Fuel consumption 10% vs. 15%  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> Fuel consumption 10% vs. 15%
Page: [1]

Login
Message << Older Topic   Newer Topic >>
Fuel consumption 10% vs. 15% - 3/29/2007 10:06:16 PM   
Luxuswaffe



Posts: 244
Joined: 4/11/2006
From: Naples, FL, USA
Status: offline 		Comparing the fuel consumption of a 2-stroke engine running with either 10% nitromethane or with a 15% or higher level of nitromethane. Will the consumption be higher due to the higher rounds per minute when running the hotter stuff?

_____________________________

"They're called missiles." Revver Bro #181
       Post #: 1

RE: Fuel consumption 10% vs. 15% - 3/29/2007 10:23:43 PM   
Jim Thomerson



Posts: 2778
Joined: 10/9/2002
From: Austin, TX, USA
Status: offline 		I would expect to set the needle a little richer when going to 15%, and therefore get a shorter run time.

(in reply to Luxuswaffe)
       Post #: 2

RE: Fuel consumption 10% vs. 15% - 3/30/2007 12:43:00 AM   
P-40 DRIVER



Posts: 876
Joined: 4/20/2005
From: Cedar Park, TX, USA
Status: offline 		Nitro is consumed at a rate of 1:2 per unit of O2 where alcohal is about 1/6. More nitro means you will burn fuel faster not mention the fact that the engine may be turning faster as wel burning more fuel. Run the lowest nitro an engine will be happy with. Needing to use high nitro for performance reasons may indicate you should of used a bigger engine to begin with. Nitro is very expensive over the long run for performance gains.

_____________________________

RC budget, $10 per week, time spent building and flying, priceless.

(in reply to Jim Thomerson)
       Post #: 3

RE: Fuel consumption 10% vs. 15% - 3/30/2007 8:09:47 AM   
KC36330


 

Posts: 2468
Joined: 4/19/2006
From: Enterprise, AL, USA
Status: offline
quote:

ORIGINAL: P-40 DRIVER

Nitro is consumed at a rate of 1:2 per unit of O2 where alcohal is about 1/6. More nitro means you will burn fuel faster ...............


that isn't correct, nitro produces its own O2 as it burns and it slows the burn rate of the methanol. the extra O2 it provides is why you can burn more of it (a richer mixture) giving more power, it is also a cooling agent so the engine will run cooler.

kc


< Message edited by KC36330 -- 3/30/2007 8:11:30 AM >

(in reply to P-40 DRIVER)
       Post #: 4

RE: Fuel consumption 10% vs. 15% - 3/30/2007 1:17:16 PM   
Jezmo



Posts: 750
Joined: 6/26/2006
From: Spring, TX, USA
Status: offline 		Hi KC,

I think what P-40 is trying to get across is the Stoichiometric ratio of air to fuel. Nitromethane needs 2 parts air to 1 part fuel in order to get the best burn. Methanol is 6:1 and gasoline is 14.7:1. Even though nitro contains O2 in it's chain and is liberated in the combustion process it still must have 2 parts of air to burn correctly. In fact if pure nitro were ingested into the engine it would hydraulic lock it and bend the con rod or lift the head like top fuel dragsters do when they misfire and build up too much liquid in the cylinder. Also, the nitro burns slow which is why you see the big yellow flames on a top fueler but the alchohol is still burning the same speed. Otherwise, if the alchohol burn slowed down to the level of nitro, the power would drop due to the slow pressure rise while the piston is at the top of the stroke. The bottom line is some AIR is required no matter what fuel your little glow engine is running on and an amount just slightly rich of stoicheometric will provide the most power while slightly lean of stoich will provide the best economy. Just my two cents and I hope that didn't cloud things up too bad.

Luxuswaffe - It will use more fuel when you are running more nitro because of nitro's stoich requirement being 2:1 while alchohol is 6:1. The engine is ingesting the same amount of air at a given rpm so you have to increase the fuel volume to keep the mixture correct.

