Gas going up..and quality going down?

[jlee]

But idling doesn't really help with this. When I start a -20C car, it never actually heats up when idling. In fact, it doesn't even start to blow warm air until it has been driven for about 5 minutes. Not idling for 5 minutes but actual driving for 5 minutes.

Are you sure something's not wrong with your car? Mine is usually running for 7-10min by the time I am ready to leave and it's nice and warm by then.

The warm up is mostly for the car's sake rather than your sake. Some vehicles are so stiff that they don't even work properly unless they idle for a bit. My parents old Chevy van would stall if you let the clutch out in neutral. I'm not sure how that works since it's not in a gear, but there's something thick in there and it's thick enough to stop the engine. My friend's pile of shit Chevy Blazer also had a problem where the torque converter didn't work at low temperatures.

When you release the clutch, even in neutral, you're spinning transmission components. Gear oil at -20 is a pretty thick.

To get around the ice cube problem, go to Walmart and buy a $10 heated seat cover. Best $10 you'll ever spend.

I have heated seats already, but if it's below 30 I still like to start the car a few minutes early. That also lets me hit boost on the drive home instead of driving most of the way on a cold/cool engine.

Edit: temps referred to in F, not C.

 

[Zenmervolt]

relax dude. i am reporting reality. there are hundreds of factors in methanol use in gasoline engines, and every model of car is different. my truck just so happens to not adjust well to ethanol. most newer cars adapt a lot better, but there are still tons of engines out there that just like straight gas a lot better.

You're not "reporting reality", you're making a claim that is not possible within the realms of thermodynamics.

I've been living in places that sell E10 for over a decade now and I've never once had a vehicle that got less than rated mileage, even when using E10. There just isn't any meaningful difference.

The biggest reasons that mileage drops in the winter are the increase in anti-freeze additives in all gasoline (in places where it gets cold enough for this to be a worry), the fact that every lubricant in your car (engine oil, transmission oil, differential oil, bearing grease, etc) gets much thicker when cold and causes a significant increase in drag even after the engine itself warms up (it can take 15-20 miles before the lube in the final drive gets up to temp in the winter, for example), the extended open-loop warm-up period, and the fact that most automatic transmissions will not engage the lockup clutch until the transmission has warmed up, which generally means that you're operating with torque converter slip for the first 2-5 miles as well, which absolutely kills mileage.

ZV

 

[ShawnD1]

You're not "reporting reality", you're making a claim that is not possible within the realms of thermodynamics.

You're only looking at enthalpy of combustion, but that's not how a car works. Cars work by generating exhaust gas. Your ultimate goal here is to create exhaust gas. Let's try an example of this. Isooctane (a major component of gasoline) has 8 carbons and it has a mass of 114g/mol with a density of 688g/L. With 8 carbons we can make 8 CO2 molecules.
(8 carbons / 114g) * (688g / 1L) = 48.2 moles of CO2 gas created per litre of gasoline

Ethanol has 2 carbons, weight of 46, density of 789g/L
(2 carbons / 46g) * (789g / 1L) = 34.3 moles of CO2 gas per litre of ethanol

So right away you'll notice there's a huge difference in the amount of cylinder pressure that each one will create. Gasoline creates a lot of exhaust gas. This gas then builds a huge amount of pressure, and this pressure is what moves the pistons. They don't move because they are hot. They move because there is a huge amount of gas being created.
The difference here is that gasoline creates 40% more exhaust gas per unit of volume.


We can take this further and look at diesel. Instead of an octane rating, diesel has a cetane rating, so we'll just assume all diesel is cetane. Cetane has 16 carbons, 226 g/mol, density of ~850g/L.
(16 carbons / 226g) * (850g / 1L) = 60.2 moles CO2 per litre of diesel

Notice that diesel creates 25% more gas per unit of volume than gasoline does. This is why diesel fuel seems so efficient in terms of how far a tank of fuel will take you. Since it also releases more energy, that added heat also adds to the cylinder pressure.

In general, longer chain molecules contain a lot more usable energy in internal combustion engines. If we were looking at steam engines then yes we would only look at enthalpy of combustion and nothing else.

