[NSRCA-discussion] Gas vs Alcohol (was Newslist is flawed)
Bill Glaze
billglaze at bellsouth.net
Tue Dec 15 14:08:51 AKST 2009
Several top-notch flyers seem to feel that they can get a more reliable idle with 30%, I have been advised. Exactly what the problem was with their engine idle before using the higher nitro, I have no idea.
As the article referred to in another communication demonstrates, it is necessary to carefuly tailor the compression ratio of the engine to take advantage of the nitro's characteristics, without accidentally running into detonation, or, in some cases, overly slow combustion which, in the case of a blown fuel engine, is guaranteed to take off the blower and blower manifold. Suddenly.
Also, let me state that I've onlly been talking about the small experiments that I have been making; my sampling is probably too small to mean anything to anybody else but me. I have, however, been answering some of my long-held questions. Fun playing around with this stuff off-season.
Bill Glaze
----- Original Message -----
From: Atwood, Mark
To: General pattern discussion
Sent: Monday, December 14, 2009 8:43 PM
Subject: Re: [NSRCA-discussion] Gas vs Alcohol (was Newslist is flawed)
I’m curious Bill, knowing virtually nothing about any of these chemical properties, if most of us don’t run the higher nitro primarily to improve low end idle, and transition characteristics, rather than top end RPM. That seems to be where the real difference is between 20% and 30%, though an added 100-150RPM can be a HUGE difference on a 90deg day…
-Mark
Mark Atwood
Paragon Consulting, Inc. | President
5885 Landerbrook Drive Suite 130, Cleveland Ohio, 44124
Phone: 440.684.3101 x102 | Fax: 440.684.3102
mark.atwood at paragon-inc.com | www.paragon-inc.com
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Bill Glaze
Sent: Monday, December 14, 2009 5:26 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Gas vs Alcohol (was Newslist is flawed)
Assuredly, it's not a direct trade-off; Stochiometric is different for the different fuels, of course. And the fact remains that running pure methanol will provide approximately 15% more horsepower for the fuel burned, which, again, is about twice that required for gasoline. What it amounts to is that gasoline is the most efficient of the three substances, but, in our case, I will admit readily that efficiency is far down the list of requirements. I have been running some tests, (of which the sampling is small, admittedly) and I was surprised at the small rpm difference between 15% standard Morgan Cool Power, and 30% Heli. If you need, or can discern, the small difference involved, then of course it justifies the use of the 30% stuff. In my case, it doesn't seem to justify the usage. When one mixes in the Latent Heat of Vaporization, the waters are muddied even more, but it probably is of small concern in engines the size of ours, due to the small swept volume, and the variation of conditions having to do with cooling, both external and internal.
Bill Glaze
----- Original Message -----
From: Bob Richards
To: General pattern discussion
Sent: Monday, December 14, 2009 5:08 PM
Subject: Re: [NSRCA-discussion] Gas vs Alcohol (was Newslist is flawed)
Bill,
The heat energy per unit has little to do with the power we get from an internal combustion engine. The limiting factor is how much air we can get into the engine. Each fuel has an optimum ratio to be mixed with the amount of air that enters the engine. Gasoline burns the leanest. Methanol burns much richer, so more fuel goes into the engine per stroke. Nitro is even richer.
I've also read that nitro expands to a much larger volume when it burns, even though it puts out less heat per unit than methanol, which is one reason why nitro by itself puts out much more power than methanol. I may open a can of worms when I say this, but it has been my experience in both pattern planes and helicopters that higher nitro makes the engine run cooler.
Think about it, methanol puts out less heat per unit, but develops more power than gasoline. Gasoline engines must have larger cooling fins, even though less power is being developed. Gasoline burns so lean compared to methanol, this is the reason why gasoline carbs are more complicated than alcohol carbs. Add nitro, then the needle must be opened more and becomes less sensitive. This may be an over-simplistic explanation because the thermodynamics are vastly different (methanol provides a lot of internal cooling as it atomizes) but it works for me. :-)
Bob R.
