MISTRAL4

In my country, nitro methane it is too expensive.
We are trying other substances to replace it
(amyl nitrate and methyl nitrate) that we use at 0.1% vol/vol in methyl alcohol/castor oil mix, and improves accelerating and running but not increase rpm.
These substances are easy and cheap to make but
We asked ourselves if the glow engines could be
damage with the course of the time.
We have not found information about this, just that amyl nitrate is used in diesel RC engines but not in glow engines.
Any information about this matter will be appreciated.

andrew66

i read somewhere that acetone can be used, but be very careful as this stuff is very flamable. i would test it in very small percentages and work your way up to the ideal amount.
hopefully someone else has a little more info/advice about using acetone. i personally would try it, but then again i'd try anything twice

fokker20planes

I have about 200 old R/C Modeler magazines and I bet 25% of them have Clarence Lee answering the same question. The answer is always the same. No there is not a practical substitution for Nitro Methane. Some time back I believe Sig did have some success replacing it with Nitro Ethane. If acetone worked that would be great. That's a lot easier to obtain. If there is a practical replacement, let me know. I will go back to making my own fuel.

MISTRAL4

Thanks for you support, but I have to explain my previous question.

Looking for a replace nitro methane, I have found the following page:

http://www.hosenose.com/hevener/rcflight/5pctfuel.htm

A fragment of this page say the following:

"The nitromethane lowers the octane of the glow fuel so that it will more easily ignite under pressure. This is why nitromethane makes a glow engine easier to start and idle more reliably"

According to this concept, a substances that could lowers the octane, or on the other hand, increase the cetane of the fuel, could produce a similar effect than nitro methane.

Amyl nitrate is a cetane improver that is used in diesel engines and
RC diesel engines.

Methyl nitrate was used in experimental way like
cetane improver to allow the use the alcohol
in diesel engines.

(There are a lot of alkyl nitrates that could be used like cetane improvers)

We are using since 3 months ago, methyl nitrate and amyl nitrate in glow engines at 0.1%vol/vol (1ml per liter of 4/1 alcohol/castor oil mix) with good results, increasing acceleration, making starting easy and improving running.

We do no detected increasing in RPM, but we do not need it for our kind of flights

I can not believe, that we are the first that have used cetane improver in glow engines with good results (at least for the moment).

Due to that, I am asking if somebody have some previos information about that.
(Sorry for my bad English)


Thanks and regards

Newc

Nitromethane is much more than simply an octane reducer. You are correct that an octane improver is a cetane reducer, and vice versa, but that doesn't explain the complete function of nitromethane. As an example, Nitromethane (CH3NO2 - the numbers are actually subscripts) contains oxygen which in and of itself allows the higher power that is seen when using this as a fuel component. (Sort of like the racers using Nitrous Oxide in their engines for short bursts of additional power since it gives the engine increased oxygen) OK, you say, the chemical formula of amyl nitrate also contains oxygen, so why don't we see the same benefits and increased RPM? Simple. You are using Amyl Nitrate at 0.1% versus the use of Nitromethane at volumes ranging from 5 - 40%. Hence, a lot less oxygen is being added to your fuel.

Why are you seeing "...and improves accelerating and running but not increase rpm."? I would bet that if you actually measured the properties that you think are improved (very difficult without extremely finely tuned and calibrated specific equipment) that they really aren't, compared to the same fuel without 0.1% Amyl Nitrate. You aren't seeing an increase in RPM for the same reason - it isn't really there - but in this case you can measure it.

If your engines are running well on the mix you mention, they will likely run just as well with 0% Nitro FAI fuel.

By the way, the link you provided has just enough correct information as to make you believe everything that's said, and you shouldn't. For example, it is stated that "Nitromethane isn't added to sport fuels to provide power." This is simply not correct! A given glow engine will develop more power if it is given a higher dose of nitro - ask the folks that use 40% and higher on their race (plane and car and boat) engines, or the YS engines folks that suggest the use of 30% for optimum performance of their engines, or even ask yourself why it is that organizers of race events with controlled engine sizes provide the fuel to the competitors? It's to keep the competition level, so that one person doesn't use a high nitro content fuel to achieve a power - speed - advantage.

