The last time I looked at Mercury outboard spec sheet, the DI was down
on power -cleaner lean burn DI uses up some of your
vol eff and encourages stratified charge - NOTHING is all good good
Vance

Vance,
Good to see you bouncing back and I hope your feeling much better.

Thanks for that info - interesting point on reduced power and volumetric
efficiency, I don't quite understand why - perhaps the much greater
atomised charge takes up more area for less fuel?
However encouraging stratified charge is what I thought we were after -
my understanding of stratified charge was that there was a greater and
more dense charge surrounding the ignition point, which leads to better
ignition and burn of a leaner charge?
George ( down under)

Actually, I bet the DI setup is power limited because you can't get a
single injector with enough dynamic range.  They're going for emissions so
they pick an injector which will deliver just a whiff of fuel while at
idle state, but can't flow enough to make big horsepower.  Staged
injectors might be a good answer.  One DI injector for idle and low power
cruising, and a fire hose in a conventional location to make launches more
fun.

I wonder if the VE numbers are lower because they used an engine with a
little lower compression ratio to control combustion speed - still going
for emissions - lower NOx.  Nah.  Vance is probably right here..
Turbulent intake leads to better stiring, but lower mass of air injested
for a given operating condition (throttle setting/RPM).

Total speculation on my part.

I think aircraft and especially rotaries can benefit from DI - put the
well atomized cloud of fuel close to the spark plugs, and so that it
pushes the rotor in the right direction equals less crevice loss, better
BSFC.  Probably forget the stratified charge intake..

Paul, does the combustion event on the rotary happen slower than it does
on a piston engine for a given output shaft RPM (intake to intake for a
single rotor face)?


Regards,

Matt-

That is a good question. Chapters have been written on the subject.
I suspect there is no direct analogy with a piston engine because
of the moving combustion chamber. Here is some stuff from Yamamoto.
Also a drawing of an old idea I had. Won't work as it will suck
HP to compress the air required. Unless of course the air compressor
is run off the waste exhaust energy alone.

You may be on to something about injector dynamic range.
It might take two direct injectors to get the full benefit.

I can hardly wait to see what Mazda does. A lot of other people
that have tried DI have failed to significantly improve the rotary engine
BSFC.

Paul Lamar

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