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I read most of your Articles on the yahoo page( awful to navigate by the way) and I reckon ye should publish them in a chapter format somehow.... Didn't jump in right away coz well to many posts makes Aussiedave a PITA... But I was wondering about mixture flow as it leaves the injector manifold into the inlet chamber ( bowl?) does the bowl act as a Venturi type affair and speed up the flow as it reduces volume to the inlet port or does it act to slow the flow down and increase the static pressure? Or should it try to maintain the existing velocity? Also previous posts have mentioned that the length of the efi manifold functioned to decrease turbulence- I think some one said their mileage decreased when they put pods directly on the injector. But isn't turbulence a good thing - keeping the fuel in suspension and helping an efficient burn?
Okay Dave, I'll take these things in order.
First, your terminology of "inlet chamber(bowl)" is probably more accurately termed "inlet port", and there is a "bowl" there at the valve end of the inlet port, where the port turns a bit and opens up behind the valve itself.
The injector nozzle in the UCE is essentially a port injector, and it is aimed into the inlet port at an angle that is as close to the back of the inlet valve as they can make it. The object of this is to have the least reliance on the air flow for atomization and delivery of the fuel. The fuel is sprayed in a very fine mist at the last moment as the valve opens, so that it is carried in by the air immediately when the valve is open. This helps to reduce fuel drop-out and puddling, in comparison to what is often seen in carbureted engines. Injected engines generally do better at delivering the fuel in a better atomized state as it enters the cylinder.
This question about whether the port is acting as a venturi for speeding up or slowing down the mixture, or keeping it at the same speed is dependent on the design of the port, which can vary greatly on different engine designs. In the Bullet, and our Ace ports, the shape turns and expands into the bowl as it approaches the valve, with the purpose of slowing the flow and increasing the pressure recovery there, so the air can better make the turn, and become partially pressure-recovered as it will then make its way past the valve into the combustion chamber where it will recover more pressure and then move down into the cylinder itself. During all of this pressure recovery phase, it is slowing down and trading velocity energy for pressure energy, because energy must be conserved. If it does not recover pressure properly, it will become turbulent and produce vortices and eddies and find all possible ways to dissipate the energy in that turbulence. When it does that, the flow energy is released into this chaotic mess, and the speed plummets, and pressure is slow to recover, and the turbulence creates blockage and impediments to the air stream coming behind it. These are flow losses, but they come after the valve. Flow losses after the valve comprise about 50% of all the flow losses in the system, but we have very little methods to control these losses, and just concentrated on what we could control with the port and valve. It's only recently that these flow losses after the valve are being addressed, and we use methods with our porting to address this to reduce some of our flow losses in our heads.
The purpose of the port is to speed up the air in a venturi as it travels from the outside atmosphere into the port, trading the atmospheric air pressure for air stream velocity, and then as it gets near the cylinder, trade off the velocity for pressure recovery in a controlled way, to get the air back into its atmospheric-pressure condition in the cylinder with the least loss of flow energy. Ideally, you want it to behave as close to a Bernoulli lab experiment venturi as possible, like we see the tube with the narrow waist in the middle that has gradual narrowing and expanding on each side of the narrow portion. Of course, it never gets anywhere near that good, but that is the ideal which we are trying to simulate with our efforts. The shapes and sizes and methods use will vary, based on the challenges of the physical restraints of the engine shape and intention of the design, so not all ports are designed the same.
Regarding the turbulence in the UCE throttle body, it seems that this turbulence influences/confuses the mass-air pressure sensor, and thus has a negative influence on the accuracy of way the ECU delivers its fuel charge to the injector. That system seems to respond better to a smoother air flow, which is typically served by a still-air column or chamber prior to entering the throttle body, so that the sensor gets a better reading.
Turbulence is a fact of life, and we try to minimize it in most cases, but in other circumstances it can be utilized in small and local ways to do some jobs for us, as long as we keep it under control to do only/mostly what we want it to do.
This is a really big subject on fluid dynamics which could have MUCH more detail, but I hope that I got the highlights across in an understandable way with the brief discussion above.