--- On Mon, 12/14/09, Bill Glaze <billglaze at bellsouth.net> wrote:
From: Bill Glaze <billglaze at bellsouth.net>
Subject: Re: [NSRCA-discussion] This email list is flawed in my opinion.
To: "General pattern discussion" <nsrca-discussion at lists.nsrca.org>
Date: Monday, December 14, 2009, 6:28 PM
The specific heat generated by gasoline is about twice the specific heat generated by alcohol, which, in turn is about twice the specific heat generated by nitro. In other words, on a mass basis, nitro is a more inefficient fuel on a pure basis than alcohol, which is less efficient than gasoline. (from a volume/efficiency standpoint)
Or so my handbook stated when I was building competition engines. Then why use nitro at all? Well, because it generates more O2 than it needs to burn, thereby helping the other "combustibles" complete their combustion, and it's possible to run a hellacious load of nitro per cycle because of it's burn characteristics.
Bill Glaze
----- Original Message -----
From: Vicente "Vince" Bortone
To: General pattern discussion
Sent: Sunday, December 13, 2009 8:48 AM
Subject: Re: [NSRCA-discussion] This email list is flawed in my opinion.
Matt,
It will be very interesting to see your results. I had the chance to build and fly the Abbra with ZDZ 40. I was able to comparare the same plane with OS160 back-to-back. Clearly the ZDZ 40 was behind in power (or power-to-weight ratio) when compared with the OS 160 when doing the Master schedule of that time. I am sure that less fuel consumption with less BTU content means less power. The Abbra with the ZDZ 40 was ~3-4 oz over 11 lbs. The OS 160 Abbra was 9.8 lbs. I am not sure now what the new gasoline engines manufactures are doing to increase the power. I believe that an improvement in the design of gas engines is required to make it usable for pattern.
Vicente "Vince" Bortone
----- Original Message -----
From: rcmaster199 at aol.com
To: nsrca-discussion at lists.nsrca.org
Sent: Saturday, December 12, 2009 10:46:09 PM GMT -06:00 US/Canada Central
Subject: Re: [NSRCA-discussion] This email list is flawed in my opinion.
Yes that's true. When I was mixing my fuel I needed to do it by volume until I figgered what the volume weighed for each of the nitro blends I was mixing..... 30% nitro is around 10% denser (weighs around 10% more for a tankful) than 15% nitro.
Soooo....the guys who are running the YS not only use much larger tanks but their tanks weigh more when full than they would have running lower nitro. But YS is a dawg on lower nitro. You gotta admire YS Marketing strategy
Yet another reason I am looking into gasoline powerplants for pattern. Gas is significantly less dense than 30% nitro blend and gas engines demand less fuel to begin with. A 320 cc tank (around 11 ozs) will run the 30 cc engine for around 12 minutes, enough for about 1 2/3 master schedules.
MattK
-----Original Message-----
From: Verne Koester <verne at twmi.rr.com>
To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org>
Sent: Sat, Dec 12, 2009 11:24 pm
Subject: Re: [NSRCA-discussion] This email list is flawed in my opinion.
The weight of fuel is going to depend in large part on the percentage of nitro. Nitro is the heaviest component. Don’t believe it? Go to the hobby shop and pick up a gallon of 5% with one hand and 30% with the other, preferably from the same manufacturer. You’ll be surprised. I know I was when a fuel manufacturer showed me at Toledo about twenty years ago. Fortunately, pilots with glow planes are weighed without the fuel so they don’t have to worry about that…
Verne
From: nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Bill's Email
Sent: Saturday, December 12, 2009 8:16 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] This email list is flawed in my opinion.
Ed Alt wrote:
About 0.75 oz per fluid oz.
I just weighed a gallon of fuel I have here. It was 7.8 pounds including the plastic jig. 0.75 ounces per fluid ounce would mean the jug weighs +/- 29 ounces (1.8 pounds).
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