 

[LTC8K6]

It's an eighth of a gallon. On a 20 mile trip at 20mpg, it will cost you 12.5%. Is that a 'little effect' or a big one?

I mean, in the greater scheme of things, all the fuel you will personally ever use is a small amount.

IIRC, it's 1/16 of a gallon. ~64 ounces per hour. ~1 ounce a minute. And that's if you have a big V8.

I don't warm up my car unless I can't see out the windshield, so it doesn't matter to me. The claim was that idling uses a lot of fuel, and the claim is incorrect. Idling uses very little fuel, even with a big V8.

 

[LTC8K6]

Originally Posted by ShawnD1
But idling doesn't really help with this. When I start a -20C car, it never actually heats up when idling. In fact, it doesn't even start to blow warm air until it has been driven for about 5 minutes. Not idling for 5 minutes but actual driving for 5 minutes.

Fleabag said this once before, that idling doesn't warm up gas engines. I actually tested 2 engines that winter with a scangauge 2. Both of them warmed up quickly while idling.

Diesels are actually difficult to warm up just idling, but gasoline engines warm up rapidly.

 

[Zenmervolt]

Isooctane (a major component of gasoline)

See, the quoted part is where someone who actually knows about gasoline will know that you're pulling this all out of your ass.

Iso-octane is added in small amounts to fine-tune the resultant octane rating (many modern gasolines use other additives such as toluene and/or benzene as well). The majority of gasoline is non-aromatics however. Not only this, but for some ridiculous reason, you seem to be assuming that the only gas produced by combustion is CO2, which simply is not the case.

Also, even if one accepted your fundamentally-flawed foundations, you are comparing against pure ethanol.

I have already stipulated that E85 (85% ethanol, 15% gasoline) yields between a 15%-30% decrease in mileage (older cars tending towards 30%, brand new cars tending towards 15%).

Unfortunately for you, however, we are discussing E10, which is 10% ethanol and 90% gasoline and can only affect mileage on the order of 1.5% to 3%.

 

[SandInMyShoes]

Fleabag said this once before, that idling doesn't warm up gas engines. I actually tested 2 engines that winter with a scangauge 2. Both of them warmed up quickly while idling.

Diesels are actually difficult to warm up just idling, but gasoline engines warm up rapidly.

My observation has been that an idling engine does not warm up as quickly as a loaded engine. If it's just 10-25F, I tend to just idle for a few seconds, then start driving slowly, keeping the engine approximately at the cold idle speed for a couple minutes, coasting where possible. This seems to warm the engine up faster, as well as the transmission.

 

[jlee]

My observation has been that an idling engine does not warm up as quickly as a loaded engine. If it's just 10-25F, I tend to just idle for a few seconds, then start driving slowly, keeping the engine approximately at the cold idle speed for a couple minutes, coasting where possible. This seems to warm the engine up faster, as well as the transmission.

That's correct. However, an idling engine will still warm up - it just takes longer.

Edit: for those saying a gasoline engine will not warm up at idle..current outside temp is four below zero (F). I started the time right after I started the engine. As you can see, coolant temp was 16f at its coldest (before starting), and got much warmer in less than seven minutes:

 

[LTC8K6]

My observation has been that an idling engine does not warm up as quickly as a loaded engine. If it's just 10-25F, I tend to just idle for a few seconds, then start driving slowly, keeping the engine approximately at the cold idle speed for a couple minutes, coasting where possible. This seems to warm the engine up faster, as well as the transmission.

Well, no one is arguing that...

Of course it warms up more quickly with a load. The claim was that it wouldn't warm up at all while idling, and that simply isn't true, except for some diesels, such as a VW TDI.

I generally don't warm up my car anyway. The only time I do is if I need to scrape ice off the windshield, and I'll idle it while I'm scraping.

 

[TraumaRN]

I usually dont idle my car because...well the engine warms the car and once it hits 108F it flips over to electric mode. So I usually just deal with the cold car for 5 minutes and just drive.

 

[ShawnD1]

I have already stipulated that E85 (85% ethanol, 15% gasoline) yields between a 15%-30% decrease in mileage (older cars tending towards 30%, brand new cars tending towards 15%).

