Tzippi,
When Hashem gave man permission to eat meat, there was no difference in kosher and non-kosher. Noach and his sons and all the other people of that time ate everything. yes Hashem did make a distinction between clean and unclean animals but It doesnt state in the torah that more clean animals were brought onto the ark so that there would be more to sacrifice. Kosher animals are for the most part, the ones that helped man, working the fields and such. Nobody is going to have a pig or a lion help plow his field is he? It was more practical to have more kosher animals than non-kosher animals because they were more useful. Noach wasnt told to bring any sacrifice, he brought them on his own. It doesnt say anywhere that he was told to bring sacrifices. Although man did not eat meat up to this point, i am sure that they brought sacrifices, probably to the sun god and other such gods. When Noach brought a sacrifice to hashem, it says it was a pleasing aroma to god because he was doing it for Hashem and not another god. The sacrifice he brought was a burnt offering which is not eaten, but burnt because man wasnt yet given permission to eat meat. The whole concept of animal sacrifice is deeply rooted in paganism. It was impossible to ask people to give that up so instead god created the laws we have, to offer sacrifice to him and not to other pagan gods.