< Message edited by Jezmo -- 3/30/2007 1:24:07 PM >

_____________________________

Raptor 50 V2 OS 50 Hyper, T-Rex 450XL CDE, Spektrum DX7, SuperTigre OS FOX Saito Enya Jett TT

(in reply to KC36330)
       Post #: 5

RE: Fuel consumption 10% vs. 15% - 3/30/2007 2:59:29 PM   
STG



Posts: 3498
Joined: 7/3/2003
From: New Richmond, WI, USA
Status: offline 		You may have a hard time distinguishing between 10% and 15% depending on your fuel manufacturer--10%-15%nitro (based on weight or volume and does this total include oil content or not?)

Here is an example using a small block chev-- Fuel Comparison: Gasoline, Methanol, Nitromethane...same(well almost) happens with our little motors--at full throttle--

http://www.smokemup.com/tech/fuels.php


_______________________

As long the plane is powered adequately, I like to run the least amount of nitro the motor is happy with.

The only motor I have that seems to know the difference between 10% and 15% is my OS160FX. It will tolerate 15% if I richen it up a bit, it likes 10% but prefers 5%.






< Message edited by STG -- 3/30/2007 3:37:09 PM >

_____________________________

Good Flying to you!
See Blog for RCU Video's

(in reply to Jezmo)
       Post #: 6

RE: Fuel consumption 10% vs. 15% - 3/30/2007 3:12:48 PM   
STG



Posts: 3498
Joined: 7/3/2003
From: New Richmond, WI, USA
Status: offline
quote:

ORIGINAL: KC36330
that isn't correct, nitro produces its own O2 as it burns and it slows the burn rate of the methanol. the extra O2 it provides is why you can burn more of it (a richer mixture) giving more power, it is also a cooling agent so the engine will run cooler.


Are you thinking NOS injection, with a stoichiometric ratio of 1:11 or greater (1 part fuel to 11 parts air).

http://www.dudeworld.com.au/ARTINOS.HTML





_____________________________

Good Flying to you!
See Blog for RCU Video's

(in reply to KC36330)
       Post #: 7

RE: Fuel consumption 10% vs. 15% - 3/30/2007 6:31:53 PM   
KC36330


 

Posts: 2468
Joined: 4/19/2006
From: Enterprise, AL, USA
Status: offline
quote:

ORIGINAL: Jezmo

................In fact if pure nitro were ingested into the engine it would hydraulic lock it and bend the con rod or lift the head like top fuel dragsters do when they misfire and build up too much liquid in the cylinder...........


top fuel is 100% nitro and they do have unburned nitro pumped through the cylinder, this is why you have the huge flames out the exhaust.


quote:

ORIGINAL: STG

Are you thinking NOS injection,


NO, nitrous oxide causes a Very lean mixture, that is why when injected (as a liquid) you have to increase fuel flow dramatically, it also increases the operating temperature dramatically.

kc

(in reply to STG)
       Post #: 8

RE: Fuel consumption 10% vs. 15% - 3/30/2007 7:10:26 PM   
STG



Posts: 3498
Joined: 7/3/2003
From: New Richmond, WI, USA
Status: offline
quote:

ORIGINAL: KC36330


quote:

ORIGINAL: STG

Are you thinking NOS injection,


NO, nitrous oxide causes a Very lean mixture, that is why when injected (as a liquid) you have to increase fuel flow dramatically, it also increases the operating temperature dramatically.
kc


Is the very lean mixture you are talking about is the transition from a stoichiometric ratio of about 1:13 on gas to a 1:11 or greater when NOS is injected? More gas has to be injected with the nos to get the mixture to 1:11 or you will run lean?

_____________________________

Good Flying to you!
See Blog for RCU Video's

(in reply to KC36330)
       Post #: 9

RE: Fuel consumption 10% vs. 15% - 3/30/2007 7:29:12 PM   
KC36330


 

Posts: 2468
Joined: 4/19/2006
From: Enterprise, AL, USA
Status: offline 		nitrous makes the air more dense in the manifold because it cools the intake as it's injected (expanding from a liquid to a gas, this is why your N2O bottle has to be mounted in a valve down position), this in turn leans the air/fuel mixture because you now have allot more air (the nitrous also gives more available O2 for the engine to burn then atmospheric air), nitrous is NOT flammable (nitro is VERY flammable) it just allows more of an air/fuel mixture to be burned so you have to increase the amount of fuel entering the engine.

on multi port fuel injected systems the injector solenoid sends the pressure of the N2O bottle to the fuel rail pressure regulator which increases the fuel pressure delivered to each injector, this increases the fuel delivery to each cylinder (requires higher poundage injectors), on a carbureted system you have a fuel plate mounted between the carb and the intake manifold with a direct injection port for extra fuel to be 'dumped' in.

