Experimental with a diesel engine

[Yenn]

Are there many diesels running with inline pumps nowadays. I have been out of the mechanics business for so long that I don't know what is current.

My preference for direct injection is because it is easier to start. No glow plugs required, even in sub zero weather. So less battery drain.

[onetrack]

Yes, the majority of heavy industrial diesels still use inline injection pumps. But Common Rail injection is gradually becoming the dominant style of diesel fuel injection.

[facthunter]

Whether the motor starts easy is about compression ratio. COLD and altitude make ALL of them harder to start unless you chuck ether down the intake.  Nev

[Ian]

23 hours ago, turboplanner said:

I haven't seen anything on biodiesel since the reports on a Victorian farmer who had set up a collection deal with fish and chip shops and was running his tractor with biodiesel.

Diesel engines can generally run on waste oil vegetable oil or biodiesel. Biodiesel is similar in viscosity to dino diesel so is a drop in replacement in most cases. Running on pure vegetable oil generally requires a preheater and there are more issues associated with residuals.

Biodiesel is created by the transesterification of vegetable oils using methanol/ethanol and a catalyst like sodium hydroxide (NaOH). Basically you mix the ingredients and the lighter alcohols replace the heavier glycerols in the vegetable oils making it less viscous and lowering the cloud and pour point. However the cloud point and pour point remain higher than traditional dino diesel which is an issues for planes. The source oils or fat is the key determinant on the cloud and pour point with tallow and solid fats creating having higher pour points than biodiesel made from oils like canola.

It's also a better solvent than traditional biodiesel so it will dissolve all the deposits that have built up over the years which tend to then clog fuel filters etc. So you need to replace filters after the first tank of biodiesel. It may also dilute your engine oil if your engine relies on a burn off process to clean your particulate filter. This is because it doesn't vapourise quite as well as diesel and car manufacturers were too cheap to put a separate injector into the exhaust system and instead activate engine injectors on the exhaust stroke to initiate the particulate burn process. More biodiesel ends up on the cylinder wall and then into the sump as a result diluting the oil.

It may also react with  gaskets, hoses and seals which were fine with diesel, however most European and Japanse engines made since the 90s are made from materials that don't react.

 

On the bright side it has much better lubrication properties than traditional diesel so injectors, engines, etc last longer. Testing in the US found that it was  used as an additive to traditional diesel it performed better than the commercially available additives. There have been a number of studies which support this so adding biodiesel to your dino diesel is likely make your engine last longer. https://www.sciencedirect.com/science/article/pii/S1876610215013879

 

As for aircraft use, there have been a number of studies on various biodiesel blends or pure biodiesel fuelstock in turbine engines and it appears to be a workable solution. Economically not so much with the current price of oilseed crops. But it is significantly cheaper than hydrogen.

 

Basically if you live in a reasonably warm climate (most of Australia), run diesels and have access to waste vege oil it's an option.

 

 

[Ian]

1 hour ago, facthunter said:

Whether the motor starts easy is about compression ratio. COLD and altitude make ALL of them harder to start unless you chuck ether down the intake.

Does the cetane number impact startability? It's essentially the measure of combustion rate of diesel.

[facthunter]

Yes . That's why the ether.  "Start Ya Bastard".  is one. Model aeroplane fuel is ether, kero and castor oil in equal parts for diesel types  Nev

Edited May 28, 2022 by facthunter

[onetrack]

Around 8% of the diesel sold in Europe in 2019 was biodiesel, the Europeans use large amounts of Australian Canola oil to add to regular diesel. There's a substantial improvement in exhaust emissions by using biodiesel blends.

The Europeans specify biodiesel as a way of keeping their dino oil imports down, and to meet their requirements for lower emissions levels. They set a 10% biodiesel target for 2020, but didn't meet it. The target for 2030 is 14% biodiesel.

