Failed esterification of 1-butanol and ethanoic acid I did an esterification experiment of 1-butanol and ethanoic acid.

30 mL of 1-butanol was added followed by 30 mL of ethanoic acid, and then 1.5 mL of concentrated sulphuric acid and some boiling chips.

The mixture was colorless at first. However, it turned brown during the reflux of esterification immediately after heating the solution, and the solution had a burnt fruity smell.

I suspect this is because I didn't swirl the mixture before heating. Also, before heating, the bottom of the round bottom-flask felt warm, and I suspect this could be the reaction between the concentrated sulphuric acid and ethanoic acid.

One thing that I can't seem to understand is, how did the color of the solution turn brown? Could it be that the product of the reaction between sulphuric acid and ethanoic acid reacted with the 1-butanol to produce a colored solution?

P.s: I couldn't obtain any pure ester after the distillation of the ester as the temperature didn't rise above 100 °C.
I don't think the brown color necessarily means that the reaction failed. It could be due to some contaminant in your reagents but in a small quantity that wouldn't cause the reaction to fail. The fruity smell could very well be due to your product see: n-butyl acetate has a sweet banana smell. I would take the distillate you collected (or skip the distillation altogether) and try an aqueous work-up: Add very carefully aqueous $\ce{Na2CO3}$ until basic $\ce{pH}$ and then extract this mixture with ether. This way any ester product will be in the the organic layer and sulfuric/acetic acid will stay in the aqueous together with most of the alcohol. 

To finish the work-up dry the ether layers over $\ce{Na2SO4}$, filter and remove the ether (unless you have access to a Buchi evaporator, the safest way is to leave it in an open flask/beaker overnight). You can further purify the final product by distillation.

You might improve the yield if you cool the reaction mixture in an ice bath before adding sulfuric acid