MTBE..what is it?

[yz250roost]

I was at the local 76 today, and saw a sign that said non-MTBE fuel now available at all 76 stations. What is MTBE and since I run pump gas, what effect does it have on my bike, do I want MTBE or no MTBE in the gas I put in my motocrosser? thanks in advance
Jeff

 

[jmics19067]

Just to add on to bclapham post

If the air quality in your area recquires oxygenated fuel, mtbe was used to try and help lower emisions in cars<more oxygen in the combustion chamber less hydrocarbons out the tailpipe>. A lot of people complained of flu like symptons that they blamed on mtbe. Try and find out what they are using for an additive in your area. If they are using alcohol you will have fun chasing down water problems and jetting snafus.

I now buy racing fuel to avoid water problems. My bike,lawnmower, weed whacker , anything that might set for a period of time was always giving me a headache with water forming inside the tank/carb. Expensive for not using the fuel for its purpose< me being lazy compared to actually trying to get the most power out of my engines> but it is well worth it to me to not have to drain tanks and carbs of water just to cut the lawn or go out for a quick ride.

Racing fuels may or may not have mtbe in it. Mtbe is great for instant throttle/more hit/power now type of feeling but can be a handfull in no traction situations.<my newbie to the world of fuels seat of pants impression.
If you are interested in getting the most out of your engines look up anything that Rich Rohrich has to say about fuels,jetting and spark plug readings.

 

[jho410]

Hmm, I heard that MTBE's resulted in less power and poorer fuel economy but was better for the air. Not sure it's true - just heard it.

 

[jmics19067]

Although I am far from being able to give an in depth analysis I beleive that would be more related to the state and tuning of the engine. MTBE is an oxygen carrying additive in the fuel. When you want performance you want as much oxygen in the engine so you can burn more fuel for more power. If the engine is not tuned for the specific fuel you are running that is when you are going to have problems.

 

[SuzookKING]

oxygnated fuels get less MPG than non-oxygenated ones in the same motor... the amount of oxygenation determines this (as fuel is being displaced by oxygen bearing compounds... measurable in volume and weight).
oxygenated fuels weigh less generally (lower SG *specific gravity).

bear in mind that with oxygenated fuels you are putting more oxygen into the combustion process so more fuel must be added to take advantage of this (and prevent engine damage as well *jetting is mandatory with major O2 additions). I have been playing with O2 bearing additives in my fuel and have been witnessing some nice things (power :) ) that override the less mpg disadvantage from them. :yeehaw: vroom, vroom :thumb:

 

[dirt bike dave]

Originally posted by jho410
Hmm, I heard that MTBE's resulted in less power and poorer fuel economy but was better for the air. Not sure it's true - just heard it.

I did some searching on the web a few months ago about this. To generalize, California's 'clean air' MTBE laced pump fuel has lower engergy content than pump fuel in many other parts of the country. CA fuel is approx. 111,000 - 113,000 BTU's gallon, about 2% less than the 115,000+- BTU's typical in other regions. Diesel #2 is about 130,000 btu/gallon.

One study by the Univ. of Wisconsin showed that passenger car/truck loss in mpg on lower energy content fuel varies from vehicle to vehicle, from 0-14%, but the typical loss was 2%, about the same as the % difference in energy.

Race fuels with lots of MTBE differ in many ways from what we get at the pump in CA, and probably have much greater energy content per gallon.

 

[Rich Rohrich]

Originally posted by dirt bike dave
Race fuels with lots of MTBE differ in many ways from what we get at the pump in CA, and probably have much greater energy content per gallon.

Not usually. AMA legal race fuels with MTBE generally contain about 15% by volume and subsequently have a lower energy per pound. You have to look at the big picture to see how this works in our favor.

Here's a few numbers to explain things :


Typical leaded race fuel (no oxygenates) = 18636 (BTU/lb)
Typical unleaded race fuel (with ~15% MTBE by vol) = 17876 (BTU/lb)
MTBE = 16353 (BTU/lb)

As you can see the addition of MTBE lowers the overall energy value. So on the surface it looks like the leaded race fuel with highery energy content would make more power. But we know it doesn't. HOW COME?

We have to look a little deeper and figure out the heat available in the cylinder per pound of air. If we look at the chemically correct (Stoichiometric Ratio) air/fuel ratio of our non-MTBE fuel we see it's 14.88 while the MTBE laced fuel has a Stoichiometric Ratio of 14.15 (for reference MTBE is 11.76) . So that tells us we need to add more fuel for each pound of air we ingest into the cylinder when we are using an MTBE based fuel. In this particualr example we would need to add 1.016 times more fuel with the MTBE based fuel (1.228 for pure MTBE).

