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Study finds ethanol blends reduce GDI tailpipe PM

A new study finds that ethanol blends reduce particulate matter (PM) coming out of the tailpipe, which in turn reduces overall toxic emissions. The study was conducted by the University of California Riverside and the University of Wisconsin, Madison and commissioned by the Urban Air Initiative. It was published in the journal Science of the Total Environment.

The study assessed the gaseous and particulate emissions, as well as the toxicological properties of particulate matter (PM), from a flex fuel vehicle equipped with a wall-guided gasoline direct injection (GDI) engine over triplicates cold-start and hot-start LA92 cycles.


The vehicle was operated on a Tier 3 E10 fuel, an E10 fuel with higher levels of aromatics than the Tier 3 E10, an E30, and an E78 blend.

Total hydrocarbon (THC), non-methane hydrocarbon (NMHC), carbon monoxide (CO), particulate emissions, and gaseous toxics (of benzene, toluene, ethylbenzene, xylenes (BTEX), and 1,3-butadiene) reduced for E30 and E78 blends compared to both E10 fuels.

Formaldehyde and acetaldehyde emissions substantially increased with the higher ethanol blends.

The high aromatic E10 fuel increased the emissions of THC, NMHC, particulates, and BTEX compared to the Tier 3 E10 fuel and the higher ethanol blends, as well as showed higher concentrations of accumulation mode particles.

The GDI PM did not exhibit any measurable mutagenicity at the PM concentrations tested. Cytotoxicity varied only within a small range and concentrations of PM, eliciting a cytotoxic response similar to those by ambient aerosol.

The outcomes of two measures of PM oxidative potential (macrophage ROS and DTT) were significantly correlated, with the E78 blend exhibiting the least oxidative potential and the E30 the greatest.

Gene expression analysis at both the mRNA and protein level indicates that there is the potential for GDI PM emissions to contribute to inflammation and etiology of disease such as asthma, and in contrast to the ROS and DTT outcomes, the E78 fuel PM exhibited the greatest potential to elicit pro-inflammatory cytokine (TNFα) production.

Overall, the trends in toxicity emission rates (activity/mi) across the ethanol blends was driven primarily by PM mass emission rate contrasts and only secondarily by the differences in intrinsic toxicity of the PM.

The results of this study continue to validate the variety of health and environmental benefits of ethanol blends. PM emissions are some of the most toxic emissions coming from the tailpipe and connected with causing a host of health and pollution problems. The fact that simply adding more ethanol to gasoline can reduce emissions and improve public health is a story that every driver needs to hear.

—Urban Air Technical Director Steve Vander Griend

This is one of the few studies available to test the health effects from PM with varying levels of ethanol. It found that as ethanol was added to gasoline, it diluted aromatics such as benzene and toluene in the fuel. These aromatics used to boost octane are the most toxic compounds in gasoline and also create the most PM. This is why researchers found that as ethanol diluted aromatics it also reduced PM.


  • Jiacheng Yang, Patrick Roth, Thomas D. Durbin, Martin M. Shafer, Jocelyn Hemming, Dagmara S. Antkiewicz, Akua Asa-Awuku, Georgios Karavalakis (2019) “Emissions from a flex fuel GDI vehicle operating on ethanol fuels show marked contrasts in chemical, physical and toxicological characteristics as a function of ethanol content,” Science of The Total Environment, Volume 683, Pages 749-761 doi: 10.1016/j.scitotenv.2019.05.279.



But PM emissions during cold starts at low ambient temperature (lower than +25, as in the tests) might be much higher for ethanol than for gasoline. Not so important for California but definitely for Wisconsin.


Not only PM, but also hard starting.

This makes me wonder if there are possibilities with the A20 fuel tested by FCA.  At 15% MeOH, it should be possible to catalytically dehydrate some of the methanol to make dimethyl ether.  Using DME as an on-board generated starting fluid should enhance starting performance and slash startup PM emissions.


This is GDI, so getting the engine to start at low temperature is not such an issue it was with MPI (there is info on this in the literature). However, current GDI technology is, most likely, not good enough to get low PM/PN at cold starts at low ambient temperature. Ethanol with MPI was a disaster in that respect. The latest 500 bar DI should fix most of the mentioned problems but it remains to be seen how well it can be adapted to ethanol. Diesel engines running on ethanol with DI, such as Scania, start at a few seconds at -30 deg. C. They actually start much better than the corresponding engine on diesel fuel. But here we talk about "real" high-pressure injection.

Some basics: DME is a fuel with extremely high cetane number, while the octane number is very low. Its octane number is actually too low to be measured in an octane test engine. The cetane number for DME is higher than for diesel fuel. It is an ideal fuel for a diesel engine. Consequently, you cannot run an otto engine on DME.


Scania uses an ignition improver in the ethanol fuel to raise the cetane number. To reduce the necessary concentration of this (expensive) additive, the compression ratio is also higher than for normal diesel engines. I realized that this information was missing in the previous post.


I wasn't thinking of running an Otto-cycle engine on just DME.  I was thinking of it as a way to guarantee ignition in a cold engine and make certain that the fuel spray saw a flame front.  The flammability limits of DME span an almost 8:1 range (3.4% to 27%) so a lean mix of DME plus other fuel might be just the thing for the first few revolutions of a cold engine to make sure everything burns before it hits the exhaust manifold.

Per the references I can find, DME has a higher autoignition temperature than diethyl ether:  350 C compared to 160 C.

Being able to start a cold engine with a lean mixture would tend to reduce the initial "puff" of hydrocarbons out the exhaust.


It would have been nice to see the charts to verify this story. Maybe they don't want us to see something.


Maybe if the pollution is less at the tail pipe it can counter the damage making corn ethanol causes, like polluted water from fertilizer, insecticide pollution, ozone pollution, and a host of others.

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