F1 Start-up Cranking RPM

[Shafto]

I apologize if this has been covered to death but I am curious as to what RPM they turn the engine at for fire up? I was thinking it is an interesting concept cause I would assume that the dynamic compression ratio on these engines are not as high as you might think. With such a small stroke and assuming again rather large valve overlap with long dwell times no wonder these engines have to idle at 4000rpm - just to get some mean effective pressure going on. I would also think that these engines are pushing greater than 100% VE.

Sorry I am venturing a little more than cranking rpm but i would appreciate it if someone could correct me on some of these figures. What are there static and dynamic compression ratios? what are there rod-stroke ratios? What is there overlap? Anyone know when ignition happens in terms of spark? I know these things are quite secretive but some people must have a rough idea. I find it hard to find quality information on F1 engines.

[spacer]

To answer some of them: static compression in current V8's won't be much higher than 1:12.5-13. Due to high valve-lift and short stroke there simply isn't much room left in the combustion chamber to increase the static compression ratio much higher without losing on VE (according to the RET issue about the toyota V8).

AS far as the 100% VE: due to intake and exhaust length tuning, VE's above 100% are actually quite common in high-end N/A engines.

[Giblet]

You can hear the speed it turns when they fire up a car. An audio analysis of the sound would give you a definitive answer.

[Shafto]

To answer some of them: static compression in current V8's won't be much higher than 1:12.5-13. Due to high valve-lift and short stroke there simply isn't much room left in the combustion chamber to increase the static compression ratio much higher without losing on VE (according to the RET issue about the toyota V8).

AS far as the 100% VE: due to intake and exhaust length tuning, VE's above 100% are actually quite common in high-end N/A engines.

hey thanks for your answer! yeah I knew quite well about >100% VE but just wanted to head out there cautiously.

And how am I going to do an audio analysis of one cranking?

[riff_raff]

Shafto,

With a spark-ignited engine, having a high dynamic CR at start-up is not so critical. The engines are fuel injected, have high voltage CD ignitions, and can be preheated before start-up. The start-up cranking speed is probably only about 400 or 500 rpm. Even though the engines use external starters, going faster would require excessively large starter motors.

The engines idle at high speeds mostly due to low polar intertia in the engine's rotating components. They accelerate fast, but they also lose speed just as fast.

As others noted, VE can far exceed 100% at some engine speeds, due to charge inertia and acoustic effects.

riff_raff

[Shafto]

Shafto,

With a spark-ignited engine, having a high dynamic CR at start-up is not so critical. The engines are fuel injected, have high voltage CD ignitions, and can be preheated before start-up. The start-up cranking speed is probably only about 400 or 500 rpm. Even though the engines use external starters, going faster would require excessively large starter motors.

The engines idle at high speeds mostly due to low polar intertia in the engine's rotating components. They accelerate fast, but they also lose speed just as fast.

As others noted, VE can far exceed 100% at some engine speeds, due to charge inertia and acoustic effects.

riff_raff

I dont know what kind of compression you need to have ignition of the air/fuel charge inside the cylinder but I am imagining that you need some kind of pressure! I may be wrong, and again if I am please tell me, I am going off gut feelings and not a whole lot more! So in my head I was thinking that these engines will have a low dynamic compression ratio resulting in hard starting from low compression. So I know that low compression can result in hard starting but sometimes I think of a briggs and straton beast that probably has dirt low compression but will fire up first pull no problem. So that bugs me a bit. But going back the F1 engine, I was thinking that the cranking rpm would be quite high to try and get some air in the cylinders. That was also why I was thinking why they idle high. So you say that they idle high due to low polar inertia in the engines rotating components, so I cant see why they would need to idle it high as a result of low inertia. Is it so bad that in between individual cylinder firings the engine would try and lose rpm? Just elaborate a bit on that.

Aside from that I see you are a Aerospace Engineer - so are you a AME or an aeronautical engineer? I am a AME apprentice!

[Edis]

I don't know what speed they use in F1, but for a typical engine, the cranking speed is about 200 rpm.

As for compression it really isn't a big issue for a gasoline engine during startup. Sure, a higher compression ratio will help vaporise the fuel due to the higher temperature increase during compression but there is an easier way to increase the amount of fuel vapor and that is by injecting more fuel during startup. Given that F1 engines are preheated before start, vaporisation of the fuel shouldn't be a problem.

With gasoline direct injected engines it is even possible to start the engine direct from standstill; just inject fuel in a cylinder where the piston is in a suitable position and fire the spark plug. So far it isn't 100% successful but it is improving.

Diesel engines are another problem though, and they will require a certain minimum compression ratio in order to be able to ignite the injected fuel so the engine can start. Diesel fuel also have a much higher boiling point, both the initial and end boiling point.

[Shafto]

you bring up a point i want to research, I was thinking about direct injected gas engines a while back and started thinking about there ignition system. Then I thought, well if they are truly DIRECT injection then they would not need a spark plug... That is what i have to research. I am sure they do still use spark plugs but I would think that if you can inject directly then why not up the compression ratio and when the fuel gets injected it will spontaneously ignite as diesel but I am guessing that it is too erratic and un controlled in a gasoline engine. Just as detonation and pre ignition.

[Edis]

you bring up a point i want to research, I was thinking about direct injected gas engines a while back and started thinking about there ignition system. Then I thought, well if they are truly DIRECT injection then they would not need a spark plug... That is what i have to research. I am sure they do still use spark plugs but I would think that if you can inject directly then why not up the compression ratio and when the fuel gets injected it will spontaneously ignite as diesel but I am guessing that it is too erratic and un controlled in a gasoline engine. Just as detonation and pre ignition.

These engines are sometimes refered to as SIDI, Spark Ignition Direct Injection. That givesa hint to what they're using.

A SIDI engine operates very differently compared to a Compression Ignition or CI engine. The CI engine uses a fuel with a high cetane number and the fuel injection occurs during the combustion event. When injected it easily self ignite due to the low cetane number, and the fuel will burn with a diffusion flame as long fuel continue to be injected. The disadvantages with this combustion method is that it produces more particulates and NOx and that increased speed of the engine will not make the combustion event faster, this limits the engine to low speeds.

With the SIDI engine the fuel is either injected during the intake stroke, or late during the compression stroke (only used for low speed, part load operation). When the fuel is injected during the intake stroke the engine operates like a conventional spark ignition engine, the only difference is that the injector is placed in the cylinder, there is a much shorter time availible for fuel injection and no fuel will be lost with the exhaust as injection will start after the exhaust valve have closed. With injection late during the compression stroke the purpose is to create a stratified charge, that is, a rich mixture around the spark plug surrounded by air. That way the engine can use much leaner mixtures than would be possible if the mixture was homogeneous (a lean homogeneous mixture would burn slowly, and a very lean homogeneous charge wouldn't burn at all).

[Ciro Pabón]

...

And how am I going to do an audio analysis of one cranking?

This is a beginner package that allows you to estimate "by hand" the RPM. It works better with an steady engine:

http://www.tunelab-world.com/rpmsound.html

This is a sample of how it looks in action:



Notice I changed the configuration, the software is made for aviation engines, with lower RPMs.