So we have more fuel in the cylinder for each pound of air with our oxygenated fuel and the actual heat available in the cylinder per pound of air (or specific energy)looks like this:

Typical unleaded race fuel (~15% MTBE by vol) = 1263 BTU/lb of air
Typical leaded race fuel (no oxygenates) = 1252 BTU/lb of air

MTBE = 1391 BTU/lb of air

So as you can see even though the non-oxygenated fuel started with an advantage sitting in our fuel can once it got around to doing some real work it loses the race.

The super-fuels Nitromethane and Methanol have similar characteristics to our MTBE-fuel. Lower energy per pound but higher specific energy when you add in enough fuel to compensate for their lower stoichiometric ratios ( about 6.47 for Methanol and about 2.1 for Nitromethane). All that extra fuel adds up to lots of extra oomph.

I should be sitting around a big bonfire at Cooperland spouting this junk but seeing as how I'm stuck here you guys have to endure my madness. :)

 

[SuzookKING]

:worship: Rich I am always enlighted your responses and learn a new lil tidbit everytime :thumb:

Being the hydrocarbon guru that you are, how would a Phillips B32(75%)-MTBE(25%) Blend compare?


In a perfect world I would have been sitting happily at that bonfire with brain cramps and a brew :yeehaw:

 

[Rich Rohrich]

Originally posted by SuzookKING
Being the hydrocarbon guru that you are, how would a Phillips B32(75%)-MTBE(25%) Blend compare?

I've used that combination in a couple of bikes with good success, it's just kind of expensive on a per gallon basis.

 

[SuzookKING]

I prefer steel cans/drums over plastic (or similar) for storage & transport of my fuels. I use 5 gallon drums/pails from the fuel distributor for main storage (75*F climate controlled warehouse, in a flammable liquids storage cabinet :thumb: * it will hold 8+ 5gallon pails) and in 2 gallon steel type 1 safety containers for mixing and transporting to the track/riding areas. At the track I keep my fuel in a 1/2 filled ice chest (not with the munchies/liquid refreshments) & under wet towels to keep the heat down in the fuel. I have had good results with this method.

 

[Rich Rohrich]

I basically do the same thing. Steel cans that I cover with a soaking wet XL sweatshirt to get an evaporative cooling effect on the can. I do the same on the tank when the bike is sitting although the plastic doesn't really cool as efficiently it does help. . When it's really hot out I get flexible ice packs and strap them to the can amd the tank using strrey bike bungee cargo nets. It works really well and keeps the fuel in the 50-60 F range all day long.

Putting it in a cooler is still probably the best method in the long run but not always the easiest.

There is quite some talk about cool fuel (eg wet towel over the tank etc) giving more power, but i wonder if the results people are really seeing at the track is because less MTBE evaporates when it is kept cool?

That's certainly been my experience, so I'd have to say you are spot on in your thinking.

On the other topic, please don't ever drive with fuel in the cab of your truck. No amount of performance is worth a fire hazard like that.

 

[Rich Rohrich]

Originally posted by bclapham
now, if i can just get past worrying about all of the funny looks and comments i will get at the track, but i suppose thats what comes from knowing more than the next guy! :p

For me that's always been half the fun :)

soo what about race gas suggestions? or should i just see what is available and get back to you?

Figure out what fuels you have consistent access to and we can go from there.

 

[bclapham]

yeah, i shouldnt worry......i get enough funny looks with my strong english accent in california as it is! when people think you are from another planet (a lot of people think england is!), why should i worry about keeping my petrol on ice, maybe a strange habit from WWII?

 

[Rich Rohrich]

Originally posted by bclapham
why should i worry about keeping my petrol on ice, maybe a strange habit from WWII?

Warm beer and cold fuel. Those crazy Brits got everything all assbackwards :)

 

[2strok4fun]

Rich-

Funny you metion the warm beer thing. Brittish ales are supposed to be served at cellar temperature which is 48 to 50, while this may be warm by US standards that serve it at freezing temps so you cant taste how bad the beer really is, it is still not "warm". Many brittish pubs serve there beer well above cellar temps, but that is jus wrong. ;)

Actually Rich I just wanted to be right about 1 thing. :)

Speaking of beer and fuel. After Rich has helped to learn me up in the fuel dept and sent me into some more indepth reading, thank you, I have started storing my fuel in 5 gallon stainless cornillus (sp) kegs (soda kegs) on 5 lbs of nitrogen. while this might seem a little excessive I already had many leftover kegs from homebrewing and the gas regulator and the nitrogen. so it wasnt a stretch for me.

bclapham-

If you miss real beer, you cant miss the Southern California Hombrew Festival. Happens at lake Skinner in SD county the first or second weekend of may. A must do :thumb: search google for the title i listed or SCHBF