I need a fast switch ? Advice...

Im working on a electronic fuel injection technology i want a real fast switching device
the criteria is that within a second the switch should on-off arround 50 times
the switch should operate in ac voltage ..
switching loss should be as low as possible

MAINLY THE SWITCH SHOULD BE ACTING LIKE A RELAY WHERE THERE WILL BE AN INPUT TO CONTROL THE RELAY AND AC VOLTAGE OF THE RELAY

please shoot out some of the switches

Well assuming you are asking for a active semiconductor switch function, one needs to know more specific information:

What is the input voltage swing to the switch for the on and off functions, 0-12vdc?

What is the value of AC voltage being switched and how much current flow is needed for whatever the load is being switched on and off, injector solenoids ?

Your speed specifications are not too demanding as milliseconds are not a challenge for solid-state devices.

Lefty