 

https://www.politico.eu/sponsored-content/biodiesel-the-green-fuel-bridging-the-eus-climate-ambitions/

 

The cetane number is a direct measure of the speed of ignition of diesel, and is thus a measure of ease of startability. So, a high cetane number guarantees a faster start for your diesel.

Biodiesel produced from tallow and other heavy fats high in saturated fatty esters has a higher cetane number than biodiesel produced from plant-based (vegetable) oils.

Tallow-based biodiesel can actually have a higher cetane number than dino diesel.

 

Used cooking oil is full of heavy fats from cooking sausages and other low-grade "fast foods". I picked up some IBC's a couple of years ago that were supposed to be empty - but some contained up to 100 litres of used fryer oil.

This stuff was a real eye-opener, you would never eat deep-fried food again, when you see what comes from deep fryers after a few weeks of cooking. It was not only full of heavy tallow with a soft butter consistency, it also contained a large amount of food particles, a few utensils (!), and the worst part was the heavy, almost plastic-like coating on the containers.

 

This heavy coating is pthalates, a plasticiser formed when the cooking oil contains undesirable by-products, and formed when the oil is overheated. It's nasty stuff. A lot of el-cheapo cooking oils are pretty poor quality.

Pthalate coatings can be formed on combustion chambers if untreated or inadequately-treated oil is used in biodiesel. These are highly undesirable coatings, and they can result in a need for engine dismantling to remove them.

 

Edited May 28, 2022 by onetrack

[onetrack]

*my spelling and proof-reading error - it's actually spelt phthalate. Phthalates can also come from soft plastics and utensil coatings, and will migrate into cooking oils from the bottles, thus making checking for phthalate content in the original oil, difficult to track down. 

 

Edited May 28, 2022 by onetrack

[spacesailor]

Diesel  carburetor. 

My diesel 4m40 Mitsubishi has a double  butterfly carby, so it cannot run ' backwards '.

It does other things as well, but economy isn,t the best at 12.5 L,p.100 k.

And thats the best it has ever achieved. Normally 14L.p.100.k. over many thousands of Ks and 24 years.

spacesailor

[Ian]

To be clear a few of the advantages of diesel engines using diesel

• Better thermodynamic efficiency from higher combustion temperatures (due to higher compression)
• Higher energy fuel per litre 36.9MJ/l compared to 33.7MJ/l.
• Excess air ensures creates a leaner burn
• Max power occurs at RPMs that are suitable for propellers without reductions gearboxes
• Generally can run on Jetfuel (lubrication of the injectors can be an issue).
• Less flammable fuel
• Can be electronics free. ie no requirement for ignition.

Some disadvantages are

• Power/Weight generally worse than petrol
• Power pulses tend to the stronger so items designed for petrol may endure.
• Limited track record
• Low temperature cloud point and pour point issues.
• Generally require turbos to bring them close to petrol engine performance.

But I must admit I would be jealous if someone flew in an filled their piston powered plan with jetfuel.

[Old Koreelah]

1 hour ago, Ian said:

Max power occurs at RPMs that are suitable for propellers without reductions gearbox…

Unfortunately this hasn’t proven to be true: most diesels seem to be adapted from cars, for which application their best output is when spinning a bit faster than the ideal prop revs. This means to save the weight of a gearbox you never use all power available-unless you prop is doing 3,500+ rpm. Noisy. Or maybe they need smaller diameter aircrews with big paddle blades?

[skippydiesel]

1 hour ago, Ian said:

To be clear a few of the advantages of diesel engines using diesel

.....................................................................................................................................

But I must admit I would be jealous if someone flew in an filled their piston powered plan with jetfuel.

