SG Fuel cut off value

[slurp812]

Originally Posted by civic lover

When I was watching it I was going 60 mph for 2 hp. I know I know...this isn't right, but that is what it is reading. I don't really care that it doesn't work. I just wanted to let people know that the xgauge isn't great, but if someone can correct me I would love to hear from them.

I see the same thing, maybe it doesn't like Honda's? I have an 2002 si, and its never read over 100, with my foot all the way to the floor.

[R.I.D.E.]

An idling engine is producing nothing, just sitting there wasting energy.

13% of the fuel consumed by vehicles in the US is wasted idling.

"Idling", the word itself means of no consequence.

Now when you try to identify the cost of idling, it can get very complicated.

Alternator

Water Pump

Power Steering Pump

Sucking air through a restriction

Trying to produce power while only utilizing about 25% of atmospheric pressure

Oil pump drive losses

Friction of moving parts, including viscosity friction

The physical act of accelerating each reciprocating part from 0 speed at TDC to max speed at 90 degrees ATDC, then decelerating those same reciprocating parts to 0 speed again at BDC, only to reaccelerate them again to 270 degrees then stopping again at TDC. Two times this whole cycle for a single combustion pulse of 180 degrees out of 720 total degrees.

The physics calculations necessary to calculate the percentage of force attributable to reciprocation versus the part attributable to rotation, of the connecting rod, is so complicated even the most powerful computer would have trouble doing the calculations. This transition occurs over the complete mass of the connecting rod, with the most rotation at the bottom and the most reciprocation at the top.

Imagine the difference between coasting in neutral and coasting in gear tp understand the total losses in reciprocating engines.

Now imagine the difference if you removed the spark plugs, which would eliminate almost all "pumping losses", if you consider pumping losses as the actual moving of the air through the engine.

Now imagine the difference if you removed the cylinder head and all valve train related components, friction, and the corresponding losses. Even in this scenario you would still be losing your inertia moving the reciprocating components up and down in the engine, violating Newtons laws of inertia 8 times for each revolution of each reciprocating assembly.

I am actually surprized it only takes .9 horsepower to keep an engine "idling". Thats the equivilant work it would take to raise over 475 pounds of weight 1 foot every second, or 60 feet per minute.

regards
gary

[theholycow]

Originally Posted by R.I.D.E.

Imagine the difference between coasting in neutral and coasting in gear tp understand the total losses in reciprocating engines.

Hmm...that right there is something I can imagine.

I am actually surprized it only takes .9 horsepower to keep an engine "idling". Thats the equivilant work it would take to raise over 475 pounds of weight 1 foot every second, or 60 feet per minute.

Well, when you put it that way...drat, totally inconclusive.

[slurp812]

Originally Posted by R.I.D.E.

13% of the fuel consumed by vehicles in the US is wasted idling.

My personal number is MUCH less. I am anti-idle.

[R.I.D.E.]

Now the question?

Does that energy requirement increase in a linear or exponential fashion as engine speed increases?

Flywheels are exponential, twice the speed requires 4 times the energy.

Is this also true of reciprocating engines, especially knowing a lot of their energy losses are in rotating parts?

Or are reciprocation losses linear and ratational losses exponential?

If both are exponential, then the .9 HP required to idle would double with every 100% increase in engine speed, above idle.

regards
gary

[R.I.D.E.]

Lets use my old VX as an example.

At idle fuel consumption is about .2 gallons per hour.

At 55 MPH fuel consumption is 1 gallon per hour (close approximate).

What would fuel consumption be at 2000 RPM with no load?

Compare this to the fuel consumption at 55 MPH=1 GPH.

I woudl appreciate it if someone with a scan guage could do this calculation, especially the fuel consumption at 3 times the idle speed, compared to the idle speed fuel consumption.

This would answer a question that has perplexed me for some time, which is whether fuel consumption is a linear or exponential function of engine speed?

It may be that in reality it is a combination of both.

regards
gary

[theholycow]

It has been said that internal engine friction is an exponential function of RPM, so I would assume that no-load fuel usage is not linear (even if it does not follow RPM perfectly).

[palemelanesian]

Maybe we can extrapolate something from this: http://metrompg.com/posts/rpm-mpg.htm



Using a model of MPG = 1/rpm (x 120,000 to normalize the numbers into the same range), we get the following:

 rpm    mpg   model
2080   55.9   57.7
2500   47.0   48.0
3495   41.5   34.3
5175   25.9   23.2

That's a 97% correlation, according to Excel.

[theholycow]

Unfortunately, there are too many variables involved there to help us with the no-load RPM question. For example, aerodynamic drag...

[palemelanesian]

No, the test is run with the same speed each time, eliminating aero drag. It is, however, loaded and not unloaded, but loaded is where most of us drive anyway.