Diesels aren't perfect

[Kenny Phillips]

Good timing; today an AD was released for many of the Austro engines used in Diamond aircraft. It appears that the timing chain doesn't like windmilling starts (when watching DA62 engine-out videos, I always thought it was strange that they always pressed the start button.)

 

[Dan Thomas]

In the 1980s Detroit Diesel stopped building their two-stroke heavy diesels and replaced them with more fuel-efficient four-strokes. Their two-strokes had been built for many decades.

And that fuel inefficiency applies to two-stroke gasoline engines as well. Two-strokes are used where economy of manufacture and low weight per HP is required. In recent years outboard motor manufacturers have moved largely to four-stroke engines. Just about all outboards before that were two-strokes.

 

[Ted]

In the 1980s Detroit Diesel stopped building their two-stroke heavy diesels and replaced them with more fuel-efficient four-strokes. Their two-strokes had been built for many decades.

And that fuel inefficiency applies to two-stroke gasoline engines as well. Two-strokes are used where economy of manufacture and low weight per HP is required. In recent years outboard motor manufacturers have moved largely to four-stroke engines. Just about all outboards before that were two-strokes.

A lot of the cause for change was emissions rather than efficiency. That was especially the case on boats.

A 2-stroke diesel in a plane could make sense. Sacrifice some efficiency for less weight for the power output.

 

[Stickman]

I love the 8V92TA.

 

[Ted]

I love the 8V92TA.

When I was looking at semis I was somewhat hoping to find one with one of those.

A 12V92 would be ideal but those had to get swapped in.

 

[Stickman]

I've got an MCI 102-C3 with a Detroit 8V92 awesome sound, amazing torque, 478hp.

 

[GRG55]

Plus they are cheaper to operate, as Jet A is more energy dense, is often much cheaper, and the engines have higher thermodynamic efficiency. They'll become a big deal unless someone comes up with an unleaded avgas that will work in most engines.

Having a higher fuel efficiency is not necessarily "cheaper to operate". theres a lot more to keeping an engine in the air than the fuel it consumes. And going by the experience of the owners of the two Diamond twins in the maintenance shop next to my office there's no way in hell the fuel saving are offsetting the ridiculous amount of engine related downtime on those airplanes.

Also, the idea that jet fuel is more energy dense than avgas is a bit of a fallacy. On a MJ/kg (or BTU/lb, if you wish), avgas is slightly more energy dense. In aviation it's weight, not volume, that counts...because you have to lift it. And part of the Diesel engines fuel efficiency advantage is lost to the higher weight of the engine and gearbox over a direct-drive air-cooled Otto cycle engine.

Diesel engines for aircraft is just another step in making what's left of light, private GA the exclusive purvey of the very well off.

 

[Katamarino]

Actually SMA has been making and selling a direct drive diesel for over a decade. They have STCs for a few Cessna planes.
I flew in a diesel 182. It was surprisingly smooth and quite compared to the brand new 182 I demoed earlier in the day.

I have no info on the longevity or costs though....

Hasn't been available for a while, had some serious deficiencies. Soloy planning to bring it back, improved, next year - for $210,000 - $240,000 for the engine.

 

[FormerHangie]

Totally.. 2 stroke diesel is where it's at. Really, 2 stroke in general

I don't know about that. Outside of enormous ship diesels and small bore lawn equipment, I'm not seeing much action in the two stroke arena. Look at what's going on in dirt bikes, snowmobiles, and outboard marine engines. All of these were once dominated by two stroke engines, and they are increasingly being equipped with four strokes.

15 years ago nearly all jet ski/ waverunner type watercraft were two strokes, I think that now all are four stroke equipped.

 

[cowman]

I think 2 stroke is going away because of emissions requirements, not so much actual capability. Seems more like they finally got the 4 stroke technology up to the point it was a viable replacement and a lot of the powersports companies are going that route rather than trying to re-engineer the 2-stroke.

 

[tspear]

I think 2 stroke is going away because of emissions requirements, not so much actual capability. Seems more like they finally got the 4 stroke technology up to the point it was a viable replacement and a lot of the powersports companies are going that route rather than trying to re-engineer the 2-stroke.

I spent a couple of hours last night looking for emission controls on 2 stroke engines. I found them for boats in many states. Basically they were grandfathered and new sales effectively blocked.
Outside if boats, I could not find emissions restrictions for 2 stroke. In fact modern systems can make a 2 stroke almost as good as 4 stroke in terms of emmissions.

