In Europe, they use the Research method instead of R+M/2 like the US does. Therefore, your 100 octane super unleaded in Europe is probably the equivalent of US 94 octane. Just a guess on that...No math was done to arrive at that number.
Some companies used Research and others used the Motor method here in the US so as an attempt to reduce the confusion for the customer Congress made everyone average the two methods which became the (R+M)/2 method and the markings on pumps here in the US. The research numbers were always higher than the motor method numbers, but not by much. The old 91RON designation seemed to correspond with about 88-89RM2 so that would be about 86-87Motor. It would be interesting to know how they actually come up with those numbers nowadays. I can't see guys running around and testing gas on a motor. Of course what you actually get at the pump -vs- what is marked can vary a bit...
The reason nobody mentions turbocharging / supercharging is that it wont help fuel efficiency.
The main theory here, as I see it, is to increase the dynamic compression ratio, or the amount of compression in the cylinder. That can be done in a number of different ways. One, we could reduce combustion volume. That would mean smaller combustion chambers, different pistons, etc. Two, we could close the intake valve earlier. Or three, we could open the throttle farther.
Notice I didn't put forced induction in there. There's a reason. Any vehicle, no matter what motor, it is going to take a certain amount of power to make it go down the road at a certain speed, all other things being equal. When you have a large engine, you need less throttle opening to get that same power than you would if you had a small engine. So what does this mean in terms of absolute pressure in the intake manifold? In the large engine, the absolute pressure is rather low. In the small engine, the absolute pressure is higher. Thus, per revolution, each cylinder in the smaller engine intakes a greater density of air than the larger engine. So therefore, the pressures are higher in the smaller engine than in the larger one, and you get higher efficiency.
Now if you take a supercharger or turbocharger and slap it on either engine, what happens? Well, nothing really. When running down the road at the same speed, the engine will need to make exacly the same power it did before you put the forced induction on it. No more, no less. So you throttle back. Now you've got the same absolute pressure in the intake as you did without the forced induction. Therefore, you get the same efficiency. No more, no less, not counting the force it takes to drive the supercharger or spin the impeller on the turbo.
But anyway, a smaller engine displacement is the way to go for efficiency there, with or without the forced induction. But dont go thinking you can strap a turbo on your engine and have the mileage go up. It wont.
Now if you increase the compression ratio of the engine, you increase the efficiency of that engine in a number of different ways. One, you further compress whatever comes through the intake valve. This means that at any throttle position, you're extracting more energy from the fuel than you would with a low compression engine. So you throttle back from what you would have with the engines I listed above. Now you're making the same power, but using less fuel. Two, you increase the expansion ratio. See here for info about that: http://www.popularhotrodding.com/tec...on_ratio_tech/
See how this works?
Last edited by rusty70f100; 06-14-2007 at 11:35 AM.
Rusty, there are a couple of things that you didn't mention regarding supercharging.
1st, when you put on a blower, even at part throttle, it will heat the intake air. Contrary to what a lot of guys think, heating the intake air is a good thing for part-throttle operation, as it expands the air which reduces the pumping losses of the engine. (Its only at full throttle that you really want cold, dense intake air.)
2nd, when you put on a blower, you better use higher octane fuel. If the engine is properly tuned for the higher octane, you can get more part-throttle power and therefore gain a little mileage.
My Ranger w/ the blower is averaging approx 0.7 mpg higher than when in stock trim because of those factors (this is on gas, not ethanol) and many others report properly tuned supercharged engines will get better mileage - if you can keep your right foot off the floor! Yes, I know - I'm paying more for gas because the cost of premium is not offset by a 0.7 mpg improvement, but I also have 40+ more lb-ft of torque when I want/need it.
One other side of the coin or another way to describe pumping losses is as follows.
At a no-boost part throttle condition, the engine is pulling a vacuum in the manifold because of the mostly closed throttle blades. If there is a high vacuum condition in the manifold, there will be high vacuum at the face of the piston during the intake stroke. If there is vacuum (less than atmospheric) on one side of the piston, there is atmospheric pressure on the other side of that piston. That difference in pressures works against the engine running. Engines with larger bores would suffer more from this phenomena, because larger pistons have more square inches of area for that 14 pounds per square inch to work against.
This is one factor (not the only or largest) as to why diesel engines are more efficient. They are always operating at 100% open throttle (no throttle blades in a diesel).
Most people will say and have experienced that high manifold vacuum burns the least fuel. This is true, but it is also not the most efficient in a HP produced per volume of fuel used. How can this be? Because we like grossly overpowered vehicles. Even though we don't always operate at full throttle for a significant percentage of the time, we want to know that the reserve power is there when we want it. A properly sized engine for our application would be running at 80% or better throttle (but probably still running at 2000-3000rpm because that's how loaded down the engine should be). But that vehicle wouldn't have any extra power, wouldn't run much faster than 70 mph and wouldn't sell in the US.
