nitro content in fuel

[rjsanders]

I need some help in understanding how higher nitro in fuel will cause the engine temps to be cooler than if running a lower nitro fuel. If my memory is correct, I had read an article in an airplane mag that said that higher nitro causes increased internal engine temps compared to a lower nitro fuel. Someone recently told me that higher nitro in fuel will make it run cooler. Is this correct? Can someone give an explanation? Thanks alot!

Rex

[bighands3d]

It is correct the higher nitro content will make the engine run cooler I don't remember why.

[svein]

Because you can run a richer mixture without drowning out the plug, you will effectively run cooler on higher nitro content.

If you ran the same mixture as you did with a lower nitro fuel, the heat would increase.

//Svein

[DebianDog]

:D Hi Svein

[svein]

Hi, Dan.

//Svein

[rjsanders]

If you just left your needle settings the same way and did not richen the needle, the higher nitro would cause the heat to increase, but higher nitro allows you to be able to richen the needle valve which causes the extra cooling. Am I understanding this correctly now? Thanks alot for your feedback :!:

[svein]

That's the impression I have, yes.

//Svein

[rjsanders]

:thumbup: I think I've got it now

[DavidH]

It is not only the nitro content that comes into the equation.
Most 15% nitro fuel has about 18% oil content. The viscosity of the oil may vary between manufactuers.
Most of the 30% nitro heli fuel has any 20% plus oil of varying viscosity's.

With the higher oil content, the needles will need to be open a little more so the extra oil can pass thru them. That is usually the reason the needles usually have to be a little richer with the higher nitro fuel.

I was testing fuel in 2004. I was using the Cool Power 30% with 23% Low Viscosity oil. We we trying different fuels to decrease the smoke for F3C flying.
I went from the CP 30% with 23 % LV oil to CP 30% with 14% LV oil. Now exact same fuel just lower oil precentage on one. With the 30% nitro and 14% LV oil fuel I could run the main needle 10 clicks leaner than I could with the 23% oil fuel. Engine temps stayed the same with the 14%oil fuel as it did with the 23% oil fuel.
A lot of the equation of how the mixture is adjusted depends on the oil content and viscosity in the fuel.

David

[929pilot]

With the proper needle settings your motor will run cooler, as others have stated.

30% nitro fuel contains 15% less methanol than 15% nitro fuel. This is one reason you have to open your needle when using higher nitro (to let in enough methanol). DavidH points out in his example that higher % of oil will also require you to open your needle because it displaces/dillutes the fuel. In other words the more nitro and oil the fuel has the less methanol the fuel has, the more you have to open your needle to get the required fuel (methanol) air mixture. All engines require the correct fuel air ratio to run properly.

"If you just left your needle settings the same way and did not richen the needle, the higher nitro would cause the heat to increase, but higher nitro allows you to be able to richen the needle valve which causes the extra cooling."

I think your motor would get hot because it's to lean (lack of methanol), not because of the nitro itself. In DavidH's example the engine would actually run hotter with 23% oil than 14% oil, with the same needle setting. Why? Less methanol causing a lean fuel air mix. The same thing happens when nitro% is increased.


Nitromethane in glow engines is similar to using nitrous oxide in a car engine, It allows you to burn more fuel to get more power because it contains an oxygen molecule. Nitrous systems for cars not only shoot nitrous into the intake manifold but also additional gasoline to maintain the proper air/fuel ratio. Not enough fuel --- bad things happen. :(
Don't open your needle valve --- bad things happen. :(
Open your needle and be rewarded with mo power and cool temps. :D

Also, nitromethane should not be confused with nitroglycerin. One burns :smokin: the other explodes. :bomb:

:wink:

[rjsanders]

just to clarify the effects of the nitro in glow fuel and not considering the other components of glow fuel or changing needle settings, does the nitro itself cause an increase in engine temperature? Thanks :!:

[medflight]

You can't just look at the nitro by itself. I think this is what is confusing you. You're putting four things into the engine at one time (nitromethane, methanol, oil, and outside air) and you have to look at how they react together.

It didn't bother me at all to richen mine up a little when I swithced. I'm failing to see the problem with a richer, cooler running engine that is much easier to tune and has more power.

[929pilot]

The nitro itself does not increase the temperature. The lean air/fuel ratio causes an increase in temp.

If the nitro itself caused higher temps then your motor would get hotter when you opened your needle, which lets in more nitro. This proves the temp increase is due to a lean air/fuel ratio and not by the nitro itself.