Hi Ian - As a long time lover of diesel engines I agree with most of your statements however I find the following to be in need of clarification;

 

"Max power occurs at RPMs that are suitable for propellers without reductions gearboxes" - It is true that the compression engine/diesel has a longer power burn and this lends itself to power delivery at lower rpms, however the rpm that this peaks (torque & power) at is a factor of engine design rather than a characteristic of diesel engines per say. (approximate numbers from defective memory) My old DB 885 is delivering max torque power at around 1500 rpm, the last Mac I drove  1500 rpm, my Rocky 2200 rpm, my Ford Ranger 1800 rpm - most of the "car" variants will rev to say 4000 rpm not so the tractor & truck which will max out at about 1800-2000 rpm.

"Excess air ensures creates a leaner burn" - Please expand on this statement. Petrol engines require fuel for cooling (one of the reasons why they are not so economical) where diesels do not. This is not excess air or a lean burn.

"Max power occurs at RPMs that are suitable for propellers without reductions gearboxes" For a diesel to be used, in a heavier than air aircraft, it will inevitably have to be high revving & boosted to achieve a viable power to weight ratio, so a gear box or engine speed reduction must be employed. 

"Can be electronics free. ie no requirement for ignition." - Not any more. To the best of my knowledge all modern road diesels & most off road use high pressure common rail fuel systems with computer controlled injectors.

"Power/Weight generally worse than petrol" - I would say always rather than generally. In recent times the use of high performance turbos has allowed for reduced compression . The reduced compression then allows for less robust (lower weight) engine construction however diesels are at this time always heavier than their petrol equivalents.

"Generally require turbos to bring them close to petrol engine performance." Again I have an issue with "generally" Diesel engines will always require some form of boost, be it turbo or supercharger, to achieve power/weight and clean burn approaching that of petrol. Diesel engines are , in my view, unlikely to ever achieve the engine speeds (rpm) of petrol engines, due to the slower burn characteristics of diesel. However diesel engines are likely to retain their superior torque and fuel econamy characteristics, compared with petrol, hence their use in commercial applications and wherever grunt is required.

 

[Ian]

12 hours ago, skippydiesel said:

Petrol engines require fuel for cooling (one of the reasons why they are not so economical) where diesels do not. This is not excess air or a lean burn.

I'm struggle to see your point or maybe I stated it poorly, by definition an engine which always runs with excess air is lean of peak and is a lean burn engine (ie diesel) and an engine which requires operation rich of peak is not (ie o360).

 https://en.wikipedia.org/wiki/Lean-burn

It's a little more complex but in general it is true. Most Airplane engines are designed to use excess petrol for cooling and reduce detonation and may only be run lean as lower power settings. Modern car engines are not, demonstrating that this is possible not an inherent issue but a design choice.

Diesel engines are essentially constant airflow, only fuel flow changes during throttling not airflow. So they operate to the oxygen rich side of stoichiometric. ie diesels normally operate at ratios between 17:1 and 70:1 however stoichiometric for a diesel is about 14.6 an tends to leave lots of soot in the exhaust due to the slower burn of diesel.

 

12 hours ago, skippydiesel said:

Diesel engines will always require some form of boost

The guiberson diesel from ww2 era was normally aspirated and designed as an airplane engine. It's power to weight was reasonable and it's efficiency was better than most modern cars including a prius. Turbo's can improve the power to weight and allow increases in power at the same rev range. Due to the combustion properties of diesel they tend to have a narrow rev range in which combustion can proceed efficiently. This is why forced induction, allowing more air to be pushed through the engine without changing the rpm is popular.

12 hours ago, skippydiesel said:

I would say always rather than generally.

Always is a very strong word, the guiberson has a power to weight of 0.781 kW/kg and the junker ju 205e 0.903 kW/kg and 0320 makes 0.99kW/kg in comparison.  So generally works for me. I'm sure there's engines outside this rule and if I stated always someone would just prove me wrong.

 

Also electronics are pervasive however they're on an inherent part of a diesels operation, however you can't design an otto engine without an ignition system.

Edited September 16, 2022 by Ian

[RFguy]

The weight issue is only because they're generally made for transport apps  that are not weight sensitive.

Does anyone know much about the piston  engine in the Diesel/JetA Technam ?