Unfortunately for you, however, we are discussing E10, which is 10% ethanol and 90% gasoline and can only affect mileage on the order of 1.5% to 3%.

did you at least do a simple calculation to check the gas differences between 100% branched alkanes vs 90% branched alkanes mixed with ethanol?

100% gasoline:
(48.2 moles gas * 1) = 48.2
90% gasoline with 10% ethanol:
(48.2 moles gas * 0.9) + (34.3 moles gas * 0.1) = 46.81

The gas difference is another 3%. So we've already lost 3% pressure because it generates less heat and now we lose another 3% because it generates less gas. This is quickly starting to add up.

 

[jlee]

did you at least do a simple calculation to check the gas differences between 100% branched alkanes vs 90% branched alkanes mixed with ethanol?

100% gasoline:
(48.2 moles gas * 1) = 48.2
90% gasoline with 10% ethanol:
(48.2 moles gas * 0.9) + (34.3 moles gas * 0.1) = 46.81

The gas difference is another 3%. So we've already lost 3% pressure because it generates less heat and now we lose another 3% because it generates less gas. This is quickly starting to add up.

Did you completely miss the rest of his post?

 

[JCH13]

You're only looking at enthalpy of combustion, but that's not how a car works. Cars work by generating exhaust gas. Your ultimate goal here is to create exhaust gas. Let's try an example of this. Isooctane (a major component of gasoline) has 8 carbons and it has a mass of 114g/mol with a density of 688g/L. With 8 carbons we can make 8 CO2 molecules.
(8 carbons / 114g) * (688g / 1L) = 48.2 moles of CO2 gas created per litre of gasoline

Ethanol has 2 carbons, weight of 46, density of 789g/L
(2 carbons / 46g) * (789g / 1L) = 34.3 moles of CO2 gas per litre of ethanol

So right away you'll notice there's a huge difference in the amount of cylinder pressure that each one will create. Gasoline creates a lot of exhaust gas. This gas then builds a huge amount of pressure, and this pressure is what moves the pistons. They don't move because they are hot. They move because there is a huge amount of gas being created.
The difference here is that gasoline creates 40% more exhaust gas per unit of volume.


We can take this further and look at diesel. Instead of an octane rating, diesel has a cetane rating, so we'll just assume all diesel is cetane. Cetane has 16 carbons, 226 g/mol, density of ~850g/L.
(16 carbons / 226g) * (850g / 1L) = 60.2 moles CO2 per litre of diesel

Notice that diesel creates 25% more gas per unit of volume than gasoline does. This is why diesel fuel seems so efficient in terms of how far a tank of fuel will take you. Since it also releases more energy, that added heat also adds to the cylinder pressure.

In general, longer chain molecules contain a lot more usable energy in internal combustion engines. If we were looking at steam engines then yes we would only look at enthalpy of combustion and nothing else.

D:

This is NOT the underlying principal behind how IC engines work. Some statements to be assumed as true:

-the mass of air to fuel in a stoichiometric combustion with gasoline is about 15:1
-our theoretical engine has a compression ratio of 10:1, i like round numbers
-23% of the intake charge is O2, by mass (it's 21% by volume)
-all of the oxygen is consumed by combustion
-the intake charge arrives at 1ATM of pressure
-all gases are ideal (good enough for the internet)

Let us examine the contribution of pressure strictly from exhaust gases. I will do this in an ideal and simplistic sense, which is good enough for the internet.

If all of the fuel is converted in an gas by combustion, that will lead to the intake charge increasing in volume to 16/15ths of the original, or an increase of about 6.7%. This assumes that the fuel took up no volume to begin with, then created an ideal gas of equal mass. This would raise the pressure in the cylinder by about 6.7%. In a diesel engine this would be (according to your "math") about 8%, still very minor.

I will repeat that because it bears repeating: exhaust gases by themselves will raise cylinder pressure by about 6.7%. In our 10:1 CR engine that means that the intake charge of 14.7psi (absolute atmospheric pressure) gets compressed to about 360psi (a compression test will be different) the combustion gases will get this up to around 384 psi, a gain of 24psi. Real combustion pressures are around 750-1000psi, or a gain of ~340-640psi from gases and heat.

