How engine works?

arleitiss

Hey,
Just watched this video: http://www.youtube.com/watch?v=M-ZdBrerTmQ

Is that pretty much how engines work in cars? I am just starting to get into all this stuff, been only a week since I bought my first car, but really? Is it that simple? I thought it involves lots more of technically complicated stuff?

biko

An internal combustion engine is a very simple thing, in theory.
It's in practice it gets complicated

langdang

Suck squeeze bang blow

arleitiss

biko wrote: »

An internal combustion engine is a very simple thing, in theory.
It's in practice it gets complicated

so both mechanics and electronics are involved always?

pajo1981

In principle most things are quite simple.

Now refinement and optimization and all that... that's another story.

Chuck Stone

langdang wrote: »

Suck squeeze bang blow

Oohh...

firefly08

so both mechanics and electronics are involved always?

Pretty much yes. On a modern engine, many mechanical and chemical characteristics are constantly measured/monitored by electronic sensors while the engine is running. These measurements are fed into a computer, which then decides to make tiny adjustments to the engine to optimize fuel economy, emissions and power.

For instance, your man there in the video refers to the sensor in the intake - i.e. the air flow metre. This measures the amount of air going into the engine. Based on this, the computer decides how much fuel to tell the injectors to inject. Then in the exhaust, there's an oxygen sensor (aka O2 or lambda sensor) which tells the computer how much unburned oxygen is coming out. This is like fine-tuning for the injectors; combined with the air flow, the O2 reading allows the computer to inject the optimal amount of fuel. Any changes the computer makes will then show up as a change in the O2 reading, which causes the computer to make further adjustments.

Another example - the computer controls exactly when the spark happens, to ignite the fuel - but it can change the precise timing of that spark depending on the speed of the engine, and even depending on the quality of the fuel!

There are many, many sensors for temperatures, rotational speeds, angular positions etc. all over the engine and they're all feeding signals back to the computer which makes adjustments based on this info.

arleitiss

oh, I always thought mechanics are for engine and wheels, and all electronics are just extras

langdang

You might manage a basic diesel engine without electronics or electrics, but you'd have to push start it every time. And it would be awful.

firefly08

Well to be fair, you can make an engine that works with very little electronics (no computer or sensor), and that's how they were for a long time. But having all the sensors feeding back info and the computer adjusting things makes it better - more efficient, more reliable, cleaner, more powerful.

Of course, most modern cars are so dependent on this that they will not work at all without many of the sensors. But they will still work without some things - if your unplug your O2 sensor for instance, your engine will still run, but badly. It'll be down on power, up on fuel usage, and it would fail it's NCT.

Even with no computer though, you still need electricity for the spark. Electricity comes from a generator, called an 'alternator' that is driven by the engine. And since no one wants to start the engine by pushing the car you have an electric starter motor to get the engine turning - obviously that can't use the alternator since it's needed before the engine is running, so you need a battery for the starter. But you don't want the battery to go flat, so the alternator charges the battery once the engine is running. Also, it's nice to be able to have other things like lights etc. even when the engine isn't running, so all this stuff runs off the battery too, and the alternator just tops up the battery when the engine's running. If your alternator isn't working, the engine will still start and run, but the battery will soon be depleted and then the car will simply stop (no spark).

The alternator is driven by means of a rubber belt - the engine's crankshaft turns a pulley with this belt on it, and the belt turns a pulley attached to the alternator. Turning the alternator causes electricity to be generated, but it's alternating current - it needs to have some changes made before it can be used to charge the battery, so it goes through a bit of electronics and then to the battery.

arleitiss

firefly08 wrote: »

Well to be fair, you can make an engine that works with very little electronics (no computer or sensor), and that's how they were for a long time. But having all the sensors feeding back info and the computer adjusting things makes it better - more efficient, more reliable, cleaner, more powerful.

Of course, most modern cars are so dependent on this that they will not work at all without many of the sensors. But they will still work without some things - if your unplug your O2 sensor for instance, your engine will still run, but badly. It'll be down on power, up on fuel usage, and it would fail it's NCT.

Even with no computer though, you still need electricity for the spark. Electricity comes from a generator, called an 'alternator' that is driven by the engine. And since no one wants to start the engine by pushing the car you have an electric starter motor to get the engine turning - obviously that can't use the alternator since it's needed before the engine is running, so you need a battery for the starter. But you don't want the battery to go flat, so the alternator charges the battery once the engine is running. Also, it's nice to be able to have other things like lights etc. even when the engine isn't running, so all this stuff runs off the battery too, and the alternator just tops up the battery when the engine's running. If your alternator isn't working, the engine will still start and run, but the battery will soon be depleted and then the car will simply stop (no spark).

The alternator is driven by means of a rubber belt - the engine's crankshaft turns a pulley with this belt on it, and the belt turns a pulley attached to the alternator. Turning the alternator causes electricity to be generated, but it's alternating current - it needs to have some changes made before it can be used to charge the battery, so it goes through a bit of electronics and then to the battery.

