Mogas 93 Octane with Ethanol??

[jim@wrighthomesco.com]

I have not been able to get a straight answer if 93 octane with ethanol is acceptable in the TSI. It's very difficult to get 93 without ethanol.

[ibgarrett]

Check out this presentation

The TL;DR (that I'm summarizing many months after watching this) of the video is it has to do with the Rapid Vapor Point (RVP) of the fuel with or without Ethanol. The problem really comes from being at a higher altitude and the outside temperature. The presentation is on a 912, but the same should track on the 915.

Is Ethanol acceptable in a Tsi? My understanding is yes

The main issues will have to do with the RVP and how long the plane sits. Ethanol is bad for the rubber lines, but it takes months of sitting for anything to really be a problem. I liken it to the "but honey - I HAVE to go fly the plane to help keep the methanol moving". Of course the rubber issue can (and should) be mitigated by using a teflon or aluminum fuel lines to the engine. If you eliminate the rubber lines you don't have that five year fuel line replacement issue to deal with and you don't have the ethanol issue.

My take on it - if you have ethanol in the fuel or are between a summer/winter blend of fuel, be cautious about the RVP with the engine/fuel when at altitude.

Midwest Panel Builders has a series that discussed the vapor lock that can occur which is worth watching as well around this topic -

[STGove]

FWIW,

May not to so everywhere, but, here in TEXAS, we have Buc-ee's. They do sell at certain stations (ie the larger ones) an Ethanol free MoGas. Available to several octanes. Down here we ue it in our lawn equipment, so the ethanol doesn't cause problems.


6201 Gulf Fwy (IH 45)
Texas City, Texas 77591
Ethanol-Free: 87 and 92 Octane

https://buc-ees.com/locations/

[lutorm]

The Rotax position is laid out in https://rotax.my.salesforce-sites.com/D ... sPdf=false, which says up to 10% ethanol is approved for use (but also notes that it's the operator's responsibility to make sure the airframe components are OK with E10.) In the US, the relevant fuel standard is ASTM D4814 (min. AKI 91).

It also notes, as ibgarrett points out, that automotive fuels have a higher propensity for vapor lock, especially if the wrong seasonal blend is used. (RVP stands for Reid Vapor Pressure, btw.) There have been reports of Slings using automotive fuel having fuel pressure problems at high altitudes because the pressure on the suction side of the fuel pumps gets low enough that bubbles form. This is why Midwest developed that wing-mounted boost pump kit. (I'm personally planning to put one of those in my kit.)

For all the concerns about mogas, the Rotax publication above is full of cautions about how bad it is to run 100LL, and its impacts on oil change interval requirements and the formation of deposits in the engine. I'll be very happy when UL avgas becomes widely available.

[ibgarrett]

What... I like Rapid Vapor Point better. And who is this "Reid" anyway.

btw - snark aside, I stand corrected

[lutorm]

And who is this "Reid" anyway.

Good question

Harry Reid, former Senate majority leader maybe? I know my vapor pressure would rise substantially if I had that job...