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Old 6th August 2011, 20:17   #1
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Default What is ITB Stand Off fuel injection?

Hi everyone, I came across this video that has me scratching my head:





I don't understand. Is that fuel being injected at high pressure into the throttle body or is that air? I thought it was fuel but I was told it is air. It doesn't make sense? If it is air then how is air even stored and compressed into the intake like that?

What is the advantage of doing this and what is being injected into it and why is it being injected into the throttle body in such manner?

And if the thing that is being injected is fuel, why is the whole contraption left out in the open like that? Shouldn't the engine have a housing unit for that? I.E; how a camshaft sits in the cylinder head. Or do you think the makers of the video left the engine that way for display purposes?

Now I know ITB = Independent throttle body, and I know what it is , fuel injection is self explanatory. But what does the whole term mean and please explain it using the video.


Hopefully there are some pundits here who can shed some insight into this.
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Old 6th August 2011, 22:38   #2
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Default Re: What is ITB Stand Off fuel injection?

Well, as far as I understand it, a throttle body is basically a valve which controls the flow of air into the engines in fuel injected engines. An independent throttle body is nothing but having a separate throttle body for each cylinder of the engine. In a carburetted engine the carburetter controls both the fuel and air. In fuel injected engines, the fuel injectors control the fuel flow rates and throttle body controls the air flow rate.

In an F1 engine, at least the modern F1 engine, there is just an open air box, which channels air towards the air intake. The above video doesnt show the aerodynamic air box, which sits on top of the engine. In the video the engine is just sucking air from the room. Each of those eight circular top units that you see are the throttle bodies for each of the cylinders.

As to those things that you see in the video, here is my explanation, which may or may not be correct.

Obviously the engine run is being simulated for some particular track. But as you see there is no real air box. Here the engine is breathing in air from the room itself. But in reality the engine will be breathing in air from the air box, into which the air is flowing at massive speeds. The injectors are most probably an attachment which provide the requisite pressure and speed to the air to properly simluate the engines running at that particular track. Thus that system will only be there during simulated runs and not during actual running.
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Old 7th August 2011, 08:15   #3
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Default Re: What is ITB Stand Off fuel injection?

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Originally Posted by julupani View Post
Well, as far as I understand it, a throttle body is basically a valve which controls the flow of air into the engines in fuel injected engines. An independent throttle body is nothing but having a separate throttle body for each cylinder of the engine. In a carburetted engine the carburetter controls both the fuel and air. In fuel injected engines, the fuel injectors control the fuel flow rates and throttle body controls the air flow rate.

In an F1 engine, at least the modern F1 engine, there is just an open air box, which channels air towards the air intake. The above video doesnt show the aerodynamic air box, which sits on top of the engine. In the video the engine is just sucking air from the room. Each of those eight circular top units that you see are the throttle bodies for each of the cylinders.

As to those things that you see in the video, here is my explanation, which may or may not be correct.

Obviously the engine run is being simulated for some particular track. But as you see there is no real air box. Here the engine is breathing in air from the room itself. But in reality the engine will be breathing in air from the air box, into which the air is flowing at massive speeds. The injectors are most probably an attachment which provide the requisite pressure and speed to the air to properly simluate the engines running at that particular track. Thus that system will only be there during simulated runs and not during actual running.
That makes a lot of sense, especially how injector is increasing the velocity and volume of air with the speed of the car(like you said it is simulating air flow into the engine) .And I think there also seems to be a fuel rail under the "Renault F1" inscription . So I think you are correct and that is just some set up for simulations to provide air.

The air box you are speaking of is that thing that sits above the driver in an f1 car right?Or atleast that's the inlet to the air-box?
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Old 7th August 2011, 12:52   #4
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Default Re: What is ITB Stand Off fuel injection?

Standoff fuel injection is when a second set of injectors are turned on at high revs. The farther the injectors are from the valve, the better is the atomisation of fuel. At high revs, the speed of the air is so high that there's hardly any time for droplets of fuel to atomise into a small mist, which is why the secondary injectors farther away. The standoff injectors spray into air which is a lot more turbulent, which also helps with fuel atomisation. Apart from the fact that it takes longer for the air to reach the cylinder, giving more time to the fuel for atomisation. At that point, the injectors closer to the valves are usually shut off. The transition from one set to the other (in either direction) is gradual, so there are no issues with regards to over/under fuelling.

ITBs can be kept completely open, covered with a filter or a plenum. This is what an F1 airbox looks like.


With standoff injectors, the only option is running an upward facing air box like the pic above. I doubt if the F1 cars even use air filters. Rain is usually not an issue and the track is usually clean. Perhaps a fine wire mesh would be all that's used. It is not providing air lol.

On second thought, I believe F1 cars shouldn't even be running standoff injectors. They idle at around 4k-5k RPM, do not need any semblance of low-end torque and due to the throttles being vertical, the issue of fuel puddling up in the port would probably not a problem. What you are seeing in that video are its only set of injectors.

Nonetheless, standoff injection is very much in use in various other racing categories, amateur racing and daily driven cars. I run ITBs, without standoff injection however.

Last edited by pranavt : 7th August 2011 at 13:02.
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Old 8th August 2011, 07:26   #5
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Default Re: What is ITB Stand Off fuel injection?

Also, in addition to what pranav said, let me add that in the video, the fuel injection pattern is masked (F1 trade secret), so it appears that air is being injected. That is definately not the case.
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Old 8th August 2011, 08:51   #6
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Default Re: What is ITB Stand Off fuel injection?

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Originally Posted by 1self View Post
Also, in addition to what pranav said, let me add that in the video, the fuel injection pattern is masked (F1 trade secret), so it appears that air is being injected. That is definately not the case.
How can the injection pattern be concealed? Aren't all fuel injectors in the video just spraying at the same time? What is the pattern here/how do you recognize one?
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Old 8th August 2011, 09:01   #7
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Default Re: What is ITB Stand Off fuel injection?

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How can the injection pattern be concealed? Aren't all fuel injectors in the video just spraying at the same time? What is the pattern here/how do you recognize one?
At high rpm's all injectors fire simultaneously, specially for mpfi engines. They have modified the video to conceal the spray pattern...ie. the shape of the spray.

By shape of the spray i mean short throw, long throw, reflected (bouncing off from some part of the throttle body) throw etc.
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Old 9th August 2011, 00:33   #8
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Default Re: What is ITB Stand Off fuel injection?

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Originally Posted by 1self View Post
At high rpm's all injectors fire simultaneously, specially for mpfi engines.
Only if the duty cycle of the injectors is 100% or if the fuel injection is batch-fire mode. Quite a few modern car ECUs support sequential injection, so injectors fire in according to the firing order of the engine.
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Old 9th August 2011, 04:44   #9
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Default Re: What is ITB Stand Off fuel injection?

Quote:
Originally Posted by pranavt View Post
Only if the duty cycle of the injectors is 100% or if the fuel injection is batch-fire mode. Quite a few modern car ECUs support sequential injection, so injectors fire in according to the firing order of the engine.
At high rpm's, (like f1 car have), ALL injectors fire together. At lower rpm's yes it is sequential. Safe injector duty is max 80-85%.
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