Heat energy from the combustion process causing the intake charge to expand is the primary mode of energy extraction from fuel, not the creation of combustion gases.

Diesel cycle engines are generally more efficient than Otto cycle engines for two main reasons: there are no throttling losses, but more importantly the compression ratio in a diesel engine is typically much higher than an Otto cycle (gasoline) engine. A higher compression ratio means that mechanical energy is extracted more efficiently.

You also only consider CO2 as a combustion bi-product. This is very wrong. What about all the hydrogens attached to those carbons? That will make water vapor, which is also a gas. Gasoline (octane, C8H18) will produce more steam than Diesel (cetane, C16H34) because it has more hydrogen atoms per unit mass.

 

[ViviTheMage]

This thread is pretty hilarous. I am not sure where to start ... haha

 

[desy]

I do know what he means by idling not seeming to warm things up. A really efficent car like a Corolla has trouble generating enough heat to trip the thermostat for the heater core.
Its why we Canadians like our cardboard on the grille. I don't on my Versa cause I can't slide a peice in front of the radiator easily.
When I bought a Cvic new in 95 the dealer told me to shove some in there because the horz opposed 4's have a tough time with our wicked temps and windchills

 

[Zenmervolt]

D:

This is NOT the underlying principal behind how IC engines work. Some statements to be assumed as true:

-the mass of air to fuel in a stoichiometric combustion with gasoline is about 15:1
-our theoretical engine has a compression ratio of 10:1, i like round numbers
-23% of the intake charge is O2, by mass (it's 21% by volume)
-all of the oxygen is consumed by combustion
-the intake charge arrives at 1ATM of pressure
-all gases are ideal (good enough for the internet)

Let us examine the contribution of pressure strictly from exhaust gases. I will do this in an ideal and simplistic sense, which is good enough for the internet.

If all of the fuel is converted in an gas by combustion, that will lead to the intake charge increasing in volume to 16/15ths of the original, or an increase of about 6.7%. This assumes that the fuel took up no volume to begin with, then created an ideal gas of equal mass. This would raise the pressure in the cylinder by about 6.7%. In a diesel engine this would be (according to your "math") about 8%, still very minor.

I will repeat that because it bears repeating: exhaust gases by themselves will raise cylinder pressure by about 6.7%. In our 10:1 CR engine that means that the intake charge of 14.7psi (absolute atmospheric pressure) gets compressed to about 360psi (a compression test will be different) the combustion gases will get this up to around 384 psi, a gain of 24psi. Real combustion pressures are around 750-1000psi, or a gain of ~340-640psi from gases and heat.

Heat energy from the combustion process causing the intake charge to expand is the primary mode of energy extraction from fuel, not the creation of combustion gases.

Diesel cycle engines are generally more efficient than Otto cycle engines for two main reasons: there are no throttling losses, but more importantly the compression ratio in a diesel engine is typically much higher than an Otto cycle (gasoline) engine. A higher compression ratio means that mechanical energy is extracted more efficiently.

You also only consider CO2 as a combustion bi-product. This is very wrong. What about all the hydrogens attached to those carbons? That will make water vapor, which is also a gas. Gasoline (octane, C8H18) will produce more steam than Diesel (cetane, C16H34) because it has more hydrogen atoms per unit mass.

:thumbsup:

Well put. Thank you.

ZV

 

[Zenmervolt]

now we lose another 3% because it generates less gas. This is quickly starting to add up.

1) You are still making the incorrect and, frankly, stupid, assumption that CO2 is the only gas produced.

2) Even if we accept your absurd hypothetical as true exactly as you state it, the loss is still only 6%. Not enough to go from 290 miles/tank down to 230 miles/tank. Even with your wildly erroneous assumptions, you still aren't able to defend the claim you're attempting to defend.

