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View Full Version : Direct Fuel Injection on GA Piston Engines.


Ozgrade3
7th Mar 2008, 10:48
With all the known benefits of Direct Injection on cars, has anyone considered adapting current GA piston engines to a similar spec. Would there be any tangible benefits in an aero engine.

Talking about AVGAS engines not diesels.

411A
7th Mar 2008, 16:01
Well lets see...

TCM started direct fuel injection with the GTSIO series engines in 1965, and the IO470 series before that.

Lycoming?

Yep, early on as well, with the IGSO540 and IGSO480 series engines.

Any more questions, feel free to ask, as I've flown all these engines at one time or another...and personally own an aircraft with the TCM GTSIO engines installed...the best engines TCM ever made, in fact, in my considered opinion.

P210driver
7th Mar 2008, 22:11
Well 411A, I believe that Ozgrade3 was asking about direct (into the cylinder) fuel injection, NOT the FI used by TCM and Lyc which inject the fuel into the intake port.

The current systems provide a continuous spray of fuel into the intake port which is sucked/pushed (normally aspirated vs. turbo or super charged) into the cylinder when the intake valve is opened. On the other hand, direct injection employs a timed injector that sprays the fuel directly into the cylinder - usually on the compression stroke when both the intake and exhaust valves are closed.

The direct injection system is more complex, requiring precise timing (and duration) of the fuel spray "pulse". Since in these systems the fuel pressure is constant, the mixture is controlled by the duration of the fuel pulse. Automobile engines that use direct/timed injection use an oxygen sensor in the exhaust as part of the feedback loop to set the correct mixture.

Would such a system provide benefits for GA piston engines? Probably. Is the cost of getting FAA certification for such a system a barrier? Definately. :ugh:

Miraz
7th Mar 2008, 22:26
The benefits are considerably smaller too - much of the development rationale for this technology is the reduction in fuel consumption/emissions under light engine loads, above 60-70% throttle there is little benefit.

matt_hooks
7th Mar 2008, 22:40
However with the latest FSI type engines much more power can be got from a smaller engine, hence a saving in weight.

P210driver
7th Mar 2008, 22:54
Miraz -

There are benefits available if the engine can be run lean of peak (LOP) automatically. LOP operation in a TSIO-520 can result in saving 3 to 5 gallons per hour at the same TAS. With todays (and tomorrows) fuel prices, that can be HUGE.

LOP operation is becoming more common in GA engines (especially turbocharged), but it requires a properly set up engine, some training, probably a multi-cylinder engine analyzer (to watch EGT and CHT continuously on all cyls). The FADEC system being sold by TCM operates the engine LOP during cruise (but ROP for high power ops), and some engines (like the Piper Malibu/Meridian?) require LOP operation per the POH.

matt_hooks
7th Mar 2008, 23:02
I was led to believe that most aero engines were designed to run a slightly rich mixture at all times, to allow for some cooling of the cylinder walls by the excess fuel (I assume by "peak" you mean stochiometric ratio, or are you referring to peak EGT or CHT?)

P210driver
7th Mar 2008, 23:22
matt_hooks -

By "Peak" as in LOP or ROP, I am referring to the peak EGT for each cylinder. The goal of setting the mixture either lean or rich of peak EGT is to control the combustion event so that the CHT does not exceed a reasonable value (we use 380F, not the 460F that TCM/LYC might spec), and the internal cylinder pressures remain at safe levels.

The mixture guidelines ("slightly rich of peak") are fine - IF you have a normally aspirated engine, and the power setting is less than 65-70% power. For high-power ops (both turbo and normally aspirated engines), what we really want to control is the peak pressure inside the cylinder, and running the mixture well ROP (like 150 or more cooler than peak, not the 25-50 degrees specified in the POH) will prevent the combustion pressure from exceeding safe values. Note that operating LOP (by 50F or more) provides the same benefit, and you get to save lots of money on your fuel bill. :)

You can start at www.gami.com (http://www.gami.com) to find out more about LOP operations.

Brian Abraham
8th Mar 2008, 01:44
I was led to believe that most aero engines were designed to run a slightly rich mixture at all times

No, no, no, definately not. For operation of piston engines go to this link and have a read. John Deakin is the guru.

http://www.avweb.com/news/pelican/182146-1.html

matt_hooks
8th Mar 2008, 09:54
Brian, was that the right link? All I got was a thing asking me to register for AVWeb.

And the "rich of stochiometric mixture" is what we were taught during our ATPL's. :eek:

Miraz
8th Mar 2008, 10:23
P210 - but that's not a function of direct injection

Direct injection primarily allows better atomisation at lower intake air velocity - ie part throttle.

Once you the throttle is open a decent amount, it is usually more efficient to inject the fuel further upstream so it has time to mix properly with the air - many race cars have a second bank of injectors that they only use at high rpm specifically for this reason.

There are potentially lots of benefits from moving away from clockwork engines - variable ignition timing combined with well designed injection setup could make running LOP or to any other desired condition utterly foolproof.

Look at developments like ion-sensing ignition too....

Brian Abraham
8th Mar 2008, 14:07
matt, yes it's the correct link. Maybe unregistered users can't access so register - costs nothing. Re "rich of stochiometric mixture", yes there are times you NEED to be, and times when you don't NEED to be. Aircraft such as the big piston airliners routinely ran LOP in the cruise as a matter of course. John Deakin covers all the details accompanied with nice colourful graphs. Very educational even if you have no practical use.

Direct injection has been used in aviation engines - Germany was a big user in WWII (Me 109, FW 190), and some of the big P & W radials also.