MISTRAL4

Thank you for your reply.
I think that the spirit of this article is to say that for the recreationally pilot (casual sports pilots), that only wants reliability in his engines, it is sufficient the improving that produce nitro metane at 5% due to the effect of reducing octane .( at least this was my interpretation )
On the other hand , about the oxigen and the increment in power that nitromethano gives, I agree with you, and the article do not denied that.
The nitromethane has two effects:
To contribute oxigen to increase power.
To act like cetane improver, at least when is used at 5%.

We do not want (and we can not) to replace the nitro methano in the effect of increasing power,
we only want to improve reliability in the engines increasing the cetane value, that it is the more important effect that produce the nitromethane in the range of 5%.
We have tried with methyl nitrate at 5%, and the engines had erratic running. Due to that, the range of use it is in small quantities.
( like the common range of use of cetane improvers in diesel engines 0.1-0.3%)
The cetane improver decompose to generate free radicals which enhance the initiation of combustion. You do not need necessarily oxigen to do it.

About the phrase from the article:
"Nitromethane isn't added to sport fuels to provide power."
I understand the following in the context of the article:
Nitromethane is not added at 5% to increase power (you need a tach to detect rpm increase).
Nitromethane is added in this proportion to provide smooth idle and running and starting easy.
If you are a "performance pilot", of course, you need to increase % and then you will have to much power.

You are right, we do not have instrument to quantify the improvements in acceleration and running that we say that happens, but
We have the most subjective of the instruments:
The feeling of 5 pilots in several models.( one of them has more than 40 years of esperience and is not senile).
Any way, is imprudent of my part, to affirm things without parameter quantification, sorry.

Sport_Pilot

Why in the world would you want to use a cetane improver? You don't want this. The fact that nitro reduces the ignition temp and creates detonation problems is an UNDESIRABLE property. You model engine ignites the fuel with a glow plug that reacts with methanol, you don't want to improve cetane and have it go off from the heat of compression. Nitro improves idle and transition because if you use pure nitro you can actually burn it with no air, or in other words it is a monoporpelent. Even the ideal air mixture ratio is about half that for methanol. This means that it will run well when very rich, which means the carb or your tuning can be less precise and still have good results. If you improve the cetane you may have to lower the compression ratio. When you lower the compression ration with nitro it allows you to use a more advanced timing (hotter plug) or higher ratios of nitro, which means more power. You won't have this advantage with those nitrates. I suggest you read the following link on racing fuels as many model sites don't go into detail, or simply has stupid made up stuff on it.

http://www.turbofast.com.au/racefuel.html

Also read this link which contains everything but nitroethane, the only sutible substitute I know of, but I don't think it works well without some nitromethane.

http://www.turbofast.com.au/racefuel.html

jaka

Hi!
Over here in Sweden some have tried 5% gas in the fuel and this works like adding 5% nitro ...at least so they say who has tried it.

Another way is to use engines that don't ned any nitro ...like Webra and MVVS.

MISTRAL4

Thanks for your reply and the link:

From this link:
http://www.turbofast.com.au/racefuel.html
called my attention
POWER FUEL ADDITIVES/METHANOL ADDITIVES
Propylene Oxide.
From the tables of the end , I copy the following:
Propylene Oxide not known 9.6 : 1 14,000 220 Used as an ignition accelerator additive particularly with nitromethane (up to 20 percent by volume with pure nitromethane) where noticeable increases in power are possible. Easier starting and smoother running are other benefits when blended with most other fuels (up to 5 percent)

From another link that I am enclosing

www.nuigalway.ie/chem/CNF6080.pdf
(Ignition of alkyl nitrate/oxigen/argon mixtures in shock wawes and comparison with alkanes and amines)

“Nitrates an peroxides have been known since the early 1900s to promote the ignition quality of diesel fuel. They act by decomposing to form chain-initiating-radiacals, and there is also evidence to suggest that the head released during the decomposition of the additive in the pre-ignition phase contributes further to decreasing the ignition –delay-time.�...

