Diesels in aviation?

Dave Siciliano

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Dave Siciliano
Intresting post. any thoughts?

Dave
=========================================================

A Diesel Primer
Putting Diesels In Airplanes Isn't A Bad Idea By ANN Contributor Patrick Puckett

Since I do the engineering and oversee and manage the maintenance of about 70 various items of equipment (most of it

diesel) and our shop handles almost every bit of maintenance including complete overhauls. And, oh yes, I am the company pilot... which now brings us to diesel powered aircraft.

To begin with: most people need to understand that the term.

"Horsepower" is actually a measurement of time, but it's become such a common term beginning with Henry Ford's desire to replace the "HORSE" drawn buggies, that everyone has used it, and it has therefore become a huge selling tool to this very day. But now that diesel powered pickups are just "flat" out performing their gas engined counterparts, and more and more sales advertisements are now touting the true name of power of any engine -- namely, "torque."

Simply put: Torque is the amount of force -- or power -- measured in pounds of force at a certain distance. For example:

let's say that you have a TSIO-550 B swinging, (hypothetically speaking, of course) a 20-foot diameter propeller. That means that 10-feet of it extends from either side of the hub. Since the torque of a TSIO-550 is not published, we will use the formula of: HP x

5252 divided by the RPM will equal 680 pounds of force at the crank at MSL.

Now, here's why that prop is so long. If you divide it by the length of the 10-foot prop you get 68 pounds per foot, or pound/foot. Simple, eh? If you were able to put a scale at the end of the 10-foot prop, you would see 68 pounds. Multiply that by 10-feet and there you have it.

Okay, here's horse power simply put. "How fast will that engine accelerate?" That's it. It's just a measurement of time. Drag racers, (yup we did that too), like as much Horse power as is INSanely possible. Why? Just in case you didn't get the above, the answer is: acceleration.

Putting it all into perspective, a particular version of a 12 liter Detroit Diesel-powered Freightliner develops about 350 horsepower, but it makes about 1,400 lb/ft of torque. It'll pull an 80,000 pound load up to and over 70 mph, burning a gallon of fuel every five to seven miles. Now take out that engine and replace it with a gas burning 350 hp V8 engine, and you might get it up to 10 mph (before it burns up), while using two to three "gallons" per mile -- not miles per gallon.

Here's what we're aiming at: The soon to be certified, (spring 2005), Centurion 4.0 liter diesel engine makes 698 lb/ft of torque

-- but only 310 hp. The Continental TSIO-550-B produces 350hp, but only about 680 lb/ft of torque, (power). What this means is: it will take an extra two or three seconds to accelerate to full RPM.

But, because it produces more power -- it will outclimb -- and cruise faster -- than the 550 will. And it will do so using less than half the fuel, and because the Lapse rate is far less than the 550, it will also make more power at altitude. That's how you get higher cruise numbers for a fraction of the operating costs. What this means is that your go fast six-pax single that really could never carry more than two or three souls with full tanks, can now load all 6, while carrying less than half the fuel, and go gobs more miles.

Good news to us GA guys, eh? Bad news to gas burner manufacturers. This is also really bad news to a certain 450 hp turbine engine that has a particularly high lapse rate, as the diesel will run off and hide from the turbine at FL 200 for an exceptionally deep and wide reduction in costs. But if you have a problem with how fast the diesel will rev up, then hold your brakes, -- push that "single lever" all the way forward and wait an extra 3 seconds before launching, you will lift off in the same distance or less (unless you have Al Bundy's mother in law on board).

Speaking of Al's mother in law, what happened to the weight of the old diesel? To answer that question, we have to go to how the fuel was formerly delivered. Since compression is what ignites diesel fuel and the old mechanical system would squirt in a measured amount (depending on where the throttle was set) into the cylinder where the compressed air was so hot and rich in oxygen that when the fuel hit it -- it ignited, -- actually more like an actual explosion. And we're not talking just any kind of explosion here. We are talking about a really "Big Bang." And when that bang occurs, it rattles all the way down the piston, connecting rod, crankshaft, out the engine block and -- voila! The famous diesel rattle.

About seven years ago, General Motors went over to its Izusu diesel division and developed a way to introduce fuel in a controlled way via computer that literally changed the industry.

Now the fuel is introduced in stages and basically it starts the flame front with just a miniscule amount -- builds it up to the amount required -- then tapers out.

No more "Big Bang," (go

stand next to an idling Duramax, or 6.0 Ford and see for yourself), and therefore no longer requires massive amounts of steel to absorb that sudden impulse of power. The side effect is that now today's diesel's makes more power and uses even less fuel.

