Ford diesel mileage

[jayhaitch]

A tuit is a round object you need get to, somehow, sometimes, somewhere.......

 

[George2615]

Believe me, you will know what it is when you get a round tuit. Wife has been after me to get a round tuit for months now.

 

[john_bud]

That is also what I recall from class, but it's been quite a few years. So, I cheated and looked it up again. Here are the facts on a gas engine fuel to air ratio: A stoichiometric mixture is the working point that modern engine management systems employing fuel injection attempt to achieve in light load cruise situations. For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. Any mixture less than 14.7 to 1 is considered to be a rich mixture, any more than 14.7 to 1 is a lean mixture - given perfect (ideal) "test" fuel (gasoline consisting of solely n-heptane and iso-octane). In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (Methyl tertiary-butyl ether) or ethanol/methanol. These compounds all alter the stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at time of combustions; for MTBE-laden fuel, a stoichiometric ratio can be as low as 14.1:1). At no point is a gasoline engine ever anywhere close to a 25:1 ratio.

In comparison, engineers and techs say that diesel engines run at varying air/fuel ratios. At idle, with no load, it is not uncommon to have a diesel engine running at an air/fuel ratio of 60 or 100:1.

Dargo, Maybe you had to pull an "all nighter" and slept thru the class on "Lean Burn Technology"?

Lean burn - Wikipedia, the free encyclopedia

AutoZine Technical School - Engine

Nearly all engines in "economy" mode will run air in excess of that needed to meet stoichiometry. The inability to perfectly mix the fuel and air matched to flame front propogation, mixture tumble and other factors lead engine controls to a lean condition. Any reduction from perfection and a stoichiometric condition turns to a rich condition and fuel wasted. Much like power modes are rich, when the fuel can't be burned due to a lack of oxygen for combustion. That's why cars have both EGR and catalytic converters. EGR to reduce the NOx's produced by the high temperatures present in a lean burn condition and catalytic converter to reduce the extra unburnt fuel from the rich mix used for power. If the engine ONLY ran 14.7 :1 it wouldn't need either of those band-aids.

 

[rdam]

My 04' F250 6.0 averages 18 empty. I have gotten as high as 20.2 on a tank driving back roads at about 50 MPH. On a trip to NH last year from Florida, towing a 30 foot, 10,000 pound camper, I averaged 11.5 MPG. I'm real happy with these numbers, and haven't had any problems with my 6.0 with 43000 miles on it.

MPG should increase after the first 10,000 miles or so. It takes that long to break in properly.

 

[wrenchturner]

I stumbled upon this discussion about air fuel ratios in gasoline versus diesels. We have to remember that at idle diesels fill the cylinders almost 100 percent with air. On the other hand, gasoline engines only partially fill the cylinders with air. Why? Diesels do not have throttle plates to restrict air intake. Diesels are more fuel effecient due to higher dynamic compression ratios and diesels fuel has more BTUs per volume.