NefMoto

From the link: https://www.quora.com/If-a-2-0-liter-4-cylinder-four-stroke-engine-idles-at-800rpm-how-many-times-a-minute-does-each-of-the-4-spark-plugs-fire

Comes down to 1,600 firing events per minute, for a 4 stroke engine.

So, if it's a 1.8 liter engine, each cylinder displaces: 1.8liters/4 = 450ml
at 14.7:1 for Air:Fuel, 450ml/15.7 = 4.28ml per firing event

So that should be 1,600 * 4.28 = 6,848 or 6.8 liters per minute?

But, I know my display shows about 0.9 km/hr at idle. How are car engines that efficient?

You do not succ the full cylinder volume each time the pisten goes down. One reason is because of throttle blade closed, vacuum in intake manifold.

This is called volumetric efficiency.

At what air density?

What is the airmass contained in that volume?

What do you think "load" measures?

I suspect you suck in air to fill the cylinder every time. You can't have a vaccum mixed with air and fuel. And the throttle blade doesn't close completely

And the density of that air is... what?

What happens when you mix air at standard density with a vacuum in an enclosed, sealed space?


You think air comes in only two densities?

One more time: what is "load"?

Airmass contained in that volume would vary with density I guess.

I don't know what "load" measures. What does load measure?

Air with a vaccum reduces it's density.  Air comes in several densities. Temperature should affect density as well.

Was typing my second post when you asked about "load" again

But wait,
This 14.7:1, if it's the ratio of densities, that would change the values. Or a ratio of masses. So is it a volumetric, Mass, or density ratio? Haven't bothered to work out what the consumption would be for each since I'm on phone

14.7:1 is a mass ratio, not volume ratio.

Can you guess why chemical reaction ratios are based on mass, not volume?

Not sure what you mean by "mass density", that doesn't really have a useful meaning, nor does "density ratio"

If you go down this road, you may want to invest in a few basic chemistry courses..

Not sure how you lasted this long without knowing.

Did you check the s4wiki to see if there might be more information there about load?

I think I understand now. Mass will measure the weight of the molecules. So 10g of air will always have the same number of molecules regardless of how much volume they occupy.

I was never good at chemistry

Perfectly stated!

Found the wiki defining "load". And I thought I'd read through (atleast skimmed) everything. But it looks like I'd never seen it before

So from the equation on the wiki load page, using 2.72 g/s and 800 rpm at idle (got this from vagcom block 32)
mass-injected = (2.72 * 60)/(800 * 0.5) = 0.312g (for all cylinders)
Or: 0.078g per cylinder


Mass of fuel required: 0.078 * 1/15 = 0.0052.

1 liter of fuel is 0.75kg (from google). So,
Volume of fuel per spark event: (1000ml/750g) * 0.0052g = 0.0069ml

So from my 1,600 firing events per minute
1,600 * 0.0277 = 11.04ml, and per hour it's 0.662 liters/hr.

And the cluster shows between 0.9 and 1.5 when Drive is engaged. If the calculation is right, then engines are still pretty darn efficient

to answer the question in your thread title, An engines efficiency is defined by a properly calibrated ECU as well as routine maintenance and proper care for your engine.  ;D

I guess I don't understand what you mean by "darn efficient".

Sorry to burst your bubble, but a big cargoship with a 2 stroke diesel running of crude oil is way more efficient than any petrol car on the market. That puts things in a strange perspective, doesnt it  ;D

Petrol internal combustion is not what I would call super efficient.

Agreed. A 100% efficient 2.7t should be able to make 1000hp, easy :)

For reference, because this thread is making my head hurt.

https://en.wikipedia.org/wiki/Engine_efficiency

I guess what I meant by efficient was, the theoretical calculation which doesn't account for energy loss comes close to the actual observed value. Not efficient as in harvesting energy from fuel :)

That isn't efficiency, that is science (properly) meeting with reality :P

If your fuel trims are near zero, the theoretical value for injector time matches the actual requirement. Nothing miraculous about that; that is the purpose of having an ECU in the first place :)

It has nothing to do with energy loss. A certain amount of air measured requires a certain amount of fuel mass for stoich.

The engine could be 1% efficient or 100% efficient, that amount is the same.