# Light weight diesel auto conversion

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### PMD

##### Well-Known Member
As mentioned, there are very few conditions that will let a diesel run away fueled by its own lubricant - all rated to excessive wear that should never be in an operational aircraft. The beauty of having a propeller bolted onto one means the "runaway" will not likely result in a catastrophic failure...until of course the lube oil is gone. Simply not something I would ever consider for an aircraft diesel as it would introduce another failure point that itself could cause a complete uncommanded power loss.

BTW: A NICE video on turbocharger oil leakage:

#### tspear

##### Well-Known Member
Supporting Member
I know Jet-A has no guarantee of lubricity; I think bio-diesel also has the same issue. If I am correct (and that is a big if); using an auto-engine which runs on bio-diesel would likely reduce conversion complexity.
Do I have that correct?

Tim

#### PMD

##### Well-Known Member
I know Jet-A has no guarantee of lubricity; I think bio-diesel also has the same issue. If I am correct (and that is a big if); using an auto-engine which runs on bio-diesel would likely reduce conversion complexity.
Do I have that correct?

Tim
For Canola based bio-D, lubricity is excellent. Will ask Big Kid if this is also true of soy based bio-D (what I expect you have in Yusa). Her Masters thesis was making high performance bio lubes from Canola oil.

Here is some background: The Lubricity of Biodiesel.

The nice part of compression ignition engines is that they are ALL multi-fuel capable, but you are very correct in realizing that lubricity with modern HPCR equipment is ultra-critical. Thielert had a good go-around with that in their early years - as did auto manufacturers using the same pump. While I think a good lubricity additive makes sense, I never get around to using it in my HPCR engines and no issues have yet to surface. I think ULSD producers have also become a LOT more aware of these problems and now produce a better score at the pumps. BTW: There IS a lubricity value in Jet fuel - go to page 10 of this pdf and it is explained: https://www.chevron.com/-/media/chevron/operations/documents/aviation-tech-review.pdf

#### Hawk81A

##### Well-Known Member
Adding a throttle body to shut off the air means a throttle body that can shut off the air. Why not just use what all diesels use? Works fine; lasts a long time.
Had a Freightliner that blew the oil seal in the turbo. Racing smoky mess until a quick thinking mechanic pressed a cardboard box over the intake. Dennis

#### TFF

##### Well-Known Member
Yes but is it really something we need to be worried about. There is a bunch different for a truck in a garage in neutral running away and a plane circling to land with part throttle. I guess you can loose the prop and want it off, but should we have a shut down or have bought a better system in the first place? Are we to the point that we need a third mag and plug per cylinder? Most problems are from not thinking it through in the first place. If it’s a problem all the time, sure. Is it reliable enough to risk your butt? If it’s one in a million, yes that is keeping count, but I don’t think I will get a million starts to need it. Even if I’m the unlucky one.

I once shut down my regional airline’s Citation that accidentally got started in the hangar. I was talking to all our FAA friends at the time about ten ft away. Their faces were great. It was the safety system for the thrust reverser that allowed it. The guy in the cockpit was too flustered to figure it out.

#### Hawk81A

##### Well-Known Member
My point was the need for the air flow shut off plate (kind of like a choke). Someone suggested a fuel shut off. Yeah, that could be good, but I noticed this engine has a turbo and a seal failure could have it running on it's own oil. Dennis

#### challenger_II

##### Well-Known Member
Losing a seal in a roots pump will do the same. Is why the old Detroits had the emergency shut-down baffle plate.

#### dog

##### Well-Known Member
My point was the need for the air flow shut off plate (kind of like a choke). Someone suggested a fuel shut off. Yeah, that could be good, but I noticed this engine has a turbo and a seal failure could have it running on it's own oil. Dennis
My imperfect understanding is that turbos do not have soft seals,or any seal at all,they
have bearings and oil slingers,and the bearings run
in an oil bath ,high flow low pressure,the very high
speeds throw the oil off before it gets to the bushings at the end of the cassett
To get run away you need,massive bearing wear and
huge engine blow by,in a hinky engine that likely needs
a big shot of either to start at all

#### KeithO

##### Well-Known Member
I dont understand posters on this forum. All this yakking about a more reliable way to shut off the engine when in fact there are plenty of unresolved issues that have to be addressed before they will ever run.

