Did Igneel defeat Acnologia?
Outcome: Acnologia is victorious. Igneel is killed. Acnologia is moderately injured.
Who is stronger end or Acnologia?
The END that we have seen in the anime and original manga (his fight against Gray) is definitely less stronger than Mard Geer. So, as of now it is debatable whether or not a full power END is stronger than Acnologia but from what we have seen of his powers so far, it is a no.