Use of E0 Non ethanol gas in 2023 Prius Prime

You are not correct about unstable hydrocarbons only being a problem for storage. They also cause more deposits than more stable hydrocarbons during regular use (gums and varnishes mentioned). Unstable = more decomposition = more deposits. It is the same thing with engine oil—more stable base oils blended into engine oil lead to less decomposition and deposits, a fact that I am familiar with.

Do you know organic chemistry, which is a very deep subject? Even if you did know some, these are complicated research subjects that you cannot make conclusions based on an over-50-year-old paper that you ran across on the Internet, which probably does not apply to the gasoline compositions of today.

 

Deposits aren't just from degradation of the fuel. Aromatics leading to carbon deposits is because of how they burn in the cylinder. These are some of those stable compounds in premium(xylene has a shelf life of 3 years). What is happening in the tanks before they reach the injector isn't the reason for their deposits.

As for gasoline composition and stability, premium gas at the station can be a base of regular with more octane boosters. Are the molecules of the 87 octane portion going to become more stable hanging around the others. That bulletin you linked was about race fuels. They are more precisely made than what is at the gas station. When I priced them a few years ago, they were $8 to $10 a gallon around here. Then they have their own potential issues; one octane booster used can photodegrade in minutes.

It's fine. Engine design starts with ethanol free gas. It is what is used in testing, including EPA. Also what most of the world uses. Adding ethanol just requires changing the plastics in the hoses and gaskets to something that holds up to the alcohol.

I wouldn't worry about the potential carbon deposits. There are fewer aromatics that lead to them in regular octane, which is all you need. It is also something that takes time to develop, if it is happening. If the E0 isn't Top Tier, just add some fuel system cleaner or tank of TT E10 every once in a while, to clean. That is probably a good idea with Non TT E10.

 

It probably says 87 unleaded in the owners manual, my 2020 does, so yes it’s ok if it makes no distinctions. Pure gas doesn’t mix with water but adding alcohol allows water up to a point to mix in solution, and thus burned.
I think it’s worse to use pure gas in any situation where gas sits, especially in cold, moist, winter climates. In a Prime, sealed tank or not, the air has moisture in it. Better to use gas with some alcohol like e10.

 

Below is what your 2023 Prius Prime Owners Manual says about fuel. Notice that it says to not use methanol, MMT, leaded gasoline, E30, E50, E85, or anything containing more than 15% ethanol, but it does not say anything against E0 or requiring any ethanol at all.

It notes that ethanol and reformulated gasolines "are available in some cities" and recommends them "for reduced vehicle emissions." This is an indirect acknowledgement that the allowed ethanol mixtures (e.g. E10 and E15) are not available everywhere, and are not required.

 

Again, as I emphasized over and over again, you are speculating without knowing anything about the actual composition of the gasoline sold out there.

Here is some good data from a 2019 paper. As the paper states, “The actual composition of chemicals varies with the source of the crude oil, the refinery, and the time of the year.”

The actual compositions and physical properties of the eight test fuels is given in the table below. I made a plot of the total aromatics content vs. total ethanol content, and as you can see, there is no correlation between the two whatsoever. Perhaps they were able to achieve a high octane number for the fuel F1, which has no ethanol and a low aromatics content, by incorporating branched saturates (as opposed to linear saturates), which have high octane numbers. In any case, as you see, a high octane number can be achieved without ethanol and/or a higher aromatics content, and the blanket statement that high-octane and/or ethanol-free fuel has a higher aromatics content is simply false.




Of course, it is also not to mention that many other factors contribute to the cleaning and emissions as well in addition to the aromatics content. Once again, all these are unknown to you, me, and basically everyone else, and only the refinery knows about them, as they are the only ones who know the true composition.

As for the OP's question, the only thing that is known to you about the cleaning quality is the Top Tier qualification. (There is also the Tier 3 qualification for the emission standards.) If you pick a gas station from the list I posted and linked above, you will probably be fine. I personally always use Chevron 87 octane E10 fuel, and I don't think about it. Chances are that gas stations get the fuel from random refineries anyway, and you really don't what it actually is.

 

My original statement was based research results like these:
https://link.springer.com/article/10.1007/BF00724227
"Increase in the aromatic hydrocarbon content to 40–45% results in an increase in the quantity of carbon formed per unit octane number, which is approximately constant."
An Analysis of Intake Valve Deposits from Gasolines Containing Polycyclic Aromatics on JSTOR
"It was found that characterizing the amount of Ultraformer bottoms by the anthracenes + pyrenes (A+P) concentration in the finished gasoline provided an excellent correlation (cc = 0.95) to the deposits formed. Napthalenes concentration did not correlate with deposit formation."
I acknowledged that my statement may be out of date when I made it.