Edited September 16, 2022 by RFguy

[Ian]

Out of curiosity I'd like to know the performance numbers possible using a guiberson with a turbo and common rail.

[skippydiesel]

The weight issue is inherent in diesel engines due in large part to the much higher pressures  (traditionally about  22:1 modern turbo ed engines can be down around 17:1 high compression petrol about 11:1) and what is essentially an engine designed to "knock"  both features demand  more robust construction which usually results in weight increase compared with a similar petrol engine.

 

I doubt very much that a diesel engine designed/adapted for use in a fixed wing aircraft would go back to the old style (heavy & comparatively inefficient) injector pump/injectors. Sure the Germans had diesel aero engines back in W2 but they were not continued/adopted after the war,  why? The reality is that, today, a diesel engine designed/adapted for use in aircraft would have to be high revving (probably in the 3000-4000 rpm range), with a gear box, "boosted" and use common rail high pressure computer controlled  injection system to achieve competitive efficiencies in power:weight and fuel consumption. The combination of boost & high revving = higher volumetric efficiencies which may translate into better power:weight.

 

Boosting is not jut a way to improve volumetric efficiency it also can deliver, particularly when combined with HP common rail computer controlled injectors,  higher efficiencies and lower pollution due to cleaner burn and due to density altitude changes, is eminently suited to aircraft 

 

I think your terminology eg "lean of peak" adopted from petrol aircraft engines, does not sit well with diesel engines 

Edited September 16, 2022 by skippydiesel

[Yenn]

What is meant by you can't design an Otto engine without an ignition system, or maybe I should ask. What is an ignition system?

The Otto cycle includes both normal petrol and diesel systems, Diesels don't have an electrical system for ignition. They compress the charge so that it's temperature becomes hot enough to ignite the diesel, when it is injected.

Diesel power is controlled by the amount and timing of injected fuel, whereas petrol power is controlled by the amount of air in the charge and the ratio of petrol to air. The old diesels had a bad reputation for sooty exhaust, which was caused by injecting more diesel than the engine could burn with that air.

Old diesels also did run slowly and when Perkins introduced a high speed diesel it was still less than 3000rpm.

Over the years i have come to prefer diesels for their ease of operation. No worries with electric ignition, nor with a carburettor, but they are not generally designed for what we need to pull an aircraft along.

A friend of mine has flown the twin Diamond with diesels and liked it, but there are not many of them around.

[onetrack]

Weight is always the killer with a diesel engine in a lightweight aircraft. With the upgrade to 760kg MTOW for RA/kit build aircraft, there probably is the potential to fit a small automotive diesel in a light aircraft.

To that end, the Subaru EE20 2.0L horizontally-opposed 4 cyl diesel is an attractive option, because it's still relatively light (but still comes in around 170kgs, as I understand), it's turbocharged and intercooled, and the engine layout is comparable to the regular petrol aviation engine design.

But it produces its maximum of 150HP at 3600RPM. However, it would be possible to set up the Subaru EE20 to run at say, a maximum of 3300RPM, which would allow for direct drive - but this would reduce the HP output somewhat.

Regardless, it would still need to be fitted in a heavier airframe than many current kit-build aircraft, and there would need to be quite a bit of re-engineering of the engine to suit aviation use.

The electronic injectors of today have numerous advantages, in that they're more precise with injection, and they carry out multiple injection events over milliseconds, thus reducing diesel knock and vibration.

However, diesel engines with direct drive in aircraft need to have a rubberised drive mechanism for the prop, to suppress the bigger power pulses that come from the high-torque power strokes of the diesel.

[RFguy]

How about this diesel rotary

 

https://www.wankelsupertec.de/pdfs/datasheets/wst data sheet kkm350d 2021-01-27.pdf

 

67kg with all ancillaries, 60kW, 6000 RPM .

