5 millionths of a gallon!

[stevneil]

5 millionths of a US gallon is how much fuel I figure is injected each time into the cylinder of a 4 stroke engine getting 50 mpg at 2000 rpm in 5th gear which is typical for a MkIV 1.9 liter TDI with a manual transmission.

It is a sphere of liquid 0.1302 inches in diameter, a droplet a little over an 1/8th of an inch wide.

I was wondering how much it was so I did a little figuring.

Here is my math. The only thing I'm not rock solid on is how many injections per crank revolution for a four cylinder four-stroke but I think I got it right.

1.2 gallons per hour for 50 mpg at 60 mph
Or 4542 milliliters

At 2000 crankshaft revolutions per minute
That is 4000 cylinders fired per minute in a 4 cylinder 4 stroke
That is 240,000 fires per hour (4000 * 60)

Or 0.01893 ml per cylinder fire (4542 ml / 240,000)

Or 0.000005 gallon per cylinder fire (1.2 gal / 240,000)

Or a sphere of liquid diesel .1302 inches wide (complicated)

 

[icecap]

Great calculations but remember that a 4 cycle engine has to go through 720 degrees of rotation or 2 complete revolutions to fire all cylinders and only 1 of the 4 strokes of 180 degrees of rotation is a work or "power' stroke during which time injection takes place.

 

[watercop]

icecap, reread stevneils post, note 4000 cylinders fire per minute at 2000 rpm - he has correctly figured the 1-in-4 power stroke of a 4 stroke engine.

My only gripe is his mention of a .1302 inch wide sphere of gasoline - spheres of gasoline have no place in a VW TDI engine

 

[whitedog]

Great calculations but remember that a 4 cycle engine has to go through 720 degrees of rotation or 2 complete revolutions to fire all cylinders and only 1 of the 4 strokes of 180 degrees of rotation is a work or "power' stroke during which time injection takes place.

Is that a Kobleco?

Anyway, at 2000 RPMs, each cylinder will fire half that amount for 1000 fires. 1000 fires times four cylinders is 4000 fires.

I was thinking backwards too that it should be 1000, but watercop gots me squared away.

 

[stevneil]

Thanks watercop. Says "diesel: now, what it should be.

 

[EddyKilowatt]

The 5 millionths is impressive, but what really helped me to appreciate the precision of diesel injection hardware was contemplating that at idle, the injected volume per stroke is 10X or 100X LESS than that. And every cylinder needs the same volume plus or minus a few percent, injected at the exact same timing point plus or minus a few dozen microseconds. At pressures of tens of thousands of psi. And finally, not just squirted in as some blob or stream, but finely atomized into a mist of constant-size microscopic droplets that burn cleanly. Maybe even injected over several shots, in modern CR systems.

Any slip-ups on any of those requirements, and the engine won't idle smoothly... let alone cleanly enough for the EPA.

The extra thousand or two that a diesel costs over a gasser (even absent the current market-induced TDI price premium) is easier to swallow when you think about the hardware that does these jobs, that you are buying...

Eddy

 

[Fourdiesel]

The extra thousand or two that a diesel costs over a gasser (even absent the current market-induced TDI price premium) is easier to swallow when you think about the hardware that does these jobs, that you are buying...

Eddy

Not always - Mercedes Benz CDI diesels in the GL series SUVs are priced by the manufacturer at $2000 to $2500 LESS than the gasser V8s in a comparably equipped vehicle! The manufacturing costs of a gas engine are NOT necessarily less than a diesel. The M-B pricing shows that this a myth that most of us have come to accept over the years.
By the way, the torque outputs of both engines are about the same.

 

[icecap]

I stand corrected although I realized after the fact Stevneil was correct with the 4000 injections per minute. Yes that is a Kobelco in the picture although you would also find me around Hitachi, Cat, Link Belt, Komatsu and Deere. The impressive math that came up with a volume of .01893 ml per injection though would not be in the form of a droplet as the fuel would be atomized into a fine mist when the injector cracks open. I don't know what the cracking pressure of the earlier injectors is, I read that the PD injectors is up to 27,000 PSI and some of the new tier III common rail industrial engines are in the 30's.

 

[EddyKilowatt]

Not always - Mercedes Benz CDI diesels in the GL series SUVs are priced by the manufacturer at $2000 to $2500 LESS than the gasser V8s in a comparably equipped vehicle!

Interesting... and good news. I just pulled my "thousand or two" out of the air, based mainly on remarks I read somewhere that the reason we aren't seeing diesel hybrids (yet) is the "higher cost" of the diesel engine... allegedly prohibitive on top of the already high cost of the rest of the hybrid powertrain.

Eddy