Andres Tretiakov

Slow motion combustion of ethanol

Discussion created by Andres Tretiakov on Feb 10, 2014

Many thanks to student Alex Blackwood who filmed them using the Sony FS-700 camera, filming at 800 FPS

 

In the first part of this video, the whoosh bottle demo demonstrates the combustion of alcohol vapours in air inside a polycarbonate bottle. The initial jet of flame and hot expanding gases gives you an idea of how energetic this reaction is. So much so that ethanol is used as a fuel for internal combustion engines in Brazil. As an alternative to fossil fuels, ethanol has environmental and long-term economical advantages. In Brazil ethanol-powered and flexible-fuel vehicles can run on a mixture of hydrated ethanol and petrol. This greatly reduces the consumption of petroleum fuels and also reduces air pollution (see chemical equation below) since only water and carbon dioxide are produced.  
Ethanol is increasingly used as an oxygen additive for standard petrol, as a replacement for methyl t-butyl ether (MTBE), the latter chemical being responsible for considerable groundwater and soil pollution.

Ethanol can also be used to power fuel cells and to produce biodiesel.

After the initial energetic jet of flame, a pulsating effect is generated inside the bottle for a few seconds like a fire beating heart. I believe this is caused by the increasingly lack of oxygen in the air-fuel mixture whereby the combustion reaction is struggling while carbon dioxide accumulates until it finally ceases altogether.

In the second part of the video, a mixture of ethanol vapour and air is ignited with a spark remotely activated in a plastic bottle. When the button is pressed the bottle explodes off the stopper with a loud bang and shoots across the room. The significant energy produced and expanding hot gases are able to propel the coke bottle a respectable distance.

For best results stoichiometric ratios should be used:
                                 
CH3CH2OH(l) + 3O2(g) → 2CO2(g)  + 3 H2O(l)
(assuming complete combustion).

Outcomes