Thoughts on SPARK etc.

[hambone]

I was thinking the other night.
How does the engine increase RPMs by just dumping more gas into the combustion chamber? What keeps everything from flooding out? How does the engine "know" to speed up?
I know - it's a mixture of timing, spark, air. But just stomping on the gas pedal doesn't seem to translate to GO!
Maybe it's just that simple. It's still pretty cool.

[vdubyah73]

Ever heard the term "Goin' full bore"? That's what happens. The piston traveling down a large hole is trying to fill the large bore with air through a straw. The throttle plate, when at part throttle, squeezes the straw even tighter, kinda always restricting the engines intake to produce only the power you ask of it. When you give it the "full bore'' you are allowing the engine to take as much air in as it possibly can. Either the accelerator pump or the enrichment circuit with FI, throw gas on the fire so to speak and you get bigger fire in the cylinder, that has to get out and the only way is to push harder on the piston.
Did that make sense?

[hambone]

Yes it does. It just doesn't seem possible! Engines amaze me. Controlled explosions.

[Amskeptic]

Yes it does. It just doesn't seem possible! Engines amaze me. Controlled explosions.

Let's add to your rich overall understanding. As Bill pointed out, a gasoline engine is throttled back by restricting the air that is allowed in. That makes everyday driving pretty inefficient to have the engine fighting for air at part throttle. A lot of people try driving with a very light foot on the gas to save fuel, but the more efficient method is to get that gas pedal to the floor (smoothly so as not to use the accelerator pump) as you accelerate, because the engine is more efficient at full throttle. The trick with our buses all these years is having an undersized engine (properly detuned) working at full throttle is actually pretty good for economy.

But what about a diesel? No throttle plate. A diesel takes in all the air it wants all the time. Those engines are restricted by the amount of fuel injected directly into the cylinder at the exact instant combustion is needed. The injection pulse IS the spark plug in a diesel. That's why diesels are more efficient. Why don't they do that with gasoline? Well, gasoline direct injection has been a tricky engineering enigma because it is so volatile, but they want to keep trying.
Anyhoo.
Colin

[vdubyah73]

Isn't that why some diesels sound like a bucket o marbles at idle, they're running so lean they get engine knock?