Question: Will there ever be a source of bio-fuel that does not smell when combusted .

Jack Miller answered on 24 Jun 2013:

Hi Lukew16,

To be honest, I’m surprised that bio-fuels smell when combusted anyway! I strongly suspect that a better, more efficient engine would remove any lingering whiff of chips (for example).

The reason for this is simple: to extract the most energy from a fuel, we burn it completely, reducing it to nothing but carbon dioxide and water (and lots of lovely energy). We can’t really smell carbon dioxide at all.

If, however, combustion is not complete, instead of just producing CO2, you get lots of other products — partially burnt organic compounds, with complicated chemical structures. It’s these that you can smell when burning something (or cooking), and they can be pretty nasty. Instead of getting just CO2, you tend to end up producing a fair amount of CO, which is rather toxic. The actual detailed chemistry of incomplete combustion is rather complicated (and those partially-combusted, volatile organic chemicals have a nasty habit of being very bad for your health — which is part of the reason people study this area!).

Fundamentally, incomplete combustion produces less energy than complete combustion. This is a bad thing — you want to use a given fuel as best you can. A lot of engineering work goes into making engines that burn fuels completely (usually by creating very fine mists of fuel in air), producing more energy and less odours.

I think it’s therefore likely that biofuels won’t smell very much in any modern, energy-efficient car. However, I’ve never nosed around anything running solely on chip fat (jokes about my co-workers not withstanding…), so I don’t know!

Hope that helps,

— Jack