Do oxygenated fuels reduce pollution?

Here in Colorful Colorado they use oxygenated fuels in the wintertime to reduce pollution. I question whether this is actually effective because the fuels actually lower fuel efficiency. My car, a 95 Subaru Legacy gets around 29 mpg with non oxygenated fuel and 25 mpg with the oxy-fuels. I have a sneaking suspicion that the extra fuel I burn creates more pollution than the savings gained from burning the oxygenated fuel.

How about it Dopers, do oxygenated fuels actually reduce pollution?

OK. I gotta be quick.

Let’s look at octane only.

In a perfect combustion world, your engine needs 25 molecules of oxygen to completely burn 2 molecules of octane, according to the following reaction:

2 C[sub]8[/sub]H[sub]18[/sub] + 25 O[sub]2[/sub] --> 16 CO[sub]2[/sub] + 18 H[sub]2[/sub]O

However, this is never the case in your engine. You never get enough Oxygen. As a result, you don’t have enough oxygen to fully make CO[sub]2[/sub] and make lots of CO and other such stuff.

There are ways to increase the amount of oxygen getting into your engine cylinders, including: increasing the number of intake valves (not a very good way, in that the ratio of air/fuel is pretty much the same), add a blower to your engine (looks real cool), wait until the choke opens. Ah, yes. This is the good idea. (This is why it’s a good idea to let your car warm up before you drive it - that and oil circulation.)

In winter, it takes a long time for your choke to open fully. This means that there’s a longer period of time when your engine is getting way too little oxygen. Adding the oxygen to the gas helps to get oxygen to the fuel to make up for this.

Does it work? In theory, yes.

Actually? Idunno.

If this truly adds oxygen into the reaction, one would expect more efficient combustion, resulting in cleaner exhaust and increased power output (energy is released in the reaction). This leads us to ask why we get worse mileage with oxygenate fuel?

WAG, increasing oxygen in fuel displaces octane so, gallon for gallon, there’s less octane in the oxygenated fuel. Doesn’t make much sense given that the octane is the liquid mixed with the other distillates and the oxygen is dissolved in this, thereby not changing the volume of the mixture.

I have no idea what the (R + M)/2 method for determining octane ratings is. Perhaps another teemer can elucidate?

Actually, modern engines work very hard to maintain an optimum fuel/air ratio specifically to reduce pollution. The problem Holden outlines is due more to incomplete mixing of the fuel and air, not a lack of air (oxygen).

It’s been a long time since I took my internal combustion engines course but I was under the impression that the value of the oxygenated fuel was to allow more complete burning of the fuel in the low oxygen pockets of the cylinder. Which is kinda what Holden said.

In answer to the OP, you are correct that lower fuel mileage results in more combustion products coming out your tailpipe. I think the answer to your question depends on what is considered to be pollution. The automotive world doesn’t consider water and carbon dioxide (the products of complete, balanced combustion) to be pollutants. The cleaner burning fuels are designed to reduce carbon monoxides, particulates and nitrogen compounds which are pollutants. The ethanol releases less energy when it burns but it burns cleaner. Your notion of the alcohol displacing the higher energy gasoline is essentially correct.

So yes, your car spews more stuff in winter but, theoretically, it’s cleaner stuff.

Incidentally, ethanol has a pretty high octane rating so they can use a little cheaper fraction of gasoline in the mix and still get the same octane rating overall.

I’ve forgotten what the R and the M stand for but they are two different methods of measuring engine knock. (R+M)/2 means that they measure the octane rating using both methods and average the result. IIRC, they usually only differ by 3 or 4 points.

pluto, who was once a mechanical engineer.

R = research and M = motor.

Apparently the difference between the two methods is that they are run under different, but well-specified, conditions.

you get less mpg because you are forced to carry around fuel AND oxygen instead of getting O2 for free ‘out of the air’

It ‘should’ lower CO and Hydrocarb’s but modern engines will ajust A/F ratio based on the exhaust. You might have better distrubution of O2 in the fuel.

I think the -'s outweigh the +'s and is throwing more overall gasses into the air. Everyone seems to be concerned with greenhouse gasses (CO2) and this fuel contributes more.

I would like to point out that my vehicle barely runs on the 87 octane/oxy, but runs fine on 87 octane without the “oxygenation.” To get it to run, I have to go up to the “plus” in the winter (89 octane).

I think that oxygenation is just a plot by the corn farmers to sell as fuel what they can’t sell as food. (ADM is a BIG supporter of fuel oxygenation)

here we used to use MBTE which is petro based - not corn based. It was way better for the cars then alchols but is very dangerous to breath ( IIRC carcongenic, a few problems w/ people getting sick at the pumps and some DUI’s (DWI’s) handed out by the police becauce their breathilizer would count this stuff as alch.) and it got into the water supply in a few places.


