Autogas and high end engines

I am new to this group. I know that many low hp engines can get an
autogas stc.
My question is this: How hard is it to run autogas in 200+ hp engines-
say 200 to 300 hp? Both physically and legally?

"John Skorczewski" wrote in message
om...
I am new to this group. I know that many low hp engines can get an
autogas stc.
My question is this: How hard is it to run autogas in 200+ hp engines-
say 200 to 300 hp? Both physically and legally?

Maybe. Probably not easy because autogas doesn't work too well with
engines with compression over 8 atmospheres. Then you got problems with
vaporlock where the power is so high that you have a lot of heat under the
cowl.

Some low compression engines are sometimes unsuitable to mogas. The
Luscombe 8A with a 6.3 atmosphere compression engine is reputed to have
trouble with mogas, probably because of vaporlock.

It is not the horsepower that is the problem, but the compression ratio. There
are 230 horse engines for which an STC exists and is quite easy to use. There
are sub-100 horse engines for which no STC exists today, and which will either
have to be derated in some way OR have an engine modification to reduce the
compression ratio (which does an automatic derating). If the airplane cannot be
flown derated (not enough horses for the job) then an engine change to a lower
compression, more horsepower engine may be the only solution.

Understand that AOPA and other groups "working on the problem" are being torn
two ways. One is to keep their majority constituency that COULD use premium
fuel in a derated engine happy. The other is their well-heeled minority
constituency who are happy with the way things are, thank you, and will continue
to block the use of autogas at the expense of the majority.

Of course, the folks producing TEL could end the debate in a month or so if they
wished. As noted, though, if there is a market for TEL, and unless the EPA bans
the import of TEL, anybody with a class in high school chemistry could open a
plant in a third world country and start selling the stuff in barrels at a
mighty good profit if this happens.

Jim



(John Skorczewski)
shared these priceless pearls of wisdom:

-I am new to this group. I know that many low hp engines can get an
-autogas stc.
-My question is this: How hard is it to run autogas in 200+ hp engines-
-say 200 to 300 hp? Both physically and legally?

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

I appreciate the info--- but I still have questions. Say, I wanted to
built an RV-10 with a 260 lycoming engine. How do I find out if it can
be stc-ed for autogas??? ---and if not what is the biggest lycoming
engine that can burn autogas? Who has info like this??

With an experimental, you don't need an STC. You can run the engine on
whatever makes you happy... That said, look at the compression ratio for
the engine you're considering. Lower compression = happier with autogas. I
believe some engines with 8.5:1 compression can be STC'd on autogas, and
should be relatively happy with it, but 8.5:1 is right at the limit. A lower
compression engine would be happier with autogas.

Auto gas has higher vapor pressure than avgas, so vapor lock is something
you really need to consider. At high altitude on a warm day, the engine
might just decide to quit... Or on a day when you flew, then made a quick
turn-around, the engine compartment might be warm enough to cause a vapor
lock problem. Then, there is the problem of accidentally buying winter
formulation autogas (with a higher vapor pressure) during a warm spell...

Here's a link to the best info you're likely to find on autogas and STC's:

http://www.eaa.org/education/fuel/autogas_vs_avgas.pdf


"John Skorczewski" wrote in message
om...
I appreciate the info--- but I still have questions. Say, I wanted to
built an RV-10 with a 260 lycoming engine. How do I find out if it can
be stc-ed for autogas??? ---and if not what is the biggest lycoming
engine that can burn autogas? Who has info like this??

My Cherokee has an 8.5:1 O-360 with autogas STC for 91 minimum. You could get
a 6-cylinder version of the same engine (O-540 straight-valve) STC'd for 91 in some
planes. The Comanche hydrolocked the carb on autogas (Peterson told me that), so it
couldn't pass.... it's a combination of engine and airframe.

That said, if you run premium an O-540 at 8.5:1 and 2700 rpm is 260 HP on
autogas. If you keep it sufficiently cooled and well cowled, you could reduce the
vapor locking problem. I don't know of any fuel-injected Lycomings that can be STC'd
for autogas, so the O-540 is probably the biggest. If you run 7:1 compression for 235
HP (e.g. PA-28-235), it runs happily on regular 87.

-Cory

John Skorczewski wrote:
: I appreciate the info--- but I still have questions. Say, I wanted to
: built an RV-10 with a 260 lycoming engine. How do I find out if it can
: be stc-ed for autogas??? ---and if not what is the biggest lycoming
: engine that can burn autogas? Who has info like this??