Decreasing in the ignition delay time is the effect that produce an ignition accelerator
Then, nitrates and peroxides are ignition accelerators.

Summarizing:
If propylene oxide used as ignition accelerator additive produce easier starting and smoother running, why nitrates and peroxides (another ignition accelerators) could not produce the same effect?


On the other hand, I can not denied the logic of your reasoning.
I agree that the nitrates do not produce more power. ( we do not detect increasing in RPM) and I do not have in mind the mechanism to justify our feeling (improve starting and running).

MISTRAL4

sorry, the reply before was for sport pilot

Sport_Pilot

Propylene oxide is only for use with nitromethane. Nitromethane burns slowly but with great pressure. Sort of like comparing black gun powder to smokeless poweder, the smokeless has more pressure, but without a good primer will burn too slowly. The propylene oxide helps speed up the burn rate of nitromethane thus allowing less advanced timing, and less detonation. Some model fuels have had propylene oxide, but it is not necessary till you get above 20% or so.

ELTIGRE

facinating subject here. yes a lot of this material was gone over by Clarence Lee but it has been decades I believe since it was published(around 1974 i think) in a legnthy article explaining why nitro ads heat to the engine . likely one reason it inproves idle. just going from 10% to 5% in my sport motors i detected a drop in rpm & needed to readjust idle. also would not adjustments in compression ratio acomplish the same thing? adding gasoline to model fuel has been done before but with power loss i believe.

Sport_Pilot

No, that would only get you back some of the power from running higher percentage of nitro. Raising compression ratio whith the same nitro only slows the engine down, causes detonation, and makes the engine run hotter. See the recommended compression ratios in the link I provided. This has nothing to do with better idle, in fact higher compression ratios make the engine idle a bit rougher. The nitro improves the idle because it has a broader tolerance to fuel ratios. It can be run slightly rich just like lower ratios, but it can be run much richer with little loss of power. With very high percentages of nitro you may have to move the needle several clicks to see a differance on you tach, while with low percentages your ear can detect a change with just one click.

MISTRAL4

Looking for information about the use of alkyl nitrates I have found the following link

www.patentstorm.us/patents/5782937.html

"Gasoline compositions containing ignition improvers" .
I have copied the following fragments:

SUMMARY OF THE INVENTION .
It has been discovered that the use of organic nitrogen-containing compounds selected from organic nitrates and/or organic nitro compounds, in gasoline, at specific treat rates, results in improved ignition properties and therefore benefits fuel economy, cold start ignition, lean burn, and emissions. Improved ignition properties are evidenced by the reduction or complete elimination of engine misfires. The addition of organic nitrogen containing compounds typically thought of as cetane improvers to gasoline appears counterintuitive. Since additives which increase the cetane number of diesel fuels are known to be pro-knock agents when added to gasoline, the discovery that the addition of an organic nitrate compound or an organic nitro compound to gasoline, at specific treat rates, will not negatively affect fuel octane and at the same time will improve the ignition properties of the fuel is surprising. The present invention includes fuel compositions comprising a major amount of hydrocarbons in the gasoline boiling range with which has been blended from about 1 to about 1000 ppm of at least one organic nitrogen-containing compound selected from the group consisting of organic nitrates, organic nitro compounds and mixtures thereof. Further, the present invention includes a method for improving the ignition properties of a spark-ignition internal combustion engine Another embodiment of the present invention is directed to a method for reducing misfires in spark-ignition internal combustion engines, In another embodiment of the present invention, the nitrogen-containing compounds are added to fuels containing a major amount of a hydrocarbon in the gasoline boiling range, in order to improve cycle-to-cycle variation. Cycle-to-cycle variations occur as a result of uneven combustion, either among cylinders, or for consecutive cycles for a single cylinder. The fuel compositions of the present invention promote a more even combustion and thereby can reduce the cycle-to-cycle variation. The gasolines utilized in the practice of this invention can be traditional blends or mixtures of hydrocarbons in the gasoline boiling range, or they can contain oxygenated blending components such as alcohols and/or ethers having suitable boiling temperatures and appropriate fuel solubility, such as methanol, ethanol, methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), and mixed oxygen-containing products formed by "oxygenating" gasolines and/or olefinic hydrocarbons falling in the gasoline boiling range....

