June 21st 11, 04:46 PM
Howdy,
Gasoline Direct Injection (GDI) has been integrated into quite a few
automotive engines over the past few years. After reading an article
about it, and googling for the availability of GDI fuel injectors I
started thinking this might be a cool direction to go in for those
persons interested in engine design, particularly the HCI Radial
guys.
One engine I've always thought was elegant was the 29 packard aero-
diesel because it did away with the second valve per cylinder. If they
had had forced induction in those days the old packard radial might
have been a keeper rather than an oddity.
It occurs to me that GDI recreates the possibility of a uni-valve
layout. If there is no fuel in the intake manifold, there is less
reason to seperate the intake and exhaust gasses. With a big venturi
on the intake side, there may not even be a need for forced
induction.
One problem that would certainly have to be overcome in this
arrangment, is that air metering in the manifold is not preportional
to fuel metering. Some exhaust gases may be recycled during normal
operation, particularly during decelaration. If the manifold is 'T'
shaped rather than 'L' shaped, the inlet pressure does not accurately
reflect the volume of air going into the cylinder.
So you'd have to base your fuel flow on something other than manifold
pressure. Probably a combination of a known throttle map (in the form
of a cam or wedge) and a barometric lifter of some sort.
Anyway. If I was going to build a new gas aviation engine, I would be
inclined to look at a radial GDI with 1 valve per cylinder, 1 throttle
body per cylinder, a relatively low pressure centrifugal supercharging
setup on a planetary gear around the prop shaft.
The fuel system would be similar to the bosch piston pump injection
system that was used on the Packard, and many engines since. So you'd
still have 2 cams, except one is for the valves, and the other
actuates the injection pulse. How to handle mixture control still
baffles me. But this is just shooting the breeze. Anyway... Comments
welcomed.
Thanks!
Gasoline Direct Injection (GDI) has been integrated into quite a few
automotive engines over the past few years. After reading an article
about it, and googling for the availability of GDI fuel injectors I
started thinking this might be a cool direction to go in for those
persons interested in engine design, particularly the HCI Radial
guys.
One engine I've always thought was elegant was the 29 packard aero-
diesel because it did away with the second valve per cylinder. If they
had had forced induction in those days the old packard radial might
have been a keeper rather than an oddity.
It occurs to me that GDI recreates the possibility of a uni-valve
layout. If there is no fuel in the intake manifold, there is less
reason to seperate the intake and exhaust gasses. With a big venturi
on the intake side, there may not even be a need for forced
induction.
One problem that would certainly have to be overcome in this
arrangment, is that air metering in the manifold is not preportional
to fuel metering. Some exhaust gases may be recycled during normal
operation, particularly during decelaration. If the manifold is 'T'
shaped rather than 'L' shaped, the inlet pressure does not accurately
reflect the volume of air going into the cylinder.
So you'd have to base your fuel flow on something other than manifold
pressure. Probably a combination of a known throttle map (in the form
of a cam or wedge) and a barometric lifter of some sort.
Anyway. If I was going to build a new gas aviation engine, I would be
inclined to look at a radial GDI with 1 valve per cylinder, 1 throttle
body per cylinder, a relatively low pressure centrifugal supercharging
setup on a planetary gear around the prop shaft.
The fuel system would be similar to the bosch piston pump injection
system that was used on the Packard, and many engines since. So you'd
still have 2 cams, except one is for the valves, and the other
actuates the injection pulse. How to handle mixture control still
baffles me. But this is just shooting the breeze. Anyway... Comments
welcomed.
Thanks!