Yes. But not like a massive explosion. Worst case is a fireball. These things are really though for obvious reasons. If the impact is THAT violent you are dead before the gas has time to ignite. The car is not going to care much about a few seconds of additional fire.

Hmmm... Forcefully pushing them together might actually cause a little explosion. Not sure. But you also need the neutron reflectors. All in all I rate this defense a 5/10 because of how rare and special it is, but also not higher because we are talking about like 50 kg worth of stuff.