Compression, Fuel, fire(ignition), and air
Since air is never the problem look at the systems that produce fire and provide fuel. I'm ruling out compression as you said the vehicle runs after you essentially use an accelerant
Make sure everything is tightened properly and there are no leaks in the fuel system. Try priming the diesel system before starting.
Try letting the glow plugs heat up more than once (Turn the ignition to the on position more than once) before attempting to start.
I don't have this vehicle, I'm just giving the basics based on info provided.
Info about when the problem started, or how long you have been experiencing this problem would be helpful.