FYI used in an aircraft it allows an internal combustion engine to operate at a much higher altitude.


as far as air/fuel ratios go, i honestly don't have any idea on exact numbers sorry.

kc

EDIT: N2O allows an engine to burn more air/fuel, Nitro only provides more O2 As It Burns giving an engine more power, the two work nothing alike.

< Message edited by KC36330 -- 3/30/2007 7:37:26 PM >

(in reply to STG)
       Post #: 10

RE: Fuel consumption 10% vs. 15% - 3/31/2007 12:29:39 PM   
Jezmo



Posts: 750
Joined: 6/26/2006
From: Spring, TX, USA
Status: offline
quote:

ORIGINAL: KC36330


quote:

ORIGINAL: Jezmo

................In fact if pure nitro were ingested into the engine it would hydraulic lock it and bend the con rod or lift the head like top fuel dragsters do when they misfire and build up too much liquid in the cylinder...........


top fuel is 100% nitro and they do have unburned nitro pumped through the cylinder, this is why you have the huge flames out the exhaust.


kc



My bad. What I wrote sounded like I meant nitromethane with no other fuel blended in. What I was trying to convey was 'no air - just liquid nitromethane being ingested' as a liquid is uncompressable for all intents and will bend rods and lift heads (Ask me how I know this; yes I have bent more than one from liquid lock at the expense of tens of thousands of dollars). The air on that top fueler is being forced in by the big roots blower on top of that hemi.


< Message edited by Jezmo -- 3/31/2007 1:27:22 PM >

_____________________________

Raptor 50 V2 OS 50 Hyper, T-Rex 450XL CDE, Spektrum DX7, SuperTigre OS FOX Saito Enya Jett TT

(in reply to KC36330)
       Post #: 11

RE: Fuel consumption 10% vs. 15% - 3/31/2007 12:54:28 PM   
Jezmo



Posts: 750
Joined: 6/26/2006
From: Spring, TX, USA
Status: offline
quote:

ORIGINAL: KC36330



kc

EDIT: N2O allows an engine to burn more air/fuel, Nitro only provides more O2 As It Burns giving an engine more power, the two work nothing alike.


Actually, they do work alike. They both release O2 during the heat of combustion allowing more fuel, in our case alcohol, to be added to the mixture and burned in the chamber. When you run a higher nitro content fuel in your plane, you will richen up the mixture to compensate for the added O2 being released. A property of nitrous oxide is that at about 565 degrees F., it breaks down into nitrogen and oxygen. When it is introduced into the intake tract of an internal combustion engine, it is sucked into the combustion chamber and, on the compression stroke, when the charge air temperature reachs 565 deg., a very oxygen-rich mixture results. If we add extra fuel during nitrous oxide injection, the effect is like a super charger or increasing the compression ratio of the engine. I won't post any more on this subject but there is erroneous info being posted here so take what you read with a grain of salt. I am no chemical engineer but I did race cars professionally for over 30 years and learned just a wee bit about fuel. Just enough to know when I am being BSed.

_____________________________

Raptor 50 V2 OS 50 Hyper, T-Rex 450XL CDE, Spektrum DX7, SuperTigre OS FOX Saito Enya Jett TT

(in reply to KC36330)
       Post #: 12

RE: Fuel consumption 10% vs. 15% - 4/4/2007 3:30:40 PM   
balsaeater


 

Posts: 172
Joined: 5/20/2005
From: p, ANDORRA
Status: online 		Actualy I was checking something similar and found that nitro is really realy realy expensive

now I know why the 30% nitro acro 60 heli find 100 cycle lipos cheaper than fuel and most end up in the poor house

The intrinic problem is Nitro is not realy a fuel but more a fuel air mix

The maths are complex so I will use a simplex way to explain it

assume you have a 60 motor with 1bhp with no nitro normal tank 500cc for 10 minutes flying at full speed all the flight

and a choice go to a 90 motor to get 2bhp with no nitro and 1000cc tank for ten minutes flying at full speed alll the flight


Assume that you want 2bhp from 60 motor and for simplicity it would tolerate 100% nitro (lets leave oil lub out of equasion)

You would for the 60 motor need a tank roughly 9 times bigger to or 9*500cc or 4.5 litre to do the same 10 minute flight but with the nitro you would double HP to 2bhp ????