The most common thread, on why four stroke was engine life. Heat by far is the largest issue. A four stroke manages heat better, also generally has better lubrication.

Basically the old adage there is not replacement for displacement applies.

Sent from my SM-J737T using Tapatalk

 

[Tantalum]

All of these were once dominated by two stroke engines, and they are increasingly being equipped with four strokes

I'm pretty sure it was due to emissions. From a purely engineering perspective the two stroke is a much cleaner design.

Outside if boats, I could not find emissions restrictions for 2 stroke.

there may not be specific "2-stroke" emissions restrictions, but the amount of scrutiny that automobiles and just about any fossil fuel burning entity must go through is very high.. it effectively kills 2 strokes..

Even my 4-stroke lawn mower can hardly run it is so ridiculously lean.. I basically had to jerry-rig the auto choke to always be a little open in order for the thing to run.. and this is a brand new lawn mower. I remember our old friend Mr Denver Plot also said the same thing about his lawn mower

Apparently 2 stroke diesel is pretty efficient, but don't take my word for it lol, I love this guys YouTube channel

 

[tspear]

I'm pretty sure it was due to emissions. From a purely engineering perspective the two stroke is a much cleaner design.
There may not be specific "2-stroke" emissions restrictions, but the amount of scrutiny that automobiles and just about any fossil fuel burning entity must go through is very high.. it effectively kills 2 strokes..

Even my 4-stroke lawn mower can hardly run it is so ridiculously lean.. I basically had to jerry-rig the auto choke to always be a little open in order for the thing to run.. and this is a brand new lawn mower. I remember our old friend Mr Denver Plot also said the same thing about his lawn mower

Yeah, I thought so also. And that is the position I took in a debate with two others on a private thread in another forum. However, I could not back it up. There are lots of restrictions specifically on two stroke engines, and on engines that require oil in the fuel or allow for unburned fuel in the exhaust for boats. I could not find any restrictions on lawn mowers, snowmobiles, snowblowers, ATVs.....

Tim

 

[mondtster]

I spent a couple of hours last night looking for emission controls on 2 stroke engines. I found them for boats in many states. Basically they were grandfathered and new sales effectively blocked.
Outside if boats, I could not find emissions restrictions for 2 stroke. In fact modern systems can make a 2 stroke almost as good as 4 stroke in terms of emmissions.

The most common thread, on why four stroke was engine life. Heat by far is the largest issue. A four stroke manages heat better, also generally has better lubrication.

Basically the old adage there is not replacement for displacement applies.

I don’t think you’ll find emissions restrictions specifically for two strokes. As far as I know. The EPA sets emissions requirements then the OEMs can produce whatever kind of engine they want as long as the requirements are met. So if you can get it done with a 2 stroke, great. If not, you’ll be doing it with a 4 stroke.

Emissions effectively killed the two stroke plain and simple. Durability is not a valid argument. In the off road motorcycle world the 4 strokes that are worth riding really have no longer of a lifespan than the 2 strokes do.

Two strokes are indeed a replacement for displacement. If they did not have an advantage in the power generation department you would be racing 125cc 4 stroke motorcycles against 125cc 2 strokes. Instead, you race 250 4 strokes against 125 2 strokes. Same thing with 250s and 450s. I’ll take a two stroke bike over a 4 stroke any day of the week.

 

[Spring Ford]

Two stroke diesels are NOT AT ALL like two strokes that used to be used in motorbikes. Well there are differences anyway

The crankcase/crankshaft is like a conventional four stroke one with pressure oil lubrication and plain bearings. The air does not flow through the crankcase. Instead of utilising the crankcase under the pistons as an air pump to feed air into the cylinders they use an air pump that is similar to a supercharger. No oil is added to the fuel as the lubricative properties required are the same as for a four stroke. There is no requirement to lubricate the crankshaft bearings with a fuel/oil mixture.These engines are very fuel efficient. Of course the temptation is there to turn up the air a bit and actually have boost, that is up to the designer.

The HUGE marine engines work this way. I understand that they often have piston port inlets and 4 stroke style overhead exhaust valves.

The great thing about the Deltahawk idea is that they get rid of all of the camshaft/valves/associated-stuff and the entire ignition systems, which should result in greater reliability if they can get it all to work. Fuel efficiency is reportedly very good.

Someone mentioned the Junkers opposed piston engine (205?). A development of this idea is the Napier Deltic.[1][2][3] It looks insanely complicated but count the moving parts. Must have been fun to rebuild!