Since that time, people are learning that gas engine technology has maxed out and diesel technology is just beginning. Honda is currently testing a family sedan in England that will do 133 mph while getting 92 miles per gallon. It's just the beginning fellow pilots, and I'm not even close to covering all that is currently involved in aircraft diesel's, and diesel's in general.

(Pat Puckett is a pilot and engineer for American Steel in Las Vegas, NV. The company engineers and manufactures metal buildings. Pat also designed and engineered the company's own one piece hydraulic "HyMatic" hangar door. After starting American in 1981, Pat started doing extensive research on diesel engines, and now have an extensive library of facts starting with diesel powered German aircraft of pre world war

existence.)

FMI:
www.dieselpub.com

 
Dave

Thank you very much for the post I find it very interesting. Diesels I have used were on farm equipent and we use to run them at a constant rpm theri longevity was and is amazing. Also they run lean. When I was a kid on the farm my dad always reminded me to keep the rpm band with within a few 100 rpm to keep it in the torque range. I had a diesel powered car and drove it for over 10 years and 450k miles.

I feel diesels woud be a great engine for most of the small GA planes that we fly. There are some small marine diesels that are being put into smaller boats now. Also some of the newer diesel cars are using some interestng technology to make them more fuel efficient.

John J
 
Thanks for the info, Dave. The weight penalty was the biggest issue I was wondering about.
Proud driver of a Cummins Turbo 5.9L ISB 12V engine - too bad it comes packaged in a Dodge...
 
Great Post. Anyone have anything to add? I love this kind of topic. Dumb question but is Jet fuel considered diesel? When will I be able to retrofit my lowly 172 with a diesel engine, if ever
 
corjulo said:
Great Post. Anyone have anything to add? I love this kind of topic. Dumb question but is Jet fuel considered diesel? When will I be able to retrofit my lowly 172 with a diesel engine, if ever

AFaIK diesels will run on most anything that burns hot enough including jet fuel. The real issue is whether the fuel provides sufficient lubrication to the complicated (expensive) high pressure fuel injection system.

As to the article that Dave posted (not to dis Dave, it was interesting) it's crammed full of misinformation and must have been written by someone with very little technical knowledge. For one thing, in an airplane, torque by itself is irrelevant, only horsepower matters. For every additional horsepower you can lift another 33,000 lbs at 1 ft/min (or more likely 66 lbs at 500 fpm) during climb ignoring prop losses. It doesn't matter if you are swinging a large prop at low RPM or a smaller one at a higher RPM except that the smaller prop will typically be less efficient and noisier. The larger prop would require more torque and thus absorb the same horsepower at lower RPM, but whatever HP is produced at the RPM you spin the prop will give the same climb rate and cruise speed as you'd get with higher torque at lower RPM and unchanged RPM.

The talk about power lapse rate is also rather confused. A diesel is no more capable of maintaining it's power output as the air thins than any other air breathing engine, and just like a gasoline engine a diesel with a supercharger can pack more air into the engine at altitude and thus create more power. The power output in such cases is mostly a function of the engine's ability to withstand the stresses involved both thermal and mechanical. The same is true of jet and turboprops which all have a "supercharger" (compressor) as an integral part of their design.

Diesels are attractive in aircraft for two reasons. One is that the BSFC (fuel efficiency) is higher so range is better for the same amount of fuel carried. Unfortunately diesel fuel weighs a bit more so some (but not all) of that improvement is lost when you consider payload. The other is availability. In many parts of the world, avgas is simply unavailable and fuels suitable for a diesel are readily available. And given the potential to use a commonly available fuel often gives a cost advantage even when avgas is a choice. In the US, this isn't currently much of a factor, but given the strong environmentalist desire to eliminate lead, we could be in the same boat as other parts of the world in the not too distant future WRT the availablity of avgas.
 
corjulo said:
Great Post. Anyone have anything to add? I love this kind of topic. Dumb question but is Jet fuel considered diesel? When will I be able to retrofit my lowly 172 with a diesel engine, if ever
To retrofit an SMA diesel into a 182 would run about $80,000. The mod is not yet available for 172s, but as you can imagine it won't be cheap.
 
This was on Aero News Network and I was surprised at some of the claims also. Of course, the Europeans seem to be employing desiels much more effectively than we are. Part of that is attributable to the much higher fuel cost. Weight has always been a concern. The fuel injection system mentioned would certainly eliminate some of the fuels that work in your everyday desiel engine. Parts availability, mechanics with the ability to work on the new engines and TBO issues all are coming up on the Diamond desiels.

It'll be interesting to watch. ITMT, I'll stay with my TCMs until I see something much more practical.

Best,

Dave
A-36TN ADs
 
but what about the "no overhaul - engine replacement required" at TBO on the current diesels being tested?
 
gkainz said:
but what about the "no overhaul - engine replacement required" at TBO on the current diesels being tested?