I have flown 0% nitro fuel in an OS 32 powered raptor and I can tell you it definately runs cooler with nitro. :wink:

[rjsanders]

So you are saying that adding extra nitro and not adjusting the needle for a richer setting does not cause the engine temp to increase? My understanding was the when using high nitro fuel it is able to run cooler only by opening the main needle which allows extra oil to circulate through the engine :!: Are you saying that this is wrong :?: I don't have a problem with running a richer cooler engine if you want to do that! If you want to use 30% nitro and pay the extra $ for it, go for it :!: Also, I don't have a problem tuning my engines using 15% nitro fuel so the only reason that I would ever get the 30% nitro fuel would be if I decided to get a ys 91. My original question was to know what effect high nitro had on glow engines and the majority of feedback I have gotten so far indicates that increasing the nitro content will result in an increase in engine temps unless you richen the needle setting to allow more oil into the crankcase. There are alot of people out there who know a lot more about engine tuning and glow fuel than I do, so I left it up to those people to help me with the answers. I only wish I had known there were some of those experts in my area.

[929pilot]

In regard to your last post: Your understanding about the engine running cooler on higher nitro is correct.

In regard to your first post: Either your memory or the article is wrong.

[RC-Bearings]

If you increase the nitro % and don't open the needle, you are running leaner. THAT'S why it runs hotter.

All things being equal, you will generate a bit more power while running the same temp. One reason you see cooler temps is that you have a larger volume of cold fuel being sucked into your engine. As fuel is sucked through the carb, it is being evaporated which removes a lot of heat from the mixture. This colder mixture can then help cool the lower end of the engine. Many CL speed engines have most of their fins covered by cowls because they pump so much fuel through them that they don't need hardly any air over the fins for cooling.

[Sky 5]

Along the same lines; here is a good article on glow plugs;

http://members.lycos.nl/helisonly/GlowplugHowTo.PDF

[WayneBrown]

Let's go back a bit, then reanalyise the whole thing;
Glow engines are similar in construction to a two stroke diesel.
The ignition system is based on a catalytic reaction between the fuel and the platitinum coil in the glow plug.
Methanol has a certain amount of O2
Nitromethane is an oxydizer creating O2
Oil is viscous or has thickness greater than methanol, nitromethane and just for kicks, water.
Compression ratios of 12:1 or greater for model engines are common, YS is around 18:1, OS about 20:1

Running a 0 percent nitro fuel, that optimal fuel/air mix is about 15 parts air to 1 part fuel.. ( I can't remember the exact figures..)
(gasoline is approx. 22:1 just for reference)
Add an oxydizing agent (nitro) and you will have to adjust for two things, decreased fuel/air mixture, and increased cylinder pressures. (lean and hot)
Adjust the mixture richer will compensate for the increase in O2 in the fuel.
Now add the viscous effect of the oil (slight, but present nonetheless) You will have to richen the needle slightly to overcome the fluid resistance.

Good; more airflow through the motor while carrying more oil (cooling and lubrication)
Bad; Increased cylinder pressures (compensated by adding shims)
Most modern engines are designed to run on a range of nitro content, some will run better at lower content (European) with the removal of shims, while others are designed to run on Higher content (US market).
You can add/remove shims to adjust total cylinder pressure, (or compression ratio) to suit the fuel primarily used .
You can get involved with changing engine timing through porting, compression ratios, plug heat (reaction).
Run the motor hot, the timing changes, the motor detonates and rods get hammered/broke, or bearings fail due to increased stress.
Run the motor cool, the timing retards, less power is made, and overall the motor lasts longer.
TO summarize;
If the fuel you run is within the engine manufacturers specifications, and you can get it to run, go fly it!

[Gary O]

David, I saw where you posted about testing fuel to get less smoke for F3C flying. When I first started flyign helis I had been racing rc cars for several years. I had also been making fuel during that time. The cars don't run anywhere near the amount of oil content the heli engines do since they are only on max throttle for very short bursts and don't require as much. When I first started going to the field and watching the guys with the helis, I noticed that all of them looked like the old fogging trucks that used to spray for insects. I knew i didn't want that. I've been running my fuel for a little over 2 years now in helis and I still get comments on why there isn't very much smoke. I run Klotz Original Techniplate which is a HV oil. the HV's don't smoke much at all compared to say CP 30. If you still haven't found what you're looking for you might try an HV oil. I've been running it at 15% and have not had a bearing problem or wear problems yet.

[DavidH]

Gary,
The problem with the HV oil is it does not let the motor accelerate as quickly as the LV oil. I know more than several highly profile heli pilots that have tried the HV oil and they went back to the LV oil for that reason. I just basically went back off the shelf Cool Power 30%. IT gives the best performance and the smoke is just part of it. From what I have seen, most that have tried the HV oil fuel eventually go back to the LV oil fuel. They just seem to like the way it runs regardless of the smoke.

David

[Gary O]

I'm not a high profile pilot by any means, but I won't be switching. I can't stand all that smoke. I have some LV oil too but it won't get used. Everything is a trade off in some way.