OK, time for the “more than you wanted to know about reformulated/oxygenated gasoline and MtBE” hour! (well it shouldn’t take that long, I hope)

First, to answer the OP: Yes. Oxygenated gas (or Reformulated Gas or RFG) does indeed reduce air pollution.

Mostly it reduces the amount of semi-burned fuel coming out of the tailpipe (as Holden & Pluto said, by providing more oxygen for more complete combustion). These semi-burned hydrocarbons are typically not good stuff – they form ground level ozone (smog), and are often directly carcinogenic (think benzene and stuff like that). One study found RFG reduced cancer risk from gasoline by about 12 percent. Reformulated gasoline also reduces NOx pollution (which forms ozone/smog), but only by a very little bit – a percent or two.

It does reduce fuel economy, but only mildly. EPA studies show one to three percent loss in fuel economy. So yes, more CO2, but only a little bit.

Archer Daniels Midland (ADM) and all the corn farmers in Iowa definitely do have enough political pull to create all kinds of federal subsidies for ethanol (and in fact, did slightly influence the federal Clean Air Act requirements), but they didn’t create the reformulated gasoline program – it’s a real solution to the real problem of air pollution.
On to MtBE (methyl tertial-butyl ether), one of the two most common components of RFG (ethanol being the other).
The dope on that is, yes it was probably a mistake to use MtBE, but not as bad a mistake as many people think. MtBE is, in fact, not very toxic. It’s certainly far less carcinogenic than most of the other compounds in gasoline (benzene and all kinds of lovely relatives), so as far as inhaling vapors or drinking gasoline directly (if you’re into that kind of thing…), you’re actually better off with MtBE in the gas than without it. So at the time, it quite reasonably seemed like a good solution – remember it’s generally safer than the rest of gasoline (and reduced all kinds of other air pollution problems).

The problem with MtBE turned out to be that it’s very soluble in water, much more so than the rest of gasoline, so it moves through and into groundwater very well (much better than benzene and the really dangerous stuff). Combined with that is that you can smell and taste MtBE in very small concentrations (and it’s flavor is more than a little unpleasant). So even a small spill of gas with MtBE can contaminate wells in the area to the point where they’re unusable because of the taste. By the way, you taste MtBE at levels far below where it’s considered dangerous, so it’s unlikely anyone would drink enough water to be at much risk (which is not to say that losing the use of your well isn’t still a serious problem). Once the problem of it’s solubility was appreciated, regulators began acting to get it out of gasoline (by the way, regulations never required MtBE specifically, most refiners used it cause it was cheaper and easier than ethanol).
I’ve never heard of people failing blood alcohol test because of MtBE inhalation – do you have any more info or cites for that?

Oh, and if you want even more info, start with There are links to independent studies as well as EPA info.

(did I manage to sound as authoritative as Anthracite?)


Who are you kidding? There aren’t nearly the required amounts of:

  1. formulas with lots of sub- and superscripts

  2. references to other posts of long articles you have previously wrote about the subject

  3. in-depth discussions of subpoints

No, I fear that we may never see a poster the likes of Anthracite for a long long time. :slight_smile:

I recall there being another issue with RFG in California (with MTBE added) when it first was introduced, which was that they somehow ate away gaskets in cars, leading to expensive repairs. One San Francisco TV station was going on about this for a while when the issues with ground water contamination showed up, and this aspect got shoved to the back burner.

Unfortunately, my memories are inconsistant, as I remember it affecting diesel cars and trucks more, but I recall that RFG is in gasoline only, not in diesel fuel. Does anyone have any info or recollections on this?

Ok, I can believe that using the oxy-fuels reduces pollution per gallon burned, but if I am burning 10% (this is roughly the case for my car) more fuel on a given day because of the loss in fuel effciency, am I really reducing the amount of pollution?

Regarding the unburned or semi-burned hydrocarbons, I’m going to assume that even oxygenated fuels do not burn to completion, so I must be still releasing these into the atmosphere. If by using the oxy-fuels, I reduce the emission of these compounds by 10%, by my estimation I’m breaking even, while releasing more carbon dioxide.

Looking (quickly) through some of the documentation Quercus provided, it appears that in my car I’m not even doing that. With MTBU, NOAA is showing a reduction in Benzene emission of 4.1%, significant yes, but I’m burning 10% more fuel!

Am I missing something?

No, Eyer8, you’re right on cue. I actually found a place in my area that, because of the boundry requirements for sales of oxy-fuel (read worthless crapp that causes more problems than it solves), doesn’t have to sell it. They can sell “clear gas”. My engine runs much better, so I know that the reduced mileage and poor preformance were not just caused by cold weather, but by the oxy-fuel.

methyl tertiary butyl ether