The Junkers had two crankshafts, six cylinders and twelve pistons. Some bright spark noticed that if you add a third crank (50% more cranks) you can treble the number of cylinders and pistons (200% more cylinders). This must have seemed like quite a deal. Three crankshafts, 18 cylinders and 36 pistons! The US Navy[4] used them in the vietnam era. They were used in diesel-electric railway locomotives in the UK for years. Electric transmission like some modern hybrid road vehicles and ships. They were reportedly very reliable and are still in service today.[5]

The Deltahawk is not opposed piston.

Emissions to road vehicle standards will likely be a problem because of a lack of development at least, however the number of aero engines in use is so small that I would not be worried as long as they are not trailing clouds of black smoke which won't be happening since aircraft can't afford to waste the fuel. Is anyone proposing emissions standards for aero engines?

[1]

[2]

[3] https://www.dieselarmy.com/engine-t...n-history-how-the-napier-deltic-diesel-works/
[4] https://en.wikipedia.org/wiki/United_States_Nasty-class_patrol_boat
[5] https://en.wikipedia.org/wiki/Hunt-class_mine_countermeasures_vessel

 

[Kenny Phillips]

... Two strokes are indeed a replacement for displacement. If they did not have an advantage in the power generation department you would be racing 125cc 4 stroke motorcycles against 125cc 2 strokes. Instead, you race 250 4 strokes against 125 2 strokes. Same thing with 250s and 450s. I’ll take a two stroke bike over a 4 stroke any day of the week.

Obviously, the two-stroke is lighter and has twice the number of power strokes at the same speed. The range of efficient speeds is less on the two-stroke, so overall the four-stroke's cylinder pressures average a little higher. Given the weight penalty of the four-stroke, it's always been true that you need a 2:1 difference to make them roughly equal. Which isn't really a 2:1 difference at all: at any given speed, the two stroke has twice the displacement of power strokes of the four stroke.
If I was crossing the desert, or in a 3,000 km race, I'd take the four-stroke. I used to drag race Kawasaki triples; I went through a lot of pistons and rings.

 

[tspear]

I don’t think you’ll find emissions restrictions specifically for two strokes. As far as I know. The EPA sets emissions requirements then the OEMs can produce whatever kind of engine they want as long as the requirements are met. So if you can get it done with a 2 stroke, great. If not, you’ll be doing it with a 4 stroke.

Emissions effectively killed the two stroke plain and simple. Durability is not a valid argument. In the off road motorcycle world the 4 strokes that are worth riding really have no longer of a lifespan than the 2 strokes do.

Two strokes are indeed a replacement for displacement. If they did not have an advantage in the power generation department you would be racing 125cc 4 stroke motorcycles against 125cc 2 strokes. Instead, you race 250 4 strokes against 125 2 strokes. Same thing with 250s and 450s. I’ll take a two stroke bike over a 4 stroke any day of the week.

All I can say is I spent hours searching to backup the position that emission controls killed the small two stroke gas engine. I could find no data to back it up outside of autos and boats. Nothing for lawn mowers, off road vehicles, planes....
If you can point to the Federal regs to back up your statement I would appreciate it. Because I am losing the argument with some friends where I took your position.

For off road, all the four stroke stuff I found stated increased reliability. When Honda started to sell large outboard engines as four stroke, it was way before regulators on boats that I could find, the major selling pitch for the higher price was reliability. To confirm this I asked my dad, we switched one of our speed boat from Mercury to Honda for this reason.

Everything I have read says that the 250cc bike producing the same power as the 125cc bike will last a lot longer. Especially at the consumer level. Racing, I could not find any info for.

Sent from my SM-J737T using Tapatalk

 

[Kenny Phillips]

Just because there aren't any pending emission controls [or other regulations] doesn't mean that manufacturers won't do something proactively. "Back in the day", when three-wheeled ATVs were the norm, many folks misunderstood the handling characteristics, and ended up injured. Because of some grumbling at the state and federal level, the manufacturers got together and decided to shift to four-wheeled ATVs, which had "normal" handling. (I personally liked the three-wheelers; a decent operator could drive all day on any two of the three wheels, the other in the air!) And in just a few years, the three-wheelers were gone, before they were legislated out of existence. (Though they still have some mandated safety placards.)
There were plenty of articles in the bike rags about two-strokes and emissions, which ended the big-bore two and three cylinder ring-dings, and slowly killed the the singles. With Yamaha, Suzuki, and Honda all building outboard motors, what followed wasn't surprising. (There were state laws about dumping visible oil, and other restrictions, to consider; while oft ignored by boaters, the manufacturers certainly took note.) The big changeover started in the late 1970s, when emission controls hit the motorcycle industry.
I spent 15 years as everything from a lot boy to a service manager at a dealership chain that sold everything from bicycles, mopeds, the Big Four Japanese motorcycles, Rupp three-wheeled vehicles for the street (POS snowmobile engine powered!), Honda, Fiat (the rusty ones, not the modern ones), and Hyundai automobiles. It was quite easy to see what was in the wind; the big boss often had executives from these companies in his office.

