10-22-2012, 07:43 PM
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#1 (permalink)
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EcoModding Lurker
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A question directly about fuel consumption
Sorry for making this my first post; but I have a question I've been wanting an answer to for months now, and I just can't seem to find the answer for the life of me. I've asked my automotive teacher and my physics teacher, yet no one seems to know (yes I'm still a highschool student.) So I thought: "What better place to ask about fuel consumption than a forum revolving around exactly that?"
So here is my question.
Let's say I am driving a car with a 1.0 L engine (quite small; a Geo Metro perhaps?) I am cruising at 2000 RPM and have the throttle down at 20%. Let's say that the engine is currently running at 80% Volumetric Efficiency, and, it is also running a bit lean at a 15.5:1 A/F ratio.
How much fuel would I use?
Well, with MY understanding, here is my math.
1.0 L = 1000cc
2000 RPM = 1000 RPM worth of combustions as every cylinder fires only after every 2 RPM; therefore, 2000/2 is 1000.
-- So;
Fuel Consumption = 1000 (cc) * 0.20 (20% throttle) * 0.80 (80% VE) * 1000 (RPM worth of combustions) / 15.5 (:1 A/F ratio)
= 200 (cc) * 0.80 * 1000 / 15.5
= 160 (cc) * 1000 / 15.5
= 160,000 (cc) / 15.5
= 10,322.58 (cc)
So over one minute, I am using 10,322.58 cc's of fuel? Or over 10 litres of fuel per minute? That just seems absolutely insane! My math MUST be wrong!
Can someone please explain where I went wrong or perhaps supply the right way to figure this stuff out?
Thank you!
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10-22-2012, 07:54 PM
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#2 (permalink)
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Quote:
Originally Posted by elemein
= 200 (cc) * 0.80 * 1000 / 15.5
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A/F is mass (grams or pounds) not volume.
-mort |
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10-22-2012, 07:55 PM
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#3 (permalink)
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Quote:
Originally Posted by mort
A/F is mass (grams or pounds) not volume.
-mort
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Wait wait, that sounds correct... Though, could you please elaborate?
So you're saying that the injectors are NOT spraying 15.5:1 of the VOLUME of the air going in, but instead they are spraying 15.5:1 of the MASS of the AIR going in? |
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10-22-2012, 08:20 PM
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#4 (permalink)
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Hydrogen > EV
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Quote:
Originally Posted by mort
A/F is mass (grams or pounds) not volume.
-mort
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I believe pounds are weight, technically, but grams are mass. Correct me if I'm wrong.
But I am no assistance to this thread. |
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10-22-2012, 08:21 PM
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#5 (permalink)
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Quote:
Originally Posted by UltArc
I believe pounds are weight, technically, but grams are mass. Correct me if I'm wrong.
But I am no assistance to this thread.
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Yes, you are correct, weight is a measure of mass affected by gravity while grams are mass on it's own.
Though both are convertable to eachother  |
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10-22-2012, 08:26 PM
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#6 (permalink)
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Hydrogen > EV
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Quote:
Originally Posted by elemein
Yes, you are correct, weight is a measure of mass affected by gravity while grams are mass on it's own.
Though both are convertable to eachother |
454 grams to a pound, I believe. |
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10-22-2012, 08:26 PM
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#7 (permalink)
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Quote:
Originally Posted by UltArc
454 grams to a pound, I believe.
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Yes, I think that's correct  |
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10-22-2012, 08:41 PM
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#8 (permalink)
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Quote:
Originally Posted by UltArc
I believe pounds are weight, technically, but grams are mass. Correct me if I'm wrong.
But I am no assistance to this thread.
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You are wrong. The NIST allows "pounds" to refer to pounds of force usually abbreviated lbf and pounds of mass (lb). In all scientific and engineering measurement systems, and by convention, the weight of an object is the force on the object due to gravity, measured in the same units as force. So 454 grams of mass on earth weighs 454 grams. 1 lb of mass on earth weighs 1 lb.
-m |
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The Following User Says Thank You to mort For This Useful Post:
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10-22-2012, 09:00 PM
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#9 (permalink)
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Master EcoModder
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As far as i know you can use pounds of air and ponds of fuel to do the calculations so you will have to convert volume of air to weight and volume of fuel to weight. at which point you can do the calculation to find mile per gallon.
Last edited by redyaris; 10-22-2012 at 09:10 PM..
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10-22-2012, 09:03 PM
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#10 (permalink)
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Quote:
Originally Posted by mort
You are wrong. The ;; allows "pounds" to refer to pounds of force usually abbreviated lbf and pounds of mass (lb). In all scientific and engineering measurement systems, and by convention, the weight of an object is the force on the object due to gravity, measured in the same units as force. So 454 grams of mass on earth weighs 454 grams. 1 lb of mass on earth weighs 1 lb.
-m
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Disregard my previous answer; this one is most probably correct.
Though sorry, mort, could you please answer my previous question?
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