None of the fuels in your table approach the 40% level, but they are also all regular grade gas. The only premium gas on it is an E20. ethanol is the octane booster there. So it looks like any potential carbon deposit issue at risk here is limited the E0 premium octanes.

Which is besides the point of my continuing with the discussion. It was over premium being a better engine cleaner. When it comes to cleaning deposits in the engine, the actual gasoline doesn't matter. That work is done by the added detergents.

Premium has a longer shelf life that means less potential deposits over time, but that isn't a concern for regularly used cars. Parking a car for extended periods requires attending to things beyond the fuel. PHEVs should have procedures in place in the event the engine is rarely used. Toyota flat out tells the owner to add X amount of fresh gas after so much Y time without using the engine.

Which I have pointed out at least a couple times to 'pure' gas believers.

They likely don't either. Takes money to figure that out.

The EPA detergent level is a minimum level. The major car makers felt some more would be better; that is Top Tier.

Tier 3 emission standards required a change to the gasoline formulations itself, not the detergents. In order to not poison the new catalytic converters, the sulfur levels needed to be reduced. Gasoline today has as much sulfur as ULSD.

 

Yes, it turns out that the gasoline composition has entirely changed since 1990, with substantially reduced aromatics. The introduction in the 2019 UC Riverside paper I used explains it:

1. Introduction

Gasoline is a complex manufactured mixture that does not exist
naturally in the environment. Typically, gasoline contains several hundred
chemicals with varying boiling points. The hydrocarbons present in the
gasoline mixture include alkanes or straight-chain C4 to C12 compounds,
also known as paraffins, isoparaffins or branched-chain compounds, alkenes
or olefins, which are unsaturated linear and branched-chain hydrocarbons,
and naphthenics or saturated cyclic hydrocarbons [1]. The
gasoline mixture also includes aromatic hydrocarbons, such as benzene,
toluene, ethylbenzene, and xylenes. The actual composition of chemicals
varies with the source of the crude oil, the refinery, and the time of the
year [2]. Gasoline mixture is blended to meet a variety of regulatory requirements
that differ throughout the United States (U.S.). Octane, Reid
vapor pressure (RVP), which varies by season and geographic region), and
levels of sulfur and benzene are dictated by federal regulations [2].

Over the last few years, gasoline quality has been significantly
changed in the U.S., with an increase in ethanol in the gasoline pool, as
well as reductions in sulfur and benzene contents [3]. The phasing out
of toxic octane enhancers from gasoline, such as lead, and methyl tertiary-
butyl ether (MTBE), allowed refiners to increase the volume of
aromatics in gasoline to meet anti-knock requirements and boost the
octane ratings of gasoline. Changes in gasoline properties over the years
have been mainly driven by fuel regulations, as well as to changes in the
marketplace. The production of aromatics in a catalytic reformer has
become a relatively expensive process primarily because hydrogen
production can alternatively be achieved via stream-methane reforming
fueled by inexpensive natural gas. This issue, along with the yield loss
of converting branched hydrocarbons to aromatics that have lower
volumes, has discouraged reforming and resulted in a decreased volume
of aromatics in the gasoline pool. In addition, the alkylation process has
become more cost-competitive compared to reforming, leading to more
alkylate than aromatics in gasoline. These changes, in addition to
stringent regulations, are reflected in the overall lower gasoline aromatic
levels, with benzene levels being currently 60% lower to those
found in gasoline fuels in 1990 [3,4].

 

According to this paper, only the three- (anthracene) and four-ring (pyrene) aromatics lead to deposits. Benzene, toluene, etc. (one-ring) and naphthalene (two-ring) aromatics do not. These three- and four-ring compounds are basically plastics and that's why they lead to deposits.

The three-ring and four-ring aromatics mentioned are found in gasoline only in trace amounts, and today's quality gasoline probably has even less of them. Therefore, the deposit mechanism mentioned in this paper is a nonissue for modern high-quality gasoline.

Basically, these polycyclic (multiring) aromatics are plastics that are produced during the catalytic reformation of "heavy reformate," which is mostly the "iso-octane" compound (not to be confused with the octane rating) that has an octane rating of 100 by definition. Therefore, it can be used to blend high-octane gasoline. The polycyclic aromatics on the other hand are undesirable and removed by further distillation (at added cost) as the paper mentions at the beginning, noting that this improves the gum content and color. Again, I am sure that high-quality modern gasoline has very little of these plastics.

 

And it is still the detergents that keep things clean.

 

If one wants a water free gas tank and gas lines use e10. All the folks from cold climates must know this. Pure gas, I wouldn’t use it if it was less expensive. Older people remember the drains on glass bowl fuel filters to let the water out. Lawn mowers some may still have it. I think everyone knows air contains moisture in varying degrees, and moisture condenses at the dew point.