Well, in the last couple of months, I've had the unfortunate pleasure of having to have driven quite a few thousand miles. Every weekend was on average of about 1000 miles, 500 miles a day. All highway miles. All the same 2 stretches of highway. All cruise controlled pretty much at 80-85mph. Using the wife's camry which gets 30mpg pretty much all the time on the highway and about 25mpg when in town.
She always filled up around the corner at the Mini-Mart because it's convenient. The have E10 ethanol in all their pumps. I have always used Exxon because they don't have ethanol. After driving a couple of these trips, we were averaging right around 30mpg. I decided before the next few trips, to fill up the night before with Exxon non-ethanol gas. And because some people believe in the placebo affect, I didn't tell the wife. 2 weekends in a row, 4 trips later, all 4 tanks averaged about 34mpg instead of 30. I then let her fill up for the next weekend. (Didn't tell her why). She filled up at the E10 mini-mart. Both tanks that weekend were back to about 30mpg. She asked why the car varied so much on mileage. I told her what I did. She now gets gas at the Exxon without ethanol. The camry is fairly new. It is a 2003 model. It has about 70,000 mies but is in mint condition. All highway miles and well maintained.
The point of all this is; from all my research and reading, E10 and E25 ethanol many times is worse for your car, mileage, and finances than straight gas. You have to buy more of it to go the same amount of miles. With both E10 and non-ethanol costing the same, there isn't any advantages. Plus, I still lean to the fact that it's worse for the environment. Now, a vehicle that was E85 or higher, and was considerably cheaper than gasoline, would make financial sense. AND, if the vehicle was factory built for E85, then it's possible that it might be better for the environment. This hasn't been proven to my satisfaction, but I am open to that possibility. There are only 4 E85 stations in our entire state, so we don't get much comparison. Hopefuly, I can keep getting Exxon Non-ethanol gasoline for as long as I own all my existing cars. Later... mike....
financial interest in promoting ethanol for the government subsidies...
Lets see,, mmmm
turn corn into akly burn in vehicle use less foreign oil
Cattle eat corn,, , less corn for cattle,, ummmm Beef cost more because supply demand drives corn prices up,, mmmmmmmm OOPS forgot milk comes from cows that eat corn,, UMMMM Milk goes to $5.00/gal due to cost more to feed cows. UMMMMM now what.
Why not,, use corn waste etc, to make biodiesel run in diesel,, haul cattle to market save $$ reduce foreign oil pay less all
OOPS forgot we don't all drive diesel but we can dissolve our fuel system using too much alkey can't we if our car is just a weeee too bit old.
I agree alkey burns quick clean and has a faster flame front which plays into antiknock ratings.
vettdvr; you've pretty much hit many of the reasons why ethanol isn't as great as some people want us to believe. You did forget a few other things like; how much electricity, gasoline and diesel are you using to plant, harvest, process, ship the ethanol, (It can't go in the same pipeline as oil and gas), mix, etc... Rule number 1 of producing energy is; can you produce more, or better, energy than what you expend in the process of making or harnessing that energy.
What people don't want to hear, is that if the government got out of the subsidy business, and didn't subsidize the corn for companies like Archard Daniels Midland, then gasoline WITH ethanol would cost much more than normal gasoline. Where I live, 10% ethanol and regular Non-ethanol gasoline costs exactly the same amount. Where is the savings in using ethanol. So what if we do or don't use oil from the middle east. We are in a "Global Economy". Those people need to have a "Gross Domestic Product" just like everyone else. I have no problem getting our oil from the middle east. I only see advantages to reducing oil consumption from the middle east in 3 ways. If it's cheaper; (It's not. Your tax dollars are paying the difference). If it created more jobs in the USA. (It doesn't. Most of the ethanol is produced by very few actual employees. From a percentage perspective. It's only good for the company's stock). Finally, if it was better for the environment. That is my biggest concern.
I personally would pay more per gallon of fuel if it helped the environment. While I don't think we are capable of totally distroying the earth and causing all of the global warming, I do think we contribute. Unfortunately, unless you are running at least 85% ethanol and your car was ORIGINALLY designed to burn ethanol, you actually get worse gas mileage and you wind up doing more harm than good. Plus, for everything that is supposedly positive about ethanol over gasoline, there are just as many negatives. There are quite a few health concerns many researchers are starting to be concerned over concerning the use of ethanol. That's why they stopped the use of MTBE and went to ethanol. Here's a good article. http://www.calgasoline.com/factetha.htm
The bottom line is that ethanol is only where it's at for political reasons. It helps special interests. It appears to the bunny huggers that the government cares. It's a subsidy for the wrong people. This all coming from a hardcore, right wing, talk radio listening, gun toting, 2nd ammedment supporting, Bush voting, Ronald Regan was the BEST president, conservative. When something's right, it should be supported. Left or right wing. When it's wrong, it should be exposed. Left or Right wing. Later... Mike....