Textron Introduces Diesel 172
Critical altitude is probably sea level, yr right. You will definitely see a performance drop with a sudden disappearance of boost before you leave the ground - that and a load of black smoke!
The issue isn't only critical altitude, but keeping the combustion chamber hot enough to support combustion. When you're at altitude, low temps, low air pressure, the unboosted compression pressure isn't enough for the low CR these engines run at. Add in the SMA/Continental's air-cooling where you have nearly no thermostatic control, if you lose boost at altitude, chances are you can kiss goodbye to all combustion and you'll never get it started again until you reach the bottom.
The issue isn't only critical altitude, but keeping the combustion chamber hot enough to support combustion. When you're at altitude, low temps, low air pressure, the unboosted compression pressure isn't enough for the low CR these engines run at. Add in the SMA/Continental's air-cooling where you have nearly no thermostatic control, if you lose boost at altitude, chances are you can kiss goodbye to all combustion and you'll never get it started again until you reach the bottom.
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Do you understand what crictal altitude is.
Next I take it that no combustion engines work at altitude and in cold weather. That's strange I've worked at above 10000feet and we had Diesel engines working.
As for cooling yes they work better in general the hotter they get. This is also overcome with engineering. It's easier to heat an engine than to make it cooler. So still what is the crictal altitude for a complete turbo failure and to loose all performance from the engine. Next what is the crictal altitude for a normal ignition engine for a restart.
Even most turbines can't be started above 10000 feet. Your argument dose not stand up for restarting.
Next I take it that no combustion engines work at altitude and in cold weather. That's strange I've worked at above 10000feet and we had Diesel engines working.
As for cooling yes they work better in general the hotter they get. This is also overcome with engineering. It's easier to heat an engine than to make it cooler. So still what is the crictal altitude for a complete turbo failure and to loose all performance from the engine. Next what is the crictal altitude for a normal ignition engine for a restart.
Even most turbines can't be started above 10000 feet. Your argument dose not stand up for restarting.
Critical altitude
Turbochargers increase a piston engine's critical altitude, which is the maximum altitude at which an engine can maintain its full, rated horsepower. Because the maximum horsepower of a normally aspirated (nonturbocharged) engine is achieved in standard, sea level conditions, sea level is this engine's critical altitude.
From AOPA (USA) Flight Training magazine website
Quote: "Even most turbines can't be started above 10000 feet."
I would think that the PT6 qualifies as "most turbines" - this is the airstart envelope for a PT6-66D:
Turbochargers increase a piston engine's critical altitude, which is the maximum altitude at which an engine can maintain its full, rated horsepower. Because the maximum horsepower of a normally aspirated (nonturbocharged) engine is achieved in standard, sea level conditions, sea level is this engine's critical altitude.
From AOPA (USA) Flight Training magazine website
Quote: "Even most turbines can't be started above 10000 feet."
I would think that the PT6 qualifies as "most turbines" - this is the airstart envelope for a PT6-66D:
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I suspect there are a host of other "unforeseen" issues that include but are not limited to the power plant.
So much so that the massive engineering and certification effort may kill it forever.
Just my guess from joining a few dots……maybe not perfect dots, but better than average dots
So much so that the massive engineering and certification effort may kill it forever.
Just my guess from joining a few dots……maybe not perfect dots, but better than average dots
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Maybe it will not make certifcation and maybe it will. Who knows. The amount of aircraft engines that don't out weighs the ones that do.
How ever time will tell.
But still what is the max crictal alt that this engine will restart at.
Is the engine boosted from sea level or is it just normalized to alt.
you can't just put up a statement if you don't know what it performance is !!!!
Examples of turbine was to show that they can't be started at alt ether. Not many pistion engine aircraft get up of 25000 feet.
How ever time will tell.
But still what is the max crictal alt that this engine will restart at.
Is the engine boosted from sea level or is it just normalized to alt.
you can't just put up a statement if you don't know what it performance is !!!!
Examples of turbine was to show that they can't be started at alt ether. Not many pistion engine aircraft get up of 25000 feet.