This is because nitro is roughly 1 part fuel type and 8 parts oxegen type for simplisity and it will take the missing air componennts it need to burn from the air so it needs anothe two parts or so compared to methonal needing 6 parts of air

now as Nitro cost a lot approxmatly 20 times the cost of methonal which is again nearly 4 to five times cost of normal gas times due to you need twice as much alchol to do the same as gas you find nitro is some 100 times more cost than normal gas fuel

EEEEEEEEEKKKKKKKKKKKKKK

Using this rough sliding rule this same 60 motor would increase it fuel cost at 30% nitro to some 6 times from before using no nitro

or some 3 times going to 15% nitro
assuming you increased the size of the tank to accept to get ten minutes run time at full speed

If you dont increase the tank size the run time will drop a bit probably down to 8 minutes at full speed

If you replaced the 60 motor with 15% nitro and get say "1.2bhp
with the 90 motor you would double the fuel intake of the cheaper methonal

and so be a bit cheaper than 15% nitro but get your 2bhp compared to 1.2 bhp of the 60 motor

For most planes the extra weight from a bigger motor is no big deal and a lot of money to be saved if you do more than 10 flights in a year
and
IF YOU FLY AT FULL SPEED in this example

however most models dont go full speed and acro can often be half throtle most of the flight

Therein you have to run the numbers again using the 60 motor at half throtle the 30% nitro only realy equal the 20% nitro rougly
in cost
and you would get your 30% nitro kick some 1.3BHP (probably closer to 1.4 bhp )and not have the weight plus as you fly slowly with the extra power from the nitro you tick over would be slower and you use less fuel in slow flight mode

So acro plane using typical 40% throlte most of the flight might only make his fuel costs marginaly greater than a 90 motor running on zero nitro if he fly very little like 40 times in a year and a motor change might not be so interesting than simply increasing the nitro

But my maths are simplex and err on the side of caution and others might easly prove that it double my figure again

A helicopter which fights gravity a lot doing acro mostly 80% throttle forget it unless you are rich invest in bigger motor and tuned pipes or change to lipos

But realy most modelers cant tune small motors unless they got 5% nitro so until you get to 90 motors or better 120 motors most of us have to live with 5% nitro

As the cost of 55 nitro for small motors in smal tanks of of a few onzes it not woth the hassle to go to zero nitro

for motors of 60 size it often worth getting the better quality 60 motor and using no nitro and a tuned pipe to get back the power lost from 5% nitro

Above 60 forget nitro unles its a four stroke which uses half the fuel but then often you lose half the power but the thrust often remain s the same as you turn a bigger prop so for a acro plane that fly slower
that often ok
but for fast planes dropping the prop size on four stroke bumps fuel way up and so probably not worth it

The awnser to the original question will consumpition be higher

The awnswer is yes on two fronts
the motor RPM will increase and each time the piston fires fuel is used and the chemical action of nitro which carry's its oxegen
will affect the fuel as well by a multiplier affect of some 20 times roughly
so expect the fuel consumpion to go up by close to 25% at full speed
or 15% at half throttle for 5% increase in nitro by weight
less if the nitro % is by weight which most usa is using I think
roughly 15% nitro buy weight is really something like 10% buy volume or something like this

If others want to go and do spread sheets and get exact numbers go ahead
but using nitro to gain power unless its a small 15 motor
or its for a few flights in the year
is close on the most brain dead idea ever invented for the rich to partake of

This short cut to gain power exists as a result of it is too expensive to make a blower or turbo for models to get more air or oxegen into the system
and suits the cheapo motor brigade who sell low qualty motors with high nitro BHP figures and now you know why

You get what you pay for and BMW and Ferari prices are higher and Ford is Ford speeds


Balsaeater






< Message edited by balsaeater -- 4/4/2007 3:45:36 PM >

(in reply to Jezmo)