Diesel Emerging As New Technology of Choice for General Aviation

As a pilot I love seeing news like this:

http://www.marketwatch.com/story/di...ogy-of-choice-for-general-aviation-2012-07-26

-BB

Puzzles me how it can run on jetA?

Jet A = Kerosene = Diesel without the additive package

Jet A burns just fine in most diesels. Some diesel injection systems can handle it just like diesel, other systems can't due to lubricity, etc. The engine itself does not care. They want to use Jet A because it is already at airports.

The engine uses a Bosch P7100 pump unless it has changed since the last info I have.

126mm bore x 100mm stroke boxer-4, compression ratio 15.5:1.

Man you would think this day and age cesna would be running a common rail engine. Not one with a big p7100 pump. The p7100 is a great pump just seems very out dated.? Really cool to see planes with diesels. I bet they can run larger props because they might need the rpms. I bet gallons per mile is great in a small plane. Sound very cool!

HPFP inflight- Houston, we have a problem.

Toyotaguy said:

Man you would think this day and age cesna would be running a common rail engine. Not one with a big p7100 pump. The p7100 is a great pump just seems very out dated.? Really cool to see planes with diesels. I bet they can run larger props because they might need the rpms. I bet gallons per mile is great in a small plane. Sound very cool!

Click to expand...

The P7100 has its cam, followers and governor lubed with engine lube oil. That's probably why they used it. Jet A only is seen by plungers, injectors and lift pump. It is also VERY reliable. But also huge. About the size of a VW cylinder head!

While HPFP failures are certainly a problem, mechanical pumps are not 100% free of potential failure modes either.

The reason for the slow uptake of new technology is the stringency and cost of FAA certification. Period. That's why Lycoming and Continental engines dating back to the `50s are still king of the air of piston light aircraft engines.

Better safe than sorry. I guess? CP3 pumps are far better for reliability, from what i have seen compared with the cp4.1 in the TDI. I think that the failer of the pumps are starving for fuel. Cavitation.

Any ways i have heard of people converting bmw common rail diesels in to small aircraft. I don't know any FAA rules but i am sure they are very afraid of change. Because of the safety factors and things.

It depends. They'll largely let you do what you want to your own private aircraft. Once you're either selling tickets or selling airplanes/parts the regulations get a lot more...interesting.

A lot like the kit car situation, actually - you're more or less free to endanger your own life, just not anyone elses.

Check out Diamond DA42 Twin Star. (2x Centurion 1.7 or 2.0, or 2x AE 300)

Austro Engines refers their AE 300 engine as "Jet A Piston Engine"

All the above based on Mercedes-Benz automotive engines.

A little off topic, but I've been intrigued by the GA hybrid potential. Electric motor prop drive, enough batts to assist for takeoff and climbout, a gasoline, diesel or gas turbine driven generator. Two props, on wings or tail pods??

Advantage would be in safety, as the batts would allow much better landing options should generator fail.

I think the weight would be a killer using either piston engine, leaving the GT as best option.

GT's bsfc stink, but if optimized at one spot in the performance map, they seem to be "not so bad". On this rig, GT could be left operating at a very small region of the map. The weight saving may give fuel burn more of an advantage than the poor bsfc penalty detracts.

I have had a devil of a time finding out what the bsfc could be if optimized. There are APU's out there, and chopper turbines, but either bsfc data is not published or duty cycle is so different that it's an apples/oranges thing.

What do you guys think?

Total cost is probably a deal killer.

And I believe the others are using a CP3.

Wonder if they'll do smaller displacement, lower performance versions for things like a 172?

Now that's interesting.

Wonder how emissions performance is. (Compared to a 4-stroke, that is.)

It has an inverted crankshaft, so likely crankcase scavenging and oil injection. Emissions would suck but doesn't have to meet anything remotely close to automotive or on-road truck standards.

Edit: The biggest problem I immediately see in the design of the above engine is thermal flux on the piston - 2-strokes have twice-as-frequent power strokes, no cooling gas-exchange stroke and it is impossible to implement piston spray jets. The claimed 100-120 HP on only 3 cylinders and what looks to be pretty modest swept displacement also means a very high-specific output, which exacerbates the piston thermal stress.

I guess you could use piston jets, oil will just get thrown upwards rather than downwards. Hard to visualize the mess of oil being thrown around. Might have alot of losses from churning.

Some high output Detroits used a two piece crosshead piston with a semi-floating crown. A chamber was formed between the two pieces that was kept about half full of oil from a drilled rod passage. That formed a "shaker" chamber which seemed pretty effective at cooling.

Does this engine actually exist, or is it only in in the CAD realm?

Coking and oil fouling of the liner ports would be a problem.

I've worked alot with 2-stroke Detroit diesels and can boil down the experience to simply this: At low specific output, super reliable and fairly long lived. At high output, lots of problems. Mostly due to piston cooling and liner lubrication above ports. Coking was never much of a problem, but these are uniflow with only air in the ports. Exhaust through ports would be more of a challenge.

Since aircraft need to live in the high specific output world, it will be tough to engineer a reliable machine. If you can fly with low specific output, then ok.

Anyone know of any remaining Junkers Jumo OP two strokes? Amazing those things worked quite well 70 years ago. What I heard was they were all destroyed at the end of the war. And not enough power to serve warbirds.

The only reason I mentioned port coking/fouling is because of the specific case here of an inverted crankshaft and how well it would go with piston oil squirters. There would always be a puddle of oil on the pistons even as they're going up and down. It's all just a CAD concept drawing anyway. I don't think it's going to go anywhere.

Yea, probably just another bored engineer with good CAD skills designing engines. It's not going anywhere til someone starts making parts.

Regarding the oil on pistons, the acceleration of the pistons even at dead idle should be enough to throw the oil upward on decel from midstroke to BDC. Or should that be TDC??

Yes, but you would need something to catch said flung oil. It would need some kind of evacuated crankcase / dry err.. sump with scavenge pumps. Continuity in a control volume - mass in must equal mass out. The crankcase scavenge pumps could be implemented very easily here, in the same package as the Rootes scavenging blower illustrated.

Obviously 2-stroke Diesels have been successfully done. Here it would just require a realistic specific power and power per cylinder. Steel pistons would be great too. I don't know for the life of what what is the rationale to going back to indirect injection though...

My understanding is that a version with exhaust valves in the head actually does exist, and is in airplanes, but has never reached production.

Going back to IDI... most of the reasons I can think of for that don't matter for aviation (high RPM capability, reduced NOx), except for cost. IDI is still cheap, and generally even low RPM tractor motors run IDI when they can get away with it.

The main driver in aviation - and which was stated in the article - is minimum fuel consumption and IDI is antithetical to this objective. The familiar piston heat flux might actually be the reason. In DI most of the heat is through the entire bowl surface are. With IDI, the main source of heat would be much more confined to a smaller area where the torch of burning gas issues out of the pre-chamber and impinges on the piston crown, the bulk of the heat loss is through the pre-chamber itself, where it can be much more straightforwardly cooled.

Could be engine mass reasons, too, for it - IDI pistons are lighter due to not having a combustion bowl, which could allow the rods to be a little lighter. And, IIRC, IDI has less combustion shock (well, unless you have multiple pilot injections, which you won't have on a mechanical pump engine), allowing further reduction in both rod and crank mass, I'd think.

You are right.