Someone has to make a high voltage injector driver so that the injectors can be operated. Non trivial. What about the engine controller ? An engine controller for a gas engine will usually not have adequate time resolution for the injection system since this involved injection into the cylinder for a very short time period. Not like a port injector spraying against the intake valve before it opens.

The engines and parts for the engines are totally unsupported in the US. No access to OEM or aftermarket parts. I hope those attempting this have a pal in Germany or one of the other markets where parts can be obtained. You will find that the cost of courier fees has gone way up during the pandemic. A simple injection pump, for instance will cost between $200-400 just to cover courier fees from Europe to the US. I would not want to know what this means for importing complete engines, for example. Many of the engines have been out of production long enough that one would be looking for a remanufactured engine because engines from the field would all have far too many miles on them and the remanufactured engine is usually bare. So needing intake and exhaust manifolds, turbo, complete fuel system and filters etc. Add starter, alternator, water pump and whatever else is needed. Less expensive than Continental and Lycoming but definitely not cheap... Im not at all against diesels, I was living just 30 miles from Speyer when the smart engine was being developed as an airplane engine and I saw the smart diesel demonstrated there in 2003, but that was nearly 20 years ago. About the only diesels we have seen in the US were the VW based ones, many of them subject to the emissions cheating recall, thus gone forever. And as discussed, VW never deviated from the cast iron block for this market, despite having aluminum block engines in Europe. #### PMD ##### Well-Known Member About the only diesels we have seen in the US were the VW based ones, many of them subject to the emissions cheating recall, thus gone forever. And as discussed, VW never deviated from the cast iron block for this market, despite having aluminum block engines in Europe. Which takes us back to the fact that NO 4 stroke small automotive diesel with ANY block material has anywhere near the power density required to carry a redrive and fit within the SI power/weight numbers for existing designs. The disastrous Thielert conversion making a perfectly good 4 place 172 into a horrible, expensive and unreliable 2 place trainer are a perfect example. CI salvation will only come at the hands of a 2 stroke (until, it seems, up to the 500+ HP range). #### KeithO ##### Well-Known Member While I was in Germany 2000-2003 there was an aluminum VW 1.2L 3 cylinder converted to power a trike by a local university. The converted Smart CDi 800cc was successfully applied to the FK series of airplanes. Prior to that the 600cc gasoline Smart engine was also applied to the FK series airplanes. Both are turbocharged, performance with either was fine and they were very quiet and had excellent fuel consumption. They were cost competitive at that time with Rotax engines which even today are not fuel injected by default. The 1.2L VW engine was out of a special edition VW Lupo, which was certified as having a fuel consumption of 3L/100km (78mpg) which was a new standard for small passenger cars. In the meantime many more small diesels were produced in both Europe and Japan, its just that we never saw them here in the US given that our emission laws have always been tighter than other countries at a given point in time. #### PMD ##### Well-Known Member The truth is that it is the ability of ANY compression ignition engine to make as much power as you could ever want from any displacement - as they are not limited by detonation problems of aspirated charges. If you want more power you simply add more air (bigger turbo) and inject more fuel. But in the real world what DOES limit them is the ability to cool critical things as the thermal load goes up with the power level sought. These nice little diesels are designed to cool things at relatively modest power levels. When you try to adapt an automotive design to make a lot more power you soon find you will melt a piston, fry a valve, boil the coolant as they were never designed with that thermal load in mind. THAT is why a dedicated engine such as the RED 03 can make really good power in a reliable engine - it was designed from the start to be that. That BTW is also why air cooled VWs make only so-so aircraft engines - the power level needed to direct drive a prop and the design of airflow and fins around the exhaust ports hits a limit just a bit short of where we would all like it to be. Inversely, why some marine engines make horrible aircraft engines (designed to expect a LOT lower coolant temps than a recirculating system can have). Just to throw out another thing: the solution for reaching temp limits in SI or CI engines can be one and the same - ingest water. #### Geraldc ##### Well-Known Member Which takes us back to the fact that NO 4 stroke small automotive diesel with ANY block material has anywhere near the power density required to carry a redrive and fit within the SI power/weight numbers for existing designs. In true HBA style while everyone is arguing about how something is not possible there are people on the other side of the world doing it.' Scroll down to Pennec designs. #### KeithO ##### Well-Known Member Gerald, here in the US, Diesel fuel is basically the most expensive fuel on the market, typically 20-25% more costly per Gal than gasoline. Back in the days when gasoline was$2/gal or less, the premium for diesel may have been as high as 40%. So generally speaking, even though the diesel engine may consume less fuel, that does not mean it will save any money here in the US.