 

On Diesel- 273 g/kWh fuel. line ball with  Rotax 912ULS at 285g/kwh. jabiru ~ 285g/kwh

 

https://www.wankelsupertec.de/en_engine.html

 

 

 

Edited September 17, 2022 by RFguy

[onetrack]

Glen, the "mobile" application for that little diesel Wankel has a fuel consumption of 305 g/kWh. AT 6000RPM, a diesel is throwing a lot of unburnt diesel out the exhaust.

The ideal RPM for best diesel efficiency is around 2000-2200RPM, but diesel fuel burn losses are still acceptable at 3000-3300RPM. Over that RPM, the unburnt fuel losses increase substantially.

[turboplanner]

This thread is almost duplicating one we had a couple of years ago.

 

With common rail multipoint injection, diesel engines can pretty much be designed for any application, because the power and torque curves can be designed these days rather than wait to what shows up on the dyno.

 

Diesel will always have a slight weight disadvantage to petrol because of the heavier structure required for the higher compression etc.

 

So if you were designing for an aircraft engine to compete with a Rotax, you would be offesting that by going to direct crankshaft prop attachment.

 

On long distance interstate haulage trucks, some cruise as low as 1100 rpm on full power to push the wind away, and max torque is not far down, to hold speed on hills.

 

So you have the luxury of designing the engine power and torque to suit the cruise rpm requirement for the prop.

 

It's just a matter of someone here throwing a few milion in the ring to produce a batch of say 500 engines.

 

 

Edited September 17, 2022 by turboplanner

[RFguy]

Turbs, so that prompted me to look  at truck torque curves...

wow peak torque down around 1000 RPM ! some down at 800 RPM.

any reason not to use a automotive torque converter driving a prop ? I have not thought about it much. 

 

 

 

 

Edited September 17, 2022 by RFguy

[turboplanner]

1 hour ago, RFguy said:

Turbs, so that prompted me to look  at truck torque curves...

wow peak torque down around 1000 RPM ! some down at 800 RPM.

any reason not to use a automotive torque converter driving a prop ? I have not thought about it much. 

 

 

 

 

You can see from the straight line that its a designed performance.

You're basically looking at constant cruise rpm, but a truck and a prop will be at different rpm, the difference just being different design input.

By designing that way you're in the optimum for the prop, so don't need any sort of gearing and extra mass.

[RFguy]

yeah, just (need) a prop that can take the big pulses...

which brings me to :

Now, Turbs, reduction gearboxes should AMPLIFY the torque pulses IF they were 'perfect'. So the rotax should be the same  as a direct drive for same engine config and delivered torque.

But 'everybody' talks about how the rotax is easy on props because of the gearbox... so I am not a complete beleiver.

There must be some spring or loss. and the rotax book talks about how bad high loads are at low RPMs on the gearbox due to the pulses, and how not to apply WOT at low RPM because the prop isnt loaded up to RPM yet.

 

For the rotax, there are a two immediate coupling loses OR areas of 'spring' - the  Overload clutch and the gearbox  mesh. BTW early 912 engines didnt have the overload clutch.

so is there enough takeup spring in the gear meshing or the clutch in your opninion ? the gearbox mesh isnt special at all , just straight trapezoid cut (I think).

?

 

 

Edited September 17, 2022 by RFguy

[turboplanner]

I don't have any experience of the reduction gearbox or clutch so can't tell you about pulses.

 

The purpose of the reduction gearbox is to be able to use a higher revving engine (particularly in two strokes) with the prop turning at its slower, optimum speed.

The geartrain resistance will absorb some power.

Beyond that, such as pulses the best information would come from the design engineers who dyno tested the engine/reduction/prop assembly. Sometimes you can luck in and get a contact who was on the project and only too happy to share his trials and tribulations. A friend of mine dropped in on the legendary engine builder Phil Irving one night looking for some tips on getting more power out of his engine. Phil said "Where's your engine? My friend said "in the boot". Phil said "Bring it in and they ported the head there and then. He won the Australian Championship a few weeks later.