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What's the ideal injector trajectory angle?

General engine tech -- Drag Racing to Circle Track

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Re: What's the ideal injector trajectory angle?

Post by digger » Sun Aug 25, 2019 7:54 pm

af2 wrote:
Sun Aug 25, 2019 7:41 pm
The best is in the chamber... SO why is it a problem shooting at the floor like all the sprint cars do?
assuming you mean direct injection if you don't cool the air coming in surely you cant get the same VE as a system the injects proportion to airflow (and not on the walls) that maximise latent heat of vaporisation to cool IAT to fit more mass in the cylinder. direct injection once the air is trapped well its trapped, the fuel can still cool to improve knock resistance but not improve VE. there may be some improved chamber temp that improves VE for the next cycle but IDK

clearly from a fuel economy and emission DI is better otherwise OE wouldn't do it but for max effort i'm not sure DI is the answer.

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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sun Aug 25, 2019 8:32 pm

af2 wrote:
Sun Aug 25, 2019 7:41 pm
The best is in the chamber... SO why is it a problem shooting at the floor like all the sprint cars do?
I had no idea what a sprint car set up even looked like. So I checked out some pics and looked at a kinsler sprint car nozzle.

They mount them up high in the runner , I'm assuming to take advantage of it cooling the manifold?

even though the nozzle mounts 90deg to the runner, it looks like the end of the nozzle directs the spray straight down, in the same direction as the air flow.
Last edited by gmrocket on Sun Aug 25, 2019 8:37 pm, edited 1 time in total.

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Re: What's the ideal injector trajectory angle?

Post by af2 » Sun Aug 25, 2019 8:36 pm

Yes they do because the Methanol is the best cooling I have seen. The end is angled towards the port.
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Re: What's the ideal injector trajectory angle?

Post by gruntguru » Sun Aug 25, 2019 9:15 pm

If its only about power you mount the injector as far from the valve as possible and get the spray to contact as much of the air as possible - to maximise evaporation. If low speed and warm-up driveability are a concern, hit the valve with the spray.

If DI is an option it can combine power, driveability and emissions.

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Re: What's the ideal injector trajectory angle?

Post by mk e » Mon Aug 26, 2019 8:07 am

gruntguru wrote:
Sun Aug 25, 2019 9:15 pm
If its only about power you mount the injector as far from the valve as possible and get the spray to contact as much of the air as possible - to maximise evaporation.
I think, especially with lower rpm engines, you can get to the point where the fuel has evaporated and start to reheat from the runner/port temp....think.
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Re: What's the ideal injector trajectory angle?

Post by ptuomov » Mon Aug 26, 2019 8:35 am

The car factories perfected the port injection over the last couple of decades. I'd take those injector spray pattern and injector angle combinations as a pattern. I don't see a conflict between combustion efficiency and power production.

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Re: What's the ideal injector trajectory angle?

Post by Zmechanic » Mon Aug 26, 2019 10:46 am

gmrocket wrote:
Sun Aug 25, 2019 8:32 pm
af2 wrote:
Sun Aug 25, 2019 7:41 pm
The best is in the chamber... SO why is it a problem shooting at the floor like all the sprint cars do?
I had no idea what a sprint car set up even looked like. So I checked out some pics and looked at a kinsler sprint car nozzle.

They mount them up high in the runner , I'm assuming to take advantage of it cooling the manifold?

even though the nozzle mounts 90deg to the runner, it looks like the end of the nozzle directs the spray straight down, in the same direction as the air flow.
Sprint setups are a compromise between max power and throttle response. Outlaw sprints have one nozzle in the head that sprays right at the valve, and another higher up, usually spraying less fuel. The lower classes are often limited to a single injector per cylinder, and are usually in pretty traditional locations, just above manifold flange. However, not all the injectors are equal. Even with the "traditional" location, the angle is easily changed because the plumbing is rubber hoses, not fuel rails, and they have longer injectors that stick down into the ports closer to the valve.

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Re: What's the ideal injector trajectory angle?

Post by j-c-c » Mon Aug 26, 2019 12:53 pm

Its hard for me to understand how pointing an injector in a performance application at the back of a valve with injector 3-4" away with say a 80% duty cycle and state the goal is max atomization. Seems more like valve cooling and drip injection upon valve opening, which might work fine, but with a different solution.

I am also toying with a similar situation in a long small runner (30") big cube (472) low rpm(<5000) design. My thinking was to mount the injector, underneath, with an upward angle, at least to the higher velocity side of the runner that then turns down into the valve, and also considered a two stage efi option upstream to get better IA cooling at higher rpms.

Obviously underneath injector placement is usually not an option.

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Re: What's the ideal injector trajectory angle?

Post by ptuomov » Mon Aug 26, 2019 3:02 pm

There was recently a long thread on evaporative cooling increasing oxygen density vs. fuel vapors displacing oxygen. Consensus seemed to be based on some equations is that fuel evaporation is a small net negative to getting more oxygen into the cylinder.