That's more likely related to the lack of diesel aircraft experience in the field than any technical aspects of diesel technology.
 
gkainz said:
but what about the "no overhaul - engine replacement required" at TBO on the current diesels being tested?

I think Lance is correct that they are doing that just to control the quality at this early stage of using diesels in aviation. I also think they can "mass" produce the engines cheaper than it can get an overhaul in the field. One last benefit is that all the used engines would probably be shipped back to the company where they could disassemble them and find any weakness in the engine design.
 
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Steve said:
Another good article at http://www.machinedesign.com/ASP/strArticleID/55900/strSite/MDSite/viewSelectedArticle.asp

172's are mentioned as close to STC.

As I recall from reading another article, the FAA mandated the "no overhaul" exactly for the reasons Lance stated.
In the absence of a published set of true performance/power tables for the DA42, the local rep forwarded some comments from the one North American Owner. He gets 175 kts at 95% power.

95%? Can you really run that and sustain that? I'm skeptical.
Also, above 8000 feet, airspeeds decrease, which is a characteristic of the turbo setup on the Theilert. This isn't promising to replace my Seneca...wherein the utility is at 170 kts at FL 19 to get over the top. They are NOT allowing demo rides. This will require some watching....rumor says they overheat.
 
Well, I agree with the sentiment of the article, but the math and use of terms are erroneous.

My wife drives a diesel Beetle TDI. It is our second diesel in the last few years. Indeed, the quality of modern diesel technology is a lot better than the general impression of it in the US. The are reasonably quiet, clean, powerful, good on fuel. More than half the new cars sold in europe are diesel now, no doubt in part to the very high taxes levied on gasoline vs. diesel there.

Ok, a little primer on horsepower: The guy is right, horsepower = torque x RPM x k (k is a constant). Horsepower = power = watts. In europe, engines are rated in how many kilowatts of output they can produce.

Torque is a measure of force, never a measure of power. Just force.

Since RPM is part of the equation, one thing to point out is that diesel fuel burns very slowly. Diesel engines cannot turn a lot of RPM's, most redline around 4000-4500. Gasoline burns quickly, so most gas engines redline around 6000-7000 rpm. More revs equals more little explosions per minute equals more horsepower simply because of the math.

One major operating difference between diesel and gasoline (also called Otto cycle) engines is that diesels produce maximum torque output at relatively low RPM levels. This usually coincides with their optimal fuel specific RPM, since the engine is extracting the maximum power per firing cycle from the slow burning diesel fuel.

The net effect of this is that my wife's 90hp diesel engine drives very much like the same car with a 180hp engine in normal street driving. It's making good power at normal everyday RPM. It's only when you stomp the gas and run the revs up does the gas engine really make it's go power evident.

On the aircraft, most light GA piston planes employ a large displacement, gasoline engine, which is directly driving a fixed or constant speed propellor. These engines have very large cylinders compared to car engines. My Corvette and Piper have the same engine displacement of about 360 cubic inches. The O360 of course has only 4 huge cylinders compared to the Corvette's 8. The vette easily makes more than twice the horses at twice the RPM of the Lycoming. But the Lycoming can produce more torque at lower RPM and thus more power at say 2500 rpm than my Corvette motor can.

Now, how does this relate to diesel engines on planes?

A diesel conversion is available for my PA28 series planes. The net performance is similar to my existing 180hp engine. However, the diesel does some things to get there. First off, the diesel uses a constant speed prop, where I only have the fixed pitch prop. It also uses a geared engine, to put the engine RPM at around 4000 for maximum power output. The prop turns much slower, which for various reasons is more efficient to begin with. (something around 2k rpm is better for props, our gas engine 2300-2700 cruise revs are a less efficient choice). Between the constant speed prop, the gear reduction and so on, the 135hp diesel produces about the same *net thrust* at take off.

At cruise, the RPM's come back a bit and the engine operates at a more efficient range and the fuel specific gets better.

A lot of the advantage could be had simply by having a constant speed prop on my 180hp engine to begin with. But that's another STC story.

The big advantage to operators outside the USA is the availability and cost of fuel. 100ll is simply unavailable in a whole lot of the world. It can be very, very costly where avgas is available. Jet fuel is widely available though, as is diesel fuel. Although most of the diesel highway fuel is unsuitable for the aircraft diesels outside of europe.

The other big downside is the cost. I just had my engine overhauled and along with all the extras, spent a bit over $20K doing it. A conversion to the diesel engine would have been in the $50K-$80K range. Even considering the cost of 2000hrs of avgas vs. diesel, that extra cost just didn't make any sense.

If it could be done for about $30K, I probably would have jumped on it. At $40k, I would still consider it.
 
Dave Siciliano said:
Intresting post. any thoughts?