Diesel engines run at 2-3Bar (absolute) manifold pressure at sea level, yr right. They need all this air because even at full power, they are running lean. The better the combustion system, the closer they can run to stoichiometric before they reach their smoke limit - i.e. how rich before soot emissions become unacceptable.
If you don't have any boost at all, they will have half or less of their power, even at sea level, therefore the critical altitude of a heavily boosted diesel engine - which is most of them - is sea level.
Highly boosted diesel engines usually run lower compression ratios due to structural limits for the maximum cylinder pressure. Low compression ratios means low peak cylinder temperatures under compression which limits the starting capability. That's why diesel engines run glow plugs and inlet air heaters for starting assistance - these are usually only man enough to start a stationary engine - not one that has it's cooling system running flat out, as it is for air cooled engines in flight. Lower atmospheric pressure at altitude also reduces peak compression temperatures too, with similar results. Combine the two and your diesel engine might be very hard-to-impossible to restart at altitude.
Even low power levels below the turbocharger boost threshold can be enough to let the fire go out. I believe this is why the SMA engines have a minimum power level for descent.
If you don't have any boost at all, they will have half or less of their power, even at sea level, therefore the critical altitude of a heavily boosted diesel engine - which is most of them - is sea level.
Highly boosted diesel engines usually run lower compression ratios due to structural limits for the maximum cylinder pressure. Low compression ratios means low peak cylinder temperatures under compression which limits the starting capability. That's why diesel engines run glow plugs and inlet air heaters for starting assistance - these are usually only man enough to start a stationary engine - not one that has it's cooling system running flat out, as it is for air cooled engines in flight. Lower atmospheric pressure at altitude also reduces peak compression temperatures too, with similar results. Combine the two and your diesel engine might be very hard-to-impossible to restart at altitude.
Even low power levels below the turbocharger boost threshold can be enough to let the fire go out. I believe this is why the SMA engines have a minimum power level for descent.
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Andy, well said and nicely described. I just hope the effort was not wasted.
And for all the reasons you describe, when the shiny gloss of sex appeal etc are worn off, you end up with a sub optimal piston aircraft engine in my humble opinion. A turbine is another matter, but for low level ops at lower HP these are not practical.
Square pegs in square holes.
And for all the reasons you describe, when the shiny gloss of sex appeal etc are worn off, you end up with a sub optimal piston aircraft engine in my humble opinion. A turbine is another matter, but for low level ops at lower HP these are not practical.
Square pegs in square holes.
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You seam to be comparing automotive to aircraft needs. So why can't you have high comp at sea level and have turbo boost at altitude.
I'm sure that the designers have taken everything into account. I'm not pro or anti. Don't really care. But I'm surprised at all the knockers but then again I'm not supposed about that ever.
When you consider the size of rods and cranks in a 150 hp aero engine to that of good quality automotive racing type rods of around the same stenghy that will take around 700 odd hp.
And like I've said earlier. It easier to make heat than it is to cool it. So is this engine air cooled or liquid ?
Maybe the aircraft is fitted with an emergency system for in flight starting.
Comes with a can of start you bastard tapes to the engine air filter inlet.
I'm sure that the designers have taken everything into account. I'm not pro or anti. Don't really care. But I'm surprised at all the knockers but then again I'm not supposed about that ever.
When you consider the size of rods and cranks in a 150 hp aero engine to that of good quality automotive racing type rods of around the same stenghy that will take around 700 odd hp.
And like I've said earlier. It easier to make heat than it is to cool it. So is this engine air cooled or liquid ?
Maybe the aircraft is fitted with an emergency system for in flight starting.
Comes with a can of start you bastard tapes to the engine air filter inlet.
I don't recall mentioning automotive at all, although most of the (truly) available aero diesels are heavily automotive based.
You could, but the engine would be much larger than required to make the power, especially if you're still paying the weight and complication penalty of having a turbocharger hanging off the side of it. A big engine is a heavy engine, especially when the high cylinder pressures of diesel engines are concerned.
