Got my first car - Some questions

Haze said:
would not be better to teach him what a search engine is :P
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Shush you :p
I much prefer it this way, as before the trolls get in to threads you get to hear a lot of different points of view on the same subject, and sometimes someone explaining something one way works fine for them but not for others, whereas someone else explaining the same thing fits perfectly in to your head! Its nice to have lots of views together!

InvaderGIR said:
Each cylinder is a combustion chamber, so for example, your car will be a 4 cylinder engine.
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Oh I see now, so the combustion happens in the cylinders then? That explains why they all work in sequence and why you need pairs, because they provide opposite sides of the rotation for the main shaft!
 
oxygene said:
Oh I see now, so the combustion happens in the cylinders then? That explains why they all work in sequence and why you need pairs, because they provide opposite sides of the rotation for the main shaft!
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Combustion engines can have one cylinder, two, three, four, six, eight, twelve... its basically upto the designer of the engine, cost and the purpose.

Lawn mowers have one cylinder, as do small motorbikes. The reasoning for having more cylinders is I believe down to having (for example) 4 small bangs pushing your crank around, rather than one big bang.

More cylinders is normally smoother - but the tradeoff is you need more of everything else that goes around the cylinder.
 
oxygene said:
Oh I see now, so the combustion happens in the cylinders then? That explains why they all work in sequence and why you need pairs, because they provide opposite sides of the rotation for the main shaft!
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It gets comlicated as there are probably exceptions to the norm in every area of an engine. For this explanation, the 'stroke' of an engine is the distance the piston travels down (or up) in the cylinder. Nearly all car engines are 4 stroke, meaning the each piston (inside the cylinder) will need to complete 4 strokes to complete one combusions cycle - in one revolution the piston goes down and up but for each combusion cycle the piston goes down, up, down, up. The correct terminology for the stroke is Intake (piston down), Compression (up), Combustion (down) and Exhaust (up) though it will forever be to me: suck, squash, bang, blow.

I assume by "work in sequence and need pairs" you are talking about the combustion cycle and the fact 2 pistons are up and 2 are down in a 4 cylinder engine? Ideally you want as many combustions per revolution of the engine (1 engine revolution is the crank turning 360 degrees). As the engine requires 4 strokes per combusion cycle and 1 stroke is only half a revolution, a 4 stroke engine requires 2 revolutions to complete a full cycle. To improve smoothness, power deliver, effeciency etc. the 4 pistons are doing a different step of the combusions cycle at any one time, i.e. the two pistons that are 'up' one will be on the compression stroke, the other on the exhaust. The two that are 'down' one will be on the intake stroke, the other on the combustion stroke. Due to this a 4 cyclinder 4 stroke engine will have a combustion every half a revolution. The other advantage of two up, two down is also balance, the same weight is going up as going down so it is naturaly counter balanced.

EditP On a side note, a 4 cylinder 4 stroke engine with the cylinders numbered 1, 2, 3, 4 in order will generally (but not always) fire (combustion) in the order: 1, 3, 4, 2. So each cylinder for a cycle goes

Cylinder - Stoke 1 - Stroke 2 - Stroke 3 - Stroke 4
1 - Combusions - Exhaust - Intake - Compression
2 - Exhaust - Intake - Compressions - Combustion
3 - Compression - Combustion - Exhaust - Intake
4 - Intake - Compressions - Combustion - Exhaust
 
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Greboth said:
...I assume by "work in sequence and need pairs" you are talking about the combustion cycle and the fact 2 pistons are up and 2 are down in a 4 cylinder engine?...
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I do indeed mean that! Engineering is always interesting for me. I liked to read up on the progression of the steam engine and its evolution, car engines have an equally rich history. It may well be worth me going back to the start and tracking its progress! I find it a lot more enjoyable that way sometimes because then you can see the reasoning behind different parts and measures and how and why they were introduced!
 
oxygene said:
I do indeed mean that! Engineering is always interesting for me. I liked to read up on the progression of the steam engine and its evolution, car engines have an equally rich history. It may well be worth me going back to the start and tracking its progress! I find it a lot more enjoyable that way sometimes because then you can see the reasoning behind different parts and measures and how and why they were introduced!
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Indeed, the history of something certainly adds to comprehension of something modern. While advancements in manufacturing have brought on the development of an internal combustion engine, the reality is the way they work is the same as it was 100 years ago in that they still go suck, squash, bang and blow. If you want to consider a more engineering perspective then once you understand the basics you could consider things like variable valve timing, cam profiles, valve overlap, intake and exhaust manifold lengths, timing of pressure waves in manifolds - The list is pretty long :p
 
You can also get engines with 3 cylinders, they don't have to work in pairs necessarily. My car for example has an in-line triple (so three cylinders in a line) and each cylinder fires individually (1, 2, 3, 1, 2, 3).

Engines with an even number of cylinders/cylinders which fire in pairs are typically smoother. My engine has counterbalance weights on the block to stop it from shaking. This wouldn't really be an issue with a 4 cylinder. :)
 
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