Dave
=========================================================


Yes, Actually I have quite a few of them, and spelled them out in a very long post which was thrown into the ether during the server switch, I guess I couldn't post it as it was tagged for delivery (I technically know nothing of the internet, just my best guess of how it must work, so if I'm wrong, forgive me)because the routing no longer existed, then I couldn't back back into it because that routing no longer existed. Oh well, I've got time now to give a brief re-write.

First, while much of his stuff is good, there is some problem with the HP vs. Torque which changes the outcome numbers, but not the trend outcome.

Deisels for an airplane....I like it. The author references Detroit Deisel several times, so I'll assume this project is theirs. This could be a very good thing, because any such project could be backed by the full resources of Daimler Chrysler/MTU/Detroit Deisel/GM/Isuzu. Many years and $$ of combined research. No orphaned engine, and an incredible service/parts network world wide.
All of these companies have built winner and loser engines. Only time will tell, although I hope they don't screw it up. It might screw the whole market like GM did in the US in the late 70s with that converted Olds gas-deisel engine.

The power to weight ratio still concerns me some. They say they have an injector technology on the Duramax that smooths out the engine, good. I test drove one, and it was good, but brief. I haven't talked to any of the haulers who have a lot of miles under load, and haven't seen one in a boat (although a boat is an awesome testbed for an aircraft engine, same kind of load factors). We'll see how they last, but I'm hopefull. We still have to get considerably lighter than a Duramax though. I'm not sure if they can get low enough and maintain reliability at the high level duty cycle involved. There seems to be a bit of a problem there with MTU 2000 DDEC series engines in the high power/cyl ratings. It is a marketing/operation issue for the most part, but crankshafts are junking out in the 400-700 hr range. An engine with a 20% full power duty rating and a continuous duty rating doesn't belong in a boat or a plane. If the marketing department can be kept in check, there stands a good chance for deisel technology in a boat.

Another potential for burning Jet A in a non turbine, is there is a Multi Fuel Wankel out there being used in US Navy small boat applications. I'm keeping my eye on it, very promising, but I'm not sure if they have the resources or desire to go through aircaft engine certification. I may check into it for an experimental.

On the whole, I'm hopeful
 
Henning said:
The power to weight ratio still concerns me some.
The SMA SR305 engine that replaces the O-470 in a C-182 weighs 423 lb compared to the O-470R's 438 lb, although I think the SMA's is "dry" weight and the O-470's is ready to hang. However, the SMA engine only sucks about 70% of the fuel flow at the same power output, and for a typical 182 flight, that's a difference of about 60 lb of fuel.

For the Warrior/172 crowd, the Thielert Centurion 1.7 diesel weighs in at 295 lb compared to the O-320's 275 or so, which might cause some foks a bit of cg problem, especially in 172's that are already pretty nose-heavy with nothing behind the pilots' seats. The combination of higher engine weight and need for ballast might turn the 150-160HP planes into 2-seaters with any baggage at all.
 
And where are Lycoming and Continental's diesel entries? Sigh.
 
Henning said:
Another potential for burning Jet A in a non turbine, is there is a Multi Fuel Wankel out there being used in US Navy small boat applications. I'm keeping my eye on it, very promising, but I'm not sure if they have the resources or desire to go through aircaft engine certification. I may check into it for an experimental.

On the whole, I'm hopeful

Henning:

Now THAT one sounds appealing; have you any links to any resources related to this effort? I have always thought that the rotary engine was appealing for its relatively minimal reciprocating mass (although the resulting requirement of a gearbox may obviate much of the benefit). Does the rotary have an inherentability to burn the jet fuel in something other than a compression ignition (diesel) cycle? Inquiring (ignorant) minds, like mine, want to know.
 
SCCutler said:
Henning:

Now THAT one sounds appealing; have you any links to any resources related to this effort? I have always thought that the rotary engine was appealing for its relatively minimal reciprocating mass (although the resulting requirement of a gearbox may obviate much of the benefit). Does the rotary have an inherentability to burn the jet fuel in something other than a compression ignition (diesel) cycle? Inquiring (ignorant) minds, like mine, want to know.

It requires a sparkplug and ignition system which is why I called it a multi fuel engine rather than a diesel. I had a link, but lost it with the last computer.
 
Anthony said:
And where are Lycoming and Continental's diesel entries?
As an illustration of how seriously Cont appears to be treating diesel technology, here is one story as I have heard it. Cont had a deal with NASA/SATS to develop a diesel. There was a provision that if the engine flew by XYZ date, Cont would get a some amount of money as a grant. On that date, Cont "flew" its diesel as the rear engine on a Mixmaster. The airplane took off, leveled off, and landed on the remaining runway. Flight over. Engine retired. Check cashed.

Again, this is hearsay, and believe me, I hope it's wrong.
 
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