-in voltage will reduce pull-in response time. Adding a reversed-bias zener diode across the coil leads to absorb the coil flyback voltage will cut the drop-out time (the higher the zener breakdown voltage, the faster the response time). As israel stated, shorter mechanical strokes will give shorter response times also, as will higher force margins (force margin meaning how much more magnetic pull force is generated than is absolutely required to move the plunger against pressure forces. More force = more acceleration = faster plunger travel).

The fastest valves I know of were used for the Voyager RCS thrusters, and had response times of about 4 ms (0.004 seconds). They were made by Moog, and cost a bundle. EG&G Wright components also made similar valves, which could achieve similar response times if operated per above. Marotta had some too. You may be able to get under 10 ms with an off-the-shelf direct acting solenoid valve, if operated as noted above. Try over-driving a 12V solenoid with up to 24 vdc for a brief period (10ms or so) to "kick" the valve into possibly faster response times.

To measure response times, set up a dual-trace o-scope to measure coil voltage and current, and watch for a telltale "spike" (really more of a dip or bounce) in the rising/falling current trace to tell when the plunger has moved.