I personally would be happy to have a less volatile fuel in diesel (jet fuel or Kerosene does not help in that respect) because it would enhance the likelihood of surviving a crash. If someone had to set up a business providing properly overhauled core engines for conversion, that would be great but I dont think that exists currently. Thats another point, today Jet fuel is even more expensive than 100LL, which is already about 20-30% more expensive than regular unleaded fuel. It is only the airlines who pay less for their fuel based on deals with the politicians.

#### Tom DM

##### Well-Known Member
Supporting Member
Greetings,

I am interested in doing a 120 - 160 hp diesel auto conversion. I am looking fo a good, light, and turbocharged diesel engine to begin with. Any suggestions?

Cheers,
Owen

You can re-invent a (better) wheel, make a faster horse or...

WAM-diesel

Project fluked into bringing it to the market and lays dormant ever since.

It flew in the nicest (and about the lightest) of airframes. Had my discussions with the owner over another project, which fluked too due to big differences between wishes, dreams and reality.

You might kiss (with money) this sleepy beauty awake before the irreversible. However to me the aircraft equiped with it, looked - lets stay polite - down right ugly.

#### rv7charlie

##### Well-Known Member
Supporting Member
only the airlines who pay less for their fuel based on deals with the politicians.
Or, it could be simple economics of scale. Sorta like, it's often cheaper to pay an insulation contractor than doing it yourself, because you pay retail for materials and he buys it by the boxcar load.

#### challenger_II

##### Well-Known Member
Thats another point, today Jet fuel is even more expensive than 100LL, which is already about 20-30% more expensive than regular unleaded fuel. It is only the airlines who pay less for their fuel based on deals with the politicians.

I just checked AirNav and SkyVector for FBO fuel prices: 100LL is significantly higher than Jet A.
Also, the airlines getting their fuel at a lower cost isn't necessarily due to "deals and politics". It's a matter of volume. You, your self, see this at the grocery store: you pay more for a 20oz bottle of water, than you pay for a gallon.

#### KeithO

##### Well-Known Member
Local prices: $6.49 for 100LL,$6.99 for Jet A

Diesel fuel

Regular gasoline

Last edited:

#### Tom DM

##### Well-Known Member
Supporting Member
I just checked AirNav and SkyVector for FBO fuel prices: 100LL is significantly higher than Jet A.
Also, the airlines getting their fuel at a lower cost isn't necessarily due to "deals and politics". It's a matter of volume. You, your self, see this at the grocery store: you pay more for a 20oz bottle of water, than you pay for a gallon.

The lower cost of Jet A is exclusively down to politics: Jet A1 is tax exempt

Volume doesn't apply. I've never been on a airfield which charged differently Jet A1 differentely on a "small" plane compared to a bigger. However the cost of Jet A1 per l varies quite a bit from airport to airport but (in Europe) I know but of 1 operator who takes those differences into account.

#### challenger_II

##### Well-Known Member
KeithO: Perhaps you're focusing on to small a data set? Expand your search to the surrounding three states for a better average.

TomDM: The volume discount applies to the businesses purchasing the fuel, not to their selling the fuel. And, as to the FBO giving a volume discount, that DOES tend to happen. I know of four FBOs that give a discount on 100LL and Jet A sales over 500 gallons. That is at the discretion of the FBO.

Returning to the volume discount, from distributor to FBO: that applies to both Jet A and 100LL. When we purchase fuel, the delivered price depends upon the amount we order. The larger amount we order, the lower the cost per gallon. We deal in loads up to 10,000 gallons: imagine the discount to a business purchasing fuel in the 100,000 gallon range.