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Maintenance & Repair What about fuel types & gas mileage?
281 messages, Last post on Sep 22, 2009 at 3:52 PM
You are in the Maintenance & Repair Forum. Your Host is mr_shiftright
| These are most likely UNBRANDED providers who load up their trucks at the local refinery and sell to local convenience store chains, among others, in your area. It's basically the same gasoline that you would find at the branded stations. | |
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I read a lot of car forums for many different reason. But there seems be a common post in just about all the forums, GAS MILEAGE. Many people get upset or can not understand why the GAS mileage of same vehicles differs so much. It is quite simple and it is not what most people talk about. Yes how you drive has a lot to do with it but the one main reason that mileage differs on two like vehicles is ALTITUDE. ALTITUDE will determine how lean or rich your car will run. Higher altitude will provide better gas mileage if your car is tuned properly for the higher altitude. Here is a simple explanation of what I mean. With altitude, air density decreases, so a computer controlled fuel injection system will automatically decrease the fuel in the mixture to match the air density. Thus all the electronic sensors needed to keep the motor running correctly. You will find that horsepower will decrease, but mileage will actually increase. This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing. I hope this help explain why gas mileage is so different from so many people. The higher the altitude the better mileage. So people in Denver get better mileage then people in Death Valley California. If you need a better explanation your local mechanic can also explain this to you. Cheers! |
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Replying to: calisteel (Jul 10, 2007 4:29 pm)
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Replying to: imidazol97 (Jul 11, 2007 11:29 am) In thicker or more dense air you need a more rich fuel mixture increasing the power output to move you 1 mile thus burning more fuel. Even though the car is doing the same speed and distance the output of fuel needed is greater or lesser depending on the fuel mix based on air density. You can not get around it. |
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I thought the computer kept the mixture the same. The air valve in the throttle body lets more or less fuel mixture into the intake manifold to give more power. What is the difference in air resistance at 900 feet altitude compared to 0 feet? |
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Replying to: calisteel (Jul 10, 2007 4:29 pm) also, it explains why I've been seeing such lousy mpg while driving in the Marianas Trench. |
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Replying to: calisteel (Jul 10, 2007 4:29 pm) Ummm, no. Modern fuel injected cars measure the weight of the air coming into the engine and provide the exact same amount of fuel per pound of air at all altitudes and all temperatures and all humidities. Fuel economy as measured by the conventional Brake Specific Fuel Consumption (BSFC) measurement won't change one iota regardless of any of the above "Density Altitude" factors. "This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the fuel mixture after reaching cruise altitude, you leave the fuel mixture at full-rich while climbing." Ummm, no again. GA aircraft can extend their range at altitude simply because air resistance against the airframe is lower at altitude. Said another way, I take out say a Skylane and set it up as lean as possible to cruise at 100 knots in level flight at sea-level, and then measure the hourly fuel flow. I then take that plane up to say 17,000 feet and lean out to the exact same hourly fuel flow setting, that plane will have a true airspeed of 137 knots. That, and only that, is why aircraft get better economy at altitude. FWIW, I've seen anecdotal evidence that suggests that cars will see some gains in economy at altitude (but no where near as dramatic as with aircraft due to the rolling friction of the wheels), especially turbo-charged cars. Best Regards, Shipo
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Replying to: shipo (Jul 11, 2007 7:16 pm)
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Replying to: Mr_Shiftright (Jul 12, 2007 8:21 am) That said, stoichiometric is stoichiometric is stoichiometric. Given the proper air and fuel ratio, the mixture will burn exactly the same regardless of whether the aircraft is at a density altitude of sea-level or 17,000 feet.  Best Regards, Shipo
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Replying to: shipo (Jul 12, 2007 8:22 pm)
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