ZV

 

[ShawnD1]

I will repeat that because it bears repeating: exhaust gases by themselves will raise cylinder pressure by about 6.7%. In our 10:1 CR engine that means that the intake charge of 14.7psi (absolute atmospheric pressure) gets compressed to about 360psi (a compression test will be different) the combustion gases will get this up to around 384 psi, a gain of 24psi. Real combustion pressures are around 750-1000psi, or a gain of ~340-640psi from gases and heat.

I just used CO2 because it's a simplified model used in high schools and it allows direct comparison between fuels. In reality, much of the exhaust gas created in a rich fuel mixture (ie the fuel mixtured used when the car is actually driving instead of idling) is nowhere near completely oxidized. Instead of CO2, you get a lot of CO. Nitrogen in the air also has some effect on oxidation and you get things like nitric oxides. This is why the car has a catalytic converter on it. It's to oxidize the stuff that wasn't oxidized in the engine. That's also why the cat converter itself generates a lot of heat.

The other part about relying on temperature related pressure increases alone raises an interesting question. If all we want is heat, then why don't we always run a lean fuel mixture all the time? Instead of the cat converter getting extremely hot, all of that heat would be in the engine. If we're just trying to generate heat, then shouldn't that be a good thing?

 

[JCH13]

I just used CO2 because it's a simplified model used in high schools and it allows direct comparison between fuels.

Then whatever high school(s) you're talking about are stupid. Plain and simple stupid. No chemistry teacher or professor I know would completely ignore half of any hydrocarbon combustion reaction. Those are equations I worked out when I was a sophomore in HS:

25O2+ 2C8H18 -> 18H2O+16CO2+heat

H2O is a very important part of ideal combustion reaction equations.

In reality, much of the exhaust gas created in a rich fuel mixture (ie the fuel mixtured used when the car is actually driving instead of idling) is nowhere near completely oxidized. Instead of CO2, you get a lot of CO. Nitrogen in the air also has some effect on oxidation and you get things like nitric oxides. This is why the car has a catalytic converter on it. It's to oxidize the stuff that wasn't oxidized in the engine. That's also why the cat converter itself generates a lot of heat.

NOx compounds are generally made during fuel lean combustion, not fuel rich combustion. It's a result of un-used oxygen molecules breaking apart N2 and making NOx compounds.

CO can be made through both rich and lean burns.

Of course all of the fuel isn't oxidized, that's the DEFINITION of a fuel rich burn.

A catalytic converter will also heat up under lean-burn conditions because it has to catalyze reactions to break down NOx in the exhaust stream.

The other part about relying on temperature related pressure increases alone raises an interesting question. If all we want is heat, then why don't we always run a lean fuel mixture all the time? Instead of the cat converter getting extremely hot, all of that heat would be in the engine. If we're just trying to generate heat, then shouldn't that be a good thing?

One reason why lean-burn engine technologies haven't caught on is their problem with NOx emission. Another reason is that they cannot generate as much power. A third reason is that too lean of an intake charge can cause detonation issues. A fourth reason, a theory perhaps, is that under all the heat and pressure inside a cars cylinder the un-used O2 really wants to oxidize something, and that something could be your pistons (aluminum burns quite nicely).

Again, the catalytic converter gets hot trying to eliminate the products of combustion from a lean burn as well as those from a rich one. Even a lean burn will still have some unspent fuel going out of the tail pipe.

Some manufacturers have experimented with lean-burn cars, but it's a difficult problem to solve.
http://en.wikipedia.org/wiki/Lean_burn

VW has an interesting system called Fuel Stratified Injection.
http://wikicars.org/en/Fuel_Stratified_Injection

 

[ShawnD1]

Excellent post JCH13. You stayed calm and you used sound arguments without name calling. :thumbsup:

 

[Toastedlightly]

I just used CO2 because it's a simplified model used in high schools and it allows direct comparison between fuels. In reality, much of the exhaust gas created in a rich fuel mixture (ie the fuel mixtured used when the car is actually driving instead of idling) is nowhere near completely oxidized. Instead of CO2, you get a lot of CO. Nitrogen in the air also has some effect on oxidation and you get things like nitric oxides. This is why the car has a catalytic converter on it. It's to oxidize the stuff that wasn't oxidized in the engine. That's also why the cat converter itself generates a lot of heat.