 

[mondtster]

All I can say is I spent hours searching to backup the position that emission controls killed the small two stroke gas engine. I could find no data to back it up outside of autos and boats. Nothing for lawn mowers, off road vehicles, planes....
If you can point to the Federal regs to back up your statement I would appreciate it. Because I am losing the argument with some friends where I took your position

I suspect you've seen the regs you're looking for but you are looking for something that doesn't exist. As far as I know there are no rules that specifically spell out 2 stroke emissions regulations or 4 stroke emissions regulations. The EPA just sets emissions regulations period and it is up to the manufacturer to decide what to build that will meet those regulations.

A perfect example of this is IT4 off road emissions standards. Most of the OEMs used DEF in addition to other exhaust aftertreatment devices to meet regulations on their diesel engines, but Deere (and possibly others) was able to do it without using DEF. That was a manufacturer decision on how to meet the requirements. The EPA/Government did not force the use of DEF. Likewise, the EPA/Government has not forced the discontinuance of 2 stroke engines, they simply have been abandoned because they cannot meet the emissions standards set by the EPA.

For off road, all the four stroke stuff I found stated increased reliability. When Honda started to sell large outboard engines as four stroke, it was way before regulators on boats that I could find, the major selling pitch for the higher price was reliability. To confirm this I asked my dad, we switched one of our speed boat from Mercury to Honda for this reason.

The sales department may claim increased reliability as a feature of 4 strokes over 2 strokes but that cannot be claimed universally. I'm not as involved in boating as I am in motorcycles but I haven't observed the 2 stroke boat motors to be significantly less reliable than the 4 strokes are.

In motorcycles, like I said before, any 4 stroke off road bike that is going to be fun to ride is going to require as much maintenance as their 2 stroke counterparts. It all comes down to power output per displacement. I have 40+ year old 2 stroke engines that have never been rebuilt and are used on a regular basis and I have 4 stroke engines that need to be essentially rebuilt on an annual basis. The reverse can also be true.

Everything I have read says that the 250cc bike producing the same power as the 125cc bike will last a lot longer. Especially at the consumer level. Racing, I could not find any info for.

Keep looking a bit. Specifically, look at the race bikes like the CRF450, similar KTMs, etc. They will all require regular maintenance if you want them to live. Something like the old XRs that make no power would certainly have better durability than their 2 stroke counterparts. Durability was actually one of the big concerns and debates with Honda's announcement of 450L street legal bike. How long would it last before needing a rebuild? We'll know in less than a year now.

I commute daily on a DRZ400. It makes no power but is pretty durable, which is a good thing for me since I also abuse it daily. With the amount of miles I put on it annually I would likely have to rebuild a Honda or KTM once or twice a year. But those bikes still appeal to me because I'd have twice the power to play with. Or even more appealing to me would be tagging and riding an old CR or KX 500.

 

[Ted]

The prolific use of 2-stroke diesels in former OTR truck, bus, generator, and marine applications should be evidence enough that the basic concept can be plenty durable. Lots of old Detroit 6V71, 6V92, 8V71, 8V92, on up that have run just fine.

 

[mondtster]

The prolific use of 2-stroke diesels in former OTR truck, bus, generator, and marine applications should be evidence enough that the basic concept can be plenty durable. Lots of old Detroit 6V71, 6V92, 8V71, 8V92, on up that have run just fine.

The old Detroits sound the best!

 

[lancie00]

My inquiry had nothing to do with aircraft use. Let’s just say I am VERY familiar with Deere engines. At least their newer ones.

From what I’ve seen running them thousands of hours I think they’re pretty good, for the most part. But everything has its faults and everything has a chance to break. And as you’re seeing, (relatively) modern diesels get expensive to fix. Sounds to me like you’ll at least need a liner, piston, head, and injector to get it back up and running.

You are 100% correct. They thought they might be able to save the head but it looks pretty beat up to me.