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Direct Injection

So if the injectors on cars with direct injection squirt fuel directly into the combustion chamber why do they even have intake valves?

For the air.

We may see a return of 2-stroke automotive engines, small supercharged designs that are very powerful and very clean…Direct injection solves most of the 2-strokes problems…Outboard Marine uses a form of direct injection to accomplish this very thing…

Have to get the air in to combust the fuel.

BMW has basically a variable lift intake system that can vary the valve lift from low idle lift to wide open redline. These engines don’t need a throttle plate but they still need intake valves.

Direct injection has a lot of advantages, but it has some disadvantages. It’s expensive and prone malfunction at a higher rate then indirect. Otherwise, everyone out there would have direct injection.

Also, different, more effective fuel system detergents are necessary when utilizing direct injection.

The new Subie/Toyota BRZ/FRS uses a combination of direct injection and port injection. From what I read, each is the most efficient under different operating conditions, and their engine management system balances their use based on operating conditions.

Hard to imagine more difficult conditions for a fuel injector nozzle - combustion chamber temperatures and pressures combined with a light, reactive (thanks to ethanol) fuel. I’m surprised it works as well as it does. We’ll see in 10 years…

Diesel injectors have been surviving compression ratios ranging up to 22:1 for quite a while. I don’t see why gasoline injectors would be more prone to failure.

Because diesel fuel is less reactive when baked, compared to ethanol-containing gasoline. The ethanol brings its own oxygen to the party, bad things can happen.

Well ain’t that a crock, @texases. And with the marriage of oil and corn politics we can be sure that ethanol will be with US for quite some time.

I seem to remember reading that early gasoline direct injection engines tend to suffer from carbon build up

It seems that every engine line that gets any kind of update is acquiring DI. The efficiency gains are significant with relatively little additional cost and allows for technologies like Mazda’s unusually high compression SkyActiv designs. If this technology didn’t work well we’d have failing cars all over the place, as it has become very common, even on some cheap cars.

But then you can make turbine engines that survive thousands of hours,with excess oxygen in the combustion chamber-I do not see were there should be any problem with fuel injectors of course there has to be a part that requires expensive service-Kevin

The survival of a direct injector on a modern car has as much to do with the crap for fuel (including ethanol) as it does it’s general working environment. In my diesel and others where DI is common place, the fuel filter is a big item that is changed regularly and made very easy to do by the owner. It’s al up front and exposed with just the removal of a plastic panel. A little twist off bowl, two O rings reset, snap it in place, screw it back on re tighten the bowl finger tight and open the bleeder valve for 30 seconds of idling. If fuel dribbles out and about and into a small pan below…no big deal with a low volatility fuel.

So, where are the filters on some cars…if you can find it and have special tools, re torquing and a lift and are careful enough dealing with a much more volatile fuel or can welcome it as part your routine… Fuels with additives to help accommodate them are necessary, but IMHO, that’s not a big deal. The point is, direct injection in diesels and those in cars require are different. I believe that the problems are prevalent enough that Toyota supplies an auxiliary indirect set in the manifold…just in case on some of it’s motors.
http://www.motornature.com/2012/08/dual-fuel-injection-system-volkswagen-after-toyota/
I think that tells you something about the differences in the two motors, diesel and gasoline.

I don’t think the manifold injectors are there just in case the direct injectors fail in the Toyota design. From what I read, the ECU decides which works better for a given throttle opening.
With indirect injection, the vacuum in the intake manifold lowers the boiling point of the fuel for better vaporization when the engine is cold.
At full throttle or under turbo boost, direct injection after exhaust valve closing eliminates fuel/air mixture blow through during the intake/exhaust valve overlap period.

One of the advantages of indirect fuel injection is reliable burn off which is an advantage to having the indirect or, in this advantage it is indeed “just in case”. I don’t look at direct injection as the instrument mainly responsible for improved performance; I see the computer as that instrument. Direct injection allows more control over the process. But, it has it’s limitations that in some modes may be better served with help from indirect…at least for Toyota.

The old prechamber diesels sure experienced a lot of quenching,The Daedong tractor my brothers and friend own,requires heating on a summer day to start-Kevin

GDI seems somewhat trouble-prone: intake deposits, fuel dilution of oil, for instance. Especially in conjunction with turbos, they seem to really beat up oil quickly.


Time will tell how durable it is. For now, I’d let the “early adopters” discover that FOR me, and stick to proven technology. Heck, if it pans out, I might buy a used one in a decade!