Therefore the alkyl nitrates ( that are using like cetane improvers in diesel engine) improves ignition, reduce cycle to cycle variation, and reduce misfires in a spark ignition internal combustion engine in the range of 1 to 1000 ppm. (1000 ppm = 0.1%)

Looking for the meaning of misfires a have found ther following from others links:

From:

http://www.autotap.com/articles/Anal..._Misfires.html "ANALYZING

IGNITION MISFIRES"
... No engine fires every cylinder 100% of the time. Misfires can occur at idle, when the engine is pulling hard under load, at high rpm and during throttle transitions as the air/fuel mixture changes. A few misfires are to be expected under these conditions, and should cause no major performance problems or significant increase in emissions. But if the misfires get out of hand and occur too often, they can make the engine idle or run rough, stumble when accelerating, waste gas and fail an emissions test....

And from other link:

www-chaos.engr.utk.edu/pap/crg-pre57.pdf
"Observing and modeling nonlinear dynamics in an internal combustion engines"

In real engines, not all the gases during are expelled during the exhaust process. The residual fractions which includes combustions products and tipically some unreacted fuel and air, is a function of engine design. Residual fraction is affected by several design parameters, one of the most important being valve overlap, the brief period that the intake valve is open before exhaust valve close. Valve overlap is generally helpful at higher engines speeds in producing power but al lower, near idle speeds tends to degradate combustion (ie increases cyclic variability = CV)...... The course of each combustion even can by followed by monitoring the internal cylinder pressure versus crank angle, as despicted in fig 1. As energy is released during combustion, cylinder presure excceds that wich occurs without combustion, thereby producing usefull work. CV causes non repeating preasure traces during successive engine cycles. The region in fig 1 in which the pressure traces diverge is the combustion region. In some cycles combustion is incomplete, leaving residual unburned fuel. In other cycles, excess energy is produced from combustion are undesirable because they produce alternating pulse of fuel and nitrogen oxides in the exhaust and a feeling of "roughness" to the driver.


Therefore alkyl nitrates due to that are ignition improvers, avoids the incomplete combustion, leaving less unburned fuel for the subsequent cycle, reducing cyclic variability and then avoid erratic idle or run rough, stumble when accelerating, waste gas and fail an emissions test.

These articles are referred to 4 stroks spark ignition engine. In 2 stroke glow engine appear in stronger way the mixing of fresh fuel with unburned fuel and combustion residues due to the operation simplicity of 2 stroke engine ( you can put your hand near the exhaust), and the chemical action of alkyl nitrates ( in the range of 1 to 1000 ppm), increasing the ignition speed without negatively affect to fuel octane, must not be affected by the kind of engine.

From:
http://www.freepatentsonline.com/4457763.html
Diesel fuel cetane improver:
...The amount of cetane improver added depends on the type of fuel being used, the initial cetane value, and the amount of cetane number increase desired. Alcohol fuels such as methanol, ethanol, isopropanol, isobutanol, hexanol, and the like, have very low cetane values and large amounts of cetane improvers are required. A useful range in which to operate is about 5-25 weight percent cetane improver.....

5-25 weight precent is to much than the range that it is used in spark engines
(1 to 1000 ppm) 1000 ppm = 0.1%
Due to that it is not expective a negative effect on the octane of methyl alcohol that on the other hand , has an octane of 105 (very hight)

This mechanism could explain the inclusion in the first link that you have enclosed
http://www.turbofast.com.au/racefuel.html
of nitrobencene like ignition accelerator

This could explain the effect that we feel that happens since more than 3 month ago with the use at 0.1 % of methyl nitrate and or amyl nitrate in the fuel. (improving in running, start easy and acceleration)