Spray Pattern suitability 1

[rpmag]

To follow on from the multi-hole thread: What are the detirmining factors in injector spray pattern selection. I was given the impression that the very fine atomisation of a modern multi-hole injector was A Very Good Thing (TM) and that when replacing an older single pintle design, this change would give better drivability and power...comments?
In addition what change would 2v/4v make re atomisiation and spray pattern.

 

[dgallup]

If you are just replacing an existing injector it is almost impossible to make an improvement because any injector shortcomings will have been incorporated into the engine calibration. So if it is wall wetting, has poor linearity, lousy voltage sensitivity, etc. the ECU is compensating for these and an "improved" injector will probably run worse unless you can do a complete recalibration.

In general, a too narrow spray pattern is preferable to a too wide pattern because excessive wall wetting will cause a lot of drivability and emission problems. A good old pencil spray hitting a hot intake valve will work very well in many engines (obviously not the best for cold start emissions). Also, many injector spray patterns are probably not what you think. Older pintle design sprays tend to collapse into a pencil spray under partial vacuum. You either need a pretty sophisticated spray/flow booth or observe the spray in a running engine.

Nearly all 4 valve engines use a twin spray injector.

 

[jbthiel]

You did not mention if this is indirect or direct injection - but I will assume direct.

The piston design has a lot to do with what injector design will work best, as it is the combustion chamber. mexican hat vs. toroidal. You also get into the amount of swirl present, steady state vs variable RPM application, bore diameter, injection pressure, turbo vs NA, on and on.....If you are trying to update an older engine you need to look at the injector, intake port, and pistons design together.

2v vs. 4v - Most 4 valve heads are relatively new so they will have a decent amount of swirl present. This and higher injection pressures tend to disipate the fuel better so you don't need as many holes

I'm sure there is also a balance between the min and max fuel delivery rates needed VS. the atomisation that is possible.

 

[rpmag]

I can see that I did not provide enough information, but thanks for the replies so far. The application is for relatively modest levels of motorsport and as such calibration is not an issue.
The injectors are for port injection an not direct injection. The issue is that the more modern injectors that are reaching the market have finer atomisation and it would seem some advantage, particularly when the injector is placed further away from the intake valves e.g. into the bell mouth.
I am interested in the use of these injectors and the ability to decide what is an approprite injector spray pattern for a particular port/application.

 

[TStaples]

Based on your application, it isn't likely you will get an discernable benefit from a more highly atomized spray. The biggest benefit of more finely atomized sprays are in in light load, part throttle emissions. Most engines make no more measurable power. As dgallup (Hi Dave!) mentioned, wall wetting is very much a possibility if the finer sprays are employed in an intake manifold design that wasn't originally optimised for that type of spray. That can lead to some unpleasqant driveability issues, as well as emissions problems that you probably can ignore in a motorsports application.

I have worked on several motorsports applications where the best sprays were narrow cones spraying against hot intake valves. Under heavy loads, and high rpm's, there is so much energy available via intake air turbulence, that the spray is torn apart, and vaporization on hot surfaces takes care of the rest.

I would not recommend trying to incorporate newer spray designs unles you just want to spend the money on the injectors to "experiment." The chances of you hitting upon a combination that works better than the original design is very slim indeed. The bottom line is that the intake manifold and head design has to be optimized to take advantage of the more finely atomized sprays.

-Tony Staples

http://www.tscombustion.com

 

[jbthiel]

Thanks for the clarification, and it seems you have your answer.

Related to this subject - how does changing the fuel rail pressure, say +25%, change the atomization characteristics? I am curious because some people do this to get higher fuel rates out of their existing injectors. My guess is that more of the fuel would remain in a stream until it hits something.

Happy Holidays, IceStationZebra

 

[rpmag]

Since the engine was not originally injected and requires a manifold to be fabricated to positioning of the injector and its type is not set by any previous development. This is not an unusual situation as all new manifolds with individual port throttles per cylinder in the aftermarket are not really designed with injector positioning in mind.
tstaples I take your point about the turbulent nature of the port/pocket flows. I am also aware of the use of the intake valve to vapourise the fuel, which of course was the saving grace of the batch fire injection systems for many years.
Jaguar actually fired the injectors in a reverse direction in their V12 gpC cars as they found they got substantially better economy, which is important for endurance racing. Today was a day spent of the phone interviewing. It seems correct sizing and in particular correct aiming of the injector (even when the injector is outside of the trumpet bell mouth) is one of the most important things for generation of power.

 

[TStaples]

jbthiel,
There isn't a simple answer for your question. Changing the fuel rail pressure +25% can have differing impact on the spray patterns, depending on the type of spray generation technology employed by the individual injector in question. Impinging sprays (generated by blasting the fluid stream at a fixed target (i.e. pintle tip or spray splitter)) contained within the the injector tip usually benefit from the extra energy of higher pressure, but can change shape in unexpected ways. Sprays generated by one or more holes in a metering plate will also usually increase in atomization with more delta p across the plate. That can be good or bad, depending on the application.

However, I have seen instances where sprays were stable at a given pressure, and with raised pressure, moved to a multi state condition, where the spray streams appear to "dance." (i.e. flip from one state to another, sometims quite rapidly.) When I previously worked for an OEM injector mfg., we called that condition the "hippy hippy shakes!" It can occur when an upstream geometry Reynolds number gets raised with pressure from a pure laminar flow condition, to the condition of either laminar or turbulent flow, and it isn't stable.

There is no hard and fast rule. It depends on the individual injector design.


-Tony Staples

http://www.tscombustion.com

 

[jbthiel]

Thanks for the answer Tony. I am glad to get reliable info from someone that knows, not someone who heard from someone.....

Have a good '07.

IceStationZebra