However, I think most agreed that good mixture quality and the resulting higher combustion efficiency was important.

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Re: What's the ideal injector trajectory angle?

Post by Walter R. Malik » Mon Aug 26, 2019 4:24 pm

gmrocket wrote:
Sun Aug 25, 2019 8:32 pm
af2 wrote:
Sun Aug 25, 2019 7:41 pm
The best is in the chamber... SO why is it a problem shooting at the floor like all the sprint cars do?
I had no idea what a sprint car set up even looked like. So I checked out some pics and looked at a kinsler sprint car nozzle.

They mount them up high in the runner , I'm assuming to take advantage of it cooling the manifold?

even though the nozzle mounts 90deg to the runner, it looks like the end of the nozzle directs the spray straight down, in the same direction as the air flow.
Sprint car mechanical fuel injection usually only has about 10% of the fuel up high going through the intake tract and the rest of the fuel is injected through "down" nozzles going through the exhaust side of the cylinder head directly into the intake bowl with the injected fuel aimed upstream right toward the short side radius of the port floor.
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Re: What's the ideal injector trajectory angle?

Post by adam728 » Tue Aug 27, 2019 1:04 pm

Keep in mind when looking at injectors, many do not fire in a straight line with the injector's axis. It's not at all uncommon to have an angled spray pattern to help with packaging (ie, can fit the injector "here", but need it to spray "there"). Depending on the application, goals, packaging limitations, etc etc there are pencil sprays, various angle cone sprays, offset angles, split cones, and on and on. Point is, if you look at a setup and think the injectors is sprays right across the port into the floor, it may not be.

For cold starting, smooth idle, etc, spraying on the valve typically ends up the best. Heck, a TBI style with injectors before the throttle blades can make great power, but it's going to be more of a challenge to settle it into a smooth, low idle at -20 degF. And like everything else, there's a seeminly unlimited amount of variables, and plenty of "exceptions to the rule".

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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Fri Aug 30, 2019 7:05 am

This is the reason I'm asking ...this is a head I done recently which was one of the worst for carbon build up in the intake port...1/4" thick which had to be chiseled out .

It was a low mile clean well cared for engine, ran great. 2002 6ltr LQ9 #317 heads. The backside of the intakes also had really thick buildup.

The chamber burn looks clean and good top of piston was a nice tan color with no hard deposits

So why did this thing have such a buildup..one of the worst I've seen
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Re: What's the ideal injector trajectory angle?

Post by MadBill » Sun Sep 01, 2019 12:14 am

A big, largely unrecognized factor is off-brand generic vs. Top Tier™ factory-endorsed fuel. A friend of mine had bizarre start/run issues with his 30,000 km. Chev Colorado. It would clatter like crazy and miss on a couple of cylinders sometimes on start up but the next time be just fine. At one point a rocker popped off!
After three unsuccessful visits to the dealer, he called me and I asked him what he was using for fuel. The answer was "whatever's cheapest; they're all the same." I diagnosed carboned-up valve stems and suggested he try a decarbonizing treatment and if successful, stick with Top Tier rated gasoline. He went with SeaFoam, which cleared it right up and switched to a TT-rated fuel. 20,000 km later he has had zero further issues.
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Re: What's the ideal injector trajectory angle?

Post by gmrocket » Sun Sep 01, 2019 12:37 am

MadBill wrote:
Sun Sep 01, 2019 12:14 am
A big, largely unrecognized factor is off-brand generic vs. Top Tier™ factory-endorsed fuel. A friend of mine had bizarre start/run issues with his 30,000 km. Chev Colorado. It would clatter like crazy and miss on a couple of cylinders sometimes on start up but the next time be just fine. At one point a rocker popped off!
After three unsuccessful visits to the dealer, he called me and I asked him what he was using for fuel. The answer was "whatever's cheapest; they're all the same." I diagnosed carboned-up valve stems and suggested he try a decarbonizing treatment and if successful, stick with Top Tier rated gasoline. He went with SeaFoam, which cleared it right up and switched to a TT-rated fuel. 20,000 km later he has had zero further issues.
Doesn't our gas have to meet pretty high minimum standard?

When I was a kid I pumped gas at a pioneer station..the same tanker truck would fill every station on the street..seen that

Except Sunoco, they had their own tankers

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Re: What's the ideal injector trajectory angle?

Post by mk e » Sun Sep 01, 2019 7:37 am

I just read Dollar Tree (iirc) has to pay $1.2M in restitution in new york state for selling motor oil that "isn't appropriate of any engine manufactured after 1930" I think is what it said. When money is involve people will cheat and lie about anything.

Regardless of the fuel, I'm pretty sure pointing down the port will yield the best result and on a low rpm engine closer to the valve will probably help quite a bit at low power.....there is a reason the OEMs all follow this path. I'll add that with custom setups...anyway to deliver fuel is better then no way to deliver it so compromise is usually required in the name of get the project finished. I've been working on the same damn engine for 12 year now insisting things should be the way I want them vs the way they want to be.
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