The SMA and Continental CD200/TD300 are air/oil-cooled. The rest tend to be liquid cooled (and thermostatically controlled)
The SMA and Continental CD200/TD300 are air/oil-cooled. The rest tend to be liquid cooled (and thermostatically controlled)
Interesting thread so far, lots of thoughtful arguments/comments. I suspect of this forum had been around in the 1920's, we would have been arguing how will they ever get these new fangled gasoline aero-engines to be reliable.
I'm completely confident that the engineers will ultimately lick the problem. It may take a paradigm shift. My guess is SMA will ultimately make the engine liquid cooled.
However, there is another problem on the horizon for diesels that no one has mentioned. The production of diesel particulates, aka soot. Diesel particulate filters cure this problem at the expense of power and efficiency, then there's the need for active or passive regeneration in the DPF (burning off the soot in the DPF), but periodically you still need to remove the DPF to clean out the accumulated ash plugs. Don't even for a minute think that aero engines will forever escape the EPA who will eventually mandate DPF's for aero-diesels.
I've installed a water/meth injection system on my RAM3500 which keeps the DPF clean as a whistle and almost never have to do a regen.
I'm completely confident that the engineers will ultimately lick the problem. It may take a paradigm shift. My guess is SMA will ultimately make the engine liquid cooled.
However, there is another problem on the horizon for diesels that no one has mentioned. The production of diesel particulates, aka soot. Diesel particulate filters cure this problem at the expense of power and efficiency, then there's the need for active or passive regeneration in the DPF (burning off the soot in the DPF), but periodically you still need to remove the DPF to clean out the accumulated ash plugs. Don't even for a minute think that aero engines will forever escape the EPA who will eventually mandate DPF's for aero-diesels.
I've installed a water/meth injection system on my RAM3500 which keeps the DPF clean as a whistle and almost never have to do a regen.
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As for soot well I'm not sure. But anyone that's has work at a large airport will know what their car looks like after a week on shift. It's covered in black soot. It seams pa140 and moneys have now stc for fit ment as well
Last edited by yr right; 20th May 2015 at 04:50.
Seems like it'd be easier to develop and certify (or is it certificate?
) an unleaded, 100 octane avgas able to be brewed in auto refineries...
) an unleaded, 100 octane avgas able to be brewed in auto refineries...
A well timed thought, Continental ( as I recall, not Lycoming) has just announced the certification by FAA of an engine to run on 100LL or 91ULP. It did not mention whether that was motor octane or ASTM octane -- but the intent is to have a engine manufacturer certified to run on mogas, not an STC.
The threat to 100LL is not any shortage of "petrol" but the TEL (lead), which is now produced at one single site only. EPA's of this world are a lesser problem, (except in the minds of rabid greenies) because avgas consumption is sod all % of petrol consumed, the lead is now barely measurable from avgas sources.
With changed refinery processes we are now seeing 100 ULP (motor octane) as common with 105 not far away.
Tootle pip!!
Thread Starter
One reason I want to see all types of AVGAS disappear is that the market in the US, let alone Oz is too small to justify the infrastructure costs of making it available. You have Jet-A, and associated stuff to get it too the bowser, trucks etc. Then you have another fuel, AVGAS, that must be carefuly handled, separated, trucks, tanks, lines etc, duplicated infrastructure. That's not even talking about the refining costs.
Mush better I say to have the one fuel, Jet-A for everything that flies.
I cant work out why we have 3 different grades of fuel for cars. 91, 95 & 98. Why cant they just standardise on 98 and take the advantage of economies of scale.
Mush better I say to have the one fuel, Jet-A for everything that flies.
I cant work out why we have 3 different grades of fuel for cars. 91, 95 & 98. Why cant they just standardise on 98 and take the advantage of economies of scale.
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I cant work out why we have 3 different grades of fuel for cars. 91, 95 & 98. Why cant they just standardise on 98 and take the advantage of economies of scale.
I want to breed cattle that give 100% eye fillet steak, but instead you get all the other cuts in larger volume. Refining is much the same. Even avgas, the stuff from BP in WA is not the same as the Geelong stuff from what was Shell. The BP has way more lead because of a lower grade alkalyte.
As for all JetA burners……don't hold your breath.
