---Direct injection is better for fe... or this?!---

[trautotuning]

So diesels all mostly have direct fuel injection, while gas engines have the injector right outside the intake butterfly valve...

BUT

Like with water injection, the farther away the injector is from the throttle body the more time it has to be able to mix with the air...

So how about placing the injectors outside the throttle body so it mixes perfectly with the air instead of placing them in the intake runners or even inside the cylinders (aka direct injection)... ?

[dieselbenz]

What you are suggesting is called TBI or throttle body injection. It was popular in the late 70s and 80s as a cheap solution for emissions control. The problem is that its next to impossible to perfectly control the fuel air mixture from the throttle body across all cyls. The quality of the fuel air mixture does not increase with time or distance away from the combustion chamber. In fact the fuel tends to fall out of the air and form droplets on the walls of the intake runners.

[suspendedhatch]

It severely restricts the design of the intake manifold. If the bends are too tight then all the fuel ends up on the intake manifold walls. Cold weather requires extremely rich mixtures because the fuel just spills out into the intake manifold. Also, you have to batch fire for all cylinders. So basically you just pulse fuel all the time. Only one cylinder is "open" at a time.

If you spray fuel before the throttle body there's no vacuum so you'll just get a big puddle of gas.

Modern engines fire just behind the valve; which is better, but not perfect. You can time it so the fuel reaches the valve just as it opens so it all gets sucked into the combustion chamber and swirled in with the air. You can time each injector individually for when that particular cylinder is drawing in air. With a sophisticated engine management system, you could tune each cylinder individually so that you run a perfectly balanced afr. That's what they do in NASCAR and FI.

The problem with direct injection is that you need very high fuel pressure to overcome the pressure in the cylinder. Also the injectors get very dirty and very hot. The injector gets in the way of where the spark plug should be located optimally.

An even better approach would be to have solenoid actuators instead of cam driven valves. Valves get in the way of the fuel, restrict air flow and reduce efficiency. Solenoid valves would allow for a smaller displacement motor, cheaper to produce, less maintenance parts, less drag on the crank. This also gives you infinitely variable valve timing, "lift", duration, and overlap. The only problem is that valves are needed to cool the combustion chamber.

[trautotuning]

^Exactly...

BUT NOT.

Placing the injector BEFORE the throttle body, like 6-8 inches before in the intake pipe. This way it will have MUCH more time to mix with the air rather than being right at the intake runners (MPFI) and a bit more time than SPFI systems (Which is what TBI lacked, time to completley mix).

[trautotuning]

Originally Posted by suspendedhatch

If you spray fuel before the throttle body there's no vacuum so you'll just get a big puddle of gas.

Not true thought, look at nitrous systems and even performance cars that add an extra fuel injector in the intake pipe, they all have enough vacuum to suck in the minimal amount of liquid in the air...

[theholycow]

GM's new DI V6 seems to be pretty decent. Compared to a same-sized non-DI V6 in the same car, it makes a lot more power while getting the same economy.

http://www.cadillac.com/cadillacjsp/...ion=Powertrain

3.6L V6 VVT: 263 hp at 6200 rpm and 253 lb-ft of torque at 3100 rpm
3.6L Direct Injection V6: 304 hp at 6400 rpm and 273 lb-ft of torque at 5200 rpm

Both engines get 17/26 in the 3900 pound car with its .355 drag coefficient. The DI has an almost perfectly flat torque chart, most of the torque is available right at 1000 rpm.

[dieselbenz]

Originally Posted by suspendedhatch

The problem with direct injection is that you need very high fuel pressure to overcome the pressure in the cylinder. Also the injectors get very dirty and very hot. The injector gets in the way of where the spark plug should be located optimally.

Not really. The problem only exists in diesels where the the fuel is injected at TDC and after TDC (piezo injectors) in multiple squirts per cycle while the combustion process is going on. In gasoline DI, the fuel is injected before TDC during the compression stroke where the cylinder pressure is much lower. An HCCI gasoline engine would run into the same problem though.

Originally Posted by trautotuning

^Exactly...

BUT NOT.

Placing the injector BEFORE the throttle body, like 6-8 inches before in the intake pipe. This way it will have MUCH more time to mix with the air rather than being right at the intake runners (MPFI) and a bit more time than SPFI systems (Which is what TBI lacked, time to completley mix).

More time does not equal better mixture.

Originally Posted by trautotuning

Not true thought, look at nitrous systems and even performance cars that add an extra fuel injector in the intake pipe, they all have enough vacuum to suck in the minimal amount of liquid in the air...

NOS systems are designed to only function at WOT when the when the throttle is wide open and the the air inside the intake tube is at maximum velocity. At part throttle or idle, any fuel injected into the intake tube before the TB will just end up pooling inside the tube. Theres not enough air velocity or mass to carry the fuel into the manifold. Air velocity and mass are extremely critical to proper air fuel mixture.

[GasSavers_Randy]

Originally Posted by tjts1

In gasoline DI, the fuel is injected before TDC during the compression stroke where the cylinder pressure is much lower. An HCCI gasoline engine would run into the same problem though.

I thought the same thing, but apparently HCCI injects early like a normal direct-injection engine. That's why they call it homogeneous charge. The compression then sets off the combined mixture, like in a glow-plug model engine. So the only way to control timing is controlling the intake (pressure, temperature and EGR) and fuel mixture. No wonder it's taking so long to develop!

[R.I.D.E.]

HCCI will kill port fuel injection, just the same way FI killed carbs, and eventually TBI.

Fuel puddling in a manifold, maybe at 70 below.

The future will be very hot homogenized intake air-fuel charges. That wont happen with the injector close to the intake valve or direct into the combustion chamber.

the last gasp for ported FI is very high pressure injection.

It's doomed.

Smokey had it right a long time ago, the physics havent changed. Atomized fuel absorbs a lot of heat, or it doesnt atomize completely. the secret is to completely atomize the fuel and allow it into the combustion chamber at the highest possible temp. Plenty of exhaust manifold heat for that.
When accomplished catalytic converters will be unnecessary.

regards
gary

[R.I.D.E.]

If you want to see the car of the future check out (google)

Valentin Technologies the 130 MPG car.

regards
gary