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering Ph.D. Graduate Student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

In article ,
wrote:

My Cherokee has an 8.5:1 O-360 with autogas STC for 91 minimum. You
could get
a 6-cylinder version of the same engine (O-540 straight-valve) STC'd for 91
in some
planes. The Comanche hydrolocked the carb on autogas (Peterson told me
that), so it
couldn't pass.... it's a combination of engine and airframe.

That said, if you run premium an O-540 at 8.5:1 and 2700 rpm is 260
HP on
autogas. If you keep it sufficiently cooled and well cowled, you could
reduce the
vapor locking problem. I don't know of any fuel-injected Lycomings that can
be STC'd
for autogas, so the O-540 is probably the biggest. If you run 7:1
compression for 235
HP (e.g. PA-28-235), it runs happily on regular 87.

-Cory

John Skorczewski wrote:
: I appreciate the info--- but I still have questions. Say, I wanted to
: built an RV-10 with a 260 lycoming engine. How do I find out if it can
: be stc-ed for autogas??? ---and if not what is the biggest lycoming
: engine that can burn autogas? Who has info like this??


When you use autogas, you have to pay close attention to fuel system
design, to avoid sharp corners in lines, cooling paths to gascolators
and even locating boost pumps on the cabin side of the firewall, to keep
things cool.

Orval Fairbairn wrote:
: When you use autogas, you have to pay close attention to fuel system
: design, to avoid sharp corners in lines, cooling paths to gascolators
: and even locating boost pumps on the cabin side of the firewall, to keep
: things cool.

If possible, it would be great to have the return system of an automobile.
Flush most of the fuel to the engine and back to the tank. It requires double the
fuel lines (and thus double the potential for leakage, etc). It turns the fuel tanks
into a huge coldsink to keep the fuel cool as it circulates through the engine
compartment.

Of course, it's a little different since airplanes operate at a large
percentage of their maximum fuel burn. A car typically runs at 10-25% of its maximum
power, even on the freeway so fuel burn is 2-3 gph. In a high-perf engine cruising on
14 gph (max probably 20-25 gph), circulating the fuel would require faster pumps...
say 2x-3x, or about 1 gpm. Pretty beefy, now that I think about it.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering Ph.D. Graduate Student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

What is "hydrolocked" with regards to the carb?

Never heard the term used before in this context.


"Orval Fairbairn" wrote in message
news
In article ,
wrote:

My Cherokee has an 8.5:1 O-360 with autogas STC for 91 minimum.
You
could get
a 6-cylinder version of the same engine (O-540 straight-valve) STC'd for
91
in some
planes. The Comanche hydrolocked the carb on autogas (Peterson told me
that), so it
couldn't pass.... it's a combination of engine and airframe.

That said, if you run premium an O-540 at 8.5:1 and 2700 rpm is
260
HP on
autogas. If you keep it sufficiently cooled and well cowled, you could
reduce the
vapor locking problem. I don't know of any fuel-injected Lycomings that
can
be STC'd
for autogas, so the O-540 is probably the biggest. If you run 7:1
compression for 235
HP (e.g. PA-28-235), it runs happily on regular 87.

-Cory

John Skorczewski wrote:
: I appreciate the info--- but I still have questions. Say, I wanted to
: built an RV-10 with a 260 lycoming engine. How do I find out if it can
: be stc-ed for autogas??? ---and if not what is the biggest lycoming
: engine that can burn autogas? Who has info like this??


When you use autogas, you have to pay close attention to fuel system
design, to avoid sharp corners in lines, cooling paths to gascolators
and even locating boost pumps on the cabin side of the firewall, to keep
things cool.

Cy Galley wrote:
: What is "hydrolocked" with regards to the carb?

: Never heard the term used before in this context.

I understand it as an excess in pressure caused by localized fuel boiling.
Vapor lock causes the carb to get nothing but fuel vapor and the engine dies from
being too lean (carb doesn't meter vapor well). Hydrolock pressurizes the liquid fuel
and overpowers the needle valve in the float. This splooges liquid fuel out and the
engine dies from being too rich.

This is somewhat speculation, but it does make sense to me. A friend of mine
swears up and down that that's why people have such a hard time hotstarting an
injected lycoming. Most people think the fuel in the spider manifold has vaporized
and it's too lean. He says the fuel has heated, expanded, and run out the injectors
before the engine is even fired up. Thus, when trying to start, it's already flooded
before you turn the crank.

YMMV... I just work here...

-Cory

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering Ph.D. Graduate Student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************