The other part about relying on temperature related pressure increases alone raises an interesting question. If all we want is heat, then why don't we always run a lean fuel mixture all the time? Instead of the cat converter getting extremely hot, all of that heat would be in the engine. If we're just trying to generate heat, then shouldn't that be a good thing?

Answer me honestly, what is your age and what is your technical background? It seems you are shooting from the hip and hoping you get lucky.

To answer your question about temperature, the reason we don't run really lean and hot is pre-detonation of the air-fuel mixture and strength of materials (iirc).

Fuel (be it E10, E85 or regular gasoline) has a point at which it auto-ignites. If this occurs in the wrong part of the stroke, then the piston will be slowed and vibrated in its cylinder, and all sorta of bad things (this is called detonation in the engine). As an aside, diesel engines use this principle, but inject the fuel at extremely high pressure into the cylinder at just the right point so auto-ignition drives the piston down.

Its been found that specific ratios of air and fuel cause pre-ignition. By using a larger mass of fuel, it is possible to prevent this (larger mass to heat/more vaporization occurring).

The second part of my story is the strength of materials. We don't have materials which can take the pounding abuse of internal combustion while also being heated to very high temperatures (I don't recall what temperatures are reached in the material of the combustion chamber, but perhaps someone can fill me in there).

 

[ShawnD1]

The second part of my story is the strength of materials. We don't have materials which can take the pounding abuse of internal combustion while also being heated to very high temperatures (I don't recall what temperatures are reached in the material of the combustion chamber, but perhaps someone can fill me in there).

The gas temperature was posted above as 1200F.

The temperature of the engine itself (not the exhaust) is why the car has a cooling system. If you want to generate more heat, all you need is a better cooling system to compensate. That Bugatti with 1000HP has something like 10 radiators to deal with the amount of heat generated.

 

[JCH13]

Excellent post JCH13. You stayed calm and you used sound arguments without name calling. :thumbsup:

:awe:

 

[Toastedlightly]

The gas temperature was posted above as 1200F.

The temperature of the engine itself (not the exhaust) is why the car has a cooling system. If you want to generate more heat, all you need is a better cooling system to compensate. That Bugatti with 1000HP has something like 10 radiators to deal with the amount of heat generated.

Gas temperature is not the temperature of the materials. Pistons care cooled by heat transfer to the cylinder walls through the oil film, by oil being squirted at the bottoms of the pistons, and by the evaporating air charge. Cylinder walls and head are cooled by coolant in passages flowing turbulently through the cylinder head and block.

The problem that occurs when the amount of heat being absorbed by the combustion chamber components exceeds the ability of the cooling system to carry it away. The ability of the metal to transfer heat to the coolant is limited both by the thermal conductivity of the metal and the heat transfer boundary layer of the cooling within the head. If you generate excess heat which causes a temperature gradient within the metal to exceed a certain amount (I have no hard figures), cracking occurs. For some metals (aka aluminum), oxidation or melting may also occur (see other poster's comment).

For this reason it is very difficult to have high temperatures within a combustion chamber. Some engine (aka top fuel dragsters) deal with this by having their fuel, nitromethane, be responsible for all the cooling within the cylinder (no water jacket to speak of). Of course, these engines only last one run before being rebuilt.

PS: Just to throw in my technical background, I am a chemical engineer who is enamored with combustion engines as a hobby.

 

[hanoverphist]

cold weather and everyone starts complaining about fuel economy. hmmmmmmm

its not cold here, and im still bitching about the prices. the economy factor doesnt matter to me, winter my mileage only drops like .5mpg or something ridiculously small like that.

Meghan54, winter blend gasoline (for whatever reason) does signifigantly reduce fuel economy. In my Fit my I would go from ~37mpg down to ~31mpg. Right now in my Outback, I go from ~30mpg down to ~25mpg.

i think its more driving style than the fuel used personally. i dont have the waram up time the colder areas get, i also dont have the slippage and traffic problems that snow and ice bring out and i dont see these same drops in mpg. and i drive a truck with a 318, and rarely drive like im trying to save fuel.