Are ethanol and butanol reducing emissions of particle and non-regullated pollutants in the GDI vehicles? What about the use of other alternative fuels?
It depends on the fuel and on the degree to which the engine adapts to it. Generally, insufficient adaptation of the engine to alcohol fuel results in lean operation with increased NOx, while there is a reduction in PM.
We have tested multiple cars on ethanol and butanol, generally, the effects of ethanol on particle emissions are not large and not consistent, ethanol may even increase particle emissions as it is a two-carbon alcohol. We found that butanol is generally better than ethanol, both in terms of engine adaptation and in terms of particle emissions, also in terms of the emissions of carcinogenic PAH.
A possible penalty of using alcohols is the increase in unregulated pollutants - aldehydes (formaldehyde and acetaldehyde in case of ethanol, higher aldehydes in case of butanol), these, however, should be easy to oxidize in a three-way catalyst - except for engine start which will remain a problem - and is generally a problem with engines running on high concentrations of alcohol fuels.
I have seen different results in terms of PAH emissions. It seems to be pretty dependent on the engine type too.
Generally the PAH emissions are affected by multiple factors, including engine operating conditions (engine speed and load), and the air-fuel ratio. For example, some engines use "commanded enrichment" (running with excess fuel) at high loads, and out of these, some apply the adaptation factors learned with alcohol fuel to the commanded enrichment, and some do not, in which case alcohol fuels, as they contain oxygen, reduce the enrichment, generally also reducing PAH. I am afraid there is no comprehensive explanation of the effects - different studies just report on specific engines and specific conditions. I am attaching our results, also Jan Czerwinski at Berner Fachhochschule has run many tests on ethanol, including toxicity work done by Barbara Rothern-Rutishauer at Fribourg.
Data SAE-2015-24-2513-ppt
Thanks for the information Mr. Vojtisek . I actually have been working with them in the ethanol and butanol tests. I opened this question to have different opinions in this regards, as it seems that results with biofuels are very different. In my results, it seems that the use of butanol is slightly increasing PAH emissions of the highest molecular weight compounds. I will show some results in the upcoming ETH Conference on Combustion Nanoparticles. With ethanol, it also depends on the vehicle tested. Thanks for your interesting results.
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