RV-10TDI Update

[Flandy10]

Originally Posted by rv6ejguy

Scott, I was having a conversation with another guy today about your diesel RV10. We were curious as to what MAP/RPM do you have to maintain on descent to keep the fires lit so to speak? Approx fuel flow at that power setting? Thanks.

Ross,

The factory answer (currently) is 45"MAP and a CHT of 212F until landing on runway is assured. FF at that power reads approx. 4gph.
FF accuracy drops as the rpm falls below 2200rpm so it could be a little less.

To be honest, I only pull it back that far when I want to slow down in the pattern. Descent at 65"MAP is about 500-700fpm and approx. 160KIAS. And to be honest, I have never pulled it back to 45" and maintained cruise airspeed to see what it would do. Will have to check that out sometime.

So far, I have yet to encounter any conditions were it has come close to failing to light. I've flown from downwind to touchdown at idle (32-34"MAP) and it has always responded smoothly. On a 30F day with power at idle from about 500ft on final, only one CHT approached the 212F limit in the flare. There is a small power lag from idle as you would expect in a turbo diesel, but not excessive.

[rv6ejguy]

Originally Posted by Flandy10

Ross,

The factory answer (currently) is 45"MAP and a CHT of 212F until landing on runway is assured. FF at that power reads approx. 4gph.
FF accuracy drops as the rpm falls below 2200rpm so it could be a little less.

To be honest, I only pull it back that far when I want to slow down in the pattern. Descent at 65"MAP is about 500-700fpm and approx. 160KIAS. And to be honest, I have never pulled it back to 45" and maintained cruise airspeed to see what it would do. Will have to check that out sometime.

So far, I have yet to encounter any conditions were it has come close to failing to light. I've flown from downwind to touchdown at idle (32-34"MAP) and it has always responded smoothly. On a 30F day with power at idle from about 500ft on final, only one CHT approached the 212F limit in the flare. There is a small power lag from idle as you would expect in a turbo diesel, but not excessive.

Very interesting. Thank you.

Would an in-flight re-start attempt be with the glow plugs? Sorry, never owned a diesel of any kind. I find the differences like boost at idle, fascinating.

[rv6ejguy]

Originally Posted by BillL

Maybe not a drag thing, turbocharged (after cooled) diesels will increase combustion cycle temps with altitude and the turbo compressor pressure ratio increases too. The temps will tend to increase heat rejection to hot parts, and the pressure ratio yields higher pumping losses, both of which will reduce the BSFC and may throw off his HP estimates. Without a vacuum chamber ($$$$), it is very hard to simulate this on the ground, so a torque meter would be needed in the air to get a more accurate assessment of power.

So, even with fixed RPM & fuel flow, the turbo-aftercooled engines will loose a bit of power with altitude.

Manifold pressure to make the same hp at altitude would remain roughly the same if the intercooler efficiency is good. Delta P increases across the turbine with increasing altitude. This tends to offset the higher shaft hp required from the compressor as pressure ratio increases. On properly intercooled SI engines, hp actually increases at the same MAP at higher altitude.

That being said, with the high pressure ratios the diesel requires, they need massive intercoolers compared to SI engines which operate at much lower pressure ratios. I suspect that the intercooler drag may come close to the engine cooling drag.

Would be fascinating to do a side by side test against a 540 powered RV10 like I did with the Subaru and Lycoming RV6As.

[Flandy10]

Originally Posted by rv6ejguy

Very interesting. Thank you.

Would an in-flight re-start attempt be with the glow plugs? Sorry, never owned a diesel of any kind. I find the differences like boost at idle, fascinating.

I know from the manual that glowplugs are only used for ground starts. They create a localized hot spot in the cylinder to promote ignition. Inflight, they wouldn't have the same effect due to the rapid turnover of the air in each cylinder(my understanding).

The inflight restart procedure is just adjusting thrust lever between 50-90% depending on conditions and may require descent into "warmer" air. With the fuel injection timing fixed relative to a point BTDC, its just a matter of getting the right mixture atomization for auto ignition. Cold weather ground starts are similar in that it may require a thrust lever position between 50-90%, but I haven't needed above 50% and it has always started on the first attempt.

I'm sure there is someone in this group who understands and could explain it better than that.

[RV10inOz]

Interesting.

Knowing the reasons for the C182 debacle being scrapped I am keen to see how this works.

Relights were a problem for the 182.....but for a whole host of other reasons than the CHT

You also quote high MAP and thus very turbocharger reliant. I trust you wear a chute?

[rv6ejguy]

I didn't want to contaminate the RV10 speed brake thread. Dan and Scott, from the screen shots, the FF seems very high for the MAP and rpm. Are these valid numbers or do you feel there is some sort of error as Scott alluded to previously?

[DanH]

Recall how red cube fuel flow senders are pulse sensitive? Well, the diesel flow provides a plethora of pulsation (go ahead, say it real fast). The fuel system has a high volume return, so there are two senders. The fuel flows are not accurate, and worst at low flow. It's on Scott's punch list.

[DanH]

Originally Posted by RV10inOz

Knowing the reasons for the C182 debacle being scrapped I am keen to see how this works.
Relights were a problem for the 182.....but for a whole host of other reasons than the CHT

David, could you illustrate the reasons the Cessna program was scrapped, and why relights were a problem with the SMA SR305-230?

[rv6ejguy]

Scott,

Do you have any data on the compressor discharge temps and intercooler outlet temperatures. Curious.

Thanks

[lr172]

Originally Posted by Flandy10

Charlie,

I actually called the folks at FloScan to talk with them about their diesel systems. The engineer couldn't hang up the phone fast enough when I explained what type engine I was using. It didn't matter that it would be a certified aircraft engine.

Most marine diesel FF meters that would work speak DIGITAL and aviation displays speak ANALOG. The problem aviation version of the FloScan and Red Cube have are that the Bosch mechanical injector pump introduces 3200 pulses/minute(idle) and 8800 pulses/minute(flight) into the incoming fuel stream. Think shockwaves or instantaneous microstops to the incoming fuel. This drives the turbine meter systems nuts. And yes I've looked into digital to analog convertors. I've yet to find one that can work with the few number of pulses per gallon the system would produce at idle. I actually found a system that was designed to account for these pulses, but again, its output was digital.

I knew when I committed to installing this engine, I would be on the cutting edge. I just didn't think I would be the FIRST one, I expected an OEM to get there first.

An idea to consider. I know that when I encountered this problem with air, the answer was a reservoir to help stabilize readings. I wonder if a fuel reservoir of a decent size between the red cube and injector pump/controller (or whatever device is post-red cube) might not help to take some of the pulsing out of the red cube passages. Clearly, having a diaphragm in the reservoir would make a big difference, but would be challenging to fabricate.

Larry