Fuel Injector Angle Within Fuel Injector Port

[Paul B]

I'm trying to find information regarding the angle of the fuel injector with respect to the air intake. Basically, I want to know how important it is, and how changing that angle would affect the performance of a vehicle.

I'm working on a Formula SAE race car, and my team and I are looking to improve our design from last year. One of the things that wasn't looked into last year was the angle of the injector relative to the intake tube, so we want to find out if there is any importance to that. Does anyone have any input? I have two pictures of last year's fuel injector port.

 

[Fahlin Racing]

Where are the injectors located in the manifold? I would like to say the fuel itself along with the angle of the injector and the spray characteristics of the injector will be in thought here.

 

[Paul B]

They are attached directly to the cylinder head. In the days after this thread was posted, I have learned that having the injectors somehow spray fuel directly onto the intake valve is ideal, because it causes the fuel to atomize and mix with air most effectively. My question now is one of fluid dynamics, because I have to figure out how the fuel will react to being introduced to a moving column of air from the manifold. I know the stream of fuel will curve, so I'd like to have it curve just enough to hit the intake valve when the engine is making peak power. The CFM of air in the intake tube is unknown at that point, as are a lot of parts of this equation, but I'm trying to teach myself fluid dynamics so I can figure out what I need.

 

[Vadar2012]

What are your CFD skills like? I'd just run some initial 2D simulations to find out. Some programs also have combustion analysis.

 

[Fahlin Racing]

So you are using the valve itself for more of a shearing effect, does this intake valve run warm at all? if we inject onto something moderately warm (not glowing) we hope to have a greater shearing effect than vaporizing effect because the heat absorbed into the valve may or may not be great enough to turn the atomized fuel into a vapor for burning. If the valve may not be hot enough, we can build up on the back of the valve overtime.

I know of a free fluid dynamics text in PDF if I remember right, potto.org I think?? I still haven't had time to really dig into the book yet myself but I have it saved on my memory stick or a cd, somewhere lol

 

[jack action]

I know the stream of fuel will curve, so I'd like to have it curve just enough to hit the intake valve when the engine is making peak power. The CFM of air in the intake tube is unknown at that point

With Formula SAE, the engine will make peak power most likely at peak CFM because of the intake restrictor imposed by the rules (assuming your engine displacement and/or RPM is big enough). The maximum CFM is then limited by choking of the restrictor and the mass flow rate equation is given here. Then divide by the # of cylinders for an average of peak CFM of each cylinder.

 

[Paul B]

What are your CFD skills like? I'd just run some initial 2D simulations to find out. Some programs also have combustion analysis.

I'm a SolidWorks novice haha. I'm still learning about the program.

So you are using the valve itself for more of a shearing effect, does this intake valve run warm at all? if we inject onto something moderately warm (not glowing) we hope to have a greater shearing effect than vaporizing effect because the heat absorbed into the valve may or may not be great enough to turn the atomized fuel into a vapor for burning. If the valve may not be hot enough, we can build up on the back of the valve overtime.

I know of a free fluid dynamics text in PDF if I remember right, potto.org I think?? I still haven't had time to really dig into the book yet myself but I have it saved on my memory stick or a cd, somewhere lol

I think it will be hot enough to vaporize the fuel. The professor I spoke to with regards to the fluid behavior seems to think that if the fuel builds up on or around the valve, after a few crankshaft rotations, the same amount of fuel that is released by the injector will end up in the cylinder.

With Formula SAE, the engine will make peak power most likely at peak CFM because of the intake restrictor imposed by the rules (assuming your engine displacement and/or RPM is big enough). The maximum CFM is then limited by choking of the restrictor and the mass flow rate equation is given here. Then divide by the # of cylinders for an average of peak CFM of each cylinder.

Thank you. I'm going to end up using this I'm sure, I just took on the intake assembly in it's entirety as my responsibility for this year's car.


The professor I spoke to about this says that in his opinion, the spray of atomized fuel will hit the exact point that the injector is aimed at if the velocity of the fuel is greater than or equal to the velocity of the air moving into the cylinder. This makes sense to me, does anyone else think any differently?

 

[jack action]

It seems that the injector location would influence the angle. The key would be for the spray to not hit the intake walls such that it forms puddles that would drip into the cylinder. So if you put the injector far from the cylinder, the spray should be as parallel to the flow as possible, which would promote better mixing and airflow cooling. But if your injector is close enough to the cylinder head and you have to choose between hitting the back of the valve or the intake wall, you aim at the back of the hotter valve to help vaporize the fuel.

Here are some links to help you in your thinking process:

http://www.hotrod.com/pitstop/hrdp_0704_pitstop_fuel_injector_location/
http://www.guhlmotors.com/TechPages/Angle.htm
http://www.600scene.com/index.php?option=com_content&task=view&id=71&Itemid=32
http://eprints.uthm.edu.my/2297/

 

[HowlerMonkey]

What kind of fuel are you injecting?

If you are using anything with a high amount of alcohol, you could take advantage of it's evaporation/cooling to make the charge more dense by placing the injectors further away from the ports.

 

[midda samid]

with regards my inlet plenum and inlet tract angle, injector angle is very difficult to change due to the length of the inlet tract.. The only way would be to use a curved runner and mount the injector on the outside radius of the curve. I am already some 220-250mm from the inlet valve however my fuel spray is directed at the opposite wall of the runner at 45degrees(or thereabouts).. in effect, the fuel spray, especially at low air speeds(low rpm), is striking the inlet tract wall at the interface between the plenum and the head.. not ideal.

If i move to a curved runner to improve the injector angle, the injector has to move further away from the valve to ensure the spray is parallel to the airflow and at the midpoint of the inlet tract at the point of discharge. Again, I would expect not ideal..

What will be the effect of moving the injector further from the combustion chamber? I expect fuel atomisation to improve, and therefore lower emissions(better fuel burn) and better economy, but there are also issues with relation to low air speed & engine response, among others

Is there data available that gives an idea of performance v's distance of injector from combustion chamber for a given inlet air speed?

In an ideal world, I would like to see a parallel to airstream injector directing it's spray more or less at the inlet valve at a distance where the injector spray pattern reaches inlet tract diametre at the valve head and spray velocity has equalled inlet air velocity(at low RPM)... Since injector patterns vary, the distance from the valve head would depend on the spray pattern of the injector, fuel rail pressure and the diametre of the valve as seen by the injector. This for me and my understanding of fuel atomisation would seem the ideal design.

I am sure my understanding is flawed however..