So basically if you turn power on but not engine, and turn radio on and leave it the battery will die? but if you turn engine on and are idle and radio on, it wont drain?

Jimdagym

arleitiss wrote: »

So basically if you turn power on but not engine, and turn radio on and leave it the battery will die? but if you turn engine on and are idle and radio on, it wont drain?

But you can run out of petrol. Energy isn't free. It has to come from somewhere.

arleitiss

Jimdagym wrote: »

But you can run out of petrol. Energy isn't free. It has to come from somewhere.

What would average fuel consumption be on idle?

langdang

arleitiss wrote: »

What would average fuel consumption be on idle?

ONE ZILLION mpgs sorry, silly answer - typical "fuel consumption" is quoted as miles per gallon or Litres per 100km.
So as you're not going anywhere, just sitting there turning petrol into electricity, you can't use normal fuel consumption measure.

In Litres per hour, depends on the electrical load is I suppose.
In Litres per Watt? Who knows! Not as good as a little Honda generator I'd say.

Stinicker

=The theory of how a engine operates by definition is a description of the act of copulation. Intake, compression, ignition, exhaust - essentially suck, squeeze, bang, blow.

*I'll get me coat

YouTookMyName

firefly08

A quick bit of googling gives estimates of around 1 litre per hour of idling...of course it'll vary depending on the engine and how much stuff you have turned on. Because of course, every accessory uses power somehow. In any case, you are right - running the stereo will drain the battery, and idling the engine will prevent this from happening. You could alternate between 5-10 minutes of engine idling vs. perhaps 20-30 with it off...or maybe more if you're felling lucky Remember once you start the engine, you have to run it for a few minutes to replace the battery power you just used to start it!

With the engine turning the alternator on idle, the alternator is sapping some power from the engine. As you draw more current from the alternator, it begins to give more resistance to turning, and you have to supply more turning force to keep it going at the same speed! Now, of course, the engine has to idle at a certain minimum speed, or else it will stall. So if the alternator was allowed to slow the engine down, that would suck. So, the engine's idle is regulated at a certain speed, and if the speed drops below this level, the throttle is automatically opened a tiny bit and more fuel is added (computer to the rescue again).

Therefore, turning on more and more electrical stuff causes more and more fuel to be used! In fact the stereo would have very little effect, but it does add up. The stereo, heater, headlights etc. - all these things combined would make a difference.

CiniO

arleitiss wrote: »

What would average fuel consumption be on idle?

In most cars it would be between 0.5 and 1 litres per hour.

Dartz

firefly08 wrote: »

A quick bit of googling gives estimates of around 1 litre per hour of idling...of course it'll vary depending on the engine and how much stuff you have turned on. Because of course, every accessory uses power somehow. In any case, you are right - running the stereo will drain the battery, and idling the engine will prevent this from happening. You could alternate between 5-10 minutes of engine idling vs. perhaps 20-30 with it off...or maybe more if you're felling lucky Remember once you start the engine, you have to run it for a few minutes to replace the battery power you just used to start it!

With the engine turning the alternator on idle, the alternator is sapping some power from the engine. As you draw more current from the alternator, it begins to give more resistance to turning, and you have to supply more turning force to keep it going at the same speed! Now, of course, the engine has to idle at a certain minimum speed, or else it will stall. So if the alternator was allowed to slow the engine down, that would suck. So, the engine's idle is regulated at a certain speed, and if the speed drops below this level, the throttle is automatically opened a tiny bit and more fuel is added (computer to the rescue again).

Therefore, turning on more and more electrical stuff causes more and more fuel to be used! In fact the stereo would have very little effect, but it does add up. The stereo, heater, headlights etc. - all these things combined would make a difference.

Heater less so.

Heat is normally generated by the engine anyway. Running the heater actually helps cool it down on hot days... which is good for it, especially in traffic. (Provided you don't forget to open the windows)

dr.fuzzenstein

langdang wrote: »

Suck squeeze bang blow

Dang, beat me to it.

firefly08

Fascinating article here while we're on the subject of idle fuel consumption...

http://www.iwilltry.org/b/projects/how-many-seconds-of-idling-is-equivalent-to-starting-your-engine/

Spoiler:

He reckons that

• starting the engine uses the same amount of fuel as 7 seconds (or less) of idling
  
• idling for around 1 minute is enough to replace the energy used to start the car
  
• if you switched off your engine instead of idling on a typical comute you'd save around 5% in fuel consumption

Nissan doctor

The principle of how a piston engine works is very simple, its basically just an air pump.

However, it takes dozens of very exacting measurements, assembly/repair techniques as well as external systems to make one run properly and efficiently.

The electronics on modern engines are as much an integral part of their function as the mechanical parts.