Engine puttering question

TheCleaner

Active Member
Joined
Nov 22, 2005
Messages
304
Location
Newcastle, England
Car(s)
2004 Clio dCi 1.5 100HP
This isnt anything to do with a car problem, mainly just an observation.

When a car is idling, the exhaust is puttering, maybe twice a second, kind of like waves of exhaust gas coming from, what i used to think, each manifold on each side of the engine (eg a V config engine)

then i got to thinking, this is impossible, because for say the 2 'pops' of gas per second, would result in that the engine is only turning over at 1RPM.

This also go me think on the massive amount of explosions which happen in even the most basic engines.

Take my clio 1.2 engine, for example, plodding along at 3000rpm.. for every revolution theres 4 explosions, so in one single second, theres 50 engine revolutions and 200 single explosions.. thats so much..

but nothing compared to say, a V12 going at 6000rpm, which results in 1200 single explosions a second.. i guess i had just never thought about it like that, and its remarkable how much an engine has to deal with.

but my question is then, if its crazy to think you can detect the explosions of say, an idling V8 at say a low 600rpm (which is 80 explosions a second still), then what is the rumbling coming from which occurs maybe 3 times per second... and on a side note, i love the sound, especially of an idling V8, mmmm

sorry if its a silly question, its just thats its become obvious it isnt the exhaust gasses from each individual combustion cycle
 
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First of all, you don't get that many 'explosions'. Remember that in a four stroke engine, to complete one cycle requires two rotations of the crankshaft, so you need to halve your number of explosions.

To answer your question, pop can come from unburnt fuels being forced out the exhaust valves, which can ignite from the heat, causing a pop. It's also to do with the frequency response of the exhaust headers as fluid or gas flow through it.
 
Unless there is something wrong with your engine, the fuel/air mixture doesn't explode, it deflagrates.

To summarize the difference between deflagration and and explosion, the flame front propagates at subsonic speed in deflagration, whereas it propagates at supersonic speed in an explosion.
 
Unless there is something wrong with your engine, the fuel/air mixture doesn't explode, it deflagrates.

Commonly known as burning :p

As has already been said....it's most likely down to resonance in the exhaust system and unburnt fuel igniting. If it wasn't for the silencers and cat, you'd probably see the odd flame coming out :)
 
V8s get their distinct sound from the fact that two cylinders fire in a row on one side, and then on the other later on in the firing order.

Chevy Small Block:
L R R L R L L R L R R L R L L R L R R L R L L R

There are some V8s that don't sound like this, such as Ferrari V8s. This is because they use a four-cylinder style crankshaft instead of the "special" V8 one that most cars have. Any big-inch V8 will need the counterweighted crank, and therefore have that characteristic sound. There are advantages to both designs, and as with everything, each one has it's application.
 
There are some V8s that don't sound like this, such as Ferrari V8s. This is because they use a four-cylinder style crankshaft instead of the "special" V8 one that most cars have. Any big-inch V8 will need the counterweighted crank, and therefore have that characteristic sound. There are advantages to both designs, and as with everything, each one has it's application.

they use a flat-plane crank whereas most use cross-plane crank ;)

http://www.autozine.org/